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BEGIN:VEVENT
SUMMARY:Diego Rubiera-Garcia (UCM\, Madrid\, Dept. Phys.)
DTSTART:20200929T131500Z
DTEND:20200929T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/1
DESCRIPTION:Title: Understanding space-time singularities inside black holes: a proposal fo
r their resolution\nby Diego Rubiera-Garcia (UCM\, Madrid\, Dept. Phys
.) as part of Theoretical physics seminar @ Tartu\n\nLecture held in Physi
cum room A101\, University of Tartu\, Estonia.\n\nAbstract\nSpace-time sin
gularities are an ubiquitous prediction of Einstein's General Relativity (
GR). They represent (perhaps) the most important conundrum in our understa
nding of the nature of the gravitational interaction and\, moreover\, are
the pivotal point for our theoretical attempts to extend the theory. In th
is talk I will describe one of such attempts - metric-affine gravity -\, a
nd tackle the resolution of such singularities according to several perspe
ctives for detecting potentially pathological behaviours.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/1/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Yong Gao and Rui Xu (Peking University\, Beijing\, China)
DTSTART:20201006T131500Z
DTEND:20201006T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/2
DESCRIPTION:Title: Deformed neutron stars and their characteristics in electromagnetic and
gravitational radiation\nby Yong Gao and Rui Xu (Peking University\, B
eijing\, China) as part of Theoretical physics seminar @ Tartu\n\nLecture
held in Physicum room A101\, University of Tartu\, Estonia.\n\nAbstract\nT
he shape of a neutron star (NS) is closely linked to its internal structur
e and the equation of state of supranuclear matters. In the first part of
the talk\, we will present the results that extend previous work and descr
ibe the free precession of a triaxially deformed NS. Such a NS is a unique
object that carries abundant information for multimessenger observation\,
as the free precession could manifest in\, (i) the spectra of continuous
gravitational waves\, and (ii) the timing behavior and pulse-profile of pu
lsars. Then\, in the second part\, we consider violation of Lorentz invari
ance\, one of the fundamental principles in General Relativity\, as one po
ssible beyond-the-standard-model origin for the deformation of a NS. An es
timate for the continuous gravitational waves from such a source will be m
ade\n
LOCATION:https://researchseminars.org/talk/UTPhysics/2/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Konstantinos F. Dialektopoulos (Yangzhou University)
DTSTART:20201013T131500Z
DTEND:20201013T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/3
DESCRIPTION:Title: Recent developments in Horndeski theory and beyond\nby Konstantinos
F. Dialektopoulos (Yangzhou University) as part of Theoretical physics sem
inar @ Tartu\n\nLecture held in Physicum room A101\, University of Tartu\,
Estonia.\n\nAbstract\nThe most general scalar-tensor theory with a single
scalar field\, in four dimensions\, leading to second order field equatio
ns was introduced by Gregory Horndeski in 1974 and it took his name since.
Even though G. Horndeski abandoned physics to become a painter soon after
he developed this theory\, in the late '00s the theory was rediscovered a
s generalized Galileons. In this talk\, I will review its recent discovery
and discuss why it is a powerful tool to explore cosmology and astrophysi
cs beyond general relativity. I will also present its current status after
GW170817 and I will give a brief introduction in its generalizations\, i.
e.\, Degenerate Higher Order Scalar Tensor (DHOST) theories.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/3/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Francisco José Maldonado Torralba (University of Cape Town and Un
iversity of Groningen)
DTSTART:20201020T131500Z
DTEND:20201020T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/4
DESCRIPTION:Title: Poincaré Gauge Gravity: stability\, phenomenology\, and prospects.\
nby Francisco José Maldonado Torralba (University of Cape Town and Univer
sity of Groningen) as part of Theoretical physics seminar @ Tartu\n\nLectu
re held in Physicum room A101\, University of Tartu\, Estonia.\n\nAbstract
\nPoincaré Gauge Gravity is a theory quadratic in both curvature and tors
ion\, which is constructed by requiring that the gravitational theory must
be invariant under local Poincaré transformations. In this talk I will p
resent the main outcomes of my PhD thesis related to this theory. First\,
I will expose some results about the stability of the quadratic Poincaré
Gauge Lagrangian\, and prove that only the two scalar degrees of freedom c
an propagate without introducing pathologies. I will make emphasis on the
form of the bi-scalar stable Lagrangian\, and give some applications of th
is particular theory. Then\, in order to see which kind Black Hole solutio
ns we can expect in Poincaré Gauge theories\, I will study Birkhoff's and
no-hair theorems under physically relevant conditions. Finally\, I will s
how an ultraviolet extension of Poincaré Gauge theories by introducing no
n-local terms into the action\, which can ameliorate the singular behaviou
r at large energies. I will present solutions of this theory at the linear
level\, and prove that such solutions are ghost- and singularity-free\n
LOCATION:https://researchseminars.org/talk/UTPhysics/4/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Kristjan Müürsepp (University of Tartu\, National Institute of C
hemical Physics and Biophysics)
DTSTART:20201027T141500Z
DTEND:20201027T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/5
DESCRIPTION:Title: The particle physics and astrophysical properties of dark compact object
s\nby Kristjan Müürsepp (University of Tartu\, National Institute of
Chemical Physics and Biophysics) as part of Theoretical physics seminar @
Tartu\n\nLecture held in Physicum room A101\, University of Tartu\, Eston
ia.\n\nAbstract\nThe detection of the Higgs boson in 2012 strongly suggest
s that at least one fundamental scalar particle exists in the Nature. More
over\, although no compact objects consisting of fundamental scalar bosons
have been observed\, there is\, as of now\, no fundamental principle ruli
ng out the existence of compact objects consisting of scalar fields. In th
is seminar\, I will present an introduction to a subset of the compact obj
ects comprising of scalar fields that are known as boson stars. I will dis
cuss various astrophysical properties of boson stars and show how those ca
n markedly differ from the properties of neutron stars. Furthermore\, I wi
ll highlight the mathematical formalism underlying a proper description of
these stars and briefly outline the first results I have obtained on the
topic. Finally\, contingent on time constraints\, I will briefly elucidate
the possible connection between boson stars and dark matter.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/5/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Davi C. Rodrigues (Espirito Santo University)
DTSTART:20201103T141500Z
DTEND:20201103T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/6
DESCRIPTION:Title: Dark matter and gravity\nby Davi C. Rodrigues (Espirito Santo Univer
sity) as part of Theoretical physics seminar @ Tartu\n\nLecture held in Ph
ysicum room A101\, University of Tartu\, Estonia.\n\nAbstract\nDark matter
was introduced in the 30's as an additional kind of matter that could not
be directly detected from any electromagnetic waves\, but whose presence
could be inferred from gravitational phenomena. What was in the beginning
a curious fact turned out to be the start of a solid\, although indirect\,
evidence for an "invisible giant": it was far from an additional detail\,
it was the main gravitational actor at the scales of galaxies and beyond\
, while no one could "see" it. It is therefore tempting to dismiss this in
visible giant as an illusion caused by using the wrong gravitational theor
y. I will argue why this is even less likely. In particular\, I will talk
about a well known proposal called "modified newtonian dynamics" and why
it is relevant as a phenomenological relation\, not as a theory for gravit
y.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/6/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Mir Faizal (Lethbridge University)
DTSTART:20201110T141500Z
DTEND:20201110T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/7
DESCRIPTION:Title: Quantum Gravity Beyond General Relativity\nby Mir Faizal (Lethbridge
University) as part of Theoretical physics seminar @ Tartu\n\nLecture hel
d in Physicum room A101\, University of Tartu\, Estonia.\n\nAbstract\nI wi
ll talk about different works done on quantum gravity. As quantum gravity
is usually studied by quantizing general relativity\, I will highlight the
new areas and open problems\, about the possibility of analyzing quantiz
ation of other theories of classical gravity. My talk will include but not
be limited to string theory.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/7/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Maria Benito (NICPB\, Tallinn)
DTSTART:20201124T141500Z
DTEND:20201124T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/8
DESCRIPTION:Title: The Milky Way's Dark Matter halo\nby Maria Benito (NICPB\, Tallinn)
as part of Theoretical physics seminar @ Tartu\n\nLecture held in Physicum
room A101\, University of Tartu\, Estonia.\n\nAbstract\nThe distribution
of Dark Matter in galaxies is one remarkable output of structure formation
in a cosmological context\, and an important input for searches of the na
ture of Dark Matter. In this talk\, I will describe the sources of uncerta
inty that affect the observational determination of the Dark Matter conten
t in the Milky Way\, and I will quantify their effect on the estimated Dar
k Matter density by means of a data-driven analysis. I will further show t
hat the uncertainties on the Dark Matter distribution\, and their impact o
n searches of physics beyond the standard model\, stays sizable even with
state-of-the-art determinations of astrophysical quantities of relevance (
such as the Sun’s circular velocity and its distance to the Galactic cen
ter).\n
LOCATION:https://researchseminars.org/talk/UTPhysics/8/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Anna Pachol (Queen Mary University of London)
DTSTART:20201208T141500Z
DTEND:20201208T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/9
DESCRIPTION:Title: Observables and quantum spacetimes\nby Anna Pachol (Queen Mary Unive
rsity of London) as part of Theoretical physics seminar @ Tartu\n\nLecture
held in Physicum room A101\, University of Tartu\, Estonia.\n\nAbstract\n
Noncommutative geometry\, as the generalised notion of geometry\, can be h
elpful in providing the phenomenological models quantifying the effects of
quantum gravity. The noncommutative nature allows for obtaining quantum g
ravitational corrections to the classical solutions. One of the mostly stu
died possible phenomenological effects of quantum gravity is the modificat
ions in wave dispersion.\n\nIn my talk I will introduce the mathematical f
ramework for quantum spacetimes within the Hopf algebras and Drinfeld twis
ts formalisms. Twisted differential calculus and twisting generators of th
e Hopf algebra symmetry allow on a fresh look on modifications in dispersi
on relations and offer a proper choice of physical observables as generato
rs of the quantum Lie algebra of symmetries. Wave equations on noncommutat
ive spaces are derived from a quantum Hodge star operator. The formalism a
lso allows for study of the curved backgrounds. I will present recent resu
lts on propagation of waves in noncommutative cosmology and on the modific
ation of the dispersion relations due to noncommutativity combined with cu
rvature of spacetime.\n\nThe talk will base on the results developed in co
llaboration with P. Aschieri and A. Borowiec [Observables and Dispersion R
elations in k-Minkowski Spacetime J. High Energ. Phys. 2017\, 152 (2017) a
rXiv:1703.08726\, Dispersion Relations in κ-Noncommutative Cosmology arXi
v:2009.01051].\n
LOCATION:https://researchseminars.org/talk/UTPhysics/9/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Evgenii Strugovshchikov
DTSTART:20201215T141500Z
DTEND:20201215T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/10
DESCRIPTION:by Evgenii Strugovshchikov as part of Theoretical physics semi
nar @ Tartu\n\nLecture held in Physicum room A101\, University of Tartu\,
Estonia.\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/UTPhysics/10/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alejandro Jiménez-Cano (Universidad de Granada)
DTSTART:20210209T141500Z
DTEND:20210209T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/11
DESCRIPTION:Title: Gravitational wave solutions in metric-affine gravity\nby Alejandro
Jiménez-Cano (Universidad de Granada) as part of Theoretical physics sem
inar @ Tartu\n\nLecture held in Physicum room A101\, University of Tartu\,
Estonia.\n\nAbstract\nIn this work we derived exact gravitational wave so
lutions in a general class of quadratic metric-affine gauge gravity models
. The Lagrangian includes all possible linear and quadratic invariants con
structed from the torsion\, nonmetricity and the curvature. The ansatz for
the gravitational wave configuration and the properties of the wave solut
ions are patterned following the corresponding ansatz and the properties o
f the plane-fronted electromagnetic wave.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/11/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Swagat S. Mishra (Inter-University Centre for Astronomy and Astrop
hysics\, Post Bag 4\, Ganeshkhind\, Pune 411 007\, India)
DTSTART:20210216T141500Z
DTEND:20210216T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/12
DESCRIPTION:Title: Curing inflationary degeneracies using reheating predictions and relic
gravitational waves\nby Swagat S. Mishra (Inter-University Centre for
Astronomy and Astrophysics\, Post Bag 4\, Ganeshkhind\, Pune 411 007\, Ind
ia) as part of Theoretical physics seminar @ Tartu\n\nLecture held in Phys
icum room A101\, University of Tartu\, Estonia.\n\nAbstract\nAs a conseque
nce of the remarkable developments in cosmology over the past three decade
s\, both in the theoretical as well as observational fronts\, cosmic infla
tion has emerged as the leading scenario of the very early universe\, sett
ing natural initial conditions for the standard cosmological model prior t
o the commencement of the radiative hot Big Bang Phase. It is well known t
hat the inflationary scenario often displays different sets of degeneracie
s in its predictions for the CMB observables. These degeneracies usually a
rise either because multiple inflationary models predict similar values fo
r the scalar spectral index n_s and the tensor-to-scalar ratio r\, or beca
use within the same model\, the values of {n_s\, r} are insensitive to som
e of the model parameters\, making it difficult for the CMB observations a
lone to constitute a unique probe of inflationary cosmology. Similarly ano
ther key aspect of inflationary cosmology\, namely the epoch of 'reheating
'\, also remains observationally inaccessible at present\, despite a profu
sion of theoretical progress in this direction. After providing a consumma
te introduction of the inflationary cosmology\, the speaker will demonstra
te that by taking into account the constraints on the post-inflationary re
heating parameters such as the duration of reheating\, its temperature and
especially its equation of state (EOS)\, it is possible to break this deg
eneracy in certain classes of inflationary models. The relic gravitational
wave (GW) spectrum provides us with another tool to break inflationary de
generacies and probe the epoch of reheating. This is because the GW spectr
um is sensitive to the post-inflationary EOS of the universe. Indeed a sti
ff EOS (w > 1/3) during reheating gives rise to a blue tilt in the spectra
l index of the GWs while a soft EOS (w<1/3) results in a red tilt.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/12/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Viktor Gakis (National Technical University of Athens\, Greece)
DTSTART:20210316T141500Z
DTEND:20210316T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/13
DESCRIPTION:Title: Generalised Proca theories in teleparallel gravity\nby Viktor Gakis
(National Technical University of Athens\, Greece) as part of Theoretical
physics seminar @ Tartu\n\nLecture held in Physicum room A101\, Universit
y of Tartu\, Estonia.\n\nAbstract\nGeneralised Proca theories of gravity r
epresent an interesting class of vector–tensor theories where only three
propagating degrees of freedom are present. In 2012.11959\, we propose a
new teleparallel gravity analog to Proca theories where the generalised Pr
oca framework is extended due to the lower-order nature of torsion-based g
ravity. We develop a new action contribution and explore the example of th
e Friedmann equations in this regime. We find that teleparallel Proca theo
ries offer the possibility of a much larger class of models in which do ha
ve an impact on background cosmology.\n\nIn this talk we will review how t
he Generalised Proca theories are constructed and then present a way of ad
apting them in the teleparallel regime\n
LOCATION:https://researchseminars.org/talk/UTPhysics/13/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Celia Escamilla-Rivera (Universidad Nacional Autónoma de México)
DTSTART:20210323T141500Z
DTEND:20210323T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/14
DESCRIPTION:Title: Extended theories of gravity to explain the Hubble-Lemaitre tension
\nby Celia Escamilla-Rivera (Universidad Nacional Autónoma de México) as
part of Theoretical physics seminar @ Tartu\n\nLecture held in Physicum r
oom A101\, University of Tartu\, Estonia.\n\nAbstract\nThe current cosmolo
gical probes have provided an extraordinary confirmation of the standard L
CDM cosmological model\, that has been constrained with unprecedented accu
racy. However\, with the increase of the experimental sensitivity a few st
atistically significant tensions between different independent cosmologica
l datasets emerged. While these tensions can be in portion the result of
systematic errors\, the persistence after several years of accurate analys
is strongly hints at cracks in the standard cosmological scenario and the
need for new physics. In this talk I will list a few interesting new physi
cs models in the direction of extended theories of gravity that could solv
e this tension and discuss how the new computational techniques will be cr
ucial in this role.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/14/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Daniel Blixt (University of Tartu\,Estonia)
DTSTART:20210406T131500Z
DTEND:20210406T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/15
DESCRIPTION:Title: Hamiltonian analysis of covariant teleparallel gravity\nby Daniel B
lixt (University of Tartu\,Estonia) as part of Theoretical physics seminar
@ Tartu\n\nLecture held in Physicum room A101\, University of Tartu\, Est
onia.\n\nAbstract\nThe conventional action formulation for general relativ
ity is by the Einstein-Hilbert action\, which depends on the Levi-Civita c
onnection and the metric. However\, a classically equivalent theory can be
done by formulating the action in terms of torsion (related to the antisy
mmetric part of the affine connection) and tetrads. This is done in the th
eory called teleperallel equivalent to general relativity. From this formu
lation as a starting point it is not evident from a quick look that this t
heory should be selected in favor of other modified teleparallel theories
of gravity. This gives a motivation from a fundamental point of view to in
vestigate the theory further\, where the Hamiltonian analysis is useful si
nce it can give insights of the canonical structure of a theory.\n\nIn the
literature there is some work on the Hamiltonian analysis for the most ba
sic teleparallel theories of gravity. However\, they are either incomplete
\, contradicting to other work\, not formulated in a covariant way\, or a
combination of these. In this talk I will outline the derivation of the so
-called primary Hamiltonian for the most basic covariant teleparallel theo
ries of gravity. I explicitly write out these Hamiltonians without putting
the so-called spin connection to zero. Then\, I will briefly talk about p
erturbations in the aforementioned theories and use this to show that they
are most likely not viable theories. The irreducible decomposition of the
torsion scalar will be discussed in order to reach some insights on the f
undamental relevance for the irreducible components and their relation to
propagating fields. If time allows I will spend some time on discussing fu
ture directions where a teleparallel bigravity construction might avoid th
eoretical pathologies while providing an interesting theory of gravity.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/15/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Nico Benincasa (cNational Institute of Chemical Physics and Biophy
sics\, Tallinn\, Estonia)
DTSTART:20210427T131500Z
DTEND:20210427T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/16
DESCRIPTION:by Nico Benincasa (cNational Institute of Chemical Physics and
Biophysics\, Tallinn\, Estonia) as part of Theoretical physics seminar @
Tartu\n\nLecture held in Physicum room A101\, University of Tartu\, Estoni
a.\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/UTPhysics/16/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Priidik Gallagher (University of Tartu\,Estonia)
DTSTART:20210511T131500Z
DTEND:20210511T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/17
DESCRIPTION:by Priidik Gallagher (University of Tartu\,Estonia) as part of
Theoretical physics seminar @ Tartu\n\nLecture held in Physicum room A101
\, University of Tartu\, Estonia.\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/UTPhysics/17/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Hardi Veermäe (NICPB\, Tallinn)
DTSTART:20210309T141500Z
DTEND:20210309T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/18
DESCRIPTION:Title: Probing primordial black holes with gravitational waves\nby Hardi V
eermäe (NICPB\, Tallinn) as part of Theoretical physics seminar @ Tartu\n
\nLecture held in Physicum room A101\, University of Tartu\, Estonia.\n\nA
bstract\nPrimordial black holes are hypothetical black holes that formed w
ithin the first seconds of our Universe. They may form a part or even all
of dark matter. This talk will briefly review general aspects of gravitati
onal wave astronomy and primordial black hole physics. In the second half
of the talk\, we will focus on gravitational waves signals associated with
primordial black holes and try to answer the question of how gravitationa
l waves can be used to probe the existence of such black holes.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/18/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Aleksander Kozak (University of Wrocław)
DTSTART:20210330T131500Z
DTEND:20210330T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/19
DESCRIPTION:Title: Invariant quantities of scalar-tensor theories for stellar strucutre\nby Aleksander Kozak (University of Wrocław) as part of Theoretical phy
sics seminar @ Tartu\n\nLecture held in Physicum room A101\, University of
Tartu\, Estonia.\n\nAbstract\nStars in the scalar-tensor theories\, relat
ivistic and non-relativistic\, have been widely\nstudied in the literature
\; however\, the formalism of conformal invariants has not yet been\nappli
ed to stellar objects. In my talk\, I will present a way to describe stell
ar structure in\na frame-independent way. This will be achieved by express
ing all relevant equations in\nterms of invariants. Such a procedure will
allow us to easily compare dierent theories of\ngravity within one framew
ork. Also\, a non-relativistic limit of the Tolman-Oppenheimer-\nVolko wi
ll be presented\, and the formalism will be applied to Starobinsky theory
in the\nPalatini approach.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/19/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Vladimir Hizhnyakov (University of Tartu)
DTSTART:20210608T131500Z
DTEND:20210608T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/20
DESCRIPTION:Title: Singular long-wave vibronic interaction in superfluid helium: manifesta
tion in zero-phonon line\nby Vladimir Hizhnyakov (University of Tartu)
as part of Theoretical physics seminar @ Tartu\n\nLecture held in Physicu
m room A101\, University of Tartu\, Estonia.\n\nAbstract\nA theory is prop
osed [1] that describes the vibronic transitions in impurity atoms in supe
rfluid helium\, based on a two-fluid model of helium II. It is shown that\
, owing to the Archimedes’ principle\, the linear vibronic interaction w
ith low-frequency phonons in the liquid phase is singularly enhanced. As a
result of such a singular increase in the vibronic interaction\, a macros
copic amount of phonons with an almost zero frequency is created during th
e electronic transition in impurity atom\, which leads to a finite broaden
ing of the zero-phonon line (ZPL) in the optical spectrum already at the z
ero temperature limit. It is shown that the temperature dependence of the
ZPL has a discontinuity in the derivative at the temperature =2.17 K\, an
d above this dependence becomes linear.\nTheory is applied for the descr
iption of the studied in [2] temperature dependence of ZPL of the optical
spectrum of the inner shell transition of the Dy atom in superfluid helium
. A good agreement of the theory with experiment is achieved\, taking into
account\, in addition to the linear vibronic interaction\, the inhomogene
ous broadening of ZPL\, caused by slow fluctuations of the surface tension
of the bubbles of the surrounding helium atoms.\n\n\n\n[1] V.Hizhnyakov\,
V. Boltrushko\, G. Benedek\, Thermal broadening of zero-phonon line in su
perfluid helium\, PRB\, 2021. \n\n[2] P. Moroshkin and K. Kono\, Physical
Review B 99\, 104512 (2019).\n
LOCATION:https://researchseminars.org/talk/UTPhysics/20/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sebastian Schuster (University of Prague)
DTSTART:20210610T100000Z
DTEND:20210610T111500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/21
DESCRIPTION:Title: Wormholes\, Warp Drives\, Tractor Beam\nby Sebastian Schuster (Univ
ersity of Prague) as part of Theoretical physics seminar @ Tartu\n\nLectur
e held in Physicum room A101\, University of Tartu\, Estonia.\n\nAbstract\
nThe solutions first encountered in studying general relativity (and its a
lternatives or modifications) are solutions for a given (or absent) source
. A different approach is to reverse engineer the source terms: One posits
a given metric and asks what source term this would require. This kind of
solution is frequently encountered when the metric is supposed to “solv
e” a given problem\, like circumventing relativity's speed limit by worm
holes\, warp drives or hypertubes. So far\, all of these have ended up wit
h “odd” source terms in the sense that they violate energy conditions.
While the precise physical standing of energy conditions is complicated\,
their violation is usually still a warning sign. In this talk\, I will pr
esent a general introduction to warp drives\, a new modification resulting
in tractor beams\, and some discussion of energy conditions at large.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/21/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Erik Jensko (University College London)
DTSTART:20210907T131500Z
DTEND:20210907T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/22
DESCRIPTION:Title: Modifying General Relativity with boundary terms\nby Erik Jensko (U
niversity College London) as part of Theoretical physics seminar @ Tartu\n
\nLecture held in Physicum room A101\, University of Tartu\, Estonia.\n\nA
bstract\nIn this talk I present an outline of our recent work [2103.15906
gr-qc] which looks at yet another modification of General Relativity (GR)
of the form f(something). Here it’s based on a generalisation of the fir
st-order Einstein or Gamma-squared action\, which differs from the Einstei
n-Hilbert action by a boundary term. The underlying geometry is the usual
Riemannian structure of GR (with vanishing torsion and nonmetricity). Howe
ver\, I look at some of the equivalences with the other popular geometric
theories f(T) and f(Q) gravity\, set in different non-Riemannian geometrie
s. In the talk\, I focus on the importance of breaking the diffeomorphism
invariance of the gravitational action and field equations\, and how this
differs from many current theories. The similarities with the Lorentz non-
invariance of modified teleparallel f(T) gravity are also highlighted. Las
tly\, new boundary terms which differentiate between the gravitational act
ions of this theory and f(T) and f(Q) gravity are identified\, and I look
at how they can be used in a unified approach to modelling these apparentl
y distinct theories.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/22/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Carlos Argüelles (ICRA\, Pescara)
DTSTART:20210914T131500Z
DTEND:20210914T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/23
DESCRIPTION:Title: Dark matter in the Milky Way: from SgrA* to the entire halo\nby Car
los Argüelles (ICRA\, Pescara) as part of Theoretical physics seminar @ T
artu\n\nLecture held in Physicum room A102\, University of Tartu\, Estonia
.\n\nAbstract\nRelaxation mechanisms of collisionless self-gravitating sys
tems of fermions\, can lead to spherical equilibrium states which are stab
le\, long-lived\, and able to explain the dark matter (DM) halos in galaxi
es. The most general fermionic DM profile out of such a mechanism\, develo
ps a degenerate compact core which is surrounded by an extended halo. When
applied to the Milky Way\, it is demonstrated that while the outer halo c
an explain the rotation curve of our Galaxy\, the central DM-core explain
the dynamics of all the best resolved S-cluster stars orbiting SgrA *\, wi
thout the need of assuming a central black hole (BH). Interestingly\, when
such a novel core-halo DM profiles are applied to larger galaxies\, the d
ense DM core can reach the critical mass for gravitational collapse into a
BH of ∼ 10^8 Mo. This result provides a new mechanism for supermassive
BH formation in active galaxies directly from DM\, leading to a paradigm s
hift in the understanding of galactic cores.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/23/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Soham Bhattacharyya (Hannover\, Max Planck Inst. Grav.)
DTSTART:20210928T131500Z
DTEND:20210928T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/24
DESCRIPTION:Title: Stumbling around in the modified gravity landscape\nby Soham Bhatta
charyya (Hannover\, Max Planck Inst. Grav.) as part of Theoretical physics
seminar @ Tartu\n\nLecture held in Physicum room A101\, University of Tar
tu\, Estonia.\n\nAbstract\nParameters extracted from Gravitational Wave (G
W) data allow observers to quantify certain physical aspects of GW produci
ng sources\, like neutron stars (NS) and black holes (BH). In the case of
an isolated BH\, its physical shape in space\, as a freely falling asympto
tic observer would deduce from data\, combined with its inertial mass\, ge
ts encoded in GWs radiated from these sources. In classical terms\, a mult
ipolar structure of radiating sources can be established from the GW data\
, giving a freely falling observer a dynamic view of the 'horizon' of a BH
as it undergoes a damped oscillation towards a stable shape. However\, th
e dynamical behavior is the opposite when the source is a binary system. T
wo 'symmetric' bodies mutually deform each other to a maximally distorted
single compact object\, radiating GWs that increase in frequency and ampli
tude (to specific maximum values) along with the distortion. Using a Zange
nbewegung approach towards the maximal distortion (known in GW literature
as the merger) from both sides (ring-down and inspiral\, respectively)\, I
will talk about GR's predictions and the corresponding predictions made b
y extended theories of gravitation like f(R) and dynamical Chern-Simons.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/24/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Emanuele Zappala (Institute of Mathematics and Statistics\, Univer
sity of Tartu)
DTSTART:20210921T131500Z
DTEND:20210921T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/25
DESCRIPTION:Title: Braided matter interactions in quantum gravity via 1-handle attachment<
/a>\nby Emanuele Zappala (Institute of Mathematics and Statistics\, Univer
sity of Tartu) as part of Theoretical physics seminar @ Tartu\n\nLecture h
eld in Physicum room A102\, University of Tartu\, Estonia.\n\nAbstract\nIn
this talk I will present a topological description of elementary \nmatter
originally proposed by Bilson-Thompson\, where leptons\, quarks \nand ele
ctroweak gauge bosons are represented by topological excitations\nof triva
lent ribbon networks. I will argue that utilizing handle attachment of\nbr
aided networks in 3-space\, it is possible to preserve some of the most\na
ppealing properties of Bilson-Thompson model\, while still overcoming some
\nof the hurdles that this theory has encountered\, regarding particle int
eractions.\nIn addition\, I will explain how to derive some topological in
variants\, from \nKauffman-Lins recoupling theory\, that distinguish topol
ogical configurations \nassociated to different particles. \nThe talk will
be self-contained\, and no previous knowledge of topology is \nrequired\,
as I will introduce all the concepts used along the way.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/25/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Surajit Kalita (Indian Institute of Science\, Bangalore)
DTSTART:20211005T131500Z
DTEND:20211005T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/26
DESCRIPTION:Title: Probing violation of Chandrasekhar mass-limit through gravitational wav
es\nby Surajit Kalita (Indian Institute of Science\, Bangalore) as par
t of Theoretical physics seminar @ Tartu\n\nLecture held in Physicum room
A102\, University of Tartu\, Estonia.\n\nAbstract\nEinstein’s theory of
general relativity and quantum mechanics were among the most\nstartling di
scoveries in the 20th century. Based on these theories\, the maximum mass\
nof a non-rotating non-magnetized white dwarf is found to be about 1.4 sol
ar mass\,\nknown as the Chandrasekhar mass-limit. However\, over the past
decades\, various\nresearchers have indirectly predicted many sub- and sup
er-Chandrasekhar limiting\nmass white dwarfs (white dwarfs which violate t
he Chandrasekhar mass-limit) from\nthe luminosity-based observations of pe
culiar type Ia supernovae. Several research\ngroups worldwide\, including
us\, have proposed different models based on magnetic\nfields\, rotation\,
modified gravity\, noncommutative geometry\, etc.\, to explain these\npec
uliar white dwarfs. However\, no such white dwarfs have so far been observ
ed\ndirectly in any observations. Hence to predict the correct theory for
white dwarfs is\nstill unclear. In my presentation\, I will show that if s
uch white dwarfs rotate\nfollowing specific conditions\, they can emit con
tinuous gravitational radiation\, which\nin the future\, various detectors
\, such as LISA\, TianQin\, BBO\, DECIGO\, Einstein\nTelescope\, etc.\, ca
n detect with a significant signal-to-noise ratio. Thereby one can\npredic
t the structure of the white dwarfs and single out the correct theory of g
ravity.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/26/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Adam Zadrożny (National Center for Nuclear Research\, Poland)
DTSTART:20211012T131500Z
DTEND:20211012T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/27
DESCRIPTION:Title: Gravitational Waves: what we learned so far\nby Adam Zadrożny (Nat
ional Center for Nuclear Research\, Poland) as part of Theoretical physics
seminar @ Tartu\n\nLecture held in Physicum room A102\, University of Tar
tu\, Estonia.\n\nAbstract\nIt took us almost a hundred years from Einstein
’s publication to have observation-ready instruments. From the first det
ection GW150914\, we are able to observe the universe in gravitational wav
es. Currently\, after three observing runs of the LIGO-Virgo-KAGRA detecto
r network\, we were able to observe tens of mergers of binary black holes
and a bunch of mergers involving at least one neutron star. The most inter
esting thing was what we can get from the data\, like rates of compact obj
ects mergers\, constraints on neutron star equation of state\, tests of GR
in extreme regimes\, but also estimation of Hubble constant directly from
gravitational wave events observations.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/27/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Konstantinos Pallikaris (University of Tartu)
DTSTART:20211019T131500Z
DTEND:20211019T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/28
DESCRIPTION:Title: Horndeski with axions: shaping black holes\nby Konstantinos Pallika
ris (University of Tartu) as part of Theoretical physics seminar @ Tartu\n
\nLecture held in Physicum room A102\, University of Tartu\, Estonia.\n\nA
bstract\nWe discuss a ``user-friendly'' algorithm to systematically and ra
pidly obtain exact planar black hole solutions in the Einstein-Maxwell the
ory deformed by the most general shift- and reflection-symmetric Horndeski
sector where the usual Galileon is replaced by a tuple of scalars with pr
ofiles linear in the coordinates of the transverse manifold. Under precise
assumptions\, these axion backgrounds break the translational invariance
of the system\, causing momentum dissipation in the holographically dual f
ield theory. The success of the method relies on the simple realization th
at the bulk equations of motion become more tractable when written in term
s of the axions kinetic terms\, instead of the radial coordinate. Showcasi
ng this particularly efficient recipe\, we derive novel asymptotically AdS
black holes\, and show that their extremal counterparts always flow to an
AdS2×R2 infrared fixed point. Additionally\, we report an interesting fa
mily of new asymptotically Lifshitz black hole solutions with z>1. Finally
\, we discuss the DC transport properties of the dual relativistic field t
heories in view of possible applications to condensed matter systems.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/28/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Kristjan Müürsepp (University of Tartu\, NICPB Tallinn))
DTSTART:20211102T141500Z
DTEND:20211102T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/29
DESCRIPTION:Title: Multispinor formalism for higher spin theory: particle physics phenomen
ology\nby Kristjan Müürsepp (University of Tartu\, NICPB Tallinn)) a
s part of Theoretical physics seminar @ Tartu\n\nLecture held in Physicum
room A102\, University of Tartu\, Estonia.\n\nAbstract\nThe Standard Model
of particle physics\, despite its many triumphs\, still has flaws that ar
e yet to be convincingly addressed by new physics models. Among many other
open questions\, the nature of dark matter and the recently updated muon
g-2 anomaly remain as some of the more pertinent examples. In this talk\,
I will review a possible explanation of these issues in light of a recentl
y proposed effective field theory for higher spin particles. I will first
highlight the problems of higher spin theories of the past and then explai
n how one can construct a theory avoiding these obstacles. After that I wi
ll explain the phenomenological features of the new theory in detail\, cov
ering issues related to dark matter\, collider physics\, the g-2 anomaly\,
and nuclear physics.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/29/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marek Biesiada (National Centre for Nuclear Research\, Warsaw\, Po
land)
DTSTART:20211109T141500Z
DTEND:20211109T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/30
DESCRIPTION:Title: Strong lensing of gravitational waves - new opportunities for multimess
enger astronomy\nby Marek Biesiada (National Centre for Nuclear Resear
ch\, Warsaw\, Poland) as part of Theoretical physics seminar @ Tartu\n\nLe
cture held in Physicum room A102\, University of Tartu\, Estonia.\n\nAbstr
act\nDirect detections of gravitational waves (GW) opened a new era of GW
astronomy. Successful GW detection and observations of coalescing binary n
eutron star (NS-NS) system across a spectrum of electromagnetic waves (EM)
elevated multimessenger astronomy to the next stage. Future generations o
f GW detectors on the ground and in the space will yield a significant sta
tistics of such events reaching up to redshift z=5 and even deeper. Non-ne
gligible ammount of such events has a chance of being strongly lensed. In
my talk I will review the issue of GW lensing and discuss new opportunitie
s emerging from future detections of lensed GW signals. Wave phenomena con
cerning lensed GW signals\, like diffraction fringes and beat patterns wil
l be presented. An interesting idea of measuring dark matter self-interact
ions due to bulk viscosity attenuating GW will be discussed.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/30/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Raissa F. P. Mendes (Universidade Federal Fluminense\, Brazil)
DTSTART:20211116T141500Z
DTEND:20211116T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/31
DESCRIPTION:Title: Probing general relativity with neutron star oscillations\nby Raiss
a F. P. Mendes (Universidade Federal Fluminense\, Brazil) as part of Theor
etical physics seminar @ Tartu\n\nLecture held in Physicum room A102\, Uni
versity of Tartu\, Estonia.\n\nAbstract\nWith the dawn of the era of gravi
tational wave astronomy\, a new window has opened to probe general relativ
ity in the regime of strong gravitational fields. For this purpose\, it is
important to understand how predictions of modified theories of gravity c
ompare to those of general relativity in this regime\, and whether they ca
n be discerned by observations. In this talk I will discuss some implicati
ons of modified theories of gravity for equilibrium and perturbative prope
rties of neutron stars\, focusing on their oscillation spectrum.\n(Based o
n arXiv:1802.07847 and arXiv:2107.07036.)\n
LOCATION:https://researchseminars.org/talk/UTPhysics/31/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Carlo Marzo (NICPB\, Tallinn)
DTSTART:20211130T141500Z
DTEND:20211130T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/32
DESCRIPTION:Title: Radiatively stable unitarity in higher-spin models\, and applications i
n metric-affine gravity\nby Carlo Marzo (NICPB\, Tallinn) as part of T
heoretical physics seminar @ Tartu\n\nLecture held in Physicum room A102\,
University of Tartu\, Estonia.\n\nAbstract\nThe scrutiny of gravitational
theories beyond Einstein-Hilbert enjoys a different standard than flat mo
dels probed at collider-level energies. Of the proposed extensions\, only
a subset are explicitly required to be free of ghosts. Even in such cases\
, only dipole ghosts are usually targeted\, thus still allowing\, in gener
al\, wrong-sign states to propagate. Moreover\, even in rare cases where a
thorough spectral analysis is performed\, the stability of the resulting
action under radiative corrections is uncertain.\nIn this talk\, I discuss
the strong constraining power of requiring\, as standard for lower-spin m
odels\, a radiatively stable ghost- and tachyon-free action for the paradi
gmatic scenario of metric-affine gravity. I will describe the role of non-
accidental symmetries and their interplay with diffeomorphism invariance.
I will also provide\, in a more general way\, an overview of the computati
onal challenges on the way of the spectrum of higher-spin theories.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/32/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Vladimir Hizhnyakov (University of Tartu)
DTSTART:20211207T141500Z
DTEND:20211207T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/33
DESCRIPTION:Title: Mechanisms of motion of vibrational solitons\nby Vladimir Hizhnyako
v (University of Tartu) as part of Theoretical physics seminar @ Tartu\n\n
Lecture held in Physicum room A102\, University of Tartu\, Estonia.\n\nAbs
tract\nPrevious studies of nonlinear dynamics have shown that local vibrat
ional excitations\, both stationary and moving\, can exist in ideal anharm
onic atomic lattices [1\,2]. These excitations are called vibrational soli
tons\, intrinsic localized modes\, or discrete breathers (DBs). Large-size
low-frequency DBs in atomic chains have high mobility. However\, when the
size of the DB is small\, the discreteness of the atomic lattice breaks t
he continuous symmetry and leads to the capture of the moving DB by the Pe
ierls-Nabarro potential barrier. Nevertheless\, as we have shown [3\,4]\,
DBs in metals Fe\, Cu\, Ni\, Nb and in some other crystals can move on a l
ong distance. DBs are most likely responsible for the transmission of sign
als in biological chains.\nWe investigated in detail the mobility of DBs i
n the Fermi\, Pasta and Ulam lattice (FPU) and found that the odd (cubic (
k_3) and fifth (k_5)) anharmonicity strongly promotes the mobility of DB.
We also found that the mobility of BDs strongly depends on the linear loca
lized modes (LLMs) previously predicted by us [6] – the phonons captured
by DB: these modes promote the interaction of DBs with phonon continuum.\
nMoreover\, we found that initially stationary or captured after moving a
DB of the high or medium frequency range is sooner or later converted into
a DB of medium frequency with a long service life\, propagating along the
chain over a long distance without capture. The process begins with an in
crease in the amplitude of vibrations of the energy centers DB in time\; t
he movement begins when this amplitude reaches half the distance between t
he atoms. And in this case\, odd anharmonicity is also an important factor
– it greatly contributes to the mobility of DBs. The amplification of t
he vibrations of the energy center and the subsequent movement occur due t
o the radiation of low frequency phonons with a momentum. This radiation i
s the result of the common nonlinear action of DB and LLM. Thus\, a moving
DB in the lattice is like a rocket: it emits particles (here low-frequenc
y phonons) with a pulse in the opposite direction\, which makes it possibl
e to overcome the braking caused by radiation processes. We also found tha
t a well-chosen fifth anharmonicity leads to the disappearance of the Peie
rls-Nabarro barrier and to an inversion of stability between bond-centered
and site-centered DBs\, and\, in fact\, to essentially non-radiative prop
agation of a DB along the chain.\n\n1. A.J. Sievers\, S. Takeno\, Phys. Re
v. Lett. 61\, 970 (1988).\n2. S. Flach and C. R. Willis\, Phys. Repts. 295
\, 181 (1998).\n3. M. Haas\, V. Hizhnyakov\, A. Shelkan\, M. Klopov\, and
A. J. Sievers\, Phys. Rev. B 84\, 144303 (2011).\n4. V. Hizhnyakov\, M. Ha
as\; A. Shelkan\, M. Klopov\, Physica Scripta\, 89 (4) (2014).\n5. A. Shel
kan\, M. Klopov\, V. Hizhnyakov\, Phys. Lett. A 383\, 1893 (2019).\n6. V.
Hizhnyakov\, A. Shelkan\, M. Klopov\, S.A. Kiselev\, A.J. Sievers\, Phys.
Rev. B 73\, 224302 (2006).\n
LOCATION:https://researchseminars.org/talk/UTPhysics/33/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Joosep Pata (NICPB\, Tallinn)
DTSTART:20211214T141500Z
DTEND:20211214T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/34
DESCRIPTION:Title: Machine learning for data reconstruction at the LHC\nby Joosep Pata
(NICPB\, Tallinn) as part of Theoretical physics seminar @ Tartu\n\nLectu
re held in Physicum room A102\, University of Tartu\, Estonia.\n\nAbstract
\nPhysics analyses at the CERN experiments rely on detector hits being int
erpreted or reconstructed as particle candidates. The data reconstruction
systems are built on decades of physics and detector knowledge and must op
erate reliably on petabytes of data in diverse computing centers spread ar
ound the world. In the recent years\, machine learning (ML) is playing an
increasingly important role at the LHC experiments for reconstructing and
interpreting the data\, from calibrating the detector readouts to the fina
l interpretation for complex signal processes. We will discuss the various
aspects of ML at the LHC experiments\, focusing on data reconstruction an
d particle identification approaches using modern machine learning methods
such as graph neural networks.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/34/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Nico Alexis Benincasa (NICPB-KBFI\, Tallinn)
DTSTART:20220125T141500Z
DTEND:20220125T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/35
DESCRIPTION:Title: Multi-step phase transitions and gravitational waves in the inert doubl
et model\nby Nico Alexis Benincasa (NICPB-KBFI\, Tallinn) as part of T
heoretical physics seminar @ Tartu\n\nLecture held in Physicum room A102\,
University of Tartu\, Estonia.\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/UTPhysics/35/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Flavio Bombacigno (University of Valencia)
DTSTART:20220208T141500Z
DTEND:20220208T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/36
DESCRIPTION:Title: Quasinormal modes of Schwarzschild black holes in projective invariant
Chern-Simons gravity\nby Flavio Bombacigno (University of Valencia) as
part of Theoretical physics seminar @ Tartu\n\nLecture held in Physicum r
oom A102\, University of Tartu\, Estonia.\n\nAbstract\nWe generalize the C
hern-Simons theory of gravity to the metric-affine case\, where projective
invariance is recovered by enlarging the Pontryagin density with homothet
ic curvature terms which do not spoil topologicity. This one is then broke
n by promoting the coupling to the Chern-Simons term to a dynamical scalar
field\, and we derive at the perturbative level the solutions for torsion
and nonmetricity\, showing that they can be iteratively obtained from the
background metric and the derivative of the scalar field. That allows us
to describe the dynamics for the metric and the scalar field perturbations
in a self-consistent way\, and we apply the formalism to the study of qua
sinormal modes for a Schwarzschild black hole. By adopting numerical techn
iques\, we show that in the absence of the kinetic term for the scalar fie
ld the latter is still endowed with a proper dynamical character\, contrar
y to non dynamical Chern-Simons theory in metric formalism. Finally\, we c
ompute the quasinormal frequencies and characterize the late-time power la
w tails\, comparing the results with the outcomes of the purely metric app
roach.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/36/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sree Kanth Hari Kumar (NCBJ\, Warsaw)
DTSTART:20220215T141500Z
DTEND:20220215T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/37
DESCRIPTION:Title: Gravitational lensing of gravitational waves\nby Sree Kanth Hari Ku
mar (NCBJ\, Warsaw) as part of Theoretical physics seminar @ Tartu\n\nLect
ure held in Physicum room A102\, University of Tartu\, Estonia.\n\nAbstrac
t\nGravitational lensing has now become an unavoidable tool in astrophysic
s. Like lensing of electromagnetic waves\, matter distribution between the
gravitational wave (GW) source and the detector can act as a gravitationa
l lens and produce multiple GW images. Lensing of GW signals leads to the
amplification of the signal and increases the signal to noise ratio. Unlik
e EM waves\, the wavelength of the gravitational waves is comparable to t
he Schwarschild radius of the lens which leads to some interesting effects
such as interference and diffraction. In this talk I will discuss such po
ssible effects of lensing of gravitational waves that could be observed wi
th current and next generation gravitational wave detectors.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/37/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Francisco José Maldonado Torralba (University of Tartu)
DTSTART:20220222T141500Z
DTEND:20220222T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/38
DESCRIPTION:Title: Explaining Dark Matter with torsion\nby Francisco José Maldonado T
orralba (University of Tartu) as part of Theoretical physics seminar @ Tar
tu\n\nLecture held in Physicum room A102\, University of Tartu\, Estonia.\
n\nAbstract\nIn this talk I will explain how the pseudoscalar degree of fr
eedom of the quadratic Poincaré Gauge theory of gravity can act as a dark
matter candidate. I will give the parameter space of the theory for which
such dark matter candidate can account for all predicted cold dark matter
\, and constrain such parameters based on current astrophysical observatio
ns.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/38/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Débora Aguiar Gomes (State University of Ceará\, Brazil)
DTSTART:20220301T141500Z
DTEND:20220301T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/39
DESCRIPTION:Title: Symmetric Teleparallel Equivalent of General Relativity\nby Débora
Aguiar Gomes (State University of Ceará\, Brazil) as part of Theoretical
physics seminar @ Tartu\n\nLecture held in Physicum room A102\, Universit
y of Tartu\, Estonia.\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/UTPhysics/39/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Adrià Delhom I Latorre (University of Tartu)
DTSTART:20220308T141500Z
DTEND:20220308T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/40
DESCRIPTION:Title: Ghosts in curvature-based metric-affine gravity and the role of project
ive symmetry\nby Adrià Delhom I Latorre (University of Tartu) as part
of Theoretical physics seminar @ Tartu\n\nLecture held in Physicum room A
102\, University of Tartu\, Estonia.\n\nAbstract\nWe will explicitly show
how ghost degrees of freedom arise in a sub-class of metric-affine theorie
s unless projective symmetry is enforced. Then\, we will generalize the te
chniques employed in that particular case to argue why ghosts will arise i
n generic metric-affine theories of gravity around arbitrary backgrounds.
We will also discuss some results on possible ways to avoid them.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/40/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sreekanth Harikumar (NCBJ\, Warsaw)
DTSTART:20220315T141500Z
DTEND:20220315T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/41
DESCRIPTION:Title: Moffat MOdified Gravity(MOG) / Scalar Tensor Vector Gravity (STVG)\
nby Sreekanth Harikumar (NCBJ\, Warsaw) as part of Theoretical physics sem
inar @ Tartu\n\nLecture held in Physicum room A102\, University of Tartu\,
Estonia.\n\nAbstract\nScalar Tensor Vector Gravity / MOG is a metric theo
ry of gravity with dynamical scalar fields and a massive vector field intr
oduced in addition to the metric tensor. In the weak field approximation M
OG modifies the Newtonian acceleration with a Yukawa like repulsive term d
ue to Maxwell-Proca type Lagrangian. This associates matter with a fifth f
orce and a modified equation of motion. MOG has been successful in explain
ing galaxy rotation curves\, gravitational lensing\, cosmological observat
ions and all other solar system observation without the need of dark matte
r. In this talk I will discuss the key concepts of MOG theory. Then I will
discuss existing observational bounds on STVG weak field parameters. In
particular I will present the results obtained from X-COP sample of galax
y clusters.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/41/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alejandro Hernandez-Arboleda (Universidade Federal do Espírito Sa
nto\, Brazil)
DTSTART:20220322T141500Z
DTEND:20220322T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/42
DESCRIPTION:Title: Additional velocity Distribution: A fast sample analysis for dark matte
r or modified gravity models\nby Alejandro Hernandez-Arboleda (Univers
idade Federal do Espírito Santo\, Brazil) as part of Theoretical physics
seminar @ Tartu\n\nLecture held in Physicum room A102\, University of Tart
u\, Estonia.\n\nAbstract\nWe propose a new complementary and fast approach
to study galaxy rotation curves straight from the sample data\, instead o
f individual rotation curve fits. It is based on the difference between th
e observational rotation curve and the expected one from the baryonic matt
er\, under certain normalization (𝛿𝑉2). The first step is to find th
e observational data distribution of 𝛿𝑉2\, which is estimated from t
he observational data from a 2D kernel density estimation. The estimate is
then contrasted with specific model predictions for the same baryonic dat
a. Here we consider the following five models: Burkert profile\, MOND\, Pa
latini 𝑓(𝑅) gravity\, Eddington-inspired-Born-Infeld (EiBI) model an
d general relativity with renormalization group effects (RGGR). We stress
the following method properties: i) the method deals with the sample behav
iour\, not the individual galaxy fits: it provides quicker evaluation and
it promptly presents sample properties\; ii) it studies the form of the ve
locity curve added by the model\, not its magnitude (typically\, this impl
ies one less parameter for the analysis)\; iii) it can be applied to modif
ied gravity models even if the observational 3D baryonic matter distributi
on is not known: it is based on the baryonic velocity contribution to the
rotation curve together with minimal hypothesis on the average 3D modeling
. About the tested models\, and considering the tests that the method can
perform\, the Burkert profile\, MOND and RGGR have good sample behaviour\,
nonetheless\, the method points out specific difficulties for these three
cases. Palatini 𝑓(𝑅) and EiBI gravities cannot be used to replace d
ark matter and\, if considered together with some dark matter halo\, large
amounts of the latter will be necessary.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/42/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sotirios Karamitsos (Pisa University)
DTSTART:20220405T131500Z
DTEND:20220405T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/43
DESCRIPTION:Title: Metric to Palatini (and vice versa): the strong limit and potential rec
onstruction in attractor theories of inflation\nby Sotirios Karamitsos
(Pisa University) as part of Theoretical physics seminar @ Tartu\n\nLectu
re held in Physicum room A102\, University of Tartu\, Estonia.\n\nAbstract
\nThe same model of inflation can be written in many different ways\, ofte
n concealing its true physical degrees of freedom. In this talk\, I will d
emonstrate how scalar-tensor theories of inflation are linked through equi
valence classes in the absence of kinetic poles. When poles are introduced
\, this equivalence is broken\, but the resulting "attractor" models give
particularly robust predictions that do not depend on the inflationary pot
ential\, in the so-called "strong coupling limit". However\, this independ
ence may also be broken when switching to a different underlying formalism
of gravity (metric or Palatini). I will discuss the conditions for the st
rong limit to be maintained regardless the gravitational formalism employe
d\, and the conditions for the potential to be reconstructed in a formalis
m-independent way.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/43/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Arpan Chatterjee (University of Tartu)
DTSTART:20220419T131500Z
DTEND:20220419T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/44
DESCRIPTION:Title: A modern shape for the non-local Nambu Jona-Lasinio model\nby Arpan
Chatterjee (University of Tartu) as part of Theoretical physics seminar @
Tartu\n\nLecture held in Physicum room A102\, University of Tartu\, Eston
ia.\n\nAbstract\nThe Standard Model of Particle Physics is based on two fu
ndamental theories: the Electroweak theory of Glashow\, Weinberg and Salam
\, and Quantumchromodynamics (QCD) developed by Gross\, Wilczek and Politz
er. Of these\, QCD has two features\, not common to the other interactions
: Asymptotic Freedom\, which can be explained by the running of the strong
coupling due to renormalization\, and Quark Confinement which does not al
low us to “see” quarks as individual particles. The necessity to descr
ibe particles which have not and will never be “seen” as free particle
s led to the development of Effective Field Theories (EFTs). One of these
EFT approaches is the one developed by Nambu and Jona-Lasinio in 1961\, ba
sed on the principles of the BCS theory of superconductivity developed by
Bardeen\, Cooper and Schrieffer. While the original approach replaces the
interaction vector bosons effectively by local four-fermion interactions (
hence non-renormalisable)\, in our project we consider a non-local version
of the NJL model which has been shown to be both renormalisable and confi
ning and hence much more appropriate to be used in elementary particle phy
sics. The main aim of our project is to present a modern and non-local ver
sion of the NJL model\, applied to particle physics phenomenology\, in par
ticular as an EFT approach for QCD.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/44/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alice Boldrin (NCBJ\, Warsaw)
DTSTART:20220503T131500Z
DTEND:20220503T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/45
DESCRIPTION:Title: Dirac procedure and the Hamiltonian formalism for cosmological perturba
tions in a Bianchi I universe\nby Alice Boldrin (NCBJ\, Warsaw) as par
t of Theoretical physics seminar @ Tartu\n\nLecture held in Physicum room
A102\, University of Tartu\, Estonia.\n\nAbstract\nWe apply the Dirac proc
edure for constrained systems to the Arnowitt–Deser–Misner formalism l
inearized around the Bianchi I universe. We discuss and employ basic conce
pts such as Dirac observables\, Dirac brackets\, gauge-fixing conditions\,
reduced phase space\, physical Hamiltonian\, canonical isomorphism betwee
n different gauge-fixing surfaces and spacetime reconstruction. We relate
this approach to the gauge-fixing procedure for non-perturbative canonical
relativity. We discuss the issue of propagating a basis for the scalar-ve
ctor-tensor decomposition as\, in an anisotropic universe\, the wavefronts
of plane waves undergo a non-trivial evolution. We show that the definiti
on of a gravitational wave as a traceless-transverse mode of the metric pe
rturbation needs to be revised. Moreover there exist coordinate systems in
which a polarization mode of the gravitational wave is given entirely in
terms of a scalar metric perturbation. We first develop the formalism for
the universe with a single scalar field and then extend it to the multi-fi
eld case. The obtained fully canonical formalism will serve as a starting
point for a complete quantization of the cosmological perturbations and th
e cosmological background.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/45/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Laxmipriya Pati (BITS-Pilani Hyderabad)
DTSTART:20220607T131500Z
DTEND:20220607T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/46
DESCRIPTION:Title: Rip Cosmological Models in Extended Symmetric Teleparallel Gravity\
nby Laxmipriya Pati (BITS-Pilani Hyderabad) as part of Theoretical physics
seminar @ Tartu\n\nLecture held in Physicum room A102\, University of Tar
tu\, Estonia.\n\nAbstract\nIn this work\, we have investigated some rip co
smological models in an extended symmetric teleparallel gravity theory. We
consider the form f(Q\,T)=aQm+bTf(Q\, T) = aQ^m+bT in the Einstein–Hilb
ert action and express the field equations and the dynamical parameters in
terms of the non-metricity QQ. Three rip models such as Little Rip\, Big
Rip\, and Pseudo Rip are presented\, also the energy conditions and the co
smographic parameters are derived and analyzed for all these models.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/46/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Adrián Casado-Turrión (Complutense University of Madrid\, Spain)
DTSTART:20220920T131500Z
DTEND:20220920T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/47
DESCRIPTION:Title: (Im)possibility of gravitational collapse in f(R) gravity\nby Adri
án Casado-Turrión (Complutense University of Madrid\, Spain) as part of
Theoretical physics seminar @ Tartu\n\nLecture held in Physicum room A102\
, University of Tartu\, Estonia.\n\nAbstract\nGravitational collapse is st
ill poorly understood in the context of f(R) theories of gravity. The arch
etypal Oppenheimer-Snyder model (which is an exact solution of General Rel
ativity) is known to be\nincompatible with the junction conditions of f(R)
models\, both in the metric and Palatini formalisms. In this talk\, we sh
all explain how the Oppenheimer-Snyder construction must be generalised so
as to fit within f(R) theories of gravity. By means of a systematic analy
sis of the relevant junction conditions\, we will show that some paradigma
tic vacuum metrics cannot represent spacetime outside collapsing stars in
f(R) gravity.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/47/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Fernando Izaurieta (University of Concepción\, Chile)
DTSTART:20220927T131500Z
DTEND:20220927T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/48
DESCRIPTION:Title: Gravitational Waves: A falsification Tool for Riemann-Cartan Gravity Th
eories?\nby Fernando Izaurieta (University of Concepción\, Chile) as
part of Theoretical physics seminar @ Tartu\n\nLecture held in Physicum ro
om A102\, University of Tartu\, Estonia.\n\nAbstract\nWe develop general m
athematical tools to study the propagation of waves on Riemann-Cartan back
grounds in a way as model-independent as possible. Using this\, we prove t
hat torsional backgrounds can induce\nanomalous propagation of amplitude a
nd polarization and assess whether it could allow using gravitational wave
s as a probe to detect torsion.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/48/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Adrián Casado Turrión (UCM\, Madrid\, Dept. Theor. Phys. II)
DTSTART:20221004T131500Z
DTEND:20221004T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/49
DESCRIPTION:Title: An 'Unruhduction' to particle creation by acceleration and Quantum Fiel
d Theory in curved spacetimes\nby Adrián Casado Turrión (UCM\, Madri
d\, Dept. Theor. Phys. II) as part of Theoretical physics seminar @ Tartu\
n\nLecture held in Physicum room A102\, University of Tartu\, Estonia.\n\n
Abstract\nThis talk will consist in a brief\, pedagogical introduction to
all the relevant concepts and techniques employed in Quantum Field Theory
in curved spacetimes. After reviewing the Unruh effect and its relationshi
p with the concept of particle in standard QFT in Minkowski spacetime\, we
will move on to study particle creation due to the presence of classical
gravitational fields. In particular\, we shall focus on Hawking radiation
and black-hole thermodynamics.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/49/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Abdel Nasser Tawfik (Future University in Egypt)
DTSTART:20221101T141500Z
DTEND:20221101T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/50
DESCRIPTION:Title: Quantum-induced aspects imposed on Einstein tensor\nby Abdel Nasser
Tawfik (Future University in Egypt) as part of Theoretical physics semina
r @ Tartu\n\nLecture held in Physicum room A102\, University of Tartu\, Es
tonia.\n\nAbstract\nWhen generalized noncommutative Heisenberg algebra acc
ommodating impacts of a finite gravitational field as specified by doubly-
special relativity\, loop quantum gravity\, and string theory\, is extende
d to an eight-dimensional Finsler manifold\, quantum-induced aspects could
be imposed on the Riemann curvature tensor and its unique contractions. I
n the same manner\, the Einstein tensor could be constructed. We found th
at the covariant derivative of the Einstein tensor\, in which besides the
quantization additional geometric structures have emerged\, vanishes.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/50/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marco Barsanti (Università di Pisa)
DTSTART:20221206T141500Z
DTEND:20221206T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/51
DESCRIPTION:Title: Baryons as topological solitons\nby Marco Barsanti (Università di
Pisa) as part of Theoretical physics seminar @ Tartu\n\nLecture held in Ph
ysicum room A102\, University of Tartu\, Estonia.\n\nAbstract\nIn this tal
k\, I will discuss the mathematical and physical motivations that allow us
to identify the solitonic solutions of a Mesonic Field Theory\, called th
e Skyrme model\, as Baryons in Large-N QCD. In the first part of the talk\
, I will present the general idea of solitons in Physics\, giving a simple
example from Classical Mechanics. Then\, I will finally introduce the Sky
rme model\, a possible candidate for the low-energy QCD Lagrangian at larg
e N\, and I will show the existence of solitonic solutions\, known as Skyr
mions\, in that theory. These solutions are characterized by a conserved c
harge called topological index and for this reason are known as topologica
l solitons. That conserved charge has been physically identified with the
baryon number and thus consequently the Skyrmions have been identified wit
h the Baryons. Physical predictions concerning baryon physics\, as well as
nuclear physics\, can be computed and compared with the experiments. In t
his regard\, I will present some good results and some problems of the mod
el.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/51/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Damianos Iosifidis (University of Tartu)
DTSTART:20230103T141500Z
DTEND:20230103T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/52
DESCRIPTION:Title: Non-Riemannian Effects in Cosmology\nby Damianos Iosifidis (Univers
ity of Tartu) as part of Theoretical physics seminar @ Tartu\n\nLecture he
ld in Physicum room A102\, University of Tartu\, Estonia.\n\nAbstract\nWe
investigate the cosmological aspects of the most general parity preserving
Metric-Affine Gravity theory quadratic in torsion and non-metricity in th
e presence of a cosmological hyperfluid.The latter is a generalization of
the usual Perfect Fluid notion that includes also a non-vanishing hypermom
entum tensor that is compatible with the Cosmological Principle and encode
s the microscopic characteristics of matter. Then\, the equations of motio
n are obtained by varying the action with respect to the metric and the in
dependent affine connection. Subsequently\, considering a Friedmann-Lemaî
tre-Robertson-Walker background\, we derive the most general form of the m
odified Friedmann equations for the full quadratic theory. We then focus o
n a characteristic sub-case involving only two quadratic contributions giv
en in terms of torsion and non-metricity vectors. In this setup\, studying
the modified Friedmann equations along with the conservation laws of the
perfect cosmological hyperfluid\, we provide exact solutions both for pure
ly dilation and for purely spin hypermomentum sources. We then discuss the
physical consequences of our model and the prominent role of torsion and
non-metricity in this cosmological setup.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/52/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Tom Lawrence (Ronin Institute for Independent Scholarship)
DTSTART:20230124T141500Z
DTEND:20230124T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/53
DESCRIPTION:Title: The coset formulation of gravitational theories: understanding metric-p
reserving changes of basis\nby Tom Lawrence (Ronin Institute for Indep
endent Scholarship) as part of Theoretical physics seminar @ Tartu\n\nLect
ure held in Physicum room A102\, University of Tartu\, Estonia.\n\nAbstrac
t\nThe requirement of distant parallelism implicitly defines a field of or
thonormal frame bases. Such fields are related by a local Lorentz group\,
I(u). Meanwhile\, changes of coordinate basis form a wider group of genera
l linear transformations\, J(u). From this\, it can easily be shown that t
he degrees of freedom contained in the metric are the parameters of the co
set space J/I. This separation of the parallelism degrees of freedom from
the metric degrees of freedom allows a Cartan decomposition of the Weitzen
böck connection. Holonomic frames\, in which the Weitzenböck spin connec
tion vanishes\, are then found to be ones in which the frame basis is rela
ted to the coordinate basis by a transformation matrix only containing met
ric degrees of freedom. The transformation laws of such matrices – coset
space representatives – mean that this gauge choice is not consistent w
ith general covariance. This formulation allows the correct relationship b
etween inertial effects and transformations in I(u) to be explored and ide
ntified. [The presentation is based on Sections 1-5 of arXiv:2211.07586. I
t is an extended and rearranged version of that given to the Geometric Fou
ndations of Gravity 2021 conference.]\n
LOCATION:https://researchseminars.org/talk/UTPhysics/53/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Orest Hrycyna (NCBJ\, Warsaw)
DTSTART:20230214T141500Z
DTEND:20230214T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/54
DESCRIPTION:Title: Structural stability and non-singular beginning of the universe\nby
Orest Hrycyna (NCBJ\, Warsaw) as part of Theoretical physics seminar @ Ta
rtu\n\nLecture held in Physicum room A102\, University of Tartu\, Estonia.
\n\nAbstract\nTheory of gravity with a quadratic contribution of scalar cu
rvature is investigated in terms of dynamical system approach. The simples
t Friedmann-Robertson-Walker metric is used to formulate dynamics in Jorda
n frame as well as in conformally transformed Einstein frame. In both fram
es there are asymptotically stable de Sitter states for which the Hubble f
unction naturally gives terms corresponding to non-substantial dark matter
. Using invariant centre manifold I show that in the Einstein frame there
is a zero measure set of initial conditions leading from the unstable to t
he stable de Sitter state. The Jordan frame and the Einstein frame formula
tion of the theory are physically nonequivalent.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/54/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ahmet Ilker Topuz (Tartu University)
DTSTART:20230221T141500Z
DTEND:20230221T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/55
DESCRIPTION:Title: Particle generation through energy discretization and restrictive plane
s in GEANT4 simulations for potential applications of cosmic ray muon tomo
graphy\nby Ahmet Ilker Topuz (Tartu University) as part of Theoretical
physics seminar @ Tartu\n\nLecture held in Physicum room A102\, Universit
y of Tartu\, Estonia.\n\nAbstract\nIn this study\, by attempting to resolv
e the difficulties related to the angular distribution during the particle
generation for the muon tomography applications in the GEANT4 simulations
\, we exhibit an unconventional methodology that is hinged on the directio
n limitation via the vectorial construction from the generation location t
o the restriction area rather than using a certain angular distribution or
interval. In other words\, we favor a momentum direction that is determin
ed by a vector constructed between an initial point randomly chosen on a g
enerative point/plane and a second point arbitrarily selected on a restric
tive plane of the same dimensions with the basal cross section of the volu
me-of-interest (VOI). On account of setting out such a generation scheme\,
we optimize the particle loss by keeping an angular acceptance that is di
rectly dependent on the VOI geometry as well as the vertical position of t
he restrictive plane for a tomographic system of a finite size. We demonst
rate our strategy for a set of target materials including aluminum\, iron\
, copper\, lead\, and uranium with a dimension of 40×10×40 cm^3 over thr
ee restrictive planes of different positions by using a discrete energy sp
ectrum between 0.1 and 8 GeV and we compute the scattering angle\, the num
ber of absorption\, and the particle loss. Upon our simulation outcomes\,
we show that the particle generation by means of restrictive planes is an
effective strategy that is flexible towards a variety of computational obj
ectives in the GEANT4 simulations.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/55/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Damianos Iosifidis (Tartu University)
DTSTART:20230912T131500Z
DTEND:20230912T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/56
DESCRIPTION:Title: Imperfect Fluids with Intrinsic Hypermomentum\nby Damianos Iosifidi
s (Tartu University) as part of Theoretical physics seminar @ Tartu\n\nLec
ture held in Physicum room A102\, University of Tartu\, Estonia.\n\nAbstra
ct\nWe develop the Action Formulation of Relativistic Hyperfluids\, namely
fluids with intrinsic hypermomentum that describes the microproperties of
matter (spin\, dilation and shear). By extending the Perfect Fluid formul
ation we supplement the fluid action with matter-connection couplings that
reproduce the desired hypermomentum tensor of the recently developed Perf
ect Hyperfluid. More specifically\, by considering the cases of pure spin\
, dilation and shear hyperfluids separately\, we find the kinematics of ea
ch individual piece. A rather remarkable result is that for the pure spin
and shear cases\, the corresponding energy-momentum tensor does not have t
he usual Perfect Fluid form but rather that of an imperfect one whose heat
flux\, stresses and bulk viscosity are given in terms of the hypermomentu
m variables. This ultimately indicates that the so-called constitutive rel
ations for viscous fluids may naturally follow by the inclusion of the mic
ro-properties of matter (hypermomentum).\n
LOCATION:https://researchseminars.org/talk/UTPhysics/56/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Daniel Blixt (Scuola Superiore Merdionale\, Napoli\, Italy)
DTSTART:20230926T131500Z
DTEND:20230926T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/57
DESCRIPTION:Title: Teleparallelism\nby Daniel Blixt (Scuola Superiore Merdionale\, Nap
oli\, Italy) as part of Theoretical physics seminar @ Tartu\n\nLecture hel
d in Physicum room A102\, University of Tartu\, Estonia.\n\nAbstract\nThis
talk aims to give an introduction to teleparallelism and to present some
recent insights on the topic. Apart from delving into the concept of telep
arallelism\, I will discuss general relativity and the (non)importance of
boundary terms\, to then show that teleparallelism allows us to reformulat
e general relativity in terms of torsion and/or non-metricity instead of c
urvature. From this formulation there are many ways for which one can depa
rt from general relativity and look at modified theories of gravity. In th
is context\, I will discuss symmetries and how they can be used to simplif
y calculations and to count the number of degrees of freedom in the theori
es. I will further argue that teleparallelism can be useful to solve theor
etical and/or observational problems.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/57/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alejandro Jiménez Cano (Tartu University)
DTSTART:20231114T141500Z
DTEND:20231114T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/58
DESCRIPTION:Title: Junction conditions: foundations and subtleties\nby Alejandro Jimé
nez Cano (Tartu University) as part of Theoretical physics seminar @ Tartu
\n\nLecture held in Physicum room A102\, University of Tartu\, Estonia.\n\
nAbstract\nThis talk is an introduction to the junction conditions formali
sm. I will provide the basic notions to understand the topic (tensor distr
ibutions\, regular plus singular decomposition\, etc.) and a general proce
dure that we proposed to analyze particular theories. I will also unveil c
ertain ambiguities that appear when dealing with distributions in this con
text.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/58/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Miguel Bezares (University of Nottingham)
DTSTART:20231121T141500Z
DTEND:20231121T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/59
DESCRIPTION:Title: Numerical Relativity - beyond General Relativity\nby Miguel Bezares
(University of Nottingham) as part of Theoretical physics seminar @ Tartu
\n\nLecture held in Physicum room A102\, University of Tartu\, Estonia.\n\
nAbstract\nWe will explore the long path from Einstein's equations to comp
utational simulations. I will discuss how Numerical Relativity (NR) can se
rve as a tool to understand gravitational wave generation in dark energy m
odels and what challenges must be overcome to extend NR in these theories.
In particular\, I will consider a class of alternative theories of gravit
y known as k-essence. This cosmologically relevant scalar-tensor theory in
volves first-order derivative self-interactions\, which pass all existing
gravitational wave bounds and provide a screening mechanism. Specifically\
, I will present our numerical simulations of this theory considering thre
e different scenarios: nonlinear stellar oscillations\, gravitational coll
apse\, and binary neutron stars.\n
LOCATION:https://researchseminars.org/talk/UTPhysics/59/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Tomi Koivisto (Tartu University)
DTSTART:20231207T141500Z
DTEND:20231207T154500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/60
DESCRIPTION:Title: On the metageometric foundation of physics\nby Tomi Koivisto (Tartu
University) as part of Theoretical physics seminar @ Tartu\n\nLecture hel
d in Physicum room A106\, University of Tartu\, Estonia.\n\nAbstract\nFund
amental interactions in the Standard Model of particle physics are describ
ed by quantum gauge theory. I will present our novel approach to gauge int
eractions at the foundation of a new Standard Model which includes General
Relativity. It entails a completion of the latter theory and suggests a p
ossible rationale for the emergence of the Universe and its (apparently\,
mostly dark) contents. Rather than by adding new speculative assumptions\,
the proposed foundation arises by removing the scaffolding of observer-in
dependent spacetime ingrained into current formulations of fundamental phy
sics.\n\nPhysicum seminar - Physicum A106 (W. Ostwaldi str. 1)\n\nZoom lin
k:\nhttps://ut-ee.zoom.us/j/91241051766?pwd=TTBQWmszbS9GV052alpXRmo1VmFsdz
09\n\nMeeting ID: 912 4105 1766\nPasscode: 370272\n
LOCATION:https://researchseminars.org/talk/UTPhysics/60/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Manuel Hohmann (Tartu University)
DTSTART:20240416T131500Z
DTEND:20240416T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/61
DESCRIPTION:Title: How to (not) break local Lorentz invariance in gravity theory\nby M
anuel Hohmann (Tartu University) as part of Theoretical physics seminar @
Tartu\n\nLecture held in Physicum room A102\, University of Tartu\, Estoni
a.\n\nAbstract\nLocal Lorentz invariance is one of the crucial features of
general relativity which allows relating the reference systems\, and henc
e the clocks\, of relatively moving observers. Several gravity theories ar
e claimed to break local Lorentz invariance\, including theories involving
quantum corrections\, modified dispersion relations\, Finsler geometry an
d teleparallel gravity. I explain which of these correspond to an observab
le violation of local Lorentz invariance and which\, despite their name\,
cannot be observed in nature\, even if they are present in the theory.\n\n
M. Hohmann\, Int. J. Geom. Meth. Mod. Phys. 19\, Supp. 1 2240001 (2022) [a
rXiv:2112.15173 [gr-qc]]\nM. Hohmann\, C. Pfeifer and N. Voicu\, J. Math.
Phys. 63 032503 (2022) [arXiv:2106.14965 [math-ph]\nD. Läänemets\, M. Ho
hmann and C. Pfeifer\, Int. J. Geom. Meth. Mod. Phys. 19 2250155 (2022) [a
rXiv:2201.04694 [gr-qc]]\nM. Hohmann\, Class. Quant. Grav. 41 015025 (2024
) [arXiv:2310.01487 [gr-qc]]\n
LOCATION:https://researchseminars.org/talk/UTPhysics/61/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Tomi Koivisto (NICPB\, Tallinn)
DTSTART:20241015T131500Z
DTEND:20241015T144500Z
DTSTAMP:20260422T212606Z
UID:UTPhysics/62
DESCRIPTION:Title: Volume and gauge symmetry\nby Tomi Koivisto (NICPB\, Tallinn) as pa
rt of Theoretical physics seminar @ Tartu\n\nLecture held in Physicum room
A102\, University of Tartu\, Estonia.\n\nAbstract\nTheories with a prefer
red volume are called unimodular. Unimodularity has played subtle roles in
theories of gravity since the inception of General Relativity [1]\; it is
well-known that unimodularity provides an alternative view to the importa
nt problems with the cosmological constant Λ. This seminar\naims to clari
fy* unimodular physics from the perspective of relativity and gauge symmet
ries\, and to present two relevant current developments. 1) Despite variou
s teleparallel modifications of gravity considered in the literature\, the
only known viable class of modifications can be understood in\nterms of a
preferred volume [2]. In contrast to modifications of gravity\, local Lor
entz symmetry is not speculative. 2) The incorporation of this symmetry in
to a unimodular theory predicts the standard ΛCDM model of cosmology with
out postulating dark energy or dark matter [3]. It also facilitates the co
upling\nof the Standard Model gauge and Higgs fields into the theory [4].\
n\n[1] Einstein\, A. (1916) The Foundation of the General Theory of Relati
vity. Annalen der Physik\, 49\, 769-822.\n[2] Bello-Morales et al (2024) A
class of ghost-free theories in symmetric teleparallel geometry\, e-Print
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LOCATION:https://researchseminars.org/talk/UTPhysics/62/
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