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BEGIN:VEVENT
SUMMARY:Michalis Agathos (University of Cambridge & Friedrich-Schiller-Uni
versitat Jena)
DTSTART:20201217T120000Z
DTEND:20201217T130000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/1
DESCRIPTION:Title: Gravitational Waves as Probes of Strong-Field Gravity\nby Michalis A
gathos (University of Cambridge & Friedrich-Schiller-Universitat Jena) as
part of High Energy Theory\, Gravity and Cosmology Seminars @ NTUA\n\n\nA
bstract\nThe first observations of gravitational waves (GWs) from the coal
escence of a black-hole binary in 2015 and a neutron-star binary in 2017 h
eralded the beginning of a new era in experimental gravity. In just 5 year
s\, the detection of GWs has evolved from virtually non-existent to a week
ly business and has led to a plethora of results with implications for fun
damental physics\, astrophysics and cosmology. In this talk\, I will give
an overview of the GW events detected so far by LIGO and Virgo and will de
scribe how these can be used to probe the true nature of gravity and test
general relativity (GR) to unprecedented levels. I will focus on an array
of methods developed exactly for this purpose and will give an update on t
heir latest results\, with the analysis of signals from compact binaries\,
detected in the first three observing runs of the Advanced LIGO-Virgo net
work of detectors. If time allows\, I will briefly discuss the prospects o
f testing the predictions of GR with future GW detectors\, including upgra
des and extensions of the current network\, 3rd generation ground-based in
terferometers and future space-bound detectors.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/1/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Pascal Anastasopoulos (U Vienna\, Dept. Math)
DTSTART:20210120T113000Z
DTEND:20210120T123000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/2
DESCRIPTION:Title: Emergent fields from Hidden sectors\nby Pascal Anastasopoulos (U Vie
nna\, Dept. Math) as part of High Energy Theory\, Gravity and Cosmology S
eminars @ NTUA\n\n\nAbstract\nHidden theories coupled to the SM may provid
e emergent fields\, that are composites/bound-states of the hidden fields.
This is motivated by paradigms emerging from the AdS/CFT correspondence b
ut it is a more general phenomenon. We explore the general setup and we fo
cus on axions\, graviphotons (or dark photons) and neutrinos.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/2/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Kristjan Kannike (NICPB\, Tallinn)
DTSTART:20210127T113000Z
DTEND:20210127T123000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/3
DESCRIPTION:Title: Minima of Classically Scale-Invariant Potentials\nby Kristjan Kannik
e (NICPB\, Tallinn) as part of High Energy Theory\, Gravity and Cosmology
Seminars @ NTUA\n\n\nAbstract\nWe define a matrix formalism to analyze th
e minimum structure of classically scale-invariant effective potentials. W
e obtain general compact expressions for the minimum direction and the mas
s matrix\, and derive a set of conditions on the running couplings to have
a minimum. If these conditions are satisfied at two or more places along
the RG-flow\, there can be two or more minima\, of which we give examples
in a toy model.\n\nhttps://arxiv.org/abs/2011.12304\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/3/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Kostas Filippas (Swansea University)
DTSTART:20210210T123000Z
DTEND:20210210T133000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/4
DESCRIPTION:Title: Holography in 2d N=(0\,4) quantum field theory\nby Kostas Filippas (
Swansea University) as part of High Energy Theory\, Gravity and Cosmology
Seminars @ NTUA\n\n\nAbstract\nWe explore the duality between AdS3 massiv
e IIA string theory vacua and two-dimensional N=(0\,4) quiver quantum fiel
d theories. After categorizing all kinds of gravity solutions\, we demysti
fy the ones that seem to reflect anomalous dual gauge theories. In particu
lar\, we prove that there are bound states of D-branes on the boundary of
the space which provide the dual quiver theory with exactly the correct am
ount of matter in order to cancel its gauge anomalies. Then we propose tha
t the structure of the field theory should be complemented with additional
bifundamental matter\, which we argue it may only be N=(4\,4) hypermultip
lets. Finally\, we construct a BPS string configuration and use the old an
d new supersymmetric matter to build its dual ultraviolet operator.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/4/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Vasileios Letsios (York U.\, Dept. Math.)
DTSTART:20210203T113000Z
DTEND:20210203T123000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/5
DESCRIPTION:Title: The eigenmodes for spinor quantum field theory in global de Sitter space
-time\nby Vasileios Letsios (York U.\, Dept. Math.) as part of High En
ergy Theory\, Gravity and Cosmology Seminars @ NTUA\n\n\nAbstract\nThe de
Sitter space-time is famous for being able to describe an expanding Unive
rse and thus understanding physics in this space-time is of high importanc
e. It is known that N-dimensional de Sitter space-time can be viewed as an
``analytic continuation'' of the N-dimensional sphere. Hence\, given the
solutions of the Dirac equation on the N-dimensional sphere\, one can obta
in the solutions of the Dirac equation in de Sitter space-time by using ap
propriate techniques. In this talk\, I will briefly explain how one can c
onstruct a spinor quantum field theory in de Sitter space-time by making u
se of these techniques. This talk is based on https://arxiv.org/abs/2011.
07875 .\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/5/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Georgios Karananas (LMU\, Munich)
DTSTART:20210217T113000Z
DTEND:20210217T123000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/6
DESCRIPTION:Title: Spontaneous Conformal Symmetry Breaking in the Fishnet CFT\nby Georg
ios Karananas (LMU\, Munich) as part of High Energy Theory\, Gravity and
Cosmology Seminars @ NTUA\n\n\nAbstract\nQuantum field theories with exact
but spontaneously broken conformal invariance have an intriguing feature:
their vacuum energy is equal to zero. Up to now\, the only known ultravio
let complete theories where conformal symmetry can be spontaneously broken
were associated with supersymmetry\, with the most prominent example bein
g the N =4 SYM. Interestingly\, its non-supersymmetric descendant\, the ``
Fishnet theory\,'' supports at the classical level a rich set of flat dire
ctions along which conformal symmetry is spontaneously broken. At least pe
rturbatively\, some of these vacua survive in the full quantum theory - in
the planar limit - without any fine tuning. As a result\, the vacuum ener
gy vanishes along these flat directions\, providing the first non-supersym
metric example of a four-dimensional quantum field theory with “natural
” breaking of conformal symmetry.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/6/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ilias Cholis (Oakland University)
DTSTART:20210224T113000Z
DTEND:20210224T133000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/7
DESCRIPTION:Title: Antimatter Cosmic-Ray Nuclei as a probe of Dark Matter\nby Ilias Cho
lis (Oakland University) as part of High Energy Theory\, Gravity and Cosm
ology Seminars @ NTUA\n\n\nAbstract\nAntimatter cosmic ray measurements ca
n advance our understanding of high-energy astrophysical phenomena in our
own Galaxy. Over the last years\, satellite experiments as the Alpha Magne
tic Spectrometer on board the International Space Station measure antimatt
er cosmic ray fluxes\, including antiprotons and recently antimatter nucle
i. These measurements provide a novel probe to search for new physics incl
uding annihilations of dark matter in the Milky Way\, which I will present
.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/7/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ville Vaskonen (BIST\, Barcelona)
DTSTART:20210303T113000Z
DTEND:20210303T123000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/8
DESCRIPTION:Title: Primordial black holes in light of LIGO-Virgo observations\nby Ville
Vaskonen (BIST\, Barcelona) as part of High Energy Theory\, Gravity and
Cosmology Seminars @ NTUA\n\n\nAbstract\nAssuming that a fraction of dark
matter is in primordial black holes (PBHs)\, a population of PBH binaries
is formed before matter-radiation equality from large Poisson fluctuations
in their spatial distribution. Though many of these binaries are disrupte
d by a nearby PBH or a small cluster of PBHs\, a large fraction of them su
rvives until they merge. In this talk I will describe the calculation of t
he PBH merger rate and show that the LIGO-Virgo observations give strong c
onstraints on the abundance of O(10) solar mass PBHs. I will also discuss
the possibility that some of the observed GW events are from PBH mergers.\
n
LOCATION:https://researchseminars.org/talk/HETatNTUA/8/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Fotis Koutroulis (National Technical University of Athens)
DTSTART:20210310T113000Z
DTEND:20210310T123000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/9
DESCRIPTION:Title: When a UV and Quantum 1st Order Phase Transition Gives the Solution to t
he Higgs Fine-Tuning Problem\nby Fotis Koutroulis (National Technical
University of Athens) as part of High Energy Theory\, Gravity and Cosmolo
gy Seminars @ NTUA\n\n\nAbstract\nWe construct the zero temperature (no co
mpact dimensions) effective action for an SU (2) Yang–Mills theory in fi
ve dimensions\, with boundary conditions that reduce the symmetry on the f
our-dimensional boundary located at the origin to a U (1)-complex scalar s
ystem. In order to be sen- sitive to the Higgs phase\, we need to include
higher dimen- sional operators in the effective action\, which can be natu
rally achieved by generating it by expanding the corresponding lattice con
struction in small lattice spacing\, taking the naive continuum limit and
then renormalizing. In addition\, we build in the effective action non-per
turbative information\, related to a first order quantum phase transition
known to exist. As a result\, the effective action acquires a finite cut-o
ff that is low and the fine tuning of the scalar mass is rather mild.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/9/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Guillem Domènech (INFN Padua)
DTSTART:20210324T113000Z
DTEND:20210324T123000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/10
DESCRIPTION:Title: Are induced gravitational waves gauge dependent?\nby Guillem Domèn
ech (INFN Padua) as part of High Energy Theory\, Gravity and Cosmology Se
minars @ NTUA\n\n\nAbstract\nPrimordial black hole formation is always acc
ompanied by a large amount of induced gravitational waves (GWs)\, in princ
iple observable by future GWs detectors. However\, the theoretical express
ion of the induced GW spectral density is strictly speaking gauge dependen
t. This gauge dependence thus casts doubts on the theoretical predictions
of the induced GWs. In this talk\, I will investigate in detail the gauge
issue of the induced GWs. I will show that\, under reasonable assumptions
\, the induced GWs is for all practical purposes gauge independent. Thus\
, free of ambiguities\, induced GWs are an excellent source of information
about the primordial universe.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/10/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Georgios Tringas (National Technical University of Athens)
DTSTART:20210331T103000Z
DTEND:20210331T113000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/11
DESCRIPTION:Title: From Type II to 3D flux vacua on G2 orientifolds\nby Georgios Tring
as (National Technical University of Athens) as part of High Energy Theory
\, Gravity and Cosmology Seminars @ NTUA\n\n\nAbstract\nWe discuss flux c
ompactifications of Type II supergravity on G2 structures and holonomy to
three dimensions. We construct the 3D vacua using smeared O-planes and bac
kground NS and RR fluxes. Whether the internal manifold is Ricci flat or n
ot is crucial for the consistent construction of the theory. For both Type
IIA and Type IIB we find supersymmetric Minkowski vacua and AdS3 vacua wi
th full moduli stabilization and indication for scale separation. Adding S
USY breaking objects we find dS3 vacua and performing flux quantization we
discuss the fate of each example.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/11/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Stelios Karydas (National Technical University of Athens)
DTSTART:20210407T103000Z
DTEND:20210407T113000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/12
DESCRIPTION:Title: Successful (Higgs) inflation from combined non minimal and derivative c
ouplings.\nby Stelios Karydas (National Technical University of Athens
) as part of High Energy Theory\, Gravity and Cosmology Seminars @ NTUA\n
\n\nAbstract\nWe discuss an inflationary scenario based on the concurrent
presence of non-minimal coupling (NMC) and generalized non-minimal deriva
tive coupling (GNMDC). The combined construction maintains the advantages
of the individual scenarios without sharing their disadvantages. A long in
flationary phase can be achieved due to the gravitational friction effect
owed to the GNMDC\, without leading to trans-Planckian values and unitarit
y violation. Additionally\, the tensor-to-scalar ratio remains low due to
the NMC contribution. Finally\, the instabilities related to the squared
sound-speed of scalar perturbations\, which plague the Derivative Coupling
scenarios\, are now healed due to the domination of the NMC contribution
and the damping of the GNMDC effects during the reheating era.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/12/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Konstantinos Kritos (National Technical University of Athens)
DTSTART:20210414T103000Z
DTEND:20210414T113000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/13
DESCRIPTION:Title: Black Holes merging with Low Mass Gap Objects inside Globular Clusters<
/a>\nby Konstantinos Kritos (National Technical University of Athens) as p
art of High Energy Theory\, Gravity and Cosmology Seminars @ NTUA\n\n\nAb
stract\nRecently\, the LIGO-Virgo collaborations have reported the coalesc
ence of a binary involving a black hole and a low-mass gap object (LMGO) w
ith mass in the range $\\sim 2.5−5M_\\odot$. In this work we study the d
ynamical formation of compact object pairs\, via multiple binary-single ex
changes that occur at the cores of globular clusters. We find that the exc
hanges are efficient in forming hard compact object binaries at the cores
of dense astrophysical stellar environments. Furthermore\, if the populati
on size of the LMGOs is related to that of neutron stars\, the inferred me
rger rate density of black hole-LMGO binaries inside globular clusters in
the local Universe is estimated to be about $0.1\\textrm{Gpc}^{−3}\\text
rm{yr}^{−1}$.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/13/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Maria Chira (Aristotle Univ. of Thessaloniki & National Observator
y of Athens)
DTSTART:20210421T103000Z
DTEND:20210421T113000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/14
DESCRIPTION:Title: Dependence of the dynamical properties of light-cone simulation dark ma
tter halos on their environment\nby Maria Chira (Aristotle Univ. of Th
essaloniki & National Observatory of Athens) as part of High Energy Theory
\, Gravity and Cosmology Seminars @ NTUA\n\n\nAbstract\nWe study the depe
ndence of a variety of DM halo properties (shape\, spin\, virialisation st
atus) on different environments in a whole-sky ΛCDM light-cone halo catal
ogue extending to z ∼ 0.65\, using a simple and well-defined halo isolat
ion criterion. Using this definition of the environment we study if and ho
w the DM halo-properties and their interrelations depend on their environm
ent. We also study the relative orientations of the spin- and shape- vecto
rs of DM halos with their isolation\, as well as the alignment of the shap
e- and the spin- vectors of neighbouring DM halos for a vast range of sepa
rations. Lastly\, we focus on halo pairs\, which are encountered in a vari
ety of isolation states in our catalogue and\, specifically\, we study how
the shape- and spin- alignments of halo-pairs is dependent on the isolati
on of the pair. The latter can give insight in the formation and evolution
of halos formed under the dynamical interaction of their nearest neighbou
r in a region devoid of other massive halos\, i.e. not affected by the amb
ient tidal field.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/14/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Fotis Farakos (University of Padova)
DTSTART:20210513T100000Z
DTEND:20210513T110000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/15
DESCRIPTION:Title: Supergravity and applications in string theory\nby Fotis Farakos (U
niversity of Padova) as part of High Energy Theory\, Gravity and Cosmolog
y Seminars @ NTUA\n\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/15/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Steven Cunnington (Queen Mary\, U. of London)
DTSTART:20210519T103000Z
DTEND:20210519T113000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/16
DESCRIPTION:Title: Large Scale Cosmology with 21cm Intensity Mapping\nby Steven Cunnin
gton (Queen Mary\, U. of London) as part of High Energy Theory\, Gravity
and Cosmology Seminars @ NTUA\n\n\nAbstract\nNeutral hydrogen (HI) has bee
n shown to be a tracer of the underlying matter field in our Universe. Thu
s by probing the large-scale structure of HI\, we can indirectly probe cos
mic structure and from this\, infer constraints on cosmological parameters
. 21cm intensity mapping with radio telescopes is an efficient method for
this purpose\, although the success of this novel technique relies on over
coming a number of challenges which I will discuss. The ultra-large scales
of our Universe host potential signatures for new physics\, but conventio
nal galaxy surveys struggle to probe these scales with statistical signifi
cance. 21cm intensity mapping should be better suited to this task since i
t can rapidly survey large cosmic volumes. However\, to access the largest
scales with the much anticipated Square Kilometre Array (SKA)\, the singl
e-dish intensity mapping method will be relied on. I will therefore also d
iscuss the work being undertaken with MeerKAT (an SKA pathfinder telescope
) to successfully demonstrate single-dish intensity mapping\, which repres
ents an important milestone for using SKA as a large-scale structure probe
.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/16/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Andreas Goudelis (CNRS-LPC\, Clermont-Ferrand)
DTSTART:20210520T100000Z
DTEND:20210520T110000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/17
DESCRIPTION:Title: Dark Matter in Cosmology and Particle Physics\nby Andreas Goudelis
(CNRS-LPC\, Clermont-Ferrand) as part of High Energy Theory\, Gravity and
Cosmology Seminars @ NTUA\n\n\nAbstract\nThe existence of dark matter is
very well-established observational. Despite the effort that has been dedi
cated\, both at the theoretical/phenomenological and at the experimental l
evel\, in order to detect it through its potential non-gravitational inter
actions\, its microscopic nature remains unknown. In these two lectures\,
I will first present a brief overview of the evidence that corroborates it
s existence\, I will discuss different ideas about what types of particles
could constitute viable "dark matter candidates" and I will delineate dif
ferent promising strategies in order to detect it non-gravitationally. Aft
erward\, I will focus mostly on scenarios in which dark matter interacts e
xtremely weekly ("feebly") with the Standard Model particles. I will discu
ss some types of models that could contain such Feebly Interacting dark ma
tter candidates and I will highlight some of the exiting phenomenology tha
t they predict in particle and astroparticle physics experiments.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/17/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Andreas Goudelis (CNRS-LPC\, Clermont-Ferrand)
DTSTART:20210527T100000Z
DTEND:20210527T110000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/19
DESCRIPTION:Title: Dark Matter in Cosmology and Particle Physics\nby Andreas Goudelis
(CNRS-LPC\, Clermont-Ferrand) as part of High Energy Theory\, Gravity and
Cosmology Seminars @ NTUA\n\n\nAbstract\nThe existence of dark matter is
very well-established observational. Despite the effort that has been dedi
cated\, both at the theoretical/phenomenological and at the experimental l
evel\, in order to detect it through its potential non-gravitational inter
actions\, its microscopic nature remains unknown. In these two lectures\,
I will first present a brief overview of the evidence that corroborates it
s existence\, I will discuss different ideas about what types of particles
could constitute viable "dark matter candidates" and I will delineate dif
ferent promising strategies in order to detect it non-gravitationally. Aft
erward\, I will focus mostly on scenarios in which dark matter interacts e
xtremely weekly ("feebly") with the Standard Model particles. I will discu
ss some types of models that could contain such Feebly Interacting dark ma
tter candidates and I will highlight some of the exiting phenomenology tha
t they predict in particle and astroparticle physics experiments.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/19/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ioanna Stamou (University of Athens)
DTSTART:20210526T103000Z
DTEND:20210526T113000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/20
DESCRIPTION:Title: Producing PBHs and Gravitational Waves by breaking the SU(2\,1)/SU(2)xU
(1) Symmetry\nby Ioanna Stamou (University of Athens) as part of High
Energy Theory\, Gravity and Cosmology Seminars @ NTUA\n\n\nAbstract\nWe p
resent a class of models in order to explaining the generation of Primordi
al\nBlack Holes (PBHs) and Gravitational Waves (GWs) in the Universe. Thes
e models\nare based on no-scale theory. By breaking the SU(2\,1)/SU(2)×U(
1) symmetry we\nfix one of the two chiral fields and we derive effective s
calar potentials which are\ncapable of generating PBHs and GWs. Thus\, we
derive scalar potentials which\,\non the one hand\, explain the production
of PBHs and GWs and\, on the other\nhand\, they conserve the transformati
on laws\, which yield from the parametrization\nof the coset SU(2\,1)/SU(2
)×U(1) as well as they conserve the unification between\nthe models which
yield by this coset. Moreover\, we generate PBHs by modifying\nthe kineti
c term of the Langrangian (or the Kahler potential) and we keep the\nsuper
potentials unmodified. Furthermore\, we evaluate the fractional abundances
\nof PBHs in radiation dominated era by using and comparing two methods th
e\nPress–Schechter approach and the peak theory\, while focusing on expl
aining the\ndark matter in the Universe. By using the resulting scalar pow
er spectrum we\nevaluate the amount of GWs during the radiation epoch. All
proposed models are\nin complete consistence with Planck constraints.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/20/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Fotis Koutroulis (NTUA)
DTSTART:20210528T150000Z
DTEND:20210528T160000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/21
DESCRIPTION:Title: On the Spontaneous and Simultaneous Breaking of Internal and Scale symm
etry in Effective Field Theories of extra dimensional origin enhanced with
Higher Dimensional Operators: A New Approach to the Hierarchy Problem
\nby Fotis Koutroulis (NTUA) as part of High Energy Theory\, Gravity and
Cosmology Seminars @ NTUA\n\n\nAbstract\nWay before the very recent discov
ery of the Higgs boson the associated mechanism was under speculation due
to a theoretical inconsistency\, the well known Higgs hierarchy problem. T
he inconsistency refers to the sensitivity of the Higgs mass to the ultra
violet contributions which results in the need of a very strong fine tunin
g of the physical parameters in order to leave the mass almost unaffected
by the quantum corrections. Many solutions have been proposed regarding th
e Higgs mass fine tuning problem during the past years\, however\, none of
them has given a confirmation signal. In this dissertation we propose a n
ovel solution to the Higgs hierarchy problem based on a specific extra dim
ensional model with very special boundary conditions and higher that four
dimensional operators. This is the so called Non-perturbative gauge Higgs
unification model\, an SU(2) 5-d orbifold lattice model with obifold bound
ary conditions leading to a 4d boundary. On the latter lives a kind of an
Abelian Higgs model\, an ideal case for our purpose since it possesses a n
on-trivial effective potential sensitive to the UV corrections at first gl
ance and yet relieved of the complexity of the Standard Model’s higher g
auge group contributions. Therefore\, our first step is to deal with the u
sual Abelian Higgs model in four spacetime dimensions where we examine its
physicality and consistency under different gauge choices proving that th
e associated effective potential is gauge invariant. Then we introduce the
Non-perturbative gauge Higgs unification model under the assumption that
bulk and boundary are completely disconnected. Even though this hypothesis
gives consistent results does not solve the fine tuning problem and the n
eed to consider a connection between bulk and boundary becomes urgent. A c
onsequence of this is that the insertion of higher dimensional operators i
s unavoidable. Therefore\, before going back to our original model we exam
ine the effective potential of a real scalar field enhanced with dimension
six and eight operators. What we show is the various cases under which su
ch a potential is both stable and exhibits spontaneous and simultaneous br
eaking of internal and scale symmetry as it reaches an interacting or a Ga
ussian fixed point. Finally\, with these in our hands we turn back to the
5-d orbifold model and take into account the bulk-boundary connection whic
h produces an effective action enhanced with higher that four dimensional
operators\, at the 4-d boundary\, whose nature includes non-perturbative i
nformation related to a first order quantum phase transition. Under these
circumstances the effective action acquires a finite cut-off that is low a
nd the fine tuning of the scalar mass is rather mild.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/21/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theodoros Papanikolaou (APC\, Paris)
DTSTART:20210602T103000Z
DTEND:20210602T113000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/22
DESCRIPTION:Title: Constraining the early universe with ultralight primordial black holes
and vice-versa\nby Theodoros Papanikolaou (APC\, Paris) as part of Hig
h Energy Theory\, Gravity and Cosmology Seminars @ NTUA\n\n\nAbstract\nIn
our presentation\, we focus on ultralight PBHs\, not tightly constrained
in the literature\, produced naturally during the preheating instability
in the context of single-field inflationary models. In particular\, we fin
d that the PBH production mechanism can be so efficient that PBHs subseque
ntly dominate the content of the universe and reheating proceeds from thei
r evaporation. Taking into account observational constraints on the PBH ab
undance one can constrain the energy scales at the end of inflation and at
the onset of the radiation era. Vice-versa\, by studying induced second o
rder gravitational waves generated by density perturbations underlain by P
BHs themselves and taking into account GW back-reaction effects one can se
t constraints on the initial abundance of PBHs as a function of their mass
.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/22/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Carlo Angelantonj (Turin U.)
DTSTART:20210604T100000Z
DTEND:20210604T110000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/23
DESCRIPTION:Title: A short introduction to superstring theory I\nby Carlo Angelantonj
(Turin U.) as part of High Energy Theory\, Gravity and Cosmology Seminars
@ NTUA\n\n\nAbstract\nIn this series of lectures I will give a short\, pe
dagogical\, introduction to superstring theory and its applications. The f
irst lecture is devoted to the quantisation of the superstrings and the co
nstructions of consistent superstring theories in D=10. A special emphasis
will be put on the GSO projection and\nthe role of modular invariance of
the one-loop partition function. The second lecture will deal with open st
rings and we shall introduce D-branes. Finally\, in the third lecture I sh
all discuss the problem of compactification.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/23/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Carlo Angelantonj (Turin U.)
DTSTART:20210610T100000Z
DTEND:20210610T110000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/24
DESCRIPTION:Title: A short introduction to superstring theory II\nby Carlo Angelantonj
(Turin U.) as part of High Energy Theory\, Gravity and Cosmology Seminar
s @ NTUA\n\n\nAbstract\nIn this series of lectures I will give a short\, p
edagogical\, introduction to superstring theory and its applications. The
first lecture is devoted to the quantisation of the superstrings and the c
onstructions of consistent superstring theories in D=10. A special emphasi
s will be put on the GSO projection and\nthe role of modular invariance of
the one-loop partition function. The second lecture will deal with open s
trings and we shall introduce D-branes. Finally\, in the third lecture I s
hall discuss the problem of compactification.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/24/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Carlo Angelantonj (Turin U.)
DTSTART:20210617T100000Z
DTEND:20210617T110000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/28
DESCRIPTION:Title: A short introduction to superstring theory III\nby Carlo Angelanton
j (Turin U.) as part of High Energy Theory\, Gravity and Cosmology Semina
rs @ NTUA\n\n\nAbstract\nIn this series of lectures I will give a short\,
pedagogical\, introduction to superstring theory and its applications. The
first lecture is devoted to the quantisation of the superstrings and the
constructions of consistent superstring theories in D=10. A special emphas
is will be put on the GSO projection and\nthe role of modular invariance o
f the one-loop partition function. The second lecture will deal with open
strings and we shall introduce D-branes. Finally\, in the third lecture I
shall discuss the problem of compactification.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/28/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marco Scalisi (Max Planck Institute\, Munich)
DTSTART:20210623T103000Z
DTEND:20210623T113000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/29
DESCRIPTION:Title: The Gravitino and the Swampland\nby Marco Scalisi (Max Planck Insti
tute\, Munich) as part of High Energy Theory\, Gravity and Cosmology Semi
nars @ NTUA\n\n\nAbstract\nWe propose a new swampland conjecture stating t
hat the limit of vanishing gravitino mass corresponds to the massless limi
t of an infinite tower of states and to the consequent breakdown of the ef
fective field theory. We test our proposal in large classes of models comi
ng from compactification of string theory to four dimensions\, where we id
entify the Kaluza-Klein nature of the tower of states becoming light. We p
oint out a general relation between the gravitino mass and abelian gauge c
oupling in models with extended supersymmetry\, which can survive also in
examples with minimal supersymmetry. This allows us to connect our conject
ure to other well established swampland conjectures\, such as the weak gra
vity conjecture or the absence of global symmetries in quantum gravity. We
discuss phenomenological implications of our conjecture in (quasi-)de Sit
ter backgrounds and extract a lower bound for the gravitino mass in terms
of the Hubble parameter.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/29/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Carlo Angelantonj (Turin U.)
DTSTART:20210624T100000Z
DTEND:20210624T110000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/30
DESCRIPTION:Title: A short introduction to superstring theory IV\nby Carlo Angelantonj
(Turin U.) as part of High Energy Theory\, Gravity and Cosmology Seminar
s @ NTUA\n\n\nAbstract\nIn this series of lectures I will give a short\, p
edagogical\, introduction to superstring theory and its applications. The
first lecture is devoted to the quantisation of the superstrings and the c
onstructions of consistent superstring theories in D=10. A special emphasi
s will be put on the GSO projection and the role of modular invariance of
the one-loop partition function. The second lecture will deal with open st
rings and we shall introduce D-branes. Finally\, in the third lecture I sh
all discuss the problem of compactification.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/30/
END:VEVENT
BEGIN:VEVENT
SUMMARY:E. Palti (Ben-Gurion University)
DTSTART:20210701T100000Z
DTEND:20210701T110000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/31
DESCRIPTION:Title: Introduction to the Swampland\nby E. Palti (Ben-Gurion University)
as part of High Energy Theory\, Gravity and Cosmology Seminars @ NTUA\n\n
\nAbstract\nThe Swampland program aims to distinguish effective theories t
hat can be completed into quantum gravity in the ultraviolet from those wh
ich cannot. I will present an introduction to this field\, mainly by using
ideas from string theory.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/31/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Eran Palti (Ben Gurion U. of Negev)
DTSTART:20210715T100000Z
DTEND:20210715T110000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/32
DESCRIPTION:Title: Introduction to the Swampland\nby Eran Palti (Ben Gurion U. of Nege
v) as part of High Energy Theory\, Gravity and Cosmology Seminars @ NTUA\
n\n\nAbstract\nThe Swampland program aims to distinguish effective theorie
s that can be completed into quantum gravity in the ultraviolet from those
which cannot. I will present an introduction to this field\, mainly by us
ing ideas from string theory.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/32/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Stratos Pateloudis (Universität Regensburg)
DTSTART:20211103T120000Z
DTEND:20211103T130000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/33
DESCRIPTION:Title: Confinement/deconfinement transition in the D0-brane matrix model—App
earance of M-theory?\nby Stratos Pateloudis (Universität Regensburg)
as part of High Energy Theory\, Gravity and Cosmology Seminars @ NTUA\n\n
\nAbstract\nI will discuss the confinement/deconfinement transition in the
D0-brane matrix model (often called the BFSS matrix model) and its one-pa
rameter deformation (the BMN matrix model) by using lattice Monte Carlo si
mulations. The results confirm general expectations from the dual string/M
-theory picture for strong coupling. In particular\, we observe the confin
ed phase in the BFSS matrix model\, which is a nontrivial consequence of t
he M-theory picture. We suggest that these models provide us with an ideal
framework to study the Schwarzschild black hole\, M-theory\, and furtherm
ore\, the parameter region of the phase transition between type IIA supers
tring theory and M-theory.\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/33/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Frans Klinkhamer (Institute for Theoretical Physics\, Karlsruhe In
stitute of Technology)
DTSTART:20221012T103000Z
DTEND:20221012T113000Z
DTSTAMP:20260422T213052Z
UID:HETatNTUA/34
DESCRIPTION:Title: Cosmological constant problem: Revisiting the unimodular-gravity approa
ch\nby Frans Klinkhamer (Institute for Theoretical Physics\, Karlsruhe
Institute of Technology) as part of High Energy Theory\, Gravity and Cos
mology Seminars @ NTUA\n\nAbstract: TBA\n
LOCATION:https://researchseminars.org/talk/HETatNTUA/34/
END:VEVENT
END:VCALENDAR