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BEGIN:VEVENT
SUMMARY:Jakob Moritz (Cornell)
DTSTART:20200528T140000Z
DTEND:20200528T150000Z
DTSTAMP:20260422T230718Z
UID:Utrechtseminars/1
DESCRIPTION:Title: New vacua for the landscape\nby Jakob Moritz (Cornell) as part
of Utrecht seminar series\n\n\nAbstract\nThe flux landscape of type IIB s
tring theory is an ideal arena for model building and for addressing funda
mental issues such as the existence of de Sitter vacua and large field inf
lation. I will explain the main ideas behind our recent construction of a
large data set of Calabi-Yau orientifolds which determine important data o
f the 4d effective field theories that arise from the landscape. The set o
f orientifolds features interesting classes of geometric transitions that
involve colliding O-planes\, and in many cases we find that all known crit
eria are met for the existence of a very particular spectrum of ultra-ligh
t axions. If time permits\, I will also outline a new mechanism that gener
ates hierarchically small flux superpotentials as is required by the KKLT
proposal for de Sitter vacua.\n
LOCATION:https://researchseminars.org/talk/Utrechtseminars/1/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Christian Northe (Wurzburg)
DTSTART:20200611T140000Z
DTEND:20200611T150000Z
DTSTAMP:20260422T230718Z
UID:Utrechtseminars/2
DESCRIPTION:Title: Holographic RG Flows for Kondo-like Impurities\nby Christian N
orthe (Wurzburg) as part of Utrecht seminar series\n\n\nAbstract\nBoundary
\, defect\, and interface RG flows\, as exemplified by the famous Kondo mo
del\, play a significant role in the theory of quantum fields. We study in
detail the holographic dual of a non-conformal supersymmetric impurity in
the D1/D5 CFT. Its RG flow bears similarities to the Kondo model\, althou
gh unlike the Kondo model the CFT is strongly coupled in the holographic r
egime. The interface we study preserves d = 1 N = 4 supersymmetry and flow
s to conformal fixed points in both the UV and IR. The interface’s UV fi
xed point is described by d = 1 fermionic degrees of freedom\, coupled to
a gauge connection on the CFT target space that is induced by the ADHM con
struction. We briefly discuss its field-theoretic properties before shifti
ng our focus to its holographic dual. We analyze the supergravity dual of
this interface RG flow\, first in the probe limit and then including gravi
tational backreaction. In the probe limit\, the flow is realized by the pu
ffing up of probe branes on an internal S3 via the Myers effect. We furthe
r identify the backreacted supergravity configurations dual to the interfa
ce fixed points. These supergravity solutions provide a geometric realizat
ion of critical screening of the defect degrees of freedom. This critical
screening arises in a way similar to the original Kondo model. We compute
the g-factor both in the probe brane approximation and using backreacted s
upergravity solutions\, and show that it decreases from the UV to the IR a
s required by the g-theorem.\n
LOCATION:https://researchseminars.org/talk/Utrechtseminars/2/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Wilke van der Schee (CERN)
DTSTART:20200618T140000Z
DTEND:20200618T150000Z
DTSTAMP:20260422T230718Z
UID:Utrechtseminars/3
DESCRIPTION:Title: Entanglement and thermalisation at the butterfly velocity\nby
Wilke van der Schee (CERN) as part of Utrecht seminar series\n\n\nAbstract
\nAfter a quench the entanglement entropy will saturate to its thermal val
ue within a characteristic saturation time which is bounded by R/v_B with
R the radius of the largest inscribed sphere and v_B the butterfly velocit
y. In this talk I will introduce the `membrane paradigm'\, which gives a h
ydrodynamic description of entanglement growth coming both from tensor net
works as well as holography. Interestingly\, both spheres and cylinders in
neutral holographic plasmas saturate the butterfly bound\, whereas stripe
s or spheres in charged plasmas do not saturate it. In this talk I will pr
esent results for a wide variety of shapes\, showing that also a generic c
lass 'between' spheres and cylinders saturates the bound.\n
LOCATION:https://researchseminars.org/talk/Utrechtseminars/3/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Miguel Montero (Harvard)
DTSTART:20200625T141500Z
DTEND:20200625T151500Z
DTSTAMP:20260422T230718Z
UID:Utrechtseminars/4
DESCRIPTION:Title: Nothing is certain in string compactifications\nby Miguel Mont
ero (Harvard) as part of Utrecht seminar series\n\n\nAbstract\nA bubble of
nothing is a spacetime instability where a compact dimension collapses. A
fter nucleation\, it expands at the speed of light\, leaving "nothing" beh
ind. There are a couple of robust mechanisms that can prevent the existenc
e of a bubble: Either it is not energetically favourable to produce them\,
or there is a topological obstruction to their existence. The latter is o
ften the case with SUSY-preserving boundary conditions. I will explain how
to understand the topological obstruction in detail using bordism\, which
will show that it is very generically absent even for a SUSY-compatible s
pin structure. As a proof of principle\, we construct and embed in string
theory an explicit bubble of nothing for a T3 with completely periodic (SU
SY-compatible) spin structure. There is a dynamical obstruction due to a p
ositive energy theorem which is circumvented by higher-derivative correcti
ons. Our model can be embedded in string theory. Our techniques can be use
d to construct a plethora of bubbles of nothing for spaces of interest lik
e CY6's\, G2 manifolds\, or Sasaki-Einstein manifolds. We will explain how
to study and circumvent the topological and dynamical obstruction in thes
e cases. Avoiding the dynamical obstruction means avoiding a modified ener
gy condition which might be related to the Weak Gravity Conjecture. Our re
sults lend support to the conjecture that any non-supersymmetric vacuum of
quantum gravity is ultimately unstable.\n
LOCATION:https://researchseminars.org/talk/Utrechtseminars/4/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marina David (Michigan)
DTSTART:20201015T140000Z
DTEND:20201015T150000Z
DTSTAMP:20260422T230718Z
UID:Utrechtseminars/5
DESCRIPTION:Title: Holographic Approaches to AdS Black Hole Entropy\nby Marina Da
vid (Michigan) as part of Utrecht seminar series\n\n\nAbstract\nSignifican
t progress has been made regarding the microstate counting of extremal AdS
black holes in the context of AdS/CFT\, where the Cardy-like limit on the
field side theory has often been used. I will discuss the implications of
this limit on the gravity side and how it translates to a parameter space
limit on the black hole solution. This limit\, referred to as the gravita
tional Cardy limit\, is applied to the Bardeen Horowitz near-horizon geome
try to reproduce the Bekenstein-Hawking entropy via the Kerr/CFT correspon
dence\, yielding a third approach to the computation of the entropy. Relax
ing the gravitational Cardy limit\, the computation can be further extende
d to near-extremality\, where the heat capacity is found. For each case\,
extremal and near-extremal\, the entropy from these different approaches m
atch\, providing a unique and universal expression for the entropy.\n
LOCATION:https://researchseminars.org/talk/Utrechtseminars/5/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Dario Benedetti
DTSTART:20201022T140000Z
DTEND:20201022T150000Z
DTSTAMP:20260422T230718Z
UID:Utrechtseminars/6
DESCRIPTION:Title: Multiple scaling limits of an O(D)-invariant multi-matrix model\nby Dario Benedetti as part of Utrecht seminar series\n\n\nAbstract\nIn
models of D coupled NxN matrices one can consider a large-D limit\, on top
of the usual large-N limit. While the latter is well-known to lead to a g
enus expansion\, the large-D limit is relatively new: it introduces an add
itional organization of the fixed-genus diagrams\, which can be studied wi
th the methods developed for\n(rank-three) tensor models. In the simple sc
aling limit\, sending N\, and then D\, to infinity\, melonic diagrams domi
nate\, and their critical behavior is well understood.\nIn this talk I wil
l first review some of the motivations and background\, and then I will sh
ow\, in a specific model\, that the genus expansion can be resummed in a t
riple-scaling limit in which N and D go to infinity and the coupling const
ant to its critical value\, in a coordinated manner. From the point of vie
w of random surfaces\, the resulting continuum limit corresponds to a bran
ched polymer phase. A different continuum limit can be obtained\, within t
he same triple-scaling limit\, by restricting to two-particle irreducible
diagrams: in this case\, we find a mapping to an Ising model on random pla
nar graphs\, but in the high-temperature limit\, thus corresponding to the
universality class of pure 2D gravity.\n
LOCATION:https://researchseminars.org/talk/Utrechtseminars/6/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Carlo Angelantonj
DTSTART:20201105T150000Z
DTEND:20201105T160000Z
DTSTAMP:20260422T230718Z
UID:Utrechtseminars/7
DESCRIPTION:Title: String Defects\, Supersymmetry and the Swampland\nby Carlo Ang
elantonj as part of Utrecht seminar series\n\n\nAbstract\nWe test Kim\, Sh
iu and Vafa consistency conditions for six dimensional supergravity theori
es in explicit orientifold models. Based on the perturbative data\, we co
njecture the existence of null charges Q·Q= 0 for models with at least on
e tensor multiplet\, coupling to string defects of charge Q. We use the ne
w constraint to exclude some six-dimensional supersymmetric anomaly-free e
xamples that have currently no string or F-theory realization. We also inv
estigate the constraints in case where supersymmetry is broken in tachyon
free vacua\, with the breaking localised on antibranes.\n
LOCATION:https://researchseminars.org/talk/Utrechtseminars/7/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Daniel Junghans (Harvard)
DTSTART:20201112T150000Z
DTEND:20201112T160000Z
DTSTAMP:20260422T230718Z
UID:Utrechtseminars/8
DESCRIPTION:Title: Control issues of KKLT\nby Daniel Junghans (Harvard) as part o
f Utrecht seminar series\n\n\nAbstract\nWe analyze to which extent the KKL
T proposal for the construction of de Sitter vacua in string theory is qua
ntitatively controlled. Our focus is on the quality of the 10d supergravit
y approximation. As our main finding\, we uncover and quantify an issue wh
ich one may want to call the "singular-bulk problem". In particular\, we s
how that\, requiring the curvature to be small in the conifold region\, on
e is generically forced into a regime where the warp factor becomes negati
ve in a significant part of the Calabi-Yau orientifold. This implies true
singularities\, independent of the familiar\, string-theoretically control
led singularities of this type in the vicinity of O-planes.\n
LOCATION:https://researchseminars.org/talk/Utrechtseminars/8/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Blaise Goutéraux (Ecole Polytechnique)
DTSTART:20201119T150000Z
DTEND:20201119T160000Z
DTSTAMP:20260422T230718Z
UID:Utrechtseminars/9
DESCRIPTION:Title: Hydrodynamic diffusion and its breakdown near AdS2 fixed points\nby Blaise Goutéraux (Ecole Polytechnique) as part of Utrecht seminar s
eries\n\n\nAbstract\nHydrodynamics provides a universal description of int
eracting quantum field theories at sufficiently long times and wavelengths
\, but breaks down at scales that usually depend on microscopic details of
the theory. I will use gauge-gravity duality to investigate the breakdown
of diffusive hydrodynamics in two low temperatures states dual to black h
oles with AdS2 horizons. At low enough temperatures\, the breakdown is ent
irely controlled by data of the infrared AdS2 fixed point\, irrespective o
f the ultraviolet completion. This is also true in a Sachdev-Ye-Kitaev cha
in model in the limit of strong interactions\, which is controlled by the
same type of infrared fixed point.\n
LOCATION:https://researchseminars.org/talk/Utrechtseminars/9/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Prahar Mitra (Cambridge)
DTSTART:20201126T150000Z
DTEND:20201126T160000Z
DTSTAMP:20260422T230718Z
UID:Utrechtseminars/10
DESCRIPTION:Title: Covariant Phase Space and Soft Factorization in Non-abelian Gauge
Theories\nby Prahar Mitra (Cambridge) as part of Utrecht seminar seri
es\n\n\nAbstract\nWe perform a careful study of the infrared sector of mas
sless non-abelian gauge theories in four-dimensional Minkowski spacetime u
sing the covariant phase space formalism\, taking into account the boundar
y contributions arising from the gauge sector of the theory. Upon quantiza
tion\, we show that the boundary contributions lead to an infinite degener
acy of the vacua. The Hilbert space of the vacuum sector is not only shown
to be remarkably simple\, but also universal. We derive a Ward identity t
hat relates the n-point amplitude between two generic in- and out-vacuum s
tates to the one computed in standard QFT. In addition\, we demonstrate th
at the familiar single soft gluon theorem and multiple consecutive soft gl
uon theorem are consequences of the Ward identity.\n
LOCATION:https://researchseminars.org/talk/Utrechtseminars/10/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Nicolo Petri (Oviedo)
DTSTART:20201203T150000Z
DTEND:20201203T160000Z
DTSTAMP:20260422T230718Z
UID:Utrechtseminars/11
DESCRIPTION:Title: Nothing really matters\nby Nicolo Petri (Oviedo) as part of U
trecht seminar series\n\n\nAbstract\nThe UV consistency of low-energy grav
ity theories is one of the most studied and debated topics in current rese
arch in high-energy physics. In this talk I will focus on non-perturbative
instabilities of AdS vacua in (super)gravity theories and I will relate t
hem to de Sitter geometries. The set-up considered will be General Relativ
ity in presence of a cosmological constant and at generic dimension. In th
is context I will discuss the non-perturbative decay of AdS vacua through
the spontaneous process of nucleation of "bubbles of nothing". These bubb
les are expanding in time and they are defined only by their exterior\, so
they completely destroy the AdS vacuum by making it decay literally "into
nothing". The crucial feature of these instabilities is given by the fact
that an observer living on the surface of the bubbles will experience a p
ositive cosmological constant. From this point of view de Sitter geometrie
s arise as part of a higher-dimensional decaying spacetime and describe th
e dynamical expansion of the instability. I will conclude the talk by disc
ussing a simple set-up in M-theory where these ideas could be implemented.
\n________________________________________\n
LOCATION:https://researchseminars.org/talk/Utrechtseminars/11/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ivano Basile
DTSTART:20201217T150000Z
DTEND:20201217T160000Z
DTSTAMP:20260422T230718Z
UID:Utrechtseminars/12
DESCRIPTION:Title: On string vacua without supersymmetry\nby Ivano Basile as par
t of Utrecht seminar series\n\n\nAbstract\nWe discuss the existence and st
ability of vacua in string theories where supersymmetry is either absent o
r broken at the string scale. In particular we present no-go results regar
ding de Sitter compactifications\, connecting them to some Swampland conje
ctures\, thereby focusing on anti-de Sitter (AdS) flux vacua arising from
the USp(32) and U(32) orientifold models and from the SO(16) x SO(16) hete
rotic model. We investigate perturbative and non-perturbative instabilitie
s and frame the vacua in terms of brane stacks\, analyzing their back-reac
ted geometry and reproducing AdS in the near-horizon limit. Then we descri
be the instabilities as branes separating from the stack\, computing the a
ssociated decay rate matching a probe brane computation to the gravitation
al result. We conclude briefly discussing possible implications regarding
the fate of unstable vacua in string theory beyond the semi-classical limi
t\, connecting this scenario to the Weak Gravity Conjecture\, holographic
renormalization group flows and to a "de Sitter on a brane" construction t
hat was outlined in the recent literature.\n
LOCATION:https://researchseminars.org/talk/Utrechtseminars/12/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Valentin Reys
DTSTART:20210114T150000Z
DTEND:20210114T160000Z
DTSTAMP:20260422T230718Z
UID:Utrechtseminars/13
DESCRIPTION:Title: Higher-derivative Supergravity and AdS4 Holography\nby Valent
in Reys as part of Utrecht seminar series\n\n\nAbstract\nThis talk will di
scuss higher-derivative corrections to four-dimensional gauged supergravit
y\, and their holographic implications. After briefly reviewing the const
ruction of N=2 supersymmetric higher-derivative invariants\, I will introd
uce a four-derivative action parameterized by two real constants. In this
theory\, one can show that the two-derivative solutions are not modified b
y the higher-derivative corrections. This fact has important consequences
for the regularized on-shell action\, as well as for the thermodynamics of
black hole solutions. Moreover\, in the context of AdS4/CFT3 holography\,
I will explain how our results lead to an explicit expression for sublead
ing corrections in the large-N expansion of supersymmetric partition funct
ions of a large class of dual field theories arising from M2 and M5 branes
.\n
LOCATION:https://researchseminars.org/talk/Utrechtseminars/13/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Matthias Kaminski
DTSTART:20210118T150000Z
DTEND:20210118T160000Z
DTSTAMP:20260422T230718Z
UID:Utrechtseminars/14
DESCRIPTION:Title: Chiral hydrodynamics of plasma in strong magnetic fields\nby
Matthias Kaminski as part of Utrecht seminar series\n\n\nAbstract\nIn this
presentation I will motivate and construct the hydrodynamic description o
f a chiral fermion fluid subject to a strong magnetic field. Such a descri
ption can be\, for example\, applied to the quark-gluon-plasma phase gener
ated in heavy-ion-collisions\, or to Weyl semimetals. Kubo formulae are co
mputed which relate 22 transport coefficients to particular correlation fu
nctions. Among those transport coefficients\, 8 are novel. Known transport
coefficients\, such as the Hall viscosity and Hall conductivity\, are now
splitting into two each\, one longitudinal and one transverse to the magn
etic field. We provide a successful validity check by computing all transp
ort coefficients in a specific holographic model.\n
LOCATION:https://researchseminars.org/talk/Utrechtseminars/14/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Matthias Kaminski
DTSTART:20210128T150000Z
DTEND:20210128T160000Z
DTSTAMP:20260422T230718Z
UID:Utrechtseminars/15
DESCRIPTION:Title: Chiral hydrodynamics of plasma in strong magnetic fields\nby
Matthias Kaminski as part of Utrecht seminar series\n\n\nAbstract\nIn this
presentation I will motivate and construct the hydrodynamic description o
f a chiral fermion fluid subject to a strong magnetic field. Such a descri
ption can be\, for example\, applied to the quark-gluon-plasma phase gener
ated in heavy-ion-collisions\, or to Weyl semimetals. Kubo formulae are co
mputed which relate 22 transport coefficients to particular correlation fu
nctions. Among those transport coefficients\, 8 are novel. Known transport
coefficients\, such as the Hall viscosity and Hall conductivity\, are now
splitting into two each\, one longitudinal and one transverse to the magn
etic field. We provide a successful validity check by computing all transp
ort coefficients in a specific \nholographic model.\n
LOCATION:https://researchseminars.org/talk/Utrechtseminars/15/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Daniel Kläwer (Mainz)
DTSTART:20210311T160000Z
DTEND:20210311T170000Z
DTSTAMP:20260422T230718Z
UID:Utrechtseminars/16
DESCRIPTION:Title: Swampland Conjectures at Finite and Infinite Distance in Moduli S
pace\nby Daniel Kläwer (Mainz) as part of Utrecht seminar series\n\n\
nAbstract\nIn this talk\, I will discuss the realisation of various swampl
and conjectures in the moduli space of string compactifications to four di
mensions with $N=2$ and $N=1$ supersymmetry. The distance conjecture predi
cts a universal behaviour of the theory for large field displacements: Inf
inite distance loci in field space feature an infinite tower of exponentia
lly light states. The emergent string conjecture states that the dominant
tower is either a Kaluza-Klein tower or a tower of excitations of an emerg
ent critical string. These towers can provide the (super-)extremal states
required by the sub-lattice weak gravity conjecture. In the $N=2$ setting\
, mirror symmetry and heterotic/IIA duality provide valuable tools to stud
y the global geometry of the moduli space\, so we can investigate the beha
viour of the distance conjecture towers away from the infinite distance lo
ci. This allows for tests of the refined distance conjecture. The $N=1$ se
tting offers the exciting opportunity to analyse the impact of quantum cor
rections on swampland conjectures. In particular\, we will see that the in
clusion of $\\alpha'$-corrections in F-theory is crucial for the consisten
cy of the emergent string limits. I will also discuss how they affect the
weak gravity conjecture.\n
LOCATION:https://researchseminars.org/talk/Utrechtseminars/16/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Irene Valenzuela
DTSTART:20210318T150000Z
DTEND:20210318T160000Z
DTSTAMP:20260422T230718Z
UID:Utrechtseminars/17
DESCRIPTION:Title: The Convex Hull Swampland Distance Conjecture\nby Irene Valen
zuela as part of Utrecht seminar series\n\n\nAbstract\nThe Swampland Dista
nce Conjecture (SDC) restricts the geodesic distances that scalars can tra
verse in EFTs as they approach points at infinite distance in moduli space
. We argue that\, when applied to the subset of light \nfields in effecti
ve theories with scalar potentials\, the SDC restricts the amount of non-g
eodesicity allowed for trajectories along valleys of the potential\, const
raining this way the potentials that are consistent with quantum gravity.
This is necessary to ensure consistency of the SDC as a valid swampland cr
iterion at any energy scale across the RG flow\, and allows to reformulate
the conjecture as a Convex Hull condition on the scalar charge to mass ra
tios\, in analogy to the Scalar WGC. By comparing these bounds with the as
ymptotic form of the scalar potential of flux string compactifications\, I
will show that these compactifications lead to the most generic potential
s allowing for maximum non-geodesicity of the potential valleys while resp
ecting the SDC along them. I will also discuss recent lower bounds for the
SDC exponential rate\, which are important to define the Convex Hull cond
ition. In particular\, we have found a lower bound in the context of AdS/C
FT valid for any infinite distance limit in moduli space at fixed AdS radi
us. Interestingly\, it seems that a stronger and more universal version of
the SDC is valid for conformal field theories in d > 2 spacetime dimensio
ns\; namely\, that all theories at infinite distance in the Zamolodchikov
metric possess an emergent higher-spin symmetry\, generated by an infinite
tower of currents whose anomalous dimensions vanish exponentially in the
distance.\n
LOCATION:https://researchseminars.org/talk/Utrechtseminars/17/
END:VEVENT
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