BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Jakob Moritz (Cornell) DTSTART:20200528T140000Z DTEND:20200528T150000Z DTSTAMP:20260404T111414Z 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 typ e IIB string theory is an ideal arena for model building and for addressin g fundamental issues such as the existence of de Sitter vacua and large fi eld inflation. I will explain the main ideas behind our recent constructio n of a large data set of Calabi-Yau orientifolds which determine important data of the 4d effective field theories that arise from the landscape. Th e set of orientifolds features interesting classes of geometric transition s that involve colliding O-planes\, and in many cases we find that all kno wn criteria are met for the existence of a very particular spectrum of ult ra-light axions. If time permits\, I will also outline a new mechanism tha t generates hierarchically small flux superpotentials as is required by th e KKLT proposal for de Sitter vacua.\n LOCATION:https://stable.researchseminars.org/talk/Utrechtseminars/1/ END:VEVENT BEGIN:VEVENT SUMMARY:Christian Northe (Wurzburg) DTSTART:20200611T140000Z DTEND:20200611T150000Z DTSTAMP:20260404T111414Z UID:Utrechtseminars/2 DESCRIPTION:Title: Holographic RG Flows for Kondo-like Impurities\nby Chri stian Northe (Wurzburg) as part of Utrecht seminar series\n\n\nAbstract\nB oundary\, defect\, and interface RG flows\, as exemplified by the famous K ondo model\, play a significant role in the theory of quantum fields. We s tudy in detail the holographic dual of a non-conformal supersymmetric impu rity in the D1/D5 CFT. Its RG flow bears similarities to the Kondo model\, although unlike the Kondo model the CFT is strongly coupled in the hologr aphic regime. The interface we study preserves d = 1 N = 4 supersymmetry a nd flows to conformal fixed points in both the UV and IR. The interface’ s UV fixed point is described by d = 1 fermionic degrees of freedom\, coup led to a gauge connection on the CFT target space that is induced by the A DHM construction. We briefly discuss its field-theoretic properties before shifting our focus to its holographic dual. We analyze the supergravity d ual of this interface RG flow\, first in the probe limit and then includin g gravitational backreaction. In the probe limit\, the flow is realized by the puffing up of probe branes on an internal S3 via the Myers effect. We further identify the backreacted supergravity configurations dual to the interface fixed points. These supergravity solutions provide a geometric r ealization of critical screening of the defect degrees of freedom. This cr itical screening arises in a way similar to the original Kondo model. We c ompute the g-factor both in the probe brane approximation and using backre acted supergravity solutions\, and show that it decreases from the UV to t he IR as required by the g-theorem.\n LOCATION:https://stable.researchseminars.org/talk/Utrechtseminars/2/ END:VEVENT BEGIN:VEVENT SUMMARY:Wilke van der Schee (CERN) DTSTART:20200618T140000Z DTEND:20200618T150000Z DTSTAMP:20260404T111414Z 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\nA bstract\nAfter a quench the entanglement entropy will saturate to its ther mal value 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 velocity. In this talk I will introduce the `membrane paradigm'\, which gi ves a hydrodynamic description of entanglement growth coming both from ten sor networks as well as holography. Interestingly\, both spheres and cylin ders in neutral holographic plasmas saturate the butterfly bound\, whereas stripes or spheres in charged plasmas do not saturate it. In this talk I will present results for a wide variety of shapes\, showing that also a ge neric class 'between' spheres and cylinders saturates the bound.\n LOCATION:https://stable.researchseminars.org/talk/Utrechtseminars/3/ END:VEVENT BEGIN:VEVENT SUMMARY:Miguel Montero (Harvard) DTSTART:20200625T141500Z DTEND:20200625T151500Z DTSTAMP:20260404T111414Z UID:Utrechtseminars/4 DESCRIPTION:Title: Nothing is certain in string compactifications\nby Migu el Montero (Harvard) as part of Utrecht seminar series\n\n\nAbstract\nA bu bble of nothing is a spacetime instability where a compact dimension colla pses. After nucleation\, it expands at the speed of light\, leaving "nothi ng" behind. There are a couple of robust mechanisms that can prevent the e xistence of a bubble: Either it is not energetically favourable to produce them\, or there is a topological obstruction to their existence. The latt er is often the case with SUSY-preserving boundary conditions. I will expl ain how to understand the topological obstruction in detail using bordism\ , which will show that it is very generically absent even for a SUSY-compa tible spin structure. As a proof of principle\, we construct and embed in string theory an explicit bubble of nothing for a T3 with completely perio dic (SUSY-compatible) spin structure. There is a dynamical obstruction due to a positive energy theorem which is circumvented by higher-derivative c orrections. Our model can be embedded in string theory. Our techniques can be used to construct a plethora of bubbles of nothing for spaces of inter est like CY6's\, G2 manifolds\, or Sasaki-Einstein manifolds. We will expl ain how to study and circumvent the topological and dynamical obstruction in these cases. Avoiding the dynamical obstruction means avoiding a modifi ed energy condition which might be related to the Weak Gravity Conjecture. Our results lend support to the conjecture that any non-supersymmetric va cuum of quantum gravity is ultimately unstable.\n LOCATION:https://stable.researchseminars.org/talk/Utrechtseminars/4/ END:VEVENT BEGIN:VEVENT SUMMARY:Marina David (Michigan) DTSTART:20201015T140000Z DTEND:20201015T150000Z DTSTAMP:20260404T111414Z UID:Utrechtseminars/5 DESCRIPTION:Title: Holographic Approaches to AdS Black Hole Entropy\nby Ma rina David (Michigan) as part of Utrecht seminar series\n\n\nAbstract\nSig nificant progress has been made regarding the microstate counting of extre mal 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 implicat ions of this limit on the gravity side and how it translates to a paramete r space limit on the black hole solution. This limit\, referred to as the gravitational Cardy limit\, is applied to the Bardeen Horowitz near-horizo n geometry to reproduce the Bekenstein-Hawking entropy via the Kerr/CFT co rrespondence\, yielding a third approach to the computation of the entropy . Relaxing the gravitational Cardy limit\, the computation can be further extended to near-extremality\, where the heat capacity is found. For each case\, extremal and near-extremal\, the entropy from these different appro aches match\, providing a unique and universal expression for the entropy. \n LOCATION:https://stable.researchseminars.org/talk/Utrechtseminars/5/ END:VEVENT BEGIN:VEVENT SUMMARY:Dario Benedetti DTSTART:20201022T140000Z DTEND:20201022T150000Z DTSTAMP:20260404T111414Z UID:Utrechtseminars/6 DESCRIPTION:Title: Multiple scaling limits of an O(D)-invariant multi-matrix m odel\nby Dario Benedetti as part of Utrecht seminar series\n\n\nAbstra ct\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 genus expansion\, the large-D limit is relatively new: it introduces an additional organization of the fixed-genus diagrams\, which can be stu died with the methods developed for\n(rank-three) tensor models. In the si mple scaling limit\, sending N\, and then D\, to infinity\, melonic diagra ms dominate\, and their critical behavior is well understood.\nIn this tal k I will first review some of the motivations and background\, and then I will show\, in a specific model\, that the genus expansion can be resummed in a triple-scaling limit in which N and D go to infinity and the couplin g constant to its critical value\, in a coordinated manner. From the point of view of random surfaces\, the resulting continuum limit corresponds to a branched polymer phase. A different continuum limit can be obtained\, w ithin the same triple-scaling limit\, by restricting to two-particle irred ucible diagrams: in this case\, we find a mapping to an Ising model on ran dom planar graphs\, but in the high-temperature limit\, thus corresponding to the universality class of pure 2D gravity.\n LOCATION:https://stable.researchseminars.org/talk/Utrechtseminars/6/ END:VEVENT BEGIN:VEVENT SUMMARY:Carlo Angelantonj DTSTART:20201105T150000Z DTEND:20201105T160000Z DTSTAMP:20260404T111414Z UID:Utrechtseminars/7 DESCRIPTION:Title: String Defects\, Supersymmetry and the Swampland\nby Ca rlo Angelantonj as part of Utrecht seminar series\n\n\nAbstract\nWe test K im\, Shiu and Vafa consistency conditions for six dimensional supergravity theories in explicit orientifold models. Based on the perturbative data\ , we conjecture the existence of null charges Q·Q= 0 for models with at l east one tensor multiplet\, coupling to string defects of charge Q. We use the new constraint to exclude some six-dimensional supersymmetric anomaly -free examples that have currently no string or F-theory realization. We a lso investigate the constraints in case where supersymmetry is broken in t achyon free vacua\, with the breaking localised on antibranes.\n LOCATION:https://stable.researchseminars.org/talk/Utrechtseminars/7/ END:VEVENT BEGIN:VEVENT SUMMARY:Daniel Junghans (Harvard) DTSTART:20201112T150000Z DTEND:20201112T160000Z DTSTAMP:20260404T111414Z UID:Utrechtseminars/8 DESCRIPTION:Title: Control issues of KKLT\nby Daniel Junghans (Harvard) as part of Utrecht seminar series\n\n\nAbstract\nWe analyze to which extent the KKLT proposal for the construction of de Sitter vacua in string theory is quantitatively controlled. Our focus is on the quality of the 10d supe rgravity approximation. As our main finding\, we uncover and quantify an i ssue which one may want to call the "singular-bulk problem". In particular \, we show that\, requiring the curvature to be small in the conifold regi on\, one is generically forced into a regime where the warp factor becomes negative in a significant part of the Calabi-Yau orientifold. This implie s true singularities\, independent of the familiar\, string-theoretically controlled singularities of this type in the vicinity of O-planes.\n LOCATION:https://stable.researchseminars.org/talk/Utrechtseminars/8/ END:VEVENT BEGIN:VEVENT SUMMARY:Blaise Goutéraux (Ecole Polytechnique) DTSTART:20201119T150000Z DTEND:20201119T160000Z DTSTAMP:20260404T111414Z UID:Utrechtseminars/9 DESCRIPTION:Title: Hydrodynamic diffusion and its breakdown near AdS2 fixed po ints\nby Blaise Goutéraux (Ecole Polytechnique) as part of Utrecht se minar series\n\n\nAbstract\nHydrodynamics provides a universal description of interacting quantum field theories at sufficiently long times and wave lengths\, but breaks down at scales that usually depend on microscopic det ails of the theory. I will use gauge-gravity duality to investigate the br eakdown of diffusive hydrodynamics in two low temperatures states dual to black holes with AdS2 horizons. At low enough temperatures\, the breakdown is entirely controlled by data of the infrared AdS2 fixed point\, irrespe ctive of the ultraviolet completion. This is also true in a Sachdev-Ye-Kit aev chain model in the limit of strong interactions\, which is controlled by the same type of infrared fixed point.\n LOCATION:https://stable.researchseminars.org/talk/Utrechtseminars/9/ END:VEVENT BEGIN:VEVENT SUMMARY:Prahar Mitra (Cambridge) DTSTART:20201126T150000Z DTEND:20201126T160000Z DTSTAMP:20260404T111414Z UID:Utrechtseminars/10 DESCRIPTION:Title: Covariant Phase Space and Soft Factorization in Non-abelia n Gauge Theories\nby Prahar Mitra (Cambridge) as part of Utrecht semin ar series\n\n\nAbstract\nWe perform a careful study of the infrared sector of massless non-abelian gauge theories in four-dimensional Minkowski spac etime using the covariant phase space formalism\, taking into account the boundary contributions arising from the gauge sector of the theory. Upon q uantization\, we show that the boundary contributions lead to an infinite degeneracy of the vacua. The Hilbert space of the vacuum sector is not onl y shown to be remarkably simple\, but also universal. We derive a Ward ide ntity that relates the n-point amplitude between two generic in- and out-v acuum states to the one computed in standard QFT. In addition\, we demonst rate that the familiar single soft gluon theorem and multiple consecutive soft gluon theorem are consequences of the Ward identity.\n LOCATION:https://stable.researchseminars.org/talk/Utrechtseminars/10/ END:VEVENT BEGIN:VEVENT SUMMARY:Nicolo Petri (Oviedo) DTSTART:20201203T150000Z DTEND:20201203T160000Z DTSTAMP:20260404T111414Z UID:Utrechtseminars/11 DESCRIPTION:Title: Nothing really matters\nby Nicolo Petri (Oviedo) as pa rt of Utrecht seminar series\n\n\nAbstract\nThe UV consistency of low-ener gy gravity theories is one of the most studied and debated topics in curre nt research in high-energy physics. In this talk I will focus on non-pertu rbative instabilities of AdS vacua in (super)gravity theories and I will r elate them to de Sitter geometries. The set-up considered will be General Relativity in presence of a cosmological constant and at generic dimension . In this context I will discuss the non-perturbative decay of AdS vacua t hrough the spontaneous process of nucleation of "bubbles of nothing". The se bubbles are expanding in time and they are defined only by their exteri or\, so they completely destroy the AdS vacuum by making it decay literall y "into nothing". The crucial feature of these instabilities is given by t he fact that an observer living on the surface of the bubbles will experie nce a positive cosmological constant. From this point of view de Sitter ge ometries arise as part of a higher-dimensional decaying spacetime and desc ribe the dynamical expansion of the instability. I will conclude the talk by discussing a simple set-up in M-theory where these ideas could be imple mented.\n________________________________________\n LOCATION:https://stable.researchseminars.org/talk/Utrechtseminars/11/ END:VEVENT BEGIN:VEVENT SUMMARY:Ivano Basile DTSTART:20201217T150000Z DTEND:20201217T160000Z DTSTAMP:20260404T111414Z UID:Utrechtseminars/12 DESCRIPTION:Title: On string vacua without supersymmetry\nby Ivano Basile as part of Utrecht seminar series\n\n\nAbstract\nWe discuss the existence and stability of vacua in string theories where supersymmetry is either a bsent or broken at the string scale. In particular we present no-go result s regarding de Sitter compactifications\, connecting them to some Swamplan d conjectures\, thereby focusing on anti-de Sitter (AdS) flux vacua arisin g from the USp(32) and U(32) orientifold models and from the SO(16) x SO(1 6) heterotic model. We investigate perturbative and non-perturbative insta bilities and frame the vacua in terms of brane stacks\, analyzing their ba ck-reacted geometry and reproducing AdS in the near-horizon limit. Then we describe the instabilities as branes separating from the stack\, computin g the associated decay rate matching a probe brane computation to the grav itational result. We conclude briefly discussing possible implications reg arding the fate of unstable vacua in string theory beyond the semi-classic al limit\, connecting this scenario to the Weak Gravity Conjecture\, holog raphic renormalization group flows and to a "de Sitter on a brane" constru ction that was outlined in the recent literature.\n LOCATION:https://stable.researchseminars.org/talk/Utrechtseminars/12/ END:VEVENT BEGIN:VEVENT SUMMARY:Valentin Reys DTSTART:20210114T150000Z DTEND:20210114T160000Z DTSTAMP:20260404T111414Z UID:Utrechtseminars/13 DESCRIPTION:Title: Higher-derivative Supergravity and AdS4 Holography\nby Valentin Reys as part of Utrecht seminar series\n\n\nAbstract\nThis talk will discuss higher-derivative corrections to four-dimensional gauged supe rgravity\, and their holographic implications. After briefly reviewing th e construction of N=2 supersymmetric higher-derivative invariants\, I will introduce a four-derivative action parameterized by two real constants. I n this theory\, one can show that the two-derivative solutions are not mod ified by the higher-derivative corrections. This fact has important conseq uences for the regularized on-shell action\, as well as for the thermodyna mics of black hole solutions. Moreover\, in the context of AdS4/CFT3 holog raphy\, I will explain how our results lead to an explicit expression for subleading corrections in the large-N expansion of supersymmetric partitio n functions of a large class of dual field theories arising from M2 and M5 branes.\n LOCATION:https://stable.researchseminars.org/talk/Utrechtseminars/13/ END:VEVENT BEGIN:VEVENT SUMMARY:Matthias Kaminski DTSTART:20210118T150000Z DTEND:20210118T160000Z DTSTAMP:20260404T111414Z 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\n In this presentation I will motivate and construct the hydrodynamic descri ption of a chiral fermion fluid subject to a strong magnetic field. Such a description can be\, for example\, applied to the quark-gluon-plasma phas e generated in heavy-ion-collisions\, or to Weyl semimetals. Kubo formulae are computed which relate 22 transport coefficients to particular correla tion functions. Among those transport coefficients\, 8 are novel. Known tr ansport coefficients\, such as the Hall viscosity and Hall conductivity\, are now splitting into two each\, one longitudinal and one transverse to t he magnetic field. We provide a successful validity check by computing all transport coefficients in a specific holographic model.\n LOCATION:https://stable.researchseminars.org/talk/Utrechtseminars/14/ END:VEVENT BEGIN:VEVENT SUMMARY:Matthias Kaminski DTSTART:20210128T150000Z DTEND:20210128T160000Z DTSTAMP:20260404T111414Z 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\n In this presentation I will motivate and construct the hydrodynamic descri ption of a chiral fermion fluid subject to a strong magnetic field. Such a description can be\, for example\, applied to the quark-gluon-plasma phas e generated in heavy-ion-collisions\, or to Weyl semimetals. Kubo formulae are computed which relate 22 transport coefficients to particular correla tion functions. Among those transport coefficients\, 8 are novel. Known tr ansport coefficients\, such as the Hall viscosity and Hall conductivity\, are now splitting into two each\, one longitudinal and one transverse to t he magnetic field. We provide a successful validity check by computing all transport coefficients in a specific \nholographic model.\n LOCATION:https://stable.researchseminars.org/talk/Utrechtseminars/15/ END:VEVENT BEGIN:VEVENT SUMMARY:Daniel Kläwer (Mainz) DTSTART:20210311T160000Z DTEND:20210311T170000Z DTSTAMP:20260404T111414Z UID:Utrechtseminars/16 DESCRIPTION:Title: Swampland Conjectures at Finite and Infinite Distance in M oduli Space\nby Daniel Kläwer (Mainz) as part of Utrecht seminar seri es\n\n\nAbstract\nIn this talk\, I will discuss the realisation of various swampland conjectures in the moduli space of string compactifications to four dimensions with $N=2$ and $N=1$ supersymmetry. The distance conjectur e predicts a universal behaviour of the theory for large field displacemen ts: Infinite distance loci in field space feature an infinite tower of exp onentially light states. The emergent string conjecture states that the do minant tower is either a Kaluza-Klein tower or a tower of excitations of a n emergent critical string. These towers can provide the (super-)extremal states required by the sub-lattice weak gravity conjecture. In the $N=2$ s etting\, mirror symmetry and heterotic/IIA duality provide valuable tools to study the global geometry of the moduli space\, so we can investigate t he behaviour of the distance conjecture towers away from the infinite dist ance loci. This allows for tests of the refined distance conjecture. The $ N=1$ setting offers the exciting opportunity to analyse the impact of quan tum corrections on swampland conjectures. In particular\, we will see that the inclusion of $\\alpha'$-corrections in F-theory is crucial for the co nsistency of the emergent string limits. I will also discuss how they affe ct the weak gravity conjecture.\n LOCATION:https://stable.researchseminars.org/talk/Utrechtseminars/16/ END:VEVENT BEGIN:VEVENT SUMMARY:Irene Valenzuela DTSTART:20210318T150000Z DTEND:20210318T160000Z DTSTAMP:20260404T111414Z UID:Utrechtseminars/17 DESCRIPTION:Title: The Convex Hull Swampland Distance Conjecture\nby Iren e Valenzuela as part of Utrecht seminar series\n\n\nAbstract\nThe Swamplan d Distance Conjecture (SDC) restricts the geodesic distances that scalars can traverse in EFTs as they approach points at infinite distance in modul i space. We argue that\, when applied to the subset of light \nfields in effective theories with scalar potentials\, the SDC restricts the amount o f non-geodesicity allowed for trajectories along valleys of the potential\ , constraining this way the potentials that are consistent with quantum gr avity. This is necessary to ensure consistency of the SDC as a valid swamp land criterion at any energy scale across the RG flow\, and allows to refo rmulate the conjecture as a Convex Hull condition on the scalar charge to mass ratios\, in analogy to the Scalar WGC. By comparing these bounds with the asymptotic form of the scalar potential of flux string compactificati ons\, I will show that these compactifications lead to the most generic po tentials allowing for maximum non-geodesicity of the potential valleys whi le respecting the SDC along them. I will also discuss recent lower bounds for the SDC exponential rate\, which are important to define the Convex Hu ll condition. In particular\, we have found a lower bound in the context o f AdS/CFT valid for any infinite distance limit in moduli space at fixed A dS radius. Interestingly\, it seems that a stronger and more universal ver sion of the SDC is valid for conformal field theories in d > 2 spacetime d imensions\; namely\, that all theories at infinite distance in the Zamolod chikov metric possess an emergent higher-spin symmetry\, generated by an i nfinite tower of currents whose anomalous dimensions vanish exponentially in the distance.\n LOCATION:https://stable.researchseminars.org/talk/Utrechtseminars/17/ END:VEVENT END:VCALENDAR