Speakers

Stefanos Aretakis (Univ. of Toronto): Observational signatures for extremal black holes

Abstract: The event horizon and the Cauchy horizon of an extremal black hole admit conserved charges associated with scalar perturbations. We will see that these charges are externally measurable from null infinity. This suggests that these charges have the potential to serve as an observational signature for extremal black holes. The proof of this result is based on obtaining precise late-time asymptotics for the radiation field of outgoing perturbations.

Athanasios Chatzistavrakidis (RBI, Zagreb): Gauge Symmetries and Higher Structures

Abstract: I will discuss the interplay between physical theories with gauge symmetries and the mathematical notions of higher algebroids and L-infinity algebras. Applying this relation to string theory leads to "triple points", where the structure of compactifications with fluxes, the BV quantization of non-linear sigma-models and the axioms of certain algebroids are all controlled by the same set of equations. I will comment on the usefulness of this approach for duality covariant formulations of string and M theories.

Elias Kiritsis (Univ. of Crete): Two new roads to de Sitter in string theory

Abstract: De Sitter vacua in string theory are a highly debated subject currently. Conjectures state they are not possible. The KKLT constructions claims to construct an enormous number of them. In this talk I will discuss two novel ways of constructing vacua in string theory, by demostrating the prnciple in bottom up constructions.

Manuela Kulaxizi (Trinity College, Dublin): CFT an black holes

Abstract: We will review progress in studying CFTs with a large number of degrees of freedom, and discuss how we can use it to learn something about gravity and black holes.

Lampros Lamprou (MIT): Holographic order from modular chaos

Abstract: What quantum mechanical principle underlies the emergence of the local geometric structure of the holographic Universe? I will develop a notion of chaos associated to the entanglement pattern of a QFT state by introducing a bound characterizing modular flow of a subregion. In AdS/CFT, saturation of this modular chaos is intimately linked to the local Poincare symmetry and curvature about a bulk Ryu-Takayanagi surface, suggesting an appealing candidate answer to the question posed above.

Christos Likos (Univ. of Vienna):Equilibrium and flow properties of ring polymers

Abstract: Modifications of the topological state of polymers are extremely interesting and relevant operations for a vast domain of scientific inquiry ranging from knot theory and polymer science all the way to materials science and biophysics, where cyclic and knotted DNA plays a key role in biological processes. Recent work has demonstrated that joining the two ends of a linear chain to form a cyclic (ring) polymer has a number of significant consequences in the structural [1,2] and rheological [3] properties of concentrated or semidilute solutions of the same. Accordingly, a number of questions arise regarding the behavior of linear, cyclic and knotted ring polymers under flow: how does the topology of the dissolved polymer affect its orientational resistance, as well as its rotation-, tumbling- or tank-treading motion under Couette flow? What consequences does shear flow have for knot localization along a sheared polymer? Can one make use of the different flow properties of various polymer topologies to build microfluidic devices that act as filters/separators of topologically different polymers? By applying hybrid (MPCD/MD) simulation techniques that take into account the hydrodynamics, we address the questions above for polymers of varying topologies, knotedness and stiffness and we analyze quantitatively the influence of polymer topology on single- polymer properties under flow [4]. Polymer properties under Poiseuille flow will also be analyzed. Suggestions for the construction of topology-separating microfluidic devices will be presented [5].

References:[1] M. Z. Slimani, P. Bacova, M. Bernabei, A. Narros, C. N. Likos, and A. J. Moreno, ACS Macro Letters 3, 611 (2014). [2] P. Poier, S. A. Egorov, C. N. Likos and R. Blaak, Soft Matter 12, 7983 (2016). [3] M. Kapnistos, M. Lang, D. Vlassopoulos, W. Pyckhout-Hintzen, D. Richter, D. Cho, T. Chang, and M. Rubinstein, Nature Materials 7, 997 (2008). [4] M. Liebetreu, M. Ripoll, and C. N. Likos, ACS Macro Letters 7, 447−452 (2018). [5] L. Weiß, A. Nikoubashman, and C. N. Likos, Macromolecules 52, 7858-7869 (2019).

Elli Pomoni (DESY): T_N, Toda and topological strings

In this talk we will consider the long-standing problem of obtaining the 3-point functions of 2D Toda CFT. We will propose a solution to this problem employing topological strings and the AGT relation between 4D gauge theories and 2D CFTs.

Andreas Athenodorou (Pisa Univ.): Is flux-tube a bosonic string? What does Lattice say?

Abstract: I will present my work on the spectrum of the confining flux tube using lattice techniques both in 3D as well as 4D SU(N) gauge theories. Recent years have witnessed unprecedented progress in the investigation of the spectrum of the closed confining flux-tube in the Yang-Mills (YM) theory. Long flux-tubes can be thought of as infinitesimally thin strings; hence their spectrum is expected to be described by an Effective String Theory. Furthermore, the flux-tube's internal structure makes possible the existence of massive states in addition to string modes. Calculations on the spectrum of the flux tube in 3D SU(N) gauge theories have shown that this is very well described by the Nambu-Goto non-critical string up to small deviations for very short strings. Results in 4D SU(N) gauge theories demonstrate that most states exhibit spectrum which can be approximated adequately by Nambu-Goto but also provides strong evidence for the existence of a massive particle with particular (axionic) quantum numbers on the world-sheet of the QCD flux-tube.

Perseas Christodoulidis(Univ. of Groningen): Attractors, Bifurcations and Curvature in Multi-field Inflation

Abstract: Recent years have seen the introduction of various multi-field inflationary scenarios in which the curvature and geodesics of the scalar manifold play a crucial role. We outline a simple description that unifies these different proposals and discuss their stability criteria. We demonstrate how the underlying dynamics is governed by an effective potential, whose critical points and bifurcations determine the late-time behaviour of the system, thus unifying hyperinflation, angular, orbital and side-tracked inflation. Interestingly, we show that hyperinflation is a special case of side-tracked inflation, relying on the enhanced isometries of the hyperbolic manifold. We provide the explicit coordinate transformation that maps the two models into each other.

Nadav Drukker (King's College) : Hyperloops in 3d Chern-Simons matter theories

Praxitelis Ntokos (Utah State Univ.): Universal properties of Kaluza-Klein gravitons

Abstract:The AdS vacua in string/M-theory are D=10 or D=11 solutions of a specific model compactified on some internal manifold. Therefore, the properties around each vacuum in this AdS landscape depend both on the specific model considered and on the features of the internal manifold. In particular, the Kaluza-Klein (KK) towers around each vacuum are expected to be unrelated. However, the spectrum of spin-2 fields exhibits some universality properties for solutions which preserve the same amount of (super)symmetry! In this talk, I will describe these universal properties and I will present a mass matrix for KK gravitons which is valid for all the relevant AdS₄ vacua.

Kostas Rigatos (Southampton Univ.): String corrections to AdS amplitudes and the double-trace spectrum of N = 4 SYM

Abstract: There has been recent progress towards the understanding of α'-corrections to 4pt-correlation functionσ of 1/2-BPS operators in N=4 SYM in the supergravity limit. The correlator <2,2,p,p> has been computed using unitarity methods and supersymmetric localisation to the first two orders in α'. In this talk, I will discuss the solution to the mixing of double-trace operators, the form of the spectrum, new results that we obtained for 4pt correlators with arbitrary charges of the external operators at (α')^3 and the construction of the <2,3,p-1,p> correlator at the first two orders in α'.

Dimitri Skliros (MPP): Handle Operators in String Theory

Αbstract: I will discuss how to construct handle operators in string theory, namely bi-local operator insertions that implement topological features of Riemann surfaces in string amplitudes.

Orestis Vasilakis (Czech Academy of Sciences): Information recovery from pure state geometries in 3D

Abstract: We present a chiral version of the information puzzle in AdS3/CFT2, where the geometry describing a heavy left-moving primary, displays thermal behaviour in chiral correlators. Using the Liouville parametrisation in the bulk, we will then examine a special class of pure state geometries which do not display information loss. They describe heavy CFT states created by a collection of chiral operators at various positions on the complex plane. In the bulk, they take the form of multi-centered solutions from the backreaction of a collection of spinning particles, which we study for circular distributions of particles. We compute the two-point function of probe operators in these backgrounds and show that information is retrieved.