LECTURE TALKS
Luis Apolo (Amsterdam U.)
Title: “TTbar Deformations and String Theory”
Abstract: In these lectures I will describe a toy model of holography for non-AdS spacetimes that is obtained by deforming the bulk and boundary sides of the AdS$_3$/CFT$_2$ correspondence. In the bulk we will consider string theory on AdS$_3$ backgrounds supported by NS-NS flux. The spectrum of the theory admits so-called long strings which match the spectrum of a symmetric product orbifold CFT$_2$. We will then perform a marginal deformation of the worldsheet action that is equivalent to a TsT (T-duality + shift + T-duality) transformation of the background geometry. The TsT transformation yields a family of spacetimes including black holes that are no longer asymptotically AdS$_3$. On the boundary side, we will show that the marginal deformation corresponds to an irrelevant single-trace $T\bar T$ deformation of the symmetric product orbifold CFT$_2$. We will check that the perturbative spectrum of strings on the TsT-transformed background, the thermodynamics of black holes, and properties of the ground state geometry match those of the boundary theory.
Guilherme L. Pimentel (SNS, Pisa)
Title: “Cosmological Fluctuations and their Bootstrap”
Abstract: I will review what we know about the initial conditions of the universe, and show how they are computed and predicted from the framework of cosmic inflation. Then I will focus on the non-Gaussian statistics of these primordial fluctuations, showing how they can be ‘’bootstrapped’’ from symmetry, locality and unitarity. I will mostly present the theory of primordial scalar fluctuations, but time permitting will also say something about tensor fluctuations, which have their own peculiarities. The tools used involve a blend of scattering amplitudes, gauge/gravity duality, and conformal field theories.
COLLOQUIUM
Macarena Lagos (Columbia U.)
Title: “Synergy of cosmological multi messengers”
Abstract: The behaviour of the Universe on large scales is typically assumed to follow the concordance cosmological model Lambda Cold Dark Matter. This model agrees very well with a variety of cosmological observations obtained via the detection of electromagnetic (EM) waves. However, the LCDM model assumes the presence of unknown---yet fundamental---components in the Universe, such as dark matter, dark energy and inflationary field. In this talk, I will explain how the observation of gravitational waves can also be used to test cosmology, and how the combination of GW+EM observations will help constrain the behaviour of dark energy in the future.
TALKS
Raúl Rojas Mejías - Universidad de Concepción, Chile
Title: “Holography of AdS hairy black holes and Cardy-Verlinde formula”
Abstract: We discuss some aspects related to holography of Anti-de Sitter (AdS) dyonic hairy black holes, which break the conformal symmetry of the boundary. We use counterterms for the scalar field that satisfies mixed boundary conditions to compute the Euclidean action and dual stress tensor. We apply these results to show that the Cardy-Verlinde formula is not satisfied. However, when the magnetic (or electric) charge vanishes, the conformal symmetry is preserved and the entropy of the black hole can be put in the Cardy-Verlinde form.
Viktor Jahnke - Gwangju Institute of Science and Technology (GIST)
Title: “Holographic teleportation with conservation laws: diffusion on traversable wormholes.”
Abstract: We study the effects of conservation laws on wormholes that are made traversable by a double trace deformation. After coupling the two asymptotic boundaries of an eternal (d+1) dimensional AdS-Schwarzschild black hole with U(1) conserved current operators, we find that the corresponding quantum matter stress-energy tensor violates the average null energy condition (ANEC) in the bulk, rendering the wormhole traversable. We discuss how the wormhole opening depends on the charge diffusion constant and how this affects the amount of information that can be sent through the wormhole.
Cesar Agón - Instituto Balseiro
Title: “Some aspects of the N-partite information in conformal field theories”
Abstract: I will present a general procedure for computing the N-partite information in the ground state of a conformal field theory for N-disjoint spheres in the large separation regime. Then, I will apply the aforementioned procedure to reproduce previous results for the mutual and tripartite information as well to obtain a new result for the four partite information. After that, I show numerical agreement between these and lattice computations for the case of a free scalar in three spacetime dimensions. Finally, I close with an explicit check of the equivalence between the N-partite information of boundary and bulk fields in holographic theories.
Jeremias Aguilera Damia - Solvay Institutes ULB
Title: “Generalized Symmetries in QFT”
Abstract: Almost since the foundations of modern theoretical physics, it has been known that global symmetries may often play a key role to access non-perturbative dynamics. In this talk, I will briefly review some novel concepts of symmetry which transcend the classical notion of ordinary global symmetry, for instance by acting over extended objects or allowing operators without inverse. I'll provide some simple examples of physical systems hosting these novel symmetry structure in two and four dimensions and, if time permits, we will touch upon some concrete constructions in three and five dimensions.
Veronica Pasquarella - DAMTP, University of Cambridge, UK
Title: “2D vacuum transitions and their holographic interpretation ”
Abstract: We show that the behaviour of 2D vacuum transitions is reminiscent of the CFT$_2$/CFT$_2$ correspondence. In doing so, we perform the calculation in Euclidean (CDL, BT) and Lorentzian (FMP) methods. In absence of conical deficits, the total action is proportional to the central charge of the defect, thereby signalling that the spacetimes involved are extremal. The total action in the Hamiltonian method is also shown to be proportional to the difference of the entanglement entropy, SEE, of 2 $T\bar T$-deformed CFT$_2$ s. Generalisations of the c-theorem imply that the action diverges upon taking the flat limit, thereby showing an analogous behaviour to the information loss paradox, that first motivated the island proposal. This divergence can be cured by adding a non-extremal black hole, and, consequently, an island. Our findings therefore agree with the proposal made by Maldacena that false vacuum decay to a portion of AdS is allowed by the AdS/CFT correspondence. In all cases, the total action is proportional to the difference of generalised entropies. For transitions involving pure AdS$_2$ and/or AdS$_2$ black hole spacetimes, our results agree with those obtained by Van Raamsdonk et al. within the context of mutual approximation between states belonging to different CFT$_2$ s separated by a 1D interface. We further extend these arguments to the case of dS$_2$. We conclude providing a wedge-holographic embedding of these processes.
Paulina Cabrera Ramírez - Universidad Técnica Federico Santa María (Chile)
Title: “Criticality of a hairy black hole solution: how scalar field modify Van der Waals-like phase transitions in Reissner-Nördstrom black holes”
Abstract: Thermodynamic aspects of black holes have been widely studied within the last decades. During that time it turned out that black hole spacetimes can not only be assigned standard thermodynamic variables such as temperature or entropy, but were also shown to possess rich phase structures and admit critical phenomena, in complete analogy with known non-gravitational thermodynamic systems elsewhere in nature. Allowing variations of the cosmological constant, it is treated as a thermodynamic pressure, while the thermodynamic volume is included as its conjugate quantity. In this extended space phase, we are interested in introducing the first-order phase transition of the Reissner Nördstrm-AdS (RN-AdS) black hole spacetime that is superficially analogous to the Van der Waals liquid-gas phase transition. Afterwards, we are going to show how scalar fields affect the thermodynamic behaviour of the mentioned charged black holes. In particular, we study a class of exact hairy charged AdS black hole solution of Einstein-Maxwell-scalar gravity and we find that there exists an intermediate range of the charge that admits reentrant phase behaviour, the first example of this type of phase behaviour in (3+1)-dimensions in a consistent theory.
José Julián Barragán Amado - Université de Sherbrooke
Title: “Quasinormal modes of scalar fields on small Reissner-Nordström-AdS$_5$ black holes”
Abstract: We study the quasinormal modes (QNMs) of a charged scalar field on a Reissner-Nordström-anti-de Sitter (RN-AdS$_5$) black hole in the small radius limit by using the isomonodromic method. We also derive the low-temperature expansion of the fundamental QNM frequency. Finally, we provide numerical evidence that instabilities appear in the small radius limit for large values of the charge of the scalar field.
Rodolfo Abraham Sánchez Isidro - Institute of Nuclear Sciences, UNAM
Title: “Duality invariant non-linear oscillators from a $\sqrt{T\bar{T}}$ deformation”
Abstract: Inspired by a recently proposed non-linear Duality and Conformal invariant modification of Maxwell theory (ModMaX), we construct a one-parameter family of two-dimensional dynamical systems in classical mechanics that share many features with the ModMax theory. It consists of a couple of $\sqrt{T\bar{T}}$ deformed non-linear oscillators that nevertheless are duality invariant in phase space $(q \rightarrow p,p \rightarrow -q)$ and are parametrized by a continuous parameter $\gamma$ exactly as in the ModMax theory. Despite its non-linear features, the system is integrable and we are able to perform the Legendre transform. Based on the proprieties of the model, we can construct an infinite integrable hierarchy tower structure of deformed coupled oscillators with a higher and higher degree in polynomials of $q$, $p$. We show that the system can be interpreted as a pair of coupled oscillators (one of them mounted on the other) whose frequencies depend on some basic invariants that correspond to the duality symmetry and rotational symmetry. The dynamics present the phenomenon of energy transfer between the oscillators. Finally, we calculate the Hannay angle of the system.
GONG SHOW
Felipe Diaz - Universidad Andres Bello
Title: “De Sitter Entanglement and UV cutoffs”
Abstract: Two important periods of our universe may be dominated by exponential growth, generating a cosmological horizon because light rays do not manage to propagate to the entire geometry. It has been argued that the entropy associated with the horizon corresponds to the entanglement between disconnected regions of spacetime. In order to supplement the idea, we compute the logarithmic corrections to the entropy using CFT methods proposed by Carlip in an orbifold that recovers the original manifold in a limit in the orbifold parameter. This quantum corrections backreact in the Renyi entropy such that the resulting entanglement entropy contains a logarithmic divergence allowing us to interpret the orbifold parameter with an UV regulator. Moreover, we recover the Bank's proposal for the dimensionality of the Hilbert space of our universe which implies a problem of quantization of gravity starting from the Einstein--Hilbert action. We also show that the logarithmic corrections recover the correct result in three dimensions using a codimension-2 holography for de Sitter.
Quim Llorens - ICCUB Barcelona
Title: “Higher-curvature Gravities from Braneworlds and the Holographic c-Theorem”
Abstract: We study the structure of the higher-curvature gravitational densities that are induced from holographic renormalization in AdSd+1. In a braneworld construction, such densities define a d-dimensional higher-curvature gravitational theory on the brane, which in turn is dual to a (d-1)-dimensional CFT living at its boundary. We show that this CFTd−1 satisfies a holographic c-theorem in general dimensions, since at each and every order the higher-curvature densities satisfy c-theorems on their own. We examine various other features of the holographically induced higher-curvature densities.
Lucas Acito - Instituto de Física La Plata
Title: “Superradiant Black Hole Rocket”
Abstract: Superradiance is a process in which the reflected radiation due to a system is enhanced with respect to the incident radiation and that it happens under certain conditions e.g. in black holes. We investigated this phenomenon for charged scalar fields when a hemispherical mirror is placed concentric to a static charged black hole, and we call this configuration a “superradiant black hole rocket” due to its shape and the resultant thrust force. To do so, first we solve the minimally coupled Klein-Gordon equation with the gauge field in curved space, given by the Reissner-Nordström metric. The field in the whole allowed space-time region is obtained from the radial solutions that satisfy the boundary conditions at the horizon (whether they are superradiant modes or not) and at infinity, then the pieces of the field are pasted by imposing the boundary conditions on the mirror. Then, from the previous result for the classical field, we proceed with the quantization of the field considering the BH-mirror configuration immersed in a thermal bath of charged scalar particles and antiparticles which is not in thermodynamic equilibrium with the BH. Assuming that the particles follow a Bose-Einstein distribution and using the energy-momentum tensor of the system, the total force on the BH rocket is obtained. Finally, the results obtained for both the scattering of a scalar field and the BH rocket in the thermal bath were analyzed numerically. From these numerical results and the analytical expression obtained, the total BH rocket force is determined for the chosen system parameters.
Federico Manzoni - Roma Tre University
Title: “Symplexic central charges”
Abstract: The superconformal central charge is an important quantity for theories emerging from geometrical engineering of Quantum Field Theory since it is linked, for example, to the scaling dimension of fields. Butti and Zaffaroni construc- tion of the central charge for toric Calabi-Yau threefold geometries is a powerful tool but its implementation could be quite tricky. Here we present an equivalent new construction based on a 2-simplexes decomposition of the toric diagram which opens the way to possible generalizations to cases of different dimensions
Jaydeep Kumar Basak - Indian Institute of Technology Kanpur, India
Title: “Entanglement Negativity Islands and Communicating Black Holes”
Abstract: We obtain the holographic entanglement negativity for bipartite mixed states at a finite temperature in baths described by conformal field theories dual to configurations involving two communicating black holes in braneworld geometries. In this context we analyze the mixed state entanglement structure characterized by the information transfer between the black holes for two separate models. The first model involves communicating black holes in a Karch-Randall braneworld and $BCFT_2$s with two boundaries describing common bath systems for the radiation flux. The second model corresponds to a configuration of two dimensional eternal JT black holes in a braneworld geometry involving two Planck branes coupled through shared bath systems described by $CFT_2$s. For both the models our results reproduce analogue of the Page curves for the entanglement negativity obtained earlier in the context of random matrix theory and from geometric evaporation in JT black hole configurations.
Julian Hernan Toro - IMAS, FCEyN, UBA
Title: “Correlators and spectral flow in AdS_3xS^3xT^4 superstring theory”
Abstract: The duality between type IIB superstring theory on AdS_3xS^3xT^4 and some two-dimensional CFT with a large central charge corresponds to one of the best knwon examples of the AdS/CFT correspondence. Given that the AdS_3xS^3xT^4 geometry is an exact solution to the superstring theory, this duality allow us to explore the correspondence beyond the supergravity limit. In this work we study the two- and three-point function in this superstring theory, focusing our attention on the winding string modes. The usual BRST quantization and picture changing procedure, together with spectral flow, make the computation of correlators involving current insertions rather non-trivial. We derive a method for computing such correlators for arbitrary windings. Finally we focus on extremal configurations and show that our results reproduce the corresponding local correlators of the boundary theory.
Mritunjay Verma - University of Southampton
Title: “Momentum space”
Abstract: We analyse the CFT correlators for the non conserved operators in the momentum space and apply it to study the massive amplitudes in AdS. In particular, we show that taking the flat limit of the momentum space CFT correlators for the massive amplitudes reproduces the expected result in the flat space. This puts a constraint on the value of gyromagnetic ratio in AdS.
Ankit Aggarwal - UvA (Amsterdam), ULB (Brussels)
Title: “Phase transition of photons and gravitons in a Casimir box”
Abstract: A first order phase transition for photons and gravitons in a Casimir box is studied analytically from first principles with a detailed understanding of symmetry breaking due to boundary conditions. It is closely related to Bose-Einstein condensation and accompanied by a quantum phase transition whose control parameter is the chemical potential for optical helicity.
Aníbal Tomás Ignacio Neira Gallegos- Universidad de Concepción
Title: “Asymptotic symmetries in Einstein-Scalar theory with a Liouville Potential”
Abstract: We analyze asymptotically locally flat spacetimes in three and four dimensions supported by the presence of a scalar field with a self-interacting exponential potential. The set of solutions admit black holes that can be accommodated in an asymptotic set of fall-off conditions whose asymptotic symmetry group is generated by the diffeomorphisms on the celestial circle (soon the sphere will be consider too).