Program

For transparencies click on the speaker name

For photos click here

Abhay Ashtekar

An Extension of the Inflationary Scenario to the Planck Regime

Since the standard cosmological perturbation theory is based on QFT on curved space-times, it is not applicable in the Planck era. Using techniques from loop quantum gravity, the theory is extended to overcome this limitation. The new  framework sharpens conceptual issues by distinguishing between true and apparent trans-Planckian difficulties and shows that the true difficulties can be generically overcome in the standard inflationary scenario, with interesting lessons for both theory and observations. The talk will be based on joint work with I. Agullo, W. Nelson; W. Kaminski, J. Lewandowski; and T. Pawlowski and P. Singh.

Gerardo Aldazabal
“From String Fluxes to Double and Extended Field Theory”

Jorge Alfaro

Spontaneous generation of geometry in four dimensions

We present the extension to 4 dimensions of an euclidean 2-dimensional model that exhibits spontaneous generation of a metric. In this model gravitons emerge as Goldstone bosons of a global $SO(D) \times GL(D)$ symmetry broken down to $SO(D)$. The microscopic theory can be formulated without having to appeal to any particular space-time metric and only assumes the pre-existence of a manifold endowed with an affine connection. We emphasize that not even a flat metric needs to be assumed; in this sense the microscopic theory is quasi-topological. The vierbein appears as a condensate of the fundamental fermions. In spite of having non-standard characteristics, the microscopic theory appears to be renormalizable. The effective long-distance theory is obtained perturbatively around a vacuum that, if the background affine connection is set to zero, is (euclidean) de Sitter space-time. If perturbatively small connections are introduced on this background, fluctuations of the metric (i.e. gravitons) appear; they are described by an effective theory at long distances whose more relevant operators correspond to the Einstein-Hilbert action with a cosmological constant. This effective action is derived in the large $N$ limit, $N$ being the number of fermion species in the fundamental theory.
The counterterms required by the microscopic theory are directly related to the cosmological  constant and Newton constant and their couplings could eventually be adjusted to the physical values of $M_{p}$ and $\Lambda$.

Rodrigo Aros

Chern Simons Gravity induces Conformal Gravity

In this work is shown that four dimensional conformal gravity can be obtained as a dimensional reduction of a ve dimensional Chern-Simons action for the AdS group properly described in terms of a generalization of a tractor connection for the conformal group.

Max Banados

The Boulware-Deser mode in three dimensions

Jorge Bellorin

Recovering General Relativity from Horava Theory

We show that there is a consistent version of the Horava theory that propagates two physical degrees of freedom. The model is located in a subspace of the space of parameters dened by the value  = 1=3, which is protected under radiative  corrections by a constraint. The Hamiltonian formulation of the theory is consistent and has second-class constraints that drop out the extra mode that arises outside this subspace. Within this subspace, the limit when the coupling constant of the (@i lnN)2 term goes to zero leads exactly to the dynamics of (nonperturbative) general relativity; hence general relativity can be recovered smoothly without discontinuities. We further support this point by showing that the spherically  symmetric solution tends smoothly to the Schwarzschild solution in the same limit. Moreover, the perturbative version of the theory yields linearized general relativity exactly, hence it propagates ravitational waves in the usual way.

Nathan Berkovits

“ICTP-SAIFR: A new regional center for theoretical physics/New results using the pure spinor formalism of the superstring”

In the first half, I will report on the new ICTP-SAIFR center in Sao Paulo. In the second half, I will discuss some new results on multiloop amplitudes and AdS_5xS^5 vertex operators using the pure spinor formalism of the superstring.

Suddhasattwa Brahma

(Canonical) Effective Equations for QFT

In this new formulation of Quantum Field Theories using moment expansions, we not only recover the results obtained using standard methods, but also extend them, for instance, by allowing for more general states (useful for cosmology). For certain versions of (canonical) quantum gravity, these methods also provide a way of systematically deriving higher curvature corrections.

Steven Carlip

Spontaneous Dimensional Reduction?

A number of independent lines of evidence suggest that quantum gravity at distances a bit larger than the Planck scale may become effectively two-dimensional. I will summarize the evidence for this “spontaneous dimensional eduction,” and suggest a further argument based on the effect of vacuum fluctuations on light cones. If this description turns out to be correct, it suggests an interesting parallel between small-scale quantum spacetime and the behavior of cosmological spacetimes near a spacelike singularity.

Marc Casals

Semiclassical Quantum States of Fields on Black Hole Space-times

In the absence of a full theory of Quantum Gravity, it is widely believed that quantizing ‘matter’ fields on a classical black hole background space-time gives a good description of physical phenomena (such as Hawking radiation) when the physical scales are much larger than the Planck scales. The definition of the quantum state of the ‘matter’ field then becomes crucial and is neither unique nor trivial. Of particular importance is the Hartle-Hawking state, representing a black hole in thermal equilibrium with a bath of its own quantum field radiation. In this talk we will discuss the construction of various quantum states on a black hole background space-time, particularly emphasizing the differences between Schwarzschild and Kerr black holes as well as the differences between boson and fermion fields.

Diego Correa

Exact results for Wilson loops in N=4 super Yang-Mills

Seminar abstract: I will present some exact results in the computation of expectation values of certain Wilson loops in N=4 super Yang-Mills. In particular I will discuss Wilson loops with small cusp angles, whose expectation values can be related to those of supersymmetric circular Wilson loops.

Danilo Diaz

“Rényi entropy on round spheres: holographic and q-analog recipies”

Entanglement is one of the most peculiar features of quantum systems. In general, it is difficult to extract unambiguous, cut-off independent contributions to entanglement entropy. However, in the very special case of conformally invariant fields and spherical entangling surfaces, a logarithmic (in the cutoff) term can be identified whose universal coefficient is dictated by type-A trace anomaly. In this contribution we present a holographic derivation of this remarkably entropy-anomaly connection by first conformally mapping to thermal entropy in a certain hyperbolic geometry and then using an AdS/CFT-inspired holographic formula that trades boundary thermal entropy for the functional determinant (one-loop effective action) of a dual bulk field. We show that the associated Rényi entropy can be accounted for by a suitable q-analog of the previous calculations.

Bianca Dittrich

“Towards the continuum limit of spin foam and spin net models”

Spin foam models are candidate models for quantum gravity, constructed via a quantum mechanical (not Wick rotated) path integral for discrete gravity. We aim to extract the behaviour of these models on scales large compared to the discretization scale.
To this end we first introduce a conceptual framework for renormalization in background independent theories. This will also bring up the main technical tool we will be using, tensor network renormalization flow.
We then discuss a new class of models, spin nets with quantum groups, that capture key ingredients of spin foam dynamics. Finally we present first numerical results for the coarse graining flow of these models and give an outlook what to expect for spin foams.

Jose Edelstein

Black holes and phase transitions in higher curvature gravity

We revisit the study of (A)dS black holes in Lovelock theory by presenting a novel tool that allows to tackle this problem in full generality. We discuss their main features and analyze issues such as the cosmic censorship hypothesis and the existence of gravitational phase transitions that allow jumps between different branches of the theory that correspond to distinct values of the cosmological constant. This points towards an intricate phase diagram tantamount of a similarly rich behavior in the dual CFT side.

Gaston Giribet

“Baby de Sitter black holes in dS/CFT”

Unlike three-dimensional Einstein gravity, three-dimensional massive gravity does admit black hole solutions that asymptote de Sitter (dS) spacetime. This occurs at the point of the parameter space at which the theory becomes partially massless. Such black hole solutions are actually reminiscent of those of higher-dimensional General Relativity; in particular, they exhibit non-trivial thermodynamics both at the black hole event horizon and at the cosmological horizon. In turn, this provides a toy model to investigate black holes in dS spacetime. In this talk, the dS black holes of three-dimensional massive gravity will be studied in the context of the dS/CFT correspondence. It will be shown that a CFT computation in the dual theory does reproduce the thermodynamical properties of both the black hole and the cosmological horizon.

Marcos Duarte Maia

Parametric ADM

Nelson Merino

Expansion Methods, its general properties and some applications

Expansions of Lie algebras are generalizations of the Weimar-Woods (WW) contraction method that were introduced some years ago and have been used in different physical applications – particularly in gauge theories of gravity. Here we report on further developments of the so called S-method which is the most general. Some criteria and a general algorithm are proposed to know if two arbitrary algebras can related by the expansion mechanisms. We propose this procedure as a useful tool in problems where it is important to find a physical theory or a family of them that, on a certain limit, converge to some particular theory. As an example, the method can be used to study in an alternative way how standard General Relativity in five-dimensional spacetime may emerge at a special critical point of a particular Chern-Simons action.

Carmen Nunez

Flux formulation of Double Field Theory

A flux formulation of Double Field Theory is presented, in which geometric and non-geometric fluxes are dynamical and field-dependent. Gauge consistency imposes a set of quadratic constraints on the dynamical fluxes, which can be solved by truly double configurations. The constraints are related to generalized Bianchi Identities for (non-)geometric fluxes in the double space, sourced by (exotic) branes. Following previous constructions, generalized connections, torsion and
curvatures compatible with the consistency conditions are obtained. The strong constraint-violating terms needed to make contact with gauged supergravities containing duality orbits of non-geometric fluxes, systematically arise in this formulation.

Rodrigo Olea

Quasilocal vs Holographic Stress Tensor in anti de-Sitter Gravity

In the context of AdS/CFT correspondence, the holographic energy-momentum tensor is obtained by rescaling the quasilocal stress tensor, once the gravity action has been properly renormalized by the addition of local counterterms. We provide evidence that a holographic stress tensor can be also read o from the variation of a renormalized action which has been supplemented by counterterms which depend on the extrinsic curvature (a.k.a. Kounterterms), even though a  boundary stress tensor cannot be dened in that case. This argument suggests that it is possible to obtain a holographic description of a gravity theory skipping most of the technical diculties of Holographic Renormalization procedure.

Javier Olmedo

Hybrid quantization, ination and cosmological perturbations

We study the quantization of a homogeneous and isotropic spacetime lled with a massive scalar eld and with small scalar perturbations. We truncate the action to second order in the perturbations, and we consider a local gauge xing at the classical level (discussing later a description in terms of gauge invariant potentials). The reduced system is endowed with a sym-plectic structure and a Hamiltonian constraint ruling the evolution. For the quantum description, we adopt a polymeric representation for the geometry and a standard Fock quantization for the local degrees of freedom. For the latter we consider a vacuum state that is compatible with the spatial symmetries and unitary evolution. Besides, these criteria restrict the possible choices for the phase space variables. We then provide a quantum operator for the Hamiltonian constraint. We discuss how its solutions can be completely determined, together with a Born-Oppenheimer
approximation. We also study numerically the evolution at the eective dynamics level, showing the behavior of the perturbations propagating in this semiclassical spacetime and the back-reaction inuence of the inhomogeneities on the background setting.

Nelson Pinto-Neto

The Wheeler-DeWitt Quantization Can Solve the Singularity Problem

We study the Wheeler-DeWitt quantum cosmology of a spatially at Friedmann cosmological model with a massless free scalar eld. We compare the consistent histories approach with the de Broglie-Bohm theory when applied to this simple model under two di erent quantization schemes: the Schr odinger-like quantization, which essentially takes the square-root of the resulting Klein-Gordon equation through the restriction to positive frequencies and their associated Newton-Wigner states, or the induced Klein-Gordon quantization, that allows both positive and negative frequencies together. We show that the consistent histories approach can give a precise answer to the question concerning the existence of a quantum bounce if and only if one takes the single frequency approach and within a single family of histories, namely, a family containing histories concerning properties of the quantum system at only two specic moments of time: the innity past and the innity future. In that case, as shown by Craig and Singh, there is no quantum bounce. In any other situation, the question concerning the existence of a quantum bounce has no meaning in the consistent histories approach. On the contrary, we show that if one considers the de Broglie-Bohm theory, there are always states where quantum bounces occur in both quantization schemes. Hence the assertion that the Wheeler-DeWitt quantization does not solve the singularity problem in cosmology is not precise. To address this question, one must specify not only the quantum interpretation adopted but also the quantization scheme chosen.

Aleksandr Pinzul

On spectral geometry approach to Horava-Lifshitz gravity.

Recently introduced by Horava, the model of non-relativistic gravity (which is now known as Horava-Lifshitz (HL) gravity) is conjectured to be a UV/IR completion of General Relativity. We will discuss the recently initiated spectral  geometrical approach to the models with anisotropic scaling. In particular, we will present some analytical results on (classical) spectral dimension of such models as well as consider possible advantages of the spectral action principle applied to pure HL gravity and to HL gravity coupled to matter.

Jorge Pullin

The loop quantum gravity Schwarzschild black hole

We study the quantization of vacuum spherically symmetric space-times. We use variables adapted to spherical symmetry but do not fix the gauge further. One is left with a diffeomorphism constraint and a Hamiltonian constraint. Rescaling the latter turns the constraint algebra into a true Lie algebra and allows to implement the Dirac quantization procedure. We find exactly the physical states annihilated by all constraints using loop quantum gravity techniques. The space-time metric can be recovered as an evolving constant of the motion in terms of Dirac observables. The singularity is resolved as was anticipated in previous semiclassical studies. The quantum theory has new observables with respect to the
classical theory that may play a role in discussions of “firewalls” during black hole evaporation.

Israel Ramirez

Worldsheet dilatation operator for the AdS superstring

We derive a general way to compute the divergent part of composite operators in the pure spinor description of the AdS5  S5 superstring.

Martin Reuter

Asymptotic Safety and the physical mechanism behind it”

After a brief review of the Asymptotic Safety program, recent insights into the origin of its main prerequisite, a non-Gaussian RG fixed point, will be discussed. A simple physical picture based upon an analogy with magnetic systems is sufficient to explain why indeed geometry fluctuations dynamically trigger the formation of a suitable fixed point.

Jorge Russo

Massive N = 2 Gauge Theories at Large N

Using exact results obtained from localization, we explore the large N limit of N = 2 super Yang-Mills gauge theories with massive matter multiplets. In the case of N = 2* theory, we find a novel type of phase transitions, associated with the emergence of nearly massless particles in the spectrum. As the coupling is increased, the theory undergoes an infinite sequence of phase transitions that accumulate at infinite coupling. The strong coupling limit agrees with AdS/CFT and arises by a coarse-grain average over a rather irregular fractal structure at small scales. On the other hand, a massive theory with fundamental matter exhibits a smooth interpolation between the weak and strong coupling regime. We also discuss N=2 theories with arbitrary number of flavors.

Oliveira Miskovic

Holography in Poincaré gauge theories

We analyze basic features of AdS/CFT correspondence in the framework of Poincaré gauge theories. Fundamental fields in these gravity theories are naturally defined in Riemann-Cartan space. In particular, we study 3D gravity with negative cosmological constant described by most general parity-preserving quadratic action. We calculate the counterterms, finite 1-point functions, Ward identities and Weyl anomaly arising in a holographic CFT.

Kelly Stelle

Supergravity infinity cancellations and ultraviolet puzzles

Daniel Sudarski

Dynamical reduction of quantum states and the Quantum / Gravitation interface

Adolfo Toloza

Gravity around a spherically symmetric spinorial source

The Einstein-Cartan-Sciama-Kibble (ECSK) theory, that is a direct generalization of the Einstein General Relativity, has been studied from a very long time, it was first formulated by Cartan in 1922[1]. In this theory the action for gravity is the same as in the Einstein Hilbert theory, but the formalism is changed by relaxing the condition that the connection to be the Levi-Civita one, allowing for the presence of torsion. See [2] for a complete description. As a consequence of this modification the energy momentum tensor remains as the source of curvature, and the spin density tensor becomes a source of torsion.

Diego Trancanelli

Teofilo Vargas

Ponzano-Regge Model on Manifold with Torsion

The connection between angular momentum in quantum mechanics and geometric objects is extended to manifold with torsion. First, we notice the relation between the 6j symbol and Regge’s discrete version of the action functional of  Euclidean three dimensional gravity with torsion, then consider the Ponzano and Regge asymptotic formula for the Wigner 6j symbol on this simplicial manifold with torsion. In this approach, a three dimensional manifold M is decomposed into a collection of tetrahedra, and it is assumed that each tetrahedron is filled in with flat space and the torsion of M is concentrated on the edges of the tetrahedron, the length of the edge is chosen to be proportional to the length of the angular momentum vector in semiclassical limit. The Einstein-Hilbert action is then a function of the angular momentum and the Burgers vector of dislocation, and it is given by su mming the Regge action over all tetrahedra in M. We also discuss the asymptotic approximation of the partition function and their relation to the Feynmann path integral for simplicial manifold with torsion without cosmological constant.

Daniel Vieira Lopes

Resolving Exceptional Groups in F-Theory

Recently F-Theory has been explored as a promising framework to construct Grand Unified Theories (GUTs). The possibility of obtaining exceptional gauge groups not previously obtained in perturbative Type IIB string theory has brought a great deal of attention to F-Theory, and more recently the exploration of enhancements in the compact geometry lead to possible solutions to flavor hierarchy problem and the neutrino masses. In this talk we explore an explicit resolution that lead to a Yukawa point of E8 enhancement in a construction with an SU(5) gauge group. The resolution leads to a higher dimensional exceptional space in the fiber, that can be wrapped by M5-Branes and might lead to novel objects in the effective action.