Diptarka Das, IIT Kanpur
6/12/2019 (Friday)
Lecture Hall 3, New Physical Sciences Building
Abstract:
In the first part of the talk we shall generalize the modular bootstrap techniques in two dimensional conformal theories, so that they can be applied to torus correlators and spherical conformal blocks. This will give us Cardy-like expressions for weighted spectral densities. In the second part we shall systematize the Hellerman analysis, and show how under certain assumptions the c/6 upper bound on the lightest primary may be improved to c/10.38. Thereafter, we shall discuss Tauberian improvements of the bounds for the first part and highlight some applications of the results to the Eigenstate Thermalization Hypothesis criteria.
Naveen Prabhakar, TIFR(Mumbai)
27/11/2019 (Wednesday)
Lecture Hall 3, New Physical Sciences Building
Abstract:
We review recent developments in the understanding of massive phases of Chern-Simons theories coupled to vector-like matte and their behavior under Bose-Fermi duality. In particular, we discuss the recent computation of the large N free energy in the Higgsed phase of Chern-Simons gauged Wilson-Fisher scalars and its mapping to the free energy of Chern-Simons gauged regular fermions under Bose-Fermi duality. We further extend our computations to the N = 2 supersymmetric Chern-Simons theory coupled to one fundamental chiral multiplet and study the phase diagram of this the theory at zero temperature. The phase diagram shows rich features, including points where two second-order phase transition lines meet.
Suchetan Das, RKMV(Belur)
1/11/2019 (Friday)
Lecture Hall 3, New Physical Sciences Building
Abstract:
In QFT, algebra of operators often plays an important role to study different mathematical and structural aspects. Among its several applications, operator product expansion(OPE) and Tomita-Takesaki modular theory(TT theory) provide an important tool to study some interesting and useful features in QFT. In particular, OPE is used to reduce higher point correlation functions to the lower point of that and to constrain dynamical data of the theory(particularly in CFTs). On the other hand, TT theory gives a rigorous way to define quantum information quantities in QFT which can be used to study entanglement patterns in QFT subregions. In this talk, our goal is to study some simple applications in both OPE and TT theory in the context of AdS_3/CFT_2. More precisely, we will discuss kinematical quantity `OPE block', the building block of an OPE and modular Hamiltonian, a central object of TT theory in this context. Also, another goal of the talk is to show a simple connection between them in CFT_2 and its AdS_3 interpretation.
Augniva Roy, SINP(Kolkata)
29/10/2019 (Tuesday)
Lecture Hall 3, New Physical Sciences Building
Abstract:
We find the exact partition function of de Sitter Quantum Gravity partition function on Lens Spaces L(p, q) using supersymmetric localization. We also comment on one possible regularization scheme.
Abhiram Kidambi, SINP(Kolkata)
1/10/2019 (Tuesday)
Lecture Hall 3, New Physical Sciences Building
Abstract:
In this talk, I shall comment on using the number-theoretic techniques developed by Dabholkar, Murthy and Zagier in studying N = 4 black holes in 4d string compactification. A key result here is a good number-theoretic handle on wall crossing phenomena. These results from the number theory side mostly match with the degeneracies computed from the localization of the quantum entropy function. However, there are certain black hole states for which there is no matching. In this talk, I shall explain why this mismatch comes about and how one can go about resolving it.
Kausik Ghosh, CHEP, IISc
24/09/2019 (Tuesday), 2:30 pm
Lecture Hall 3, New Physical Sciences Building
Abstract
We will talk about Polyakov Mellin bootstrap (a crossing symmetric approach) in the simple setting of 1D CFT. We address the issue of contact terms in quite a generality. We study various EFTs in AdS2 using our basis and also extend this method for O(N) theory. As a completely independent check, we fix the amplitude using principle of pure transcendentality and extract ope data from it which agrees exactly with results we found using PM bootstrap. Finally, we close with few remarks on our plans to fix ambiguities in higher dimensions.
Pranjal Nayak, University of Kentucky
10/09/2019 (Tuesday)
Lecture Hall 3, New Physical Sciences Building
Abstract:
The SYK model provides an uncommon example of a theory where the Eigenstate Thermalization Hypothesis (ETH) can be verified in analytically. In this talk, I will discuss this model in the deep infrared limit where the theory has an emergent conformal (reparametrization) symmetry that is broken both spontaneously and explicitly. To study the validity of ETH, we compute the heavy- light correlation functions of operators in the conformal spectrum of the theory. We compute these correlation functions with and without the contribution of the low energy (Schwarzian) modes, which are known to be the origin of the chaotic behavior in this theory. In considering the contributions of the Schwarzian modes we find that the thermalization is closely related to the coadjoint orbits of Virasoro group to which the state belongs. In the case where Schwarzian modes aren’t considered, we find ETH in limit in which the weight of the heavy operators approach infinity. I will also discuss the implications of these results for the states in AdS2 gravity dual.
Onkar Parikkar, University of Pennsylvania, USA
28/08/2019 (Wednesday)
Abstract
Black holes are expected to be effective gravitational descriptions resulting from coarse-graining over a large number of underlying microstates. Here we explore the consequences of this coarse-graining on the phase space of excitations around the black hole. In particular, we study this phase space for an incipient black hole in the half-BPS sector of N=4 Super Yang-Mills theory, both from the AdS and CFT perspectives. On the gravity side, the coarse-graining corresponds to putting a stretched horizon away from the "core" of the solution. As a result, the phase space around the black hole has a new soft/collective mode on the stretched horizon -- i.e., the bulk Wilson line from the asymptotic boundary to the horizon -- which is absent in individual microstates. We then explicitly construct and coarse-grain the phase space in the CFT, and explain the emergence of such a soft mode from the microscopic degrees of freedom of the black hole.
Onkar Parikkar, University of Pennsylvania, USA
27/08/2019 (Tuesday)
Abstract:
We study the quantum complexity of time evolution in large N chaotic systems, with the SYK model as our main example. This complexity is expected to increase linearly for exponential time prior to saturating at its maximum value, and within Nielsen's formulation is related to the length of minimal geodesics on the manifold of unitary operators that act on Hilbert space. We demonstrate that there is always a geodesic between the identity and the time evolution operator exp(-itH) whose length grows linearly with time. This geodesic is a minimum of the distance function until there is an obstruction to its minimality, after which it can fail to be a minimum either locally or globally. We identify a criterion - the Eigenstate Complexity Hypothesis (ECH) - which bounds the overlap between off-diagonal outer products of energy eigenstates and the k-local operators of the theory and use it to show that the linear geodesic will at least be a local minimum for exponential time. In contrast, we also study the case with N=2 fermions (which is integrable) and find short-time linear complexity growth followed by oscillations.