October 2021

Date: October 7

Time: 17:30 IST (UTC + 5:30)

Speaker: K Narayan (Chennai Mathematical Institute)

Title: Cosmologies, Entanglement and Extremal Surfaces

Abstract: I will describe aspects of entanglement and extremal surfaces in certain AdS cosmologies and de Sitter space. In the first part, I will review certain families of AdS cosmologies with Big-Crunch singularities, including AdS Kasner, obtained as time-dependent deformations of AdS/CFT and their duals. I'll then describe spacetimes with cosmological singularities in 2-dimensional dilaton-gravity-matter theories, in part obtainable by dimensional reduction. I will then discuss aspects of classical and quantum extremal surfaces in these theories. In the second part, I will describe certain explorations of extremal surfaces in de Sitter space motivated by dS/CFT. I will discuss various aspects of future-past surfaces in de Sitter space, and entanglement in ghost theories, and finally close with some speculations.

This seminar is a part of the activities of Center for QIT of Spacetime and Matter and Center for Strings, Gravitation and Cosmology of IIT Madras

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Date: October 11

Time: 17:30 IST (UTC + 5:30)

Speaker: Josef Leutgeb (TU Wien)

Title: Holographic QCD and the anomalous magnetic moment of the muon

Abstract: The estimated error of the standard model prediction for the anomalous magnetic moment of the muon comes almost exclusively from hadronic vacuum polarization and hadronic light-by-light scattering, where the latter is dominated by exchanges of neutral pseudoscalars and axial vector mesons. Using holographic QCD we are able to calculate these contributions and to solve the problem of most phenomenological models to satisfy the known short-distance constraints of the hadronic light-by-light tensor, in particular the one implied by the axial anomaly pointed out by Melnikov and Vainshtein.

This seminar is a part of the activities of Center for Strings, Gravitation and Cosmology of IIT Madras

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Date: October 18

Time: 17:30 IST (UTC + 5:30)

Speaker: Harold Erbin (MIT)

Title: Non-perturbative renormalization for the neural network-QFT correspondence

Abstract: In a recent work, Halverson, Maiti and Stoner proposed a description of neural networks in terms of an effective field theory (dubbed NN-QFT correspondence). The infinite-width limit is mapped to a free field theory while finite N corrections are taken into account by interactions. In this talk, after reviewing the correspondence, I will derive non-perturbative renormalization group equations. An important difference with the usual analysis is that the effective (IR) 2-point function is known, while the microscopic (UV) 2-point function is not, which requires setting the problem with care. Finally, I will discuss preliminary numerical results for translation-invariant kernels. A major result is that changing the standard deviation of the neural network weight distribution can be interpreted as a renormalization flow in the space of networks.

This seminar is a part of the activities of Center for Quantum Information Theory of Matter and Spacetime of IIT Madras

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Date: October 27

Time: 18:30 IST (UTC + 5:30)

Speaker: Eran Palti (Ben-Gurion University )

Title: Convexity of Charged Operators in CFTs and the Weak Gravity Conjecture

Abstract: In this talk I will introduce a particular formulation of the Weak Gravity Conjecture in AdS space in terms of the self-binding energy of a particle. The holographic CFT dual of this formulation corresponds to a certain convex-like structure for operators charged under continuous global symmetries. Motivated by this, we propose a conjecture that this convexity is a general property of all CFTs, not just those with weakly-curved gravitational duals. It is possible to test this in simple CFTs, the conjecture passes all the tests performed so far.

This seminar is a part of the activities of Center for Strings, Gravity and Cosmology of IIT Madras

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Date: October 27

Time: 17:30 IST (UTC + 5:30)

Speaker: Teresa Bautista Solans (King's College London )

Title: Timelike Liouville gravity

Abstract: Liouville theory in its timelike regime is an interesting model of two-dimensional gravity because it reproduces the characteristic minus sign of the conformal-factor kinetic term of higher-dimensional Einstein-Hilbert gravity. In this talk, I will first present a proposal for two-dimensional quantum gravity with a cosmological constant based on the conformal bootstrap results of timelike Liouville theory coupled to unitary conformal matter. The spectrum of physical energies is obtained from the BRST cohomology of diffeomorphisms, and the 4-point function of states belonging to this spectrum is finite and crossing symmetric. I will then present the perturbative computation of the gravitational partition function around the sphere saddle and discuss a proposal for an all orders result. Finally, time permitting, I will discuss some work in progress on timelike Liouville with a conformal boundary.

This seminar is a part of the activities of Center for Strings, Gravity and Cosmology of IIT Madras

VIDEO: Click here