Date: November 5

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

Speaker: Marios Petropoulos (CPHT, Ecole Polytechnique, Palaiseau)

Title: Gauges, holographic fluids and hydrodynamic frames

• Abstract: Fluid/gravity correspondence relates relativistic fluids with asymptotically anti-de Sitter spacetimes. Although relativistic fluid dynamics is said to be hydrodynamic-frame invariant, such a freedom is only local and breaks down when global properties are considered. This phenomenon is revealed in the dual gravitational picture of the fluids, because the choice of boundary hydrodynamic frame translates in the sort of gauge used in the bulk, which in turn affects the asymptotic symmetries. The associated surface charges obey different algebras, which encode the hydrodynamic frame. This property is exhibited in three dimensions, where Einstein spacetimes are locally anti de Sitter. It survives the flat limit, which is mapped in the boundary to an ultra-relativistic fluid. It furthermore seems to persist in higher dimensions and sheds new light on the interplay between gauges and asymptotic symmetries. Based on 1812.04019, 2006.10082, 2006.10083 and work in progress.

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Date: November 12

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

Speaker: Aranya Bhattacharya (SINP Kolkata)

Title: Islands and complexity in multiboundary wormhole models in AdS

• Abstract: We discuss two situations in which black hole evaporation is modelled through multiboundary wormholes in AdS3. In both of the models, we discuss the analogs of island appearing at Page time. The Page curves are reproduced and the complexity of the radiation quanta throughout the evaporation is studied. The Hawking quanta are modeled in a multipartite way and therefore the models also help us to understand certain connections between island and multipartite entanglement in these models. We find two candidate complexity curves corresponding to the unitary Page curve of entanglement entropy. We also discuss two alternate ways of realising the complexity of the island through i) the kinematic space and ii) tensor networks within the scope of the multiboundary models.

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Date: November 19

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

Speaker: Shahin Sheikh Jabbari (IPM Tehran)

Title: Horizons 2020

• Abstract: Formulation of theories with local symmetries in presence of boundaries has revealed interesting features, stressing further the significance of "boundary degrees of freedom" (b.d.o.f.) and the symmetries and algebras arranging the b.d.o.f. In particular, one may apply these ideas to black hole solutions to gravity theories where the horizon can be viewed as a null boundary for the set of observers outside the horizon. The b.d.o.f. and the associated charges and algebras in these examples may remedy problem of identification of black hole microstates. In this talk I provide a general discussion on the null boundary symmetries and algebras and summarise and the latest developments in realisation of the Hawking-Perry-Strominger idea.

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Date: November 26

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

Speaker: Sachin Jain (IISER Pune)

Title: Momentum space correlation function and higher-spin equation

• Abstract: Calculation of CFT correlation function in momentum space is complicated and not explored much. In this talk we discuss how to use conserved higher spin equation (arises in free theories) and slightly broken higher spin equation (arises in CS matter theories) to calculate some of these correlators efficiently. We also discuss how one can use higher spin equation to calculate correaltion function at finite temperature and away from conformal fixed points.

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