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2 pm,Lecture Hall 804 Some aspects of black hole physics in de Sitter spacetime Sourav Bhattacharya Assistant Professor, IIT Ropar. 04-11-19 Abstract In this talk I shall discuss some properties of the black hole spacetimes located in the de Sitter universe. Such spacetimes model black holes located in either our current or in the inflationary early universe. Such a spacetime's global structure is qualitatively different from that of the asymptotically flat or anti-de Sitter ones, chiefly due to the existence of the cosmological event horizon -- a null hypersurface beyond which no causal communication is possible. I shall briefly review how the existence of this horizon may alter in cases, the usual uniqueness properties of the black hole spacetime structure, via some boundary effects. After that, I shall chiefly focus on the thermodynamic and field theoretic aspects in such spacetimes. Being equipped with two horizons, they have two temperatures, making the usual notion of the Boulware, Hartle-Hawking or the Unruh vacuum states ambiguous. I shall discuss, how to meaningfully define particle states and to associate temperatures in such kind of spacetimes, in an eternal black hole or in a gravitational collapse scenario. I shall also introduce the notion of the effective entropy and effective temperature associated with such spacetimes. I shall end with mentioning some interesting open issues for such spacetimes pertaining the early universe.
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