Polygonal Gravity Seminars
Madrid’s Polygonal Gravity Seminar Series
Wednesday, September 30th. Red Room (IFT)
11:15h Welcome coffee
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11:30h First talk
Speaker: Sameer Murthy (Kingś College, London)
Title: Near-extremal black holes in GR and in string theory
Abstract:What happens to the thermodynamics of a black hole at very low temperatures as it
approaches extremality? This question had remained a puzzle for many decades. Recent progress shows
that semi-classical physics in the near-extremal limit needs to be revisited due to the appearance
of nearly gapless modes in the near-horizon of a near-extremal black hole. Upon approaching the
extremal limit carefully, one finds that the quantum fluctuations of these gapless modes leads to
unexpectedly large effects even for a very massive black holes with weakly-curved horizons. In the
first part of this talk, I will explain this progress and discuss various applications.
In the second half of the talk, I will discuss progress regarding the calculation of entropy of
supersymmetric black holes, which has been one of the big successes of string theory. I will discuss
how the counting of entropy in string theory involves a subtlety regarding the supersymmetric index,
and how its resolution also involves, once again, taking the extremal limit carefully. Finally, I
will discuss how this procedure leads to a new class of supersymmetric solutions corresponding to
black holes and black strings.
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12:45-14:45 Lunch break and free time
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15:00h Second talk
Speaker: Luciano Rezzolla (Institute of Theoretical Physics, Goethe U., Frankfurt)
Title: Binary Neutron Stars: from macroscopic collisions to microphysics
Abstract: I will argue that if black holes represent one the most fascinating implications of
Einstein’s theory of gravity, neutron stars in binary system are its richest laboratory, where
gravity blends with astrophysics and particle physics. I will discuss the rapid recent progress made
in modelling these systems and show how the gravitational signal can provide tight constraints on
the equation of state and sound speed for matter at nuclear densities, as well as on one of the most
important consequences of general relativity for compact stars: the existence of a maximum mass.
Finally, I will discuss how the merger may lead to a phase transition from hadronic to quark matter.
Such a process would lead to a signature in the post-merger gravitational-wave signal and open an
observational window on the production of quark matter in the present Universe.
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16:00h Coffee time
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More information about these and following monthly seminars can be found at the webpage https://sites.google.com/view/polygrav (No registration is needed)