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**From**: Balog Janos <balog.janos AT wigner.mta.hu>**To**: fizinfo AT lists.kfki.hu, rmkiusers AT lists.kfki.hu**Subject**: [Fizinfo] MTA Wigner FK RMI Elméleti Osztály Szemináriuma**Date**: Tue, 04 Jul 2017 11:24:10 +0800**Authentication-results**: smtp1.kfki.hu (amavisd-new); dkim=pass (1024-bit key) reason="pass (just generated, assumed good)" header.d=wigner.mta.hu

MTA Wigner FK RMI Elméleti Osztály Szemináriuma

Tisztelettel meghívjuk

José P. S. Lemos

(University of Lisbon)

"Black hole entropy from matter entropy"

címmel tartandó szemináriumára.

Kivonat:

Black hole entropy S is one of the most fascinating issues

in contemporary physics, as one does not yet strictly know what are

the degrees of freedom at the fundamental microlevel, nor where are

they located precisely. In addition, extremal black holes, in contrast

to non-extremal ones, present a conundrum, as there are two mutually

inconsistent results for the entropy of extremal black holes. There is

the usual Bekenstein-Hawking S = A/4 value, where A is the horizon

area, obtained from string theory and other methods, and there is the

prescription S = 0 obtained from Euclidean arguments. In order to

better understand black hole entropy in its generality, we exploit a

matter based framework and use a thermodynamic approach for an

electrically charged thin shell. We find the entropy function for such

a system. We then take the shell radius into its gravitational radius

(or horizon) limit. We show that: (i) For a non-extremal shell the

gravitational radius limit yields S=A/4. The contribution to the

entropy comes from the pressure. (ii) For an extremal shell the

calculations are very subtle and interesting. The horizon limit gives

an entropy which is a function of the horizon area A alone, S(A), but

the precise functional form depends on how we set the initial

shell. The values 0 and A/4 are certainly possible values for the

extremal black hole entropy. This formalism clearly shows that

non-extremal and extremal black holes are different objects. In

addition, the formalism suggests that for non-extremal black holes all

possible degrees of freedom are excited, whereas in extremal black

holes, in general, only a fraction of those degrees of freedom

manifest themselves. We conjecture that for extremal black holes the

entropy S is restricted to the interval between 0 and A/4. Since an

extremal shell has zero pressure, the contribution to the entropy

comes from the shell's electricity. In this case, the contribution to

the entropy comes from the mass and electric potential. (iii) There is

yet another possibility that interpolates between the two previous

ones: to take the extremal limit concomitantly with the gravitational

radius limit. Remarkably, in this case, the mass, the pressure and the

electricity on the shell contribute to the entropy to give S=A/4.

Helye: MTA Wigner FK RMI III.ép. Tanácsterem

Ideje: 2017 július 7 péntek du. 14:00 óra

Szívesen látunk minden érdeklődőt.

Balog János

**[Fizinfo] MTA Wigner FK RMI Elméleti Osztály Szemináriuma**,*Balog Janos, 07/04/2017*- <Possible follow-up(s)>
**[Fizinfo] MTA Wigner FK RMI Elméleti Osztály Szemináriuma**,*Balog Janos, 07/28/2017*

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