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Entropy 2015, 17(10), 6893-6924;

Thermal BEC Black Holes

Dipartimento di Fisica e Astronomia, Alma Mater Università di Bologna, via Irnerio 46, 40126 Bologna, Italy
Istituto Nazionale di Fisica Nucleare (I.N.F.N.), Sezione di Bologna, viale Berti Pichat 6/2, 40127 Bologna, Italy
Institute of Space Science, Atomistilor 409, 077125 Magurele, Ilfov, Romania
Author to whom correspondence should be addressed.
Academic Editors: Remo Garattini and Kevin H. Knuth
Received: 9 September 2015 / Revised: 6 October 2015 / Accepted: 9 October 2015 / Published: 15 October 2015
(This article belongs to the Special Issue Entropy in Quantum Gravity and Quantum Cosmology)
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We review some features of Bose–Einstein condensate (BEC) models of black holes obtained by means of the horizon wave function formalism. We consider the Klein–Gordon equation for a toy graviton field coupled to a static matter current in a spherically-symmetric setup. The classical field reproduces the Newtonian potential generated by the matter source, while the corresponding quantum state is given by a coherent superposition of scalar modes with a continuous occupation number. An attractive self-interaction is needed for bound states to form, the case in which one finds that (approximately) one mode is allowed, and the system of N bosons can be self-confined in a volume of the size of the Schwarzschild radius. The horizon wave function formalism is then used to show that the radius of such a system corresponds to a proper horizon. The uncertainty in the size of the horizon is related to the typical energy of Hawking modes: it decreases with the increasing of the black hole mass (larger number of gravitons), resulting in agreement with the semiclassical calculations and which does not hold for a single very massive particle. The spectrum of these systems has two components: a discrete ground state of energy m (the bosons forming the black hole) and a continuous spectrum with energy ω > m (representing the Hawking radiation and modeled with a Planckian distribution at the expected Hawking temperature). Assuming the main effect of the internal scatterings is the Hawking radiation, the N-particle state can be collectively described by a single-particle wave-function given by a superposition of a total ground state with energy M = Nm and Entropy 2015, 17 6894 a Planckian distribution for E > M at the same Hawking temperature. This can be used to compute the partition function and to find the usual area law for the entropy, with a logarithmic correction related to the Hawking component. The backreaction of modes with ω > m is also shown to reduce the Hawking flux. The above corrections suggest that for black holes in this quantum state, the evaporation properly stops for a vanishing mass. View Full-Text
Keywords: black holes; horizon wave function; Hawking radiation; generalized uncertainty principle black holes; horizon wave function; Hawking radiation; generalized uncertainty principle

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Casadio, R.; Giugno, A.; Micu, O.; Orlandi, A. Thermal BEC Black Holes. Entropy 2015, 17, 6893-6924.

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