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Seminars»25.11.2021 - Ufuk Aydemir : Phenomenology of not quite black holes

25.11.2021 - Ufuk Aydemir : Phenomenology of not quite black holes

Phenomenology of not quite black holes

Ufuk Aydemir
Institute of High Energy Physics, Chinese Academy of Sciences
25 November 2021, Thursday, 14:40
Cavid Erginsoy Seminar Room, Physics Department, 3rd floor
Zoom Link

Abstract: It is now observationally certain that there are extremely compact and dark astrophysical objects that are so far consistent with black holes in General Relativity (GR). However, the current observations cannot accurately probe near-horizon physics, and it is indeed this regime where deviations from GR, possibly towards quantum gravity, might first manifest. Such deviations are strongly motivated by the information loss problem, anticipated to be resolved by new physics. One possibility is that quantum gravity prevents formation of event horizon, generating horizonless ultracompact objects instead of black holes. These objects would appear similar to black holes for current experiments, yet they could leave distinctive imprints in gravitational wave signals. As far as the current observations are concerned they remain in the picture, and therefore it is important to understand their implications in order to search for signals beyond GR, or to confirm the theory further.

In this talk, I will discuss phenomenology of such an object, namely 2-2-hole, which arises in quadratic gravity, a candidate theory for quantum gravity, as a family of classical solutions for ultracompact matter distributions. A 2-2-hole possesses essentially the exterior of a black hole without an event horizon and hence, as a probable endpoint of gravitational collapse, it provides a resolution to the information loss problem. When sourced by thermal gas, a 2-2-hole at relatively early stages of its evaporation imitates the thermodynamic characteristics of a black hole; it radiates with a Hawking-like temperature and exhibits an entropy-area law. In contrast to black holes, this behaviour explicitly arises in a self-gravitating thermal system. At late stages, the evaporation essentially stops, naturally leading to a stable remnant. Primordial 2-2-hole remnants, in comparison and contrast to the primordial black hole remnants, constitute dark matter candidates. Alternatively, the particle dark matter scenario can also be realized, where the majority of dark matter consists of particles produced by the evaporation of primordial 2-2-holes, and the remnant contribution is secondary. Moreover, 2-2-hole evaporation in the early universe can produce particles that are responsible for the baryon asymmetry, in which case baryogenesis through direct B-violating decays or through leptogenesis can both be realized.