Black Holes in Asymptotically Safe Gravity

Abstract

In this chapter we review the state-of-the-art of black holes in asymptotically safe gravity. After a brief recap of the asymptotic safety program, we shall summarize the features of asymptotic-safety-inspired black-hole models that have been constructed in the past by the so-called renormalization group improvement. Specifically, we will discuss static configurations, both in spherically-and axiallysymmetric settings, the role played by the cosmological constant, and the impact of the collapse dynamics in determining black-hole configurations realized in Nature.In particular, we will review how quantum gravity could modify the Buchdahl limit and the corresponding conditions to form ultra-compact objects and Planckian black holes. We will then proceed by describing the most recent developments, particularly those aiming at making model building in asymptotic safety more rigorous and free from ambiguities. These include self-consistent and coordinate-independent versions of the renormalization group improvement, and next steps to fill the gap between model building and renormalization group computations in asymptotic safety. Finally, we will focus on a selection of results that have been obtained from first-principle calculations or arguments, within and beyond asymptotic safety. Concretely, we will review the state-of-the-art in determining black-hole entropy in asymptotic safety from a microstate counting, and progress in deriving the quantumcorrected Newtonian potential. We will discuss how in quantum gravity theories linked to a gravitational path integral singularity resolution could be achieved by a dynamical suppression of singular configurations. Finally, we will show thatindependent of the specific ultraviolet completion of gravity-asymptotic modifications to Schwarzschild black holes are strongly constrained by the principle of least action at large distance scales.

Breaking Buchdahl: Ultracompact stars in semiclassical gravity

“…This provides another independent evidence of the plausible absence of a Buchdahl limit in semiclassical gravity. For completeness, let us mention that this result is in tune with independent analyses of the impact of modifications of gravity on stellar structure within the asymptotic safety framework [34,35].…”

Phase structure of quantum improved Schwarzschild-(Anti)de Sitter black holes

“…For the typical black holes with σ = 1, it is straightforward to plot the mass (12) with respect to the horizon radius and the temperature (13) and the heat capacity (14) with respect to the mass parameter. These are given in figures 1(a)-(c) for different choice of ω.…”

“…For topological black holes (σ = −1) in GR without quantum effects (ω = 0), we depict the mass (12) with respect to the horizon radius and the temperature (13) and heat capacity (14) with respect to the mass parameter in figure 2 by red dashed lines. We find that there is only one horizon for positive M, and two horizons for negative M larger than the lower bound, as can be seen from figure 2(a).…”

“…Given a suitable identification, it turns out that quantum effects provide a 'repulsive' force at the core of black hole which stabilizes the unstable phase of small black holes [9,10]. For discussions of black holes in this context, see [11][12][13][14] and references therein.…”

Gravitational wave hints black hole remnants as dark matter

“…For more models, see the collection in [9,19,20]. Recently, there is also growing interest within asymptotic safe gravity (see [21,22] for recent reviews). Note that these are static solutions and it is not clear what would occur when considering the initial collapse of matter.…”