HEP Colloquia 2024

by Nicolò Burzillà (INFN Roma 2)

Wednesday 23 Oct 2024, 14:30 → 16:00 Europe/Rome

Sala Consiliare (Department of Physics)

Regular black holes in higher derivative and nonlocal gravity

We present a detailed analysis of the static spherically symmetric solutions of a sixth-derivative gravity model with complex conjugate poles (Lee-Wick gravity) in the effective delta source approximation. The solutions exhibit an interesting structure that depends on the real and imaginary parts of the Lee-Wick mass, $\mu = a + ib$. In particular, due to the oscillating behavior of the metric, which depends on the ratio $b/a$, a rich structure of horizons is present.This multi-horizon structure generates a sequence of mass gaps and, consequently, multiple regimes for black hole sizes (horizon position gaps) are observed. Regarding the thermodynamics of these objects, the oscillation of the Hawking temperature determines the presence of multiple mass scales for the remnants of the evaporation process and may allow for the existence of cold black hole remnants with zero Hawking temperature $T$, as well as quasi-stable intermediate configurations with $T \approx 0$ and a long evaporation lifetime. For the sake of generality, we consider two families of solutions: one with a trivial shift function and the other with a non-trivial one (dirty black hole).

In the second part of the talk, we consider a general result regarding the regularity of curvature derivative invariants in local and nonlocal higher derivative gravity. We show that the absence of divergences in these invariants depends on the UV behavior of the propagator, or equivalently, on the number of derivatives in the action. Regularity of all invariants can be achieved in certain classes of nonlocal models.