Deformed General Relativity and Quantum Black Holes Interior

TL;DR

This paper investigates the covariance properties of polymer-inspired deformed gravity models for black hole interiors, showing that deformed covariance cannot extend beyond spherical symmetry and deriving the most general consistent deformed Hamiltonian.

Contribution

It introduces a Lagrangian formulation for deformed gravity models, analyzes covariance constraints, and explicitly solves modified Einstein equations for these models.

Findings

Deformed covariance cannot be extended beyond spherical symmetry.

Non-trivial deformations of the vectorial constraint with closed algebra do not exist.

Explicit solutions to modified Einstein equations are obtained for various models.

Abstract

Effective models of black holes interior have led to several proposals for regular black holes. In the so-called polymer models, based on effective deformations of the phase space of spherically symmetric general relativity in vacuum, one considers a deformed Hamiltonian constraint while keeping a non-deformed vectorial constraint. In this article, we revisit and study further the question of covariance in these deformed gravity models. In particular, we propose a Lagrangian formulation for these deformed gravity models where polymer-like deformations are introduced at the level of the full theory prior to the symmetry reduction and prior to the Legendre transformation. This enables us to test whether the concept of deformed covariance found in spherically symmetric vacuum gravity can be extended to the full theory, and we show that, in the large class of models we are considering, the deformed covariance can not be realized beyond spherical symmetry in the sense that the only deformed theory which leads to a closed constraints algebra is general relativity. Hence, we focus on the spherically symmetric sector, where there exist non-trivial deformed but closed constraints algebras. We investigate the possibility to deform the vectorial constraint as well and we prove that non-trivial deformations of the vectorial constraint with the condition that the constraints algebra remains closed do not exist. Then, we compute the most general deformed Hamiltonian constraint which admits a closed constraints algebra and thus leads to a well-defined effective theory associated with a notion of deformed covariance. Finally, we study homogeneous solutions of these effective theories and, remarkably, we solve explicitly and in full generality the corresponding modified Einstein equations, even for the effective theories which do not satisfy the closeness condition.