Scalar graviton and the modified black holes

TL;DR

This paper investigates how breaking general covariance to unimodular gravity introduces a scalar graviton, leading to new static spherically symmetric solutions, including a novel 'graviball' object, while maintaining Newtonian limits.

Contribution

It demonstrates the emergence of a two-parameter family of solutions and a new one-parameter 'graviball' solution absent in General Relativity.

Findings

Existence of a two-parameter family of metrics

Discovery of a 'graviball' solution

Metrics retain correct Newtonian limit

Abstract

Under the explicit violation of the general covariance to the unimodular one, the effect of the emerging scalar graviton on the static spherically symmetric metrics is studied. The main results are three-fold. First, there appears the two-parametric family of such metrics, instead of the one-parametric black-hole family in General Relativity (GR). Second, there may exist the one-parametric subfamily describing a pure gravitational object, the ``graviball'', missing in GR. Third, in a simplifying assumption, all the metrics possess the correct Newton's limit as in GR.