Horizonless ultracompact objects and dark matter in quadratic gravity
Abstract
We show that in quadratic gravity sufficiently light objects must be horizonless and construct explicit analytic examples of horizonless ultracompact objects (UCOs), which are more compact than Schwarzschild black holes. Due to the quadratic terms, gravity becomes soft and eventually vanishes in the highenergy limit leading to a "linearization mechanism": light objects can be described by the linearized theory when their Schwarzschild radius is smaller than the Compton wavelength of the new gravitational degrees of freedom. As a result, we can analytically describe UCOs with a masstoradius ratio higher than for a Schwarzschild black hole. The corresponding spacetime is regular everywhere. We show that the Ostrogradsky instabilities can be avoided and discuss the relation with the Higgs vacuum metastability. Due to the lack of a horizon, light UCOs do not evaporate. Therefore, they may play the role of dark matter. We briefly discuss their phenomenology.
 Publication:

Journal of Cosmology and Astroparticle Physics
 Pub Date:
 February 2020
 DOI:
 10.1088/14757516/2020/02/018
 arXiv:
 arXiv:1912.13333
 Bibcode:
 2020JCAP...02..018S
 Keywords:

 General Relativity and Quantum Cosmology;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 High Energy Physics  Phenomenology;
 High Energy Physics  Theory
 EPrint:
 v2: 28 pages, 2 figures. v2 has an updated list of references and minor modifications, it matches the published version