Primordial black holes in a dimensionally oxidizing Universe
Abstract
The spontaneous creation of primordial black holes in a violently expanding Universe is a well studied phenomenon. Based on quantum gravity arguments, it has been conjectured that the early Universe might have undergone a lower dimensional phase before relaxing to the current (3+1) dimensional state. In this article we combine the above phenomena: we calculate the pair creation rates of black holes nucleated in an expanding Universe, by assuming a dimensional evolution, we term "oxidation", from (1+1) to (2+1) and finally to (3+1) dimensions. Our investigation is based on the no boundary proposal that allows for the construction of the required gravitational instantons. If, on the one hand, the existence of a dilaton nonminimally coupled to the metric is necessary for black holes to exist in the (1+1) phase, it becomes, on the other hand, trivial in (2+1) dimensions. Nevertheless, the dilaton might survive the oxidation and be incorporated in a modified theory of gravity in (3+1) dimensions: by assuming that our Universe, in its current state, originates from a lowerdimensional oxidation, one might be led to consider the pair creation rate in a subclass of the Horndeski action. Our findings for this case show that, for specific values of the Galileon coupling to the metric, the rate can be unsuppressed. This would imply the possibility of compelling parameter bounds for nonEinstein theories of gravity by using the spontaneous black hole creation.
 Publication:

Journal of Cosmology and Astroparticle Physics
 Pub Date:
 October 2020
 DOI:
 10.1088/14757516/2020/10/008
 arXiv:
 arXiv:2007.13653
 Bibcode:
 2020JCAP...10..008D
 Keywords:

 General Relativity and Quantum Cosmology
 EPrint:
 12 pages, 3 figures