Defocusing of null rays in infinite derivative gravity
Abstract
Einstein's General theory of relativity permits spacetime singularities, where null geodesic congruences focus in the presence of matter, which satisfies an appropriate energy condition. In this paper, we provide a minimal defocusing condition for null congruences without assuming any ansatzdependent background solution. The two important criteria are: (1) an additional scalar degree of freedom, besides the massless graviton must be introduced into the spacetime; and (2) an infinite derivative theory of gravity is required in order to avoid tachyons or ghosts in the graviton propagator. In this regard, our analysis strengthens earlier arguments for constructing nonsingular bouncing cosmologies within an infinite derivative theory of gravity, without assuming any ansatz to solve the full equations of motion.
 Publication:

Journal of Cosmology and Astroparticle Physics
 Pub Date:
 January 2017
 DOI:
 10.1088/14757516/2017/01/017
 arXiv:
 arXiv:1605.02080
 Bibcode:
 2017JCAP...01..017C
 Keywords:

 General Relativity and Quantum Cosmology;
 High Energy Physics  Theory
 EPrint:
 8 pages plus references