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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.
Original language  English 

Article number  017 
Number of pages  12 
Journal  Journal of Cosmology and Astroparticle Physics 
Volume  2017 
Issue number  1 
DOIs  
Publication status  Published  10 Jan 2017 
Bibliographical note
8 pages plus referencesKeywords
 Cosmic singularity
 Gravity
 Modified gravity
 Physics of the early universe
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 1 Active

SRP8: Strategic Research Programme: HighEnergy Physics at the VUB
D'Hondt, J., Van Eijndhoven, N., Craps, B. & Buitink, S.
1/11/12 → 31/10/24
Project: Fundamental