Prepared for submission to JCAP A classical, non-singular, bouncing universe Özenç Güngör,a and Glenn D. Starkmana aISO/CERCA/Department of Physics, Case Western Reserve University, Cleveland, OH 44106-7079 E-mail:
[email protected],
[email protected] Abstract. We present a model for a classical, non-singular bouncing cosmology without violation of the null energy condition (NEC). The field content is General Relativity plus a real scalar field with a canonical kinetic term and only renormalizable, polynomial-type self-interactions for the scalar field in the Jordan frame. The universe begins vacuum-energy dominated and is contracting at t = −∞. We consider a closed universe with a positive spatial curvature, which is responsible for the universe bouncing without any NEC violation. An Rφ2 coupling between the Ricci scalar and the scalar field drives the scalar field from arXiv:2011.05133v2 [gr-qc] 12 Jan 2021 the initial false vacuum to the true vacuum during the bounce. The model is sub-Planckian throughout its evolution and every dimensionful parameter is below the effective-field-theory scale MP , so we expect no ghost-type or tachyonic instabilities. This model solves the horizon problem and extends co-moving particle geodesics to past infinity, resulting in a geodesically complete universe without singularities. We solve the Friedman equations and the scalar-field equation of motion numerically, and analytically under certain approximations. Keywords: cosmic singularity, alternatives to inflation, physics of the early universe, initial conditions and eternal universe 1 Introduction The Inflationary Big-Bang model, our standard model of cosmology, has had notable and numerous observational successes over the last several decades.