Cosmology with negative potentials
Abstract
We investigate cosmological evolution in models where the effective potential V(φ) may become negative for some values of the field φ. Phase portraits of such theories in the space of variables (φ,φ˙,H) have several qualitatively new features as compared with phase portraits in the theories with V(φ)>0. Cosmological evolution in models with potentials with a ``stable'' minimum at V(φ)<0 is similar in some respects to the evolution in models with potentials unbounded from below. Instead of reaching an AdS regime dominated by the negative vacuum energy, the universe reaches a turning point where its energy density vanishes, and then it contracts to a singularity with properties that are practically independent of V(φ). We apply our methods to investigation of the recently proposed cyclic universe scenario. We show that in addition to the singularity problem there are other problems that need to be resolved in order to realize a cyclic regime in this scenario. We propose several modifications of this scenario and conclude that the best way to improve it is to add a usual stage of inflation after the singularity and use that inflationary stage to generate perturbations in the standard way.
 Publication:

Physical Review D
 Pub Date:
 July 2002
 DOI:
 10.1103/PhysRevD.66.023507
 arXiv:
 arXiv:hepth/0202017
 Bibcode:
 2002PhRvD..66b3507F
 Keywords:

 98.80.Cq;
 04.65.+e;
 11.25.w;
 Particletheory and fieldtheory models of the early Universe;
 Supergravity;
 Strings and branes;
 Astrophysics;
 General Relativity and Quantum Cosmology;
 High Energy Physics  Phenomenology;
 High Energy Physics  Theory
 EPrint:
 51 page, 20 figures