9 research outputs found
On the superstrings-induced four-dimensional gravity, and its applications to cosmology
We review the status of the fourth-order (quartic in the spacetime curvature)
terms induced by superstrings/M-theory (compactified on a warped torus) in the
leading order with respect to the Regge slope parameter, and study their
(non-perturbative) impact on the evolution of the Hubble scale in the context
of the four-dimensional FRW cosmology. After taking into account the quantum
ambiguities in the definition of the off-shell superstring effective action, we
propose the generalized Friedmann equations, find the existence of their (de
Sitter) exact inflationary solutions without a spacetime singularity, and
constrain the ambiguities by demanding stability and the scale factor duality
invariance of our solutions. The most naive (Bel-Robinson tensor squared)
quartic terms are ruled out, thus giving the evidence for the necessity of
extra quartic (Ricci tensor-dependent) terms in the off-shell gravitational
effective action for superstrings. Our methods are generalizable to the higher
orders in the spacetime curvature.Comment: 33 pages, LaTeX, no figures; extensive revision, Sec.6 and references
added, stability analysis include
Mutated hybrid inflation in -gravity
A new hybrid inflationary scenario in the context of -gravity
is proposed. Demanding the waterfall field to 'support the potential from
below' [unlike the original proposal by Stewart in Phys. Lett. B345, 414
(1995)], we demonstrate that the scalar potential is similar to that of the
large-field chaotic inflation model proposed by Linde in Phys. Lett. B129, 177
(1983). Inflationary observables are used to constrain the parameter space of
our model; in the process, an interesting limit on the number of e-folds N is
found.Comment: 9 pages, 2 figures, LaTeX2e, v2: Sec.3 expanded and improved, 1 Fig.
added, a new result included, some Eqs. corrected, 2 References adde