Can inflating braneworlds be stabilized?
Abstract
We investigate scalar perturbations from inflation in braneworld cosmologies with extra dimensions. For this we calculate scalar metric fluctuations around five dimensional warped geometry with four dimensional de Sitter slices. The background metric is determined selfconsistently by the (arbitrary) bulk scalar field potential, supplemented by the boundary conditions at both orbifold branes. Assuming that the inflating branes are stabilized (by the brane scalar field potentials), we estimate the lowest eigenvalue of the scalar fluctuations—the radion mass. In the limit of flat branes, we reproduce well known estimates of the positive radion mass for stabilized branes. Surprisingly, however, we found that for de Sitter (inflating) branes the square of the radion mass is typically negative, which leads to a strong tachyonic instability. Thus, parameters of stabilized inflating braneworlds must be constrained to avoid this tachyonic instability. Instability of “stabilized” de Sitter branes is confirmed by the BRANECODE numerical calculations of Martin, Felder, Frolov, Peloso, and Kofman. If the model’s parameters are such that the radion mass is smaller than the Hubble parameter, we encounter a new mechanism of generation of primordial scalar fluctuations, which have a scale free spectrum and acceptable amplitude.
 Publication:

Physical Review D
 Pub Date:
 February 2004
 DOI:
 10.1103/PhysRevD.69.044021
 arXiv:
 arXiv:hepth/0309002
 Bibcode:
 2004PhRvD..69d4021F
 Keywords:

 04.50.+h;
 98.80.Cq;
 Gravity in more than four dimensions KaluzaKlein theory unified field theories;
 alternative theories of gravity;
 Particletheory and fieldtheory models of the early Universe;
 High Energy Physics  Theory;
 Astrophysics;
 General Relativity and Quantum Cosmology;
 High Energy Physics  Phenomenology
 EPrint:
 7 pages, RevTeX 4.0