Accelerating cosmologies from M/String theory compactifications

Abstract

We point out that the solution of $(4+n)$-dimensional gravity coupled to the dilaton and an $n$-form field strength can give rise to a flat 4-dimensional universe (with a scale factor) of the type proposed recently under time dependent compactifications. The compact internal spaces could be hyperbolic, flat or spherical and the solution is identical to the space-like two brane or S2-brane. As has been shown previously for SM2 solution with a fixed field strength we show that for $n=7$ (where the dilaton is vanishing and with a general field strength), 6 the corresponding SM2 and SD2 solutions can give accelerating cosmologies in Einstein frame for both hyperbolic and flat internal spaces, thereby meeting the challenge of obtaining such a solution from M/String theory compactifications.

Figures (2)

• Figure 1: The function $m(t)$ in eq.(26) and the l.h.s. of eq.(27) are plotted against $t$ for $c_1=1$ and $\alpha=0.92$ and are given respectively by solid and dashed lines.
• Figure 2: The function $m(t)$ in eq.(30) and the l.h.s. of eq.(31) are plotted against $t$ for $c_1=1$ and $\alpha=0.92$ and are given respectively by solid and dashed lines.