Isotropization in brane gas cosmology

Abstract

Brane Gas Cosmology (BGC) is an approach to unifying string theory and cosmology in which matter is described by a gas of strings and branes in a dilaton gravity background. TheUniverse is assumed to start out with all spatial dimensions compact and small. It has previously been shown that in this context, in the approximation of neglecting inhomogeneities and anisotropies, there is a dynamical mechanism which allows only three spatial dimensions to become large. However, previous studies do not lead to any conclusions concerning the isotropy or anisotropy of these three large spatial dimensions. Here, we generalize the equations of BGC to the anisotropic case, and find that isotropization is a natural consequence of the dynamics.

Stabilization of extra dimensions at tree level

“…From (16) we find that the zero mode energy and pressure 1 of the string gas in D − 1 compact dimensions can be written as, E = 3µN (3) e λ + 3µM (3) e −λ + 6µN (6) e ν + 6µM (6) e −ν ,…”

“…A possible resolution to this problem was suggested in [1] (see also [2]) and has since been generalized to include more realistic background geometries and the inclusion of branes [3,5,6]. The authors of [1] argued that, by considering the dynamics of the winding and momentum modes of the strings, a new symmetry specific of string theory, namely t-duality, could eliminate the big-bang singularity and also explain the dimensionality of space-time.…”

Interaction rates in string gas cosmology

“…Therefore, it seems reasonable that (23) will hold approximately even if branes are included in the thermal gas of strings. See [11,12,13,16,17,19,21,22,25,26] for some work relevant to time evolution in brane gases. Similarly, allowing the shape moduli of the spatial torus and the various form fields of supergravity to be nontrivial may alter the qualitative behavior of the dilaton, such as by providing a potential (for a review of flux compactifications with stabilized dilaton, see [44]).…”

“…One important generalization has been including branes in the early universe gas of strings [4,5,6,7], and other spacetime topologies have also been considered [8,9]. Starting with [2,3], a number of authors have examined the cosmological equations of motion appropriate to string gases as well as brane gases [10,11,12,13,14,15,16,17,18,19,20,21,22,23,24]. In particular, [25,26] showed that interesting cosmological dynamics happen when the expanding dimensions are still near the string scale, and [7,27,28,29] have begun to examine the effects of nontrivial backgrounds of fields other than the metric in the low energy supergravity.…”

Brane gases in the early universe: thermodynamics and cosmology

“…One intriguing possibility is that extended objects play a vital role in explaining the asymmetry. This is the idea behind brane gas cosmology [1,2,3,4,5,6].…”