Cosmological evolution of brane world moduli

Abstract

We study cosmological consequences of non-constant brane world moduli in five dimensional brane world models with bulk scalars and two boundary branes. We focus on the case where the brane tension is an exponential function of the bulk scalar field, U b ∝ exp (αφ). In the limit α → 0, the model reduces to the two-brane model of Randall-Sundrum, whereas larger values of α allow for a less warped bulk geometry. Using the moduli space approximation we derive the four-dimensional low-energy effective action from a supergravity-inspired five-dimensional theory.For arbitrary values of α, the resulting theory has the form of a bi-scalar-tensor theory. We show that, in order to be consistent with local gravitational observations, α has to be small (less than 10−2 ) and the separation of the branes must be large. We study the cosmological evolution of the interbrane distance and the bulk scalar field for different matter contents on each branes. Our findings indicate that attractor solutions exist which drive the moduli fields towards values consistent with observations. The efficiency of the attractor mechanism crucially depends on the matter content on each branes. In the five-dimensional description, the attractors correspond to the motion of the negative tension brane towards a bulk singularity, which signals the eventual breakdown of the four-dimensional description and the necessity of a better understanding of the bulk singularity.

How changing physical constants and violation of local position invariance may occur?

“…In Fig.3(a) of preprint [12] one finds cosmic evolution of matter composition of this model [10], which is tuned to reproduce durations of radiation, matter and scalar-dominated eras. These functions describe mutual attraction of the two branes, and thus the distance between them.…”

Graviton emission into non-Z2symmetric brane world spacetimes

“…More recently it was shown how to embed the Randall-Sundrum models within supergravities [24][25][26] and then within string theory compactifications as in [27][28][29][30]. The seemingly arbitrary feature of having an AdS bulk spacetime is actually well motivated as it is found as a supersymmetric vacuum to supergravity theories, inspiring several more recent brane world models [31][32][33][34][35][36][37]. For recent, comprehensive reviews of the subject see [38,39].…”

Moduli instability in warped compactification—4D effective theory approach

“…This is the action we obtain if we substitute Eqs. (11) and (12) into (5) and integrate over the extra dimension [10].…”

“…[9] (see Refs. [10] and [11] for different approaches). This effective theory is derived by solving the 5D equations of motion using the gradient expansion method [12], where we assume that the velocities of the branes are small compared with the curvature scale of the bulk determined by the warp factor.…”