D-branes and Cosmology

TL;DR

This paper explores the dynamics of D-branes in curved backgrounds within string theory, examining their production, fluctuations, and potential role in early universe cosmology and singularity resolution.

Contribution

It provides a detailed analysis of D-brane behavior in curved spacetime, linking their dynamics to cosmological evolution and the holography principle.

Findings

D-branes can be efficiently produced by gravitational effects.

Transverse fluctuations of D-branes can become tachyonic in curved spacetime.

A limiting curvature value may resolve cosmological singularities.

Abstract

D-branes, topological defects in string theory on which string endpoints can live, may give new insight into the understanding of the cosmological evolution of the Universe at early epochs. We analyze the dynamics of D-branes in curved backgrounds and discuss the parameter space of M-theory as a function of the coupling constant and of the curvature of the Universe. We show that D-branes may be efficiently produced by gravitational effects. Furthermore, in curved spacetimes the transverse fluctuations of the D-branes develop a tachyonic mode and when the fluctuations grow larger than the horizon the branes become tensionless and break up. This signals a transition to a new regime. We discuss the implications of our findings for the singularity problem present in string cosmology, suggesting the existence of a limiting value for the curvature which is in agreement with the value suggested by the cosmological version of the holography principle. We also comment on possible implications for the so-called brane world scenario, where the Standard Model gauge and matter fields live inside some branes while gravitons live in the bulk.