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D-branes and Cosmology

Michele Maggiore, Antonio Riotto

TL;DR

The paper investigates how D-branes behave in curved cosmological backgrounds and shows that the coupling $g$ and curvature measure $H$ organize a cosmological phase diagram where D0- and Dp-branes become light and dynamically relevant. Gravitational production of D0-branes near $H\sim 1/R_{11}$ triggers the opening of the 11th dimension, while transverse Dp-brane fluctuations acquire tachyonic mass $m^2=-(p+1)H^2/3$, driving a transition toward a brane-dominated regime and a possible M-theory description. A holographic bound implies the horizon length must satisfy $\ell_H>\ell_p$, and the resulting D0-brane gas dissipates energy via open strings, damping curvature growth and avoiding singular behavior. The findings have implications for pre-big-bang cosmology and brane-world scenarios, including avenues to connect string-scale physics with observable cosmology and to rethink the role of D-branes in early-Universe evolution.

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.

D-branes and Cosmology

TL;DR

The paper investigates how D-branes behave in curved cosmological backgrounds and shows that the coupling and curvature measure organize a cosmological phase diagram where D0- and Dp-branes become light and dynamically relevant. Gravitational production of D0-branes near triggers the opening of the 11th dimension, while transverse Dp-brane fluctuations acquire tachyonic mass , driving a transition toward a brane-dominated regime and a possible M-theory description. A holographic bound implies the horizon length must satisfy , and the resulting D0-brane gas dissipates energy via open strings, damping curvature growth and avoiding singular behavior. The findings have implications for pre-big-bang cosmology and brane-world scenarios, including avenues to connect string-scale physics with observable cosmology and to rethink the role of D-branes in early-Universe evolution.

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.

Paper Structure

This paper contains 7 sections, 35 equations, 2 figures.

Table of Contents

  1. Introduction
  2. The cosmological 'phase diagram' of M-theory
  3. D0-branes production and the opening of the $11^{th}$ dimension
  4. The D$p$-brane phase
  5. D$p$-brane dynamics in curved background
  6. The holographic principle and cosmology
  7. Discussion and conclusions

Figures (2)

  • Figure 1: The phase diagram for M-theory compactified on $S^1$.
  • Figure 2: The phase diagram of M-theory and the lowest order pre-big-bang solutions $H\sim g^{1/4}$, for two different values of the initial conditions.