Braneworlds

TL;DR

This paper introduces the physics of braneworld models with one extra dimension, focusing on their gravitational behavior, cosmological perturbations, and potential deviations from standard 4D gravity.

Contribution

It derives gravitational equations on the brane from the bulk Einstein equations and discusses how braneworld cosmology differs from traditional models.

Findings

Gravitational equations on the brane derived from bulk Einstein equations

Potential differences in cosmological perturbations compared to standard models

Foundational overview of cosmological perturbation theory

Abstract

This course is an introduction to the physics of braneworlds. We concentrate on braneworlds with only one extra-dimension and discuss their gravity. We derive the gravitational equations on the brane from the bulk Einstein equation and explore some limits in which they reduce to 4-dimensional Einstein gravity. We indicate how cosmological perturbations from braneworlds are probably very different from usual cosmological perturbations and give some examples of the preliminary results in this active field of research. For completeness, we also present an introduction to 4-dimensional cosmological perturbation theory and, especially its application to the anisotropies of the cosmic microwave background.