Stars in the braneworld

TL;DR

This paper explores how 5-dimensional graviton effects in a braneworld alter the exterior spacetime of stars, leading to non-Schwarzschild solutions and new constraints on brane tension.

Contribution

It provides an exact uniform-density stellar solution in a Randall-Sundrum II braneworld and analyzes how high-energy effects modify classical bounds and exterior solutions.

Findings

Vacuum exterior of stars is not Schwarzschild due to 5D effects.

High-energy effects reduce the maximum mass-to-radius ratio for stars.

Constraints on brane tension from neutron star existence are stronger than nucleosynthesis limits.

Abstract

We show that in a Randall-Sundrum II type braneworld, the vacuum exterior of a spherical star is not in general a Schwarzschild spacetime, but has radiative-type stresses induced by 5-dimensional graviton effects. Standard matching conditions do not lead to a unique exterior on the brane because of these 5-dimensional graviton effects. We find an exact uniform-density stellar solution on the brane, and show that the general relativity upper bound $GM/R<{4\over9}$ is reduced by 5-dimensional high-energy effects. The existence of neutron stars leads to a constraint on the brane tension that is stronger than the big bang nucleosynthesis constraint, but weaker than the Newton-law experimental constraint. We present two different non-Schwarzschild exteriors that match the uniform-density star on the brane, and we give a uniqueness conjecture for the full 5-dimensional problem.