The Cosmological Constant Problem in Brane--Worlds and Gravitational Lorentz Violations

TL;DR

This paper explores how brane-world models with extra dimensions can address the cosmological constant problem by allowing Lorentz violations in gravity, potentially explaining the smallness of the CC and predicting observable gravitational wave effects.

Contribution

It demonstrates that extra-dimensional brane-world scenarios can evade no-go theorems for CC adjustment by violating Lorentz invariance in gravity, offering a novel solution.

Findings

Lorentz violations in gravity can occur without affecting particle physics.

Such models may explain the small cosmological constant.

Gravitational waves could travel at speeds different from light, testable experimentally.

Abstract

Brane worlds are theories with extra spatial dimensions in which ordinary matter is localized on a (3+1) dimensional submanifold. Such theories could have interesting consequences for particle physics and gravitational physics. In this essay we concentrate on the cosmological constant (CC) problem in the context of brane worlds. We show how extra-dimensional scenarios may violate Lorentz invariance in the gravity sector of the effective 4D theory, while particle physics remains unaffected. In such theories the usual no-go theorems for adjustment of the CC do not apply, and we indicate a possible explanation of the smallness of the CC. Lorentz violating effects would manifest themselves in gravitational waves travelling with a speed different from light, which can be searched for in gravitational wave experiments.