Nontrival Cosmological Constant in Brane Worlds with Unorthodox Lagrangians

TL;DR

This paper explores brane-world models with unconventional Lagrangians that aim to address the cosmological constant problem, but encounters tachyonic instabilities and fine-tuning issues related to the observed positive cosmological constant.

Contribution

It introduces a class of brane-world models with nonconventional Lagrangians that attempt to avoid known problems in self-tuning scenarios.

Findings

Models suffer from tachyonic instabilities.

Curing instabilities predicts a positive cosmological constant.

Fine-tuning remains necessary for observational consistency.

Abstract

In self-tuning brane-world models with extra dimensions, large contributions to the cosmological constant are absorbed into the curvature of extra dimensions and consistent with flat 4d geometry. In models with conventional Lagrangians fine-tuning is needed nevertheless to ensure a finite effective Planck mass. Here, we consider a class of models with non conventional Lagrangian in which known problems can be avoided. Unfortunately these models are found to suffer from tachyonic instabilities. An attempt to cure these instabilities leads to the prediction of a positive cosmological constant, which in turn needs a fine-tuning to be consistent with observations.