Dilaton Brane Cosmology with Second Order String Corrections and the Cosmological Constant

TL;DR

This paper explores five-dimensional dilaton brane cosmology incorporating second-order string corrections, revealing solutions that reduce fine-tuning issues and allow a lower string scale relative to the Planck mass.

Contribution

It introduces a novel five-dimensional model with second-order string corrections that alleviates fine-tuning and permits a lower string scale than previously possible.

Findings

Logarithmic solutions are less sensitive to fine-tuning.

The string scale can be lower than the Planck mass.

Reduced fine-tuning of brane tension is achieved.

Abstract

We consider, in five dimensions, the effective action from heterotic string which includes quantum gravity corrections up to (a')^2. The expansion, in the string frame, is in terms of |a'R|, where R is the scalar curvature and uses the third order Euler density, next to the Gauss-Bonnet term. For a positive tension brane and infinite extra dimension, the logarithmic class of solutions is less dependent from fine-tuning problems than in previous formulations. More importantly, the model suggests that in the full non-perturbative formulation, the string scale can be much lower than the effective Planck mass, without the string coupling to be vanishingly small. Also a less severe fine-tuning of the brane tension in needed.