Inflation and dark energy arising from geometrical tachyons

TL;DR

This paper explores how geometrical tachyons from D3-branes in NS5-brane backgrounds can explain cosmic inflation and dark energy, with compatibility to CMB observations and implications for the number of NS5-branes.

Contribution

It introduces a model where geometrical tachyons contribute to dark energy and inflation, highlighting the role of NS5-brane number and the necessity of separate fields for inflation and dark energy.

Findings

Model compatible with CMB observations

Geometrical tachyon can explain dark energy with many NS5-branes

Single tachyon field cannot account for both inflation and dark energy

Abstract

We study the motion of a BPS D3-brane in the NS5-brane ring background. The radion field becomes tachyonic in this geometrical set up. We investigate the potential of this geometrical tachyon in the cosmological scenario for inflation as well as dark energy. We evaluate the spectra of scalar and tensor perturbations generated during tachyon inflation and show that this model is compatible with recent observations of Cosmic Microwave Background (CMB) due to an extra freedom of the number of NS5-branes. It is not possible to explain the origin of both inflation and dark energy by using a single tachyon field, since the energy density at the potential minimum is not negligibly small because of the amplitude of scalar perturbations set by CMB anisotropies. However geometrical tachyon can account for dark energy when the number of NS5-branes is large, provided that inflation is realized by another scalar field.