Closed String Tachyon: Inflation and Cosmological Collapse

TL;DR

This paper investigates how closed string tachyons influence cosmological evolution, leading to an initial inflationary expansion followed by a universe collapse, with the internal space curvature determining the vacuum energy.

Contribution

It presents a novel cosmological model derived from string theory with a specific tachyon potential, describing universe dynamics including inflation and collapse phases.

Findings

Universe undergoes initial accelerated expansion driven by tachyon potential.

Collapse begins as the tachyon field condenses, ending the expansion.

Internal space curvature determines the vacuum energy and cosmological constant.

Abstract

By compactifying a critical bosonic string theory on an internal non-flat space with a constant volume, we study the role played by the closed string tachyon in the cosmology of the effective four-dimensional space-time. The effective tachyon potential consists on a negative constant related to the internal curvature space and a polynomial with only quadratic and quartic terms of the tachyon field. Based on it, we present a solution for the tachyon field and the scale factor, which describes an accelerated universe which expands to a maximum value before collapsing. At early times, the closed string tachyon potential behaves as a cosmological constant driving the Universe to an expansion. The value of the cosmological constant is determined by the curvature of the internal space which also fixes the value of the vacuum energy. As time evolves, inflation is present in our models, and it finishes long before the collapsing. At late times, we show that the collapse of the Universe starts as soon as the tachyon field condensates. We also comment on the consistency of our solution at early times at which quantum aspects become important under the perspective of quantum cosmology. Finally we briefly mention the relation among the curvature of the internal space and the value of the energy vacuum in a non-constant internal volume scenario.