Tachyons, Scalar Fields and Cosmology

TL;DR

This paper explores the cosmological implications of tachyon fields, revealing their distinct dynamics from scalar fields, including novel singularities like the 'big brake' in certain models.

Contribution

It introduces a new class of tachyonic models with a parameter, demonstrating their unique cosmological behaviors and the necessity of modifying existing actions for certain cases.

Findings

Tachyon models can mimic scalar field cosmology under specific initial conditions.

A new singularity called 'big brake' is identified, characterized by infinite deceleration.

Modified actions are required for positive parameter values to resolve singularities.

Abstract

We study the role that tachyon fields may play in cosmology as compared to the well-established use of minimally coupled scalar fields. We first elaborate on a kind of correspondence existing between tachyons and minimally coupled scalar fields; corresponding theories give rise to the same cosmological evolution for a particular choice of the initial conditions but not for any other. This leads us to study a specific one-parameter family of tachyonic models based on a perfect fluid mixed with a positive cosmological constant. For positive values of the parameter one needs to modify Sen's action and use the sigma process of resolution of singularities. The physics described by this model is dramatically different and much richer than that of the corresponding scalar field. For particular choices of the initial conditions the universe, that does mimick for a long time a de Sitter-like expansion, ends up in a finite time in a special type of singularity that we call a "big brake". This singularity is characterized by an infinite deceleration.