Tachyon Dynamics and the Effective Action Approximation

TL;DR

This paper examines the properties of non-linear effective Lagrangians for tachyon dynamics in string theory, highlighting generic features and limitations of first-order derivative actions in describing time-dependent tachyon condensation.

Contribution

It analyzes the general properties of first-order derivative effective Lagrangians for tachyons, identifying their generic features and limitations in modeling time-dependent phenomena.

Findings

Asymptotically vanishing pressure is a generic feature of these models.

Different effective actions yield similar static properties but differ in time-dependent behavior.

Some tachyon profile features are beyond first-order Lagrangian descriptions.

Abstract

Recently effective actions have been extensively used to describe tachyon condensation in string theory. While the various effective actions which have appeared in the literature have very similar properties for static configurations, they differ for time-dependent tachyons. In this paper we discuss general properties of non-linear effective Lagrangians which are first order in derivatives. In particular we show that some observed properties, such as asymptotically vanishing pressure, are rather generic features, although the quantative features differ. On the other hand we argue that certain features of marginal tachyon profiles are beyond the reach of any first order Lagrangian description. We also point out that an effective action, proposed earlier, captures the dynamics of tachyons well.