Closed String Tachyon Condensation at c=1

TL;DR

This paper analyzes the quantum dynamics of closed string tachyon condensation at c=1, revealing how spacetime dissolves over finite time, and explores the unitarity of information transfer in different theoretical frameworks.

Contribution

It provides an exact quantum solution for tachyon condensation in the c=1 matrix model and compares collective field and fermion pictures to understand unitarity and information flow.

Findings

Tachyon condensation causes spacetime to dissolve at finite retarded time.

Quantum correlations are preserved perturbatively despite incomplete spacetime.

Non-perturbatively, information can leak, breaking unitarity in the scattering process.

Abstract

The c=1 matrix model, with or without a type 0 hat, has an exact quantum solution corresponding to closed string tachyon condensation along a null surface. The condensation occurs, and spacetime dissolves, at a finite retarded time on I^+. The outgoing quantum state of tachyon fluctuations in this time-dependent background is computed using both the collective field and exact fermion pictures. Perturbative particle production induced by the moving tachyon wall is shown to be similar to that induced by a soft moving mirror. Hence, despite the fact that I^+ for the tachyon is geodesicaly incomplete, quantum correlations in the incoming state are unitarily transmitted to the outgoing state in perturbation theory. It is also shown that, non-perturbatively, information can leak across the tachyon wall, and tachyon scattering is not unitary. Exact unitarity remains intact only in the free fermion picture.