Tachyon Matter in Boundary String Field Theory

TL;DR

The paper analyzes the classical decay of unstable D-branes in type II string theory using the BSFT action for the tachyon on a non-BPS D$p$-brane. It demonstrates that rolling tachyon solutions asymptotically approach the linear profile $T\sim \pm x^0$, driven by the pole structure of $D(z)$, with the pressure $P$ vanishing while the energy density $\rho$ remains finite, yielding tachyon matter. When gravity is included, the resulting FRW cosmology exhibits a dynamical equation of state $\omega=P/\rho$ that evolves from near $0$ to near $-1$, offering potential links to inflation or dark matter, though higher-derivative corrections may modify details. The work discusses limitations due to truncation of higher derivatives and points to future directions, including couplings to gauge fields and RR-fields and connections to boundary-state formulations.

Abstract

We analyse the classical decay process of unstable D-branes in superstring theory using the boundary string field theory (BSFT) action. We show that the solutions of the equations of motion for the tachyon field asymptotically approach to T=x^0 and the pressure rapidly falls off at late time producing the tachyon matter irrespective of the initial condition. We also consider the cosmological evolution driven by the rolling tachyon using the BSFT action as an effective action.

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