Gravitational Radiation of Rolling Tachyon

TL;DR

This work analyzes gravitational radiation from a time-dependent rolling tachyon on unstable D-branes in bosonic string theory with codimension $\\ge 3$ using boundary-state methods to couple the rolling tachyon to massless closed-string modes. It derives the asymptotic metric and dilaton perturbations, yielding a formula for the instantaneous radiation power that includes both gravity and dilaton contributions. The back-reaction analysis shows the energy loss scales with the string coupling $g_s$ and can drive significant decay only at large $g_s$, with late-time radiation diminishing as $P\\sim e^{-2t}$. The results connect closed-string radiation to the BCFT $g$-theorem, suggesting a link between boundary entropy and energy leakage into the bulk, with implications for tachyon cosmology and reheating.

Abstract

In this paper we compute the radiation of the massless closed string states due to the non-vanishing coupling to the rolling open string tachyon with co-dimensions larger than 2, and discuss the effect of back reaction to the motion of the rolling tachyon. We find that for small string coupling, the tachyonic matter remains in the late time, but it will completely evaporate away over a short time of few string scales if the string coupling is huge. Comment on the implication of our results to the g-theorem of boundary conformal field theory is given.

Figures (1)

• Figure 1: This plot shows that the function $\dot{f}(t)$(the curve B) for $d_t=3$ and $\ddot{f}(t)$(the curve C) for $d_t=5$ are localized in the early stage of the tachyon motion in contrast to the rolling profile $f(t)$(the curve A). In the plot $\sin(\lambda \pi)$ is set to $0.5$ and both $\dot{f}$ and $\ddot{f}$ have been scaled up by 10 times. This indicates that the gravitational radiation occurs in the early stage and lasts only for few stringy scale duration.