Closed Superstring Emission from Rolling Tachyon Backgrounds

Abstract

We compute the lowest components of the Type II Ramond-Ramond boundary state for the tachyon profile $T(X)=\hat{I}»e^{X^0/\sqrt{2}}$ by direct path integral evaluation. The calculation is made possible by noting that the integrals involved in the requisite disk one-point functions reduce to integrals over the product group manifold $U(n)\times U(m)$. We further note that one-point functions of more general closed string operators in this background can also be related to $U(n)\times U(m)$ group integrals. Using this boundary state, we compute the closed string emission from a decaying unstable D$p$-brane of Type II string theory. We also discuss closed string emission from the tachyon profile $T(X)=\hat{I}»\cosh (X^0/\sqrt{2})$. We find in both cases that the total number of particles produced diverges for $p=0$, while the energy radiated into closed string modes diverges for $p\le 2$, in precise analogy to the bosonic case.

23 pages