Closed Superstring Emission from Rolling Tachyon Backgrounds

We compute the lowest components of the Type II Ramond-Ramond boundary state for the tachyon profile T (X) = λe / √ 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)× 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) × U(m) group integrals. Using this boundary state, we compute the closed string emission from a decaying unstable Dp-brane of Type II string theory. We also discuss closed string emission from the tachyon profile T (X) = λ cosh(X/ √ 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 ≤ 2, in precise analogy to the bosonic case. ∗E-mail: [email protected].