The excitation of a charged string passing through a shock wave in a charged Aichelburg-Sexl spacetime

We investigate how much a first-quantized charged bosonic test string gets excited after crossing a shock wave generated by a charged particle with ma ss (M) over tilde and charge (Q) over tilde. On the basis of Kaluza-Klein t heory, we pay attention to a closed string model where charge is given by a momentum along a compactified extra-dimension. The shock wave is given by a charged Aichelburg-Sexl (CAS) spacetime where (Q) over tilde = 0 correspo nds to the ordinary Aichelburg-Sexl one. We first show that the CAS spaceti me is a solution to the equations of motion for the metric, the gauge field , and the axion field in the low-energy limit. Secondly, we compute the mas s expectation value of the charged test string after passing through the sh ock wave in the CAS spacetime, In the case of small (Q) over tildee, gravit ational and Coulomb forces are canceled out each other and hence the excita tion of the string remains very small. This is independent of the particle mass M or the strength of the shock wave. In the case of large (Q) over til de, however, every charged string gets highly excited by quantum fluctuatio n in the extra-dimension caused by both the gauge and the axion fields. Thi s is quite different from classical "molecule", which consists of two elect rically charged particles connected by a classical spring. (C) 2001 Publish ed by Elsevier Science B.V.