Sonoluminescence as a QED vacuum effect. I. The physical scenario - art. no. 085023

Several years ago Schwinger proposed a physical mechanism for sonoluminesce nce in terms of changes in the properties of the quantum-electrodynamic vac uum state during collapse of the bubble. This mechanism is most often phras ed in terms of changes in the Casimir energy (i.e., changes in the distribu tion of zero-point energies) and has recently been the subject of considera ble controversy. The present paper further develops this quantum-vacuum app roach to sonoluminescence: We calculate Bogolubov coefficients relating the QED vacuum states in the presence of a homogeneous medium of changing diel ectric constant. In this way we derive an estimate for the spectrum, number of photons, and total energy emitted. We emphasize the importance of rapid spatio-temporal changes in refractive indices and the delicate sensitivity of the emitted radiation to the precise dependence of the refractive index as a function of wave number, pressure, temperature, and noble gas admixtu re. Although the basic physics of the dynamical Casimir effect is a univers al phenomenon of QED, specific and particular experimental features are enc oded in the condensed matter physics controlling the details of the refract ive index. This calculation places rather tight constraints on the possibil ity of using the dynamical Casimir effect as an explanation for sonolumines cence, and we are hopeful that this scenario will soon be amenable to direc t experimental probes. In the following paper we discuss the technical comp lications due to finite-size effects, but for reasons of clarity in this pa per we confine our attention to bulk effects.