STATISTICAL-MECHANICS OF KINKS IN 1- NUMERICAL SIMULATIONS AND DOUBLE-GAUSSIAN APPROXIMATION(1 DIMENSIONS )

We investigate the thermal equilibrium properties of kinks in a classi cal Phi(4) field theory in 1+1 dimensions. From large-scale Langevin s imulations we identify the temperature below which a dilute-gas descri ption of kinks is valid. The standard dilute-gas or WKB description is shown to be remarkably accurate below this temperature. At higher ''i ntermediate'' temperatures, where kinks still exist, this description breaks down. By introducing a double-Gaussian variational ansatz for t he eigenfunctions of the statistical transfer operator for the system, we are able to study this region analytically. In particular, our pre dictions for the number of kinks and the correlation length are in agr eement with the simulations. The double Gaussian prediction for the ch aracteristic temperature at which the kink description ultimately brea ks down is also in accord with the simulations. We also analytically c alculate the internal energy and demonstrate that the peak in the spec ific heat near the kink characteristic temperature is indeed due to ki nks. In the neighborhood of this temperature there appears to be an in tricate energy-sharing mechanism operating between nonlinear phonons a nd kinks.