Statistical mechanics of kinks in 1+1 dimensions

We investigate the thermal equilibrium properties of kinks in a classical ${\mathrm{\phi }}^4$ field theory in 1+1 dimensions. The distribution function, kink density, and correlation function are determined from large scale simulations. A dilute gas description of kinks is shown to be valid below a characteristic temperature. A double Gaussian approximation to evaluate the eigenvalues of the transfer operator enables us to extend the theoretical analysis to higher temperatures where the dilute gas apparoximation fails. This approach accurately predicts the temperature at which the kink description breaks down.