Pyrgon annihilation in a five-dimensional model universe

On the basis of a five-dimensional cosmological model with the shrinking extra space, we investigate the annihilation process of pyrgons (i.e., massive modes corresponding to quantized excitations of the fifth dimension). It is shown that this annihilation goes on as a nonequilibrium process and a net entropy in a comoving volume is produced. However, no sufficient suppression of the pyrgon number density can be expected, because the contraction of the extra space stops immediately after the onset of the pyrgon annihilation. Dynamical effects of relic pyrgons in the universe are discussed. (author)