Scaling Distribution of Axionic Strings and Estimation of Axion Density from Axionic Domain Walls

When the amount of the axion emitted from axionic strings is evaluated, the number density of the source string should be necessarily determined. Although it is the simplest assumption that the axionic strings obey the same distribution as that of the cosmic gauged strings, this assumption has not been completely justified. The damping due to the surrounding plasma is estimated by a detailed calculation of the fermion scatter from a global string and it is shown that the friction force on the axionic strings can be neglected before the axionic domain wall formation in most cases, which is one of the important necessary conditions for the scaling distribution of the strings. The energy density of the axion produced by the collapse of the axionic domain walls is also evaluated using the axionic string distribution, and it is found to be larger or at least comparable to the axion density which originates from the axionic strings. Published in Progress of Theoretical Physics 98 (1997) 851.