Name: Toyokazu Sekiguchi
 Institution: ICRR, the Univ. of Tokyo
 Title: Improved estimation of spectrum of axion radiation from cosmological axionic strings
 Abstract: We investigate the spectrum of axion radiation from the cosmological  
axionic strings.
For this purpose, we first perform field theoretic simulations of the  
Peccei-Quinn (PQ) field
in the early universe, and then estimate the spectrum of axion  
radiation from axionic strings
from data of the field simulations. Since our simulations have higher  
spacial resolutions and
cover longer time-ranges, we achieve more accurate estimation
of the spectrum than previous studies. We also improve estimation  
method of the spectrum
by adopting the pseudo power spectrum estimator, so that  
uncertainties due to removal of
string cores are properly accounted. We conclude that the spectrum of  
axion radiation
is steeply peaked around the horizon scale, which agrees with the  
previous result of
Yamaguchi, Kawasaki and Yokoyama (1999). We also apply our result to  
a cosmological constraint
on the PQ scale.