Improved estimation of radiated axions from cosmological axionic strings
  Cosmological evolution of axionic string network is analyzed in terms of
field-theoretic simulations in a box of 512^3 grids, which are the largest
ever, using a new and more efficient identification scheme of global strings.
The scaling parameter is found to be \xi=0.87 +- 0.14 in agreement with
previous results. The energy spectrum is calculated precisely using a pseudo
power spectrum estimator which significantly reduces the error in the mean
reciprocal comoving momentum. The resultant constraint on the axion decay
constant leads to f_a <= 3*10^11 GeV. We also discuss implications for the
early Universe.
