Direct determination of cosmic string loop density from simulations
  We determine the distribution of cosmic string loops directly from
simulations, rather than determining the loop production function and inferring
the loop distribution from that. For a wide range of loop lengths, the results
agree well with a power law exponent -2.5 in the radiation era and -2 in the
matter era, the universal result for any loop production function that does not
diverge at small scales. Our results extend those of Ringeval, Sakellariadou,
and Bouchet: we are able to run for 15 times longer in conformal time and
simulate a volume 300-2400 times larger. At the times they reached, our
simulation is in general agreement with the more negative exponents they found,
-2.6 and -2.4. However, our simulations show that this was a transient regime;
at later times the exponents decline to the values above. This provides further
evidence against models with a rapid divergence of the loop density at small
scales, such as ``model 3'' used to analyze LIGO data and predict LISA
sensitivity.
