Reheating signature in the gravitational wave spectrum from
  self-ordering scalar fields
  We investigate the imprint of reheating on the gravitational wave spectrum
produced by self-ordering of multi-component scalar fields after a global phase
transition. The equation of state of the Universe during reheating, which
usually has different behaviour from that of a radiation-dominated Universe,
affects the evolution of gravitational waves through the Hubble expansion term
in the equations of motion. This gives rise to a different power-law behavior
of frequency in the gravitational wave spectrum. The reheating history is
therefore imprinted in the shape of the spectrum. We perform $512^3$ lattice
simulations to investigate how the ordering scalar field reacts to the change
of the Hubble expansion and how the reheating effect arises in the spectrum. We
also compare the result with inflation-produced gravitational waves, which has
a similar spectral shape, and discuss whether it is possible to distinguish the
origin between inflation and global phase transition by detecting the shape
with future direct detection gravitational wave experiments such as DECIGO.
