Production of gravitational waves during preheating with nonminimal
  coupling
  We study the preheating and the in-process production of gravitational waves
(GWs) after inflation in which the inflaton is nonminimally coupled to the
curvature in a self-interacting quartic potential with the method of lattice
simulation. We find that the nonminimal coupling enhances the amplitude of the
density spectrum of inflaton quanta, and as a result, the peak value of the GW
spectrum generated during preheating is enhanced as well and can reach the
limit of detection in future GW experiments. The peaks of the GW spectrum not
only exhibit distinctive characteristics as compared to those of minimally
coupled inflaton potentials but also imprint information on the nonminimal
coupling and the parametric resonance, and thus the detection of these peaks in
the future will provide us a new avenue to reveal the physics of the early
universe.
