Dependence of the amplitude of gravitational waves from preheating on the inflationary energy scale

Stochastic gravitational wave backgrounds receive increasing attention and provide a new possibility to directly probe the early Universe. In preheating process at end of inflation, parametric resonance can generate large energy density perturbations efficiently produce waves (GWs) which carry unique information about inflation. Since peak frequency such GWs is approximately proportional inflationary scale, ${\mathrm{\ensuremath{\Lambda}}}_{\mathrm{inf}}$, from are expected be observed by interferometer GW detectors in low-scale models. We investigate class models where effective potential has quadratic minimum, dependence amplitude on then find that present spectrum these does not depend ${\mathrm{\ensuremath{\Lambda}}}_{\mathrm{inf}}$ except case above critical value ${\mathrm{\ensuremath{\Lambda}}}_{c}$---a parameter depending strength. numerically obtain ${\mathrm{\ensuremath{\Lambda}}}_{c}$ terms model parameters linear approximation conduct lattice simulations verify this result. For ${\mathrm{\ensuremath{\Lambda}}}_{\mathrm{inf}}\ensuremath{\lesssim}{\mathrm{\ensuremath{\Lambda}}}_{c}$, quickly decreases with becomes challenging observe. turn, observing also helps determine strength during preheating.