General Relativistic effects in preheating

Abstract

General relativistic effects in the form of metric perturbations are usually neglected in the preheating era that follows inflation. We argue that in realistic multi-field models these effects are in fact crucial, and the fully coupled system of metric and quantum field fluctuations needs to be considered. Metric perturbations are resonantly amplified, breaking the scale-invariance of the primordial spectrum, and in turn stimulate scalar field resonances via gravitational rescattering. This non-gravitationally dominated nonlinear growth of gravitational fluctuations may have significant effects on the Doppler peaks in the cosmic background radiation, primordial black hole formation, gravitational waves and nonthermal symmetry restoration.

Figures (1)

• Figure 1: Metric perturbation evolution in 2-field preheating, with $q \equiv g \varphi_{1}^2(t_0)/m^2=8\times10^3$. The main graph shows the $k=0$ mode, the inset the $k=20$ mode. Initially, $mt_0= 100$ (well into the small amplitude phase: $\varphi_{1}(t_0)/mt_0 = 3 \times 10^{-3}$) and $\Phi_k(t_0)=10^{-5}$, $\dot\Phi_k(t_0)=0$. The $k=0$ mode becomes nonlinear at $mt \sim 150$ after less than $10$ inflaton oscillations (i.e. well before the end of preheating) and continues growing without bound. Two strong resonance bands are evident, with different Floquet indices (given by the slopes of the dotted lines), for $140\leq mt \leq 160$ and $250\leq mt \leq 300$.