Tachyonic resonance preheating in an expanding universe

In this paper the tachyonic resonance preheating generated from the bosonic trilinear φχ² interactions in an expanding universe is studied. In λφ⁴/4 inflationary model the trilinear interaction, in contrast to the four-legs φ²χ², breaks the conformal symmetry explicitly and the resonant source term becomes nonperiodic, making the Floquet theorem inapplicable. We find that the occupation number of the produced χ particles has a nonlinear exponential growth with exponent ~x3/2, where x is the conformal time. This should be contrasted with preheating from a periodic resonant source arising, for example, from the four-legs φ²χ² interaction, where the occupation number has a linear exponential growth. We present an analytic method to compute the interference term coming from phases accumulated in nontachyonic scattering regions and show that the effects of the interference term cause ripples on x3/2 curve, a result which is confirmed by numerical analysis. Studying the effects of backreaction of the χ particles, we show that tachyonic resonance preheating in our model can last long enough to transfer most of the energy from the background inflation field φ, providing an efficient model for preheating in the chaotic inflation models.