Tachyonic preheating in Palatini R <sup>2</sup> inflation
Alexandros Karam, Eemeli Tomberg, Hardi Veermäe
Abstract
Abstract We study preheating in the Palatini formalism with a quadratic inflaton potential and an added α R 2 term. In such models, the oscillating inflaton field repeatedly returns to the plateau of the Einstein frame potential, on which the tachyonic instability fragments the inflaton condensate within less than an e-fold. We find that tachyonic preheating takes place when α ≳ 10 13 and that the energy density of the fragmented field grows with the rate Γ/ H ≈ 0.011 × α 0.31 . The model extends the family of plateau models with similar preheating behaviour. Although it contains non-canonical quartic kinetic terms in the Einstein frame, we show that, in the first approximation, these can be neglected during both preheating and inflation.