Tachyonic preheating in Palatini R ² inflation

We study preheating in the Palatini formalism with a quadratic inflaton potential and an added $\alpha R^2$ term. In such models, oscillating field repeatedly returns to plateau of Einstein frame potential, on which tachyonic instability fragments condensate within less than e-fold. find that takes place when \gtrsim 10^{13}$ energy density fragmented grows rate $\Gamma/H \approx 0.011 \times \alpha^{0.31}$. The model extends family models similar behaviour. Although it contains non-canonical quartic kinetic terms frame, we show that, first approximation, these can be neglected during both inflation.