= Perturbative inflaton reheating equations
{title2=$\dot\rho_\phi+3H\rho_\phi=-\Gamma\rho_\phi,\quad\dot\rho_r+4H\rho_r=\Gamma\rho_\phi$}
A coarse-grained description in which quadratic <inflaton> <oscillations> have zero mean <pressure> and lose <energy> at constant effective decay rate $\Gamma$ to a relativistic component. Adding the equations preserves total <energy> accounting with the appropriate expansion work. Efficient transfer occurs around $H\sim\Gamma$, but producing particles and achieving <thermal equilibrium> are different steps. The potential alone does not specify the decay rate or thermalization interactions.
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