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We give new constraints on small-scale non-Gaussianity of primordialcurvature perturbations by the use of anisotropies in acoustic reheating.Mixing of local thermal or local kinetic equilibrium systems with differenttemperatures yields a locally averaged temperature rise, which is proportionalto the square of temperature perturbations damping in the photon diffusionscale. Such secondary temperature perturbations are indistinguishable from thestandard temperature perturbations linearly coming from primordial curvatureperturbations and hence should be subdominant compared to the standard ones. Weshow that small-scale higher order correlation functions (connectednon-Gaussian and disconnected Gaussian parts) of primordial curvatureperturbations can be probed by investigating auto power spectrum of thegenerated secondary perturbations and the cross power spectrum with thestandard perturbations. This is simply because these power spectra come fromhigher order correlation functions of primordial curvature perturbations withnon-linear parameters such as $f_{\rm NL}$ and $\tau_{\rm NL}$ since secondarytemperature perturbations are second order effects. Thus, the observationalresults $l(l+1)C^{TT}_l\simeq 6\times 10^{-10}$ at large scales give a robustand universal upper bound on small-scale non-Gaussianities of primordialcurvature perturbations.

Probing small-scale non-Gaussianity from anisotropies in acoustic reheating