Probing Light Mediators in the Radiative Emission of Neutrino Pair

We propose a new possibility of using the coherently enhanced neutrino pair emission to probe light-mediator interactions between electron and neutrinos. With typical momentum transfer at the atomic $\mathcal O(1$\,eV) scale, this process is extremely sensitive for the mediator mass range $\mathcal O(10^{-3} \sim 10^4$) eV. The sensitivity on the product of couplings with electron ($g^e$ or $y^e$) and neutrinos ($g^\nu$ or $y^\nu$) can touch down to $|y^e y^\nu| < 10^{-9} \sim 10^{-19}$ for a scalar mediator and $|g^e g^\nu| < 10^{-15} \sim 10^{-26}$ for a vector one, with orders of improvement from the existing constraints.