Disentangle RG Running Parameters with Medium-Baseline Reactor Experiments

Abstract

We study how the renormalization group running beta functions of mixing angles and leptonic CP phases affect the slow and fast oscillation modes at JUNO. While the slow mode is modulated by the solar parameters, its amplitude can also be affected by the solar angle beta function $\beta_s$ and its phase by the Majorana CP phase counterpart $\beta_{\rm M1}$. On the other hand, the fast mode also receives corrections from the beta functions of the Dirac CP phase $\delta_D$ and the Majorana CP phase $\delta_{\rm M3}$. Since the fast mode is essentially the one measuring the neutrino mass ordering, the RG running effect can then interfere to deteriorate the sensitivity. Fortunately, the JUNO-TAO near detector can provide supplementary measurements of the RG running parameters to restore the mass ordering sensitivity. Since the rephasing phases $\delta_{\rm M1}$ and $\delta_{\rm M3}$ can be shifted by a vector-like rephasing for Dirac neutrinos, their running is physical only in the Majorana case. In consolidated, the mild preference for a nonzero $\beta_{\rm M1}$ by the current JUNO data thus hints the Majorana nature of neutrinos.