Constraints on the charged currents in general neutrino interactions with sterile neutrinos

TL;DR

This paper explores how low-energy precision measurements constrain charged current interactions involving sterile neutrinos, using effective field theories to set bounds on new physics scales up to hundreds of TeV.

Contribution

It develops a framework combining low-energy effective field theory with sterile neutrinos and renormalization group running to derive new constraints on charged current operators.

Findings

Most stringent bounds on NP scale are 74 TeV for lepton-number-conserving operators.

Lepton-number-violating operators are constrained up to 9.8 TeV.

Constraints are stronger than those for neutral current operators.

Abstract

In this work we investigate the implication of low-energy precision measurements on the quark-lepton charged currents in general neutrino interactions with sterile neutrinos in effective field theories. The physics in low-energy measurements is described by the low-energy effective field theory extended with sterile neutrinos (LNEFT) defined below the electroweak scale. We also take into account renormalization group running and match the LNEFT onto the Standard Model (SM) effective field theory with sterile neutrinos (SMNEFT) to constrain new physics (NP) above the electroweak scale. The most sensitive low-energy probes are from leptonic decays of pseudoscalar mesons and hadronic tau lepton decays in terms of precise decay branching fractions, the lepton flavor universality and the Cabibbo-Kobayashi-Maskawa (CKM) unitarity. We also consider other constraints including nuclear beta decay. The constraints on charged current operators are generally stronger than the ones for quark-neutrino neutral current operators. We find that the most stringent bounds on the NP scale of lepton-number-conserving and lepton-number-violating operators in SMNEFT are 74 (110) TeV and 9.8 (13) TeV, respectively, for the operators with down (strange) quark.