Abstract

In this work we investigate the implication of $K\to \pi \nu \bar{\nu}$ from the recent KOTO and NA62 measurements for generic neutrino interactions and the new physics scale in effective field theories. The interactions between quarks and left-handed Standard Model (SM) neutrinos are first described by the low energy effective field theory (LEFT) below the electroweak scale. We match them to the chiral perturbation theory ($\chi$PT) at the chiral symmetry breaking scale to calculate the branching fractions of Kaon semi-invisible decays and match them up to the SM effective field theory (SMEFT) to constrain new physics above the electroweak scale. In the framework of effective field theories, we prove that the Grossman-Nir bound is valid for both dim-6 and dim-7 LEFT operators, and the dim-6 vector and scalar operators dominantly contribute to Kaon semi-invisible decays based on LEFT and chiral power counting rules. They are induced by multiple dim-6 lepton-number-conserving operators and one dim-7 lepton-number-violating operator in the SMEFT, respectively. In the lepton-number-conserving $s\to d$ transition, the $K\to \pi \nu \bar{\nu}$ decays provide the most sensitive probe for the operators with $\tau\tau$ component and point to a corresponding new physics scale of $\Lambda_{\rm NP} \in[47~\text{TeV},~72~\text{TeV}]$ associated with a single effective coefficient. The lepton-number-violating operator can also explain the observed $K\to\pi\nu\bar{\nu}$ discrepancy with the SM prediction within a narrow range $\Lambda_{\rm NP}\in [19.4~\text{TeV},~21.5~\text{TeV}]$, which is consistent with constraints from Kaon invisible decays.

Highlights

  • The KOTO experiment at J-PARC [1,2] and the NA62 experiment at CERN [3] announced preliminary results of kaon semi-invisible decays [4]BKKOL→TOπ01ν6ν=18 1⁄4 2.1þ−14..71 × 10−9; ð1ÞBNKAþ→62πþνν < 2.44 × 10−10; ð2Þ at the 95% confidence level (CL)

  • In this work we investigate the implication of K → πννfrom the recent KOTO and NA62 measurements for generic neutrino interactions and the new physics scale in effective field theories

  • We match them to the chiral perturbation theory at the chiral symmetry breaking scale to calculate the branching fractions of Kaon semi-invisible decays and match them up to the Standard Model (SM) effective field theory (SMEFT) to constrain new physics above the electroweak scale

Read more

Summary

INTRODUCTION

The KOTO experiment at J-PARC [1,2] and the NA62 experiment at CERN [3] announced preliminary results of kaon semi-invisible decays [4]. There exist quite a few works trying to explain these intriguing events reported by KOTO [4,11,12,13] (or constrain particular new physics (NP) models [14,15,16]) and avoid the violation of its relation with the Kþ → πþννdecay, that is the Grossman-Nir bound [17] These efforts require the introduction of a new invisible degree of freedom with the mass scale being around 100– 200 MeV. In order to calculate the kaon decay rate, we match the LEFT operators to chiral perturbation theory (χPT) [20,21] at the chiral symmetry breaking scale to take into account nonperturbative QCD effects. Some calculation details for kaon decays are collected in the Appendix

Generic quark-neutrino operators in LEFT basis
Matching to the leading order of χ PT
ΓEKxþp 3
Dim-6 tensor operators and dim-7 operators in the chiral Lagrangian
MATCHING TO THE SMEFT
Constraint on the LNC operators
Constraint on the LNV operator
13 G3F Λ6NP
DISCUSSIONS AND CONCLUSIONS
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call