Abstract

We review some recent progress in the theory of electroweak radiative corrections in semileptonic decay processes. The resurrection of the so-called Sirlin’s representation based on current algebra relations permits a clear separation between the perturbatively-calculable and incalculable pieces in the O(GFα) radiative corrections. The latter are expressed as compact hadronic matrix elements that allow systematic non-perturbative analysis such as dispersion relation and lattice QCD. This brings substantial improvements to the precision of the electroweak radiative corrections in semileptonic decays of pion, kaon, free neutron and JP=0+ nuclei that are important theory inputs in precision tests of the Standard Model. Unresolved issues and future prospects are discussed.

Highlights

  • Beta decays are defined as decay processes φi → φf ν triggered by charged weak interactions, where a strong-interacting particle φi decays into another particle φf, accompanied by the emission of a charged lepton and a neutrino ν

  • We describe how the contributions from the physics at the hadron scale are constrained by lattice Quantum Chromodynamics (QCD), dispersion relation or other non-perturbative methodologies to achieve a precision level of 10−4

  • We reviewed some recent progress in the calculation of the O(GFα) electroweak radiative corrections (EWRCs) to semileptonic beta decays of strongly-interacting systems, which are important avenues for precision tests of the Standard Model (SM)

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Summary

Introduction

Beta decays are defined as decay processes φi → φf ν triggered by charged weak interactions, where a strong-interacting particle φi decays into another particle φf , accompanied by the emission of a charged lepton and a neutrino ν. All the dependences on the non-perturbative QCD at the chiral symmetry breaking scale Λχ ∼ 4πFπ (where Fπ is the pion decay constant) are parameterized in terms of a few low energy constants (LECs) in the chiral Lagrangian that are not constrained by the chiral symmetry and must be estimated separately with phenomenological models [88,89] Within this theory framework, the RC to πe3 [90] and K 3 [91,92,93] were both calculated to the order O(e2 p2), with e the positron charge and p a typical small momentum scale in ChPT. These two sections set the stage for our later analysis. We provide in Appendix A a simple derivation of the relations above using the Wick’s theorem of free fields

Weak Corrections
First Diagram
Second Diagram
Third Diagram
General Theory for Beta Decays
Sirlin’s Representation We may now start to discuss the EMRCs in Figure 3:
On-Mass-Shell Perturbation Formula and Ward Identity
Bremsstrahlung
Large Electroweak Logarithms and the Higher-Order QED Effects
Effective Field Theory Representation
Spontaneously-Broken Chiral Symmetry
External Sources
Mesonic ChPT with External Sources
Nucleon Sector
Pion Semileptonic Beta Decay
EWRCs The tree-level decay rate above is corrected by EWRCs
Early Numerical Estimation
ChPT Treatment
First-Principles Calculation
Small-Q2 Contribution
Outer and Inner Corrections
Dispersive Representation
Born Contribution
Exact Isospin Relations
Free Neutron
Earlier Attempts
Future Prospects with Lattice QCD
Superallowed Beta Decays
The Nuclear Structure Correction
Earlier Treatments
Recent Developments
The Isospin-Breaking Correction
Kaon Semileptonic Decays
Kinematics
ChPT Treatment of the EWRC
Ke3 EWRC in Sirlin’s Representation
Bremsstrahlung Contribution
Results and Discussions
10. Summary
Full Text
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