Electroweak Interactions in a Chiral Effective Lagrangian for Nuclei

TL;DR

This paper develops a comprehensive chiral effective field theory for nuclei that incorporates electroweak interactions, symmetries, and resonances, enabling detailed studies of weak processes in nuclear physics.

Contribution

It introduces a nonlinear realization of chiral symmetry in a quantum hadrodynamics effective field theory including the $ ho$ and $ riangle$ resonances, with applications to neutrino scattering.

Findings

Inclusion of $ riangle$ resonance in EFT.

Consistent treatment of symmetry breaking patterns.

Application to neutrino scattering processes.

Abstract

We have studied electroweak (EW) interactions in quantum hadrodynamics (QHD) effective field theory (EFT). The Lorentz-covariant EFT contains nucleon, pion, $\Delta$, isoscalar scalar ($\sigma$) and vector ($\omega$) fields, and isovector vector ($\rho$) fields. The lagrangian exhibits a nonlinear realization of (approximate) $SU(2)_L \otimes SU(2)_R$ chiral symmetry and incorporates vector meson dominance. First, we discuss the EW interactions at the quark level. Then we include EW interactions in QHD EFT by using the background-field technique. The completed QHD EFT has a nonlinear realization of $SU(2)_L \otimes SU(2)_R \otimes U(1)_B$ (chiral symmetry and baryon number conservation), as well as realizations of other symmetries including Lorentz-invariance, $C$, $P$, and $T$. Meanwhile, as we know, chiral symmetry is manifestly broken due to the nonzero quark masses; the $P$ and $C$ symmetries are also broken because of weak interactions. These breaking patterns are parameterized in a general way in the EFT. Moreover, we have included the $\Delta$ resonance as manifest degrees of freedom in our QHD EFT, with a discussion of the irrelevance of the well-known pathologies involving high-spin fields from the modern EFT perspective. This enables us to discuss physics at the kinematics where the resonance becomes important. As a result, the effective theory uses hadronic degrees of freedom, satisfies the constraints due to QCD (symmetries and their breaking pattern), and is calibrated to strong-interaction phenomena. Applications to (anti)neutrino scattering are briefly discussed.