Ab initio calculation of symmetry-breaking observables

TL;DR

This paper develops an ab initio computational method using IMSRG to calculate symmetry-breaking observables like the anapole and Schiff moments in medium-mass and heavy nuclei, aiding fundamental physics tests.

Contribution

A new IMSRG-based framework that evolves parity-violating operators alongside the nuclear Hamiltonian for accurate predictions in heavier nuclei.

Findings

Benchmarking against no-core shell model in light nuclei shows good agreement.

First ab initio predictions of anapole moment in $^{29}$Si.

First ab initio predictions of Schiff moments in $^{129}$Xe.

Abstract

Symmetry-violating observables such as the nuclear anapole and Schiff moments provide sensitive probes of the fundamental symmetries of nature and physics beyond the Standard Model. Their interpretation has been hindered, however, by the lack of ab initio nuclear structure calculations in the medium-mass and heavy nuclei of interest to experimentalists. To provide them, we introduce a new version of the in-medium similarity renormalization group (IMSRG) designed to target parity-violating operators. By generalizing the IMSRG flow equations to evolve the weak symmetry-breaking Hamiltonian - and the anapole or Schiff operators - alongside the strong nuclear Hamiltonian, we construct a systematically improvable framework for computing these parity-violating moments. We benchmark the method against the no-core shell model in light nuclei and obtain the first ab initio predictions of the anapole moment in $^{29}$Si and the Schiff moments in $^{129}$Xe. These heavier systems are of direct experimental interest.