Session 3WFA: Nuclear Theory for New Physics I

Muonic and nuclear probes for the lepton flavor structure

The lepton number violation (LNV) and lepton flavor violation (LFV) are important possible ingredients of the lepton physics.

For instance, the neutrinoless double beta decay and the transition of the muonium into antimuonuim are related to those violations.

The former can give us an essential part of fundamental physics, and there are plenty of experimental attempts to observe the process.

The latter has also been one of the attractive phenomena, and the experimental bound will be updated in planned experiments at new high-intensity muon beamlines.

In models with a doubly charged scalar, not only can those two processes be induced, but also the active neutrino masses can be induced radiatively.

The flavor violating decays of the charged leptons constrain the flavor parameters of the models.

In this talk, I will review the current status of LNV and LFV searches and introduce our study about the neutrinoless double beta decay and the muonium-to-antimuonium transition.

I will show that the updated bound of the muonium-to-antimuonium transition rate will be useful to distinguish the models to generate the neutrinoless double beta decay via the doubly charged scalar.   

Constraining CP-violating axion couplings

Although the Standard Model of particle physics (SM) has been very successful, it is unable to explain several observations such as neutrino masses, Dark Matter (DM), and the Baryon asymmetry of the Universe (BAU). Many models that aim to explain the BAU introduce new sources of CP violation which worsens the strong-CP problem of the SM, thereby strengthening the motivation for a solution through axions. In this talk, I will discuss a class of models which extend the SM with new sources of CP violation as well as an axion-like particle. I will show how this gives rise to CP-violating axion interactions that induce long-range forces. This scenario can be probed by electric-dipole-moments, searches for long-range axion forces, and, in case the axion-like particle makes up DM, limits on the variation of fundamental constants. I will discuss how effective-field-theory techniques allow us to describe all of these different effects in the same framework, which will require input from hadronic, nuclear, and atomic physics. I conclude by comparing the different constraints, showing that electric dipole moments are the most sensitive probes in large parts of parameter space.   

Lattice QCD for Fundamental Symmetry Tests of the Standard Model in Nuclear Environments

Low-energy precision tests of the Standard Model offer competitive and complimentary means to search for new physics as compared to direct searches through colliders. Such searches look for violations of fundamental symmetries for the Standard Model, such as neutrinoless double beta decay, or small deviations from Standard Model predictions, such as with nucleon and nuclear beta decay. In both cases, our ability to predict the Standard Model background and processes, directly from quarks and gluons, may be essential for interpreting the experimental results, or lack thereof, in terms of sources of new physics. I will present an overview of the status of lattice QCD applications to this research program.