BSM PANDEMIC Delta Series: Tom Tong (Amsterdam/Oregon) and Raymond Co (Minnesota)


Tom Tong:

Sterile neutrinos in beta decay and neutrinoless double beta decay experiments

Neutrinoless double beta decay (0vbb) experiments are excellent probes of lepton number violation by two units and sterile neutrinos with Majorana mass. Meanwhile, charged currents are probed in low-energy precision beta decay experiments and at high-energy colliders, aiming to constrain signals of BSM physics. In this talk, I will discuss what 0vbb experiments can tell us if a nonzero signal from beta decay were to be found. I will be focusing on the effects that interactions with right-handed neutrinos have on 0vbb using a recently developed EFT framework, and discuss the range of neutrino masses that current and future measurements can probe, assuming neutrinos are Majorana particles. For non-standard interactions at the level suggested by recently observed hints in beta decays, I will also demonstrate how next-generation 0vbb experiments can help determine the Dirac or Majorana nature of neutrinos, for sterile neutrino masses larger than O(10) eV.

Raymond Co:

Gravitational Wave Probes of Dark Matter and the Baryon Asymmetry from Axion Rotations

We have established a paradigm where the (QCD) axion’s novel cosmological evolution, a rotation in the field space, gives rise to dark matter and the baryon asymmetry. The axion rotations also provide a natural origin for a kination era, where the total energy density is dominated by the kinetic term of the axion field, preceded by an early era of matter domination. We investigate the effects of this cosmological scenario on the spectrum of possible primordial gravitational waves from inflation or cosmic strings and find that the spectrum features a triangular peak. As a result, future gravitational wave observations can probe the viable parameter space of kination, including regions that produce axion dark matter by the kinetic misalignment mechanism or the baryon asymmetry by axiogenesis.