Beta decay studies for Physics beyond the Standard Model

Aagrah Agnihotri (University of Jyväskylä)

The study of weak interaction nuclear processes in general, and nuclear β-decay in particular play a key role in multiple avenues of searches for physics beyond the standard model. The search for the rare neutrinoless double β-decay(0νββ) and exotic dark matter in nuclear laboratory scale experiments are among such searches that aim to answer foundational questions in physics. In the searches for exotic dark matter, unknown forbidden electron-capture decay can appear as an irreducible internal background [1]. Therefore, giving theoretical estimates for branching ratios of such unknown decays is of utmost importance in experimental confirmation of the detection of exotic dark matter [1]. On the 0νββ decay front, understanding the phenomenology of effective axial vector coupling (𝑔_𝐴^𝑒𝑓𝑓) is key for determining the sensitivity of underground experiments designed to detect this rare decay [2-6]. In addition to this, investigating the connection between 0νββ decay amplitudes and Ordinary Muon Capture (OMC) rates can be a window to interesting new physics [7]. The seminar is aimed to walk through these novel facets of physics, that lie at the forefront of weak interaction physics. 

[1] Aagrah Agnihotri, Jouni Suhonen, and Hong Joo Kim, Constraints for rare electron-capture decays mimicking detection of dark-matter particles in nuclear transitions. Phys. Rev. Lett., 133:232501, Dec 2024. doi: 10. 1103/PhysRevLett.133.232501. 
[2] Aagrah Agnihotri and Jouni Suhonen, Novel way of evaluating gA quenching in β+/EC decays : Introducing the Branching-Ratio Method (BRM) 2025, arXiv:2501.07370. 
[3] Suhonen, J.T., Value of the Axial-Vector Coupling Strength in 𝛽 and 𝛽𝛽 Decays: A Review. Frontiers in Physics 2017;5:55. 
[4] Suhonen, J., Kostensalo, J. Double 𝛽 decay and the axial strength. Frontiers in Physics 2019;7:29. 
[5] Ejiri, H., Suhonen, J., Zuber, K.. Neutrino–nuclear responses for astro-neutrinos, single beta decays and double beta decays. Physics Reports 2019;797:1. 
[6] J.Suhonen, Impact of the quenching of gA on the sensitivity of 0νββ experiments, Phys.Rev.C 96 (2017) 055501. 
[7] Aagrah Agnihotri. Vikas Kumar, and Jouni Suhonen, Correlating the 0νββ-decay amplitudes of 136Xe with the ordinary muon capture (OMC) rates of 136Ba (work in progress).