### Conveners

#### Theory

- Osvaldo Civitarese (Department of Physics. University of La Plata.Argentina)

#### Theory

- Osvaldo Civitarese (Department of Physics. University of La Plata.Argentina)

#### Theory

- Jouni Suhonen (University of Jyväskylä)

#### Theory

- Sabin Stoica (International Centre for Advanced Training and Research in Physics)

#### Theory

- Lukas Graf (Max Planck Institute for Nuclear Physics)

#### Theory

- There are no conveners in this block

#### Theory

- Javier Menendez (University of Barcelona)

Beta-decay and double-beta-decay experiments measure neutrino masses by using as large a source mass as possible. At present, there are many of these experiments running, notable examples being KATRIN (beta-minus decay of tritium), ECHo (electron capture in holmium) and NEMO (double beta decays of several nuclear species). The first two experiments are clean experiments in the sense that they...

The observation of neutrinoless double beta decay would have far-reaching consequences for particle physics, as it would be a clear manifestation of lepton number violation and it would give a hint on the origin of neutrino masses. While searching for neutrinoless double beta decay, a significant amount of the two-neutrino double beta decay data has been collected by a number of experiments....

In my talk I will first give a brief review of the last results in the theoretical study of double-beta decay obtained by our Bucharest group. Next, I will focus on testing the Lorentz invariance violation (LIV) in double beta decay. I will present the calculation of the LIV perturbations in the energy electron spectra and in angular correlation between electrons and show possible...

Abstract: Among cold dark-matter candidates are low-mass neutral bosons. The existence of such pseudo-scalar particles has been proposed long ago by Peccei and Quinn to explain the spontaneous breaking of CP in the early Universe. In this talk we discuss a possible mechanism to explain for non-zero neutrino masses, which is based on the treatment of neutrino-axions interactions.From the known...

Reliable nuclear matrix elements play a crucial role in planning future neutrinoless double-beta-decay experiments, and in extracting the exciting new physics from them. Unfortunately, currently the nuclear matrix elements are not well constrained, and different many-body methods notably disagree on the values of them. Another open question is the possible need of quenching the axial-vector...

It is well known that the neutrino medium, such as the cosmic neutrino background, produces a tiny birefringence effect on electromagnetic waves. Recently, it was claimed that this effect may be enhanced by an additional presence of a plasma characterized by the electron plasma frequency. In our work, instead of considering the plasma, we consider a ordinary transparent refractive medium...

Reliable nuclear matrix elements for the neutrinoless double-beta decay of Germanium, Molibdenum, Tellurium and Xenon are necessary to determine the physics reach of next generation experiments and to fully exploit their findings. In this talk I will present recent improvements in calculations with the nuclear shell model, one of the leading many-body methods to obtain these nuclear matrix...

Although the neutrinoless double-beta decay has not been experimentally proven yet, there is work undergoing to improve the theoretical description of the decay.

In this work, we computed the nuclear matrix elements using the shell model techniques and the electron phase-space factors for several nuclei of interest. The latter were computed using three different descriptions for the...

Neutrinoless double beta decay ($0\nu\beta\beta$) is a proposed decay which turns out to be the most promising process to observe lepton number violation in the laboratory, and to establish whether neutrinos are its own antiparticle. Due to this unique potential, a very active experimental program aims to detect this rare decay. In order to plan these searches, reliable estimations for the...

Neutrinoless double beta decay (0νββ) nuclear matrix elements (NME) are the object of many theoretical calculation methods, and are very important for analysis and guidance of a large number of experimental efforts. However, there are large discrepancies between the NME values provided by different methods. In this paper we propose a statistical analysis of the 48Ca 0νββ NME using the...

The nuclear matrix element of neutrinoless double-β decay is an essential input for determining the neutrino effective mass, if the half-life of this decay is measured. Reliable calculation of this nuclear matrix element has been a long-standing problem because of the diversity of the predicted values of the nuclear matrix element, which depends on the calculation method. In this study, we...

Precise calculations of nuclear matrix elements provide a solid foundation in order to extract relevant data from current and upcoming neutrinoless double-beta decay experiments. These searches are key to unveil the nature of neutrinos as well as to access physics beyond the Standard Model due to the violation of the lepton number conservation in neutrinoless double-beta decay.

In this...

As experiments searching for neutrinoless double beta decay are in the planning phase of a next generation with hopes to completely probe the inverted mass hierarchy, the need for reliable nuclear matrix elements, which govern the rate of this decay, is stronger than ever. Since a large discrepancy is found when computing this quantity with different nuclear models, a large unknown still...

Theoretical and experimental studies on the beta decays of the most prominent fission products in nuclear reactors are needed to unravel the source of the anomalies detected in the related anti-neutrino flux. One of these fission products, 92Rb, was recently studied for its beta decay to 92Sr by using large-scale nuclear shell-model (NSM) calculations to analyze the role of forbidden beta...

We will discuss possibilities of how to experimentally distinguish different mechanisms of $0\nu\beta\beta$-decay and thereby identify potential non-standard contributions. The different mechanisms possibly contributing to $0\nu\beta\beta$-decay are classified following an effective field theory approach. We find that when utilizing measurements of the leptonic phase space, i.e., the spectra...

The two-neutrino double-beta decay ($2\nu\beta\beta$-decay) process is attracting more and more attention from the physics community due to its potential to explain nuclear structure aspects of involved atomic nuclei and constrain new (beyond the Standard Model) physics scenarios. Topics of interest are energetical and angular distributions of the emitted electrons, which might allow the...