Neutrinoless Double Beta Decay Rate Research Articles

νDoBe — A Python tool for neutrinoless double beta decay

We present νDoBe, a Python tool for the computation of neutrinoless double beta decay (0νββ) rates in terms of lepton-number-violating operators in the Standard Model Effective Field Theory (SMEFT). The tool can be used for automated calculations of 0νββ rates, electron spectra and angular correlations for all isotopes of experimental interest, for lepton-number-violating operators up to and including dimension 9. The tool takes care of renormalization-group running to lower energies and provides the matching to the low-energy effective field theory and, at lower scales, to a chiral effective field theory description of 0νββ rates. The user can specify different sets of nuclear matrix elements from various many-body methods and hadronic low-energy constants. The tool can be used to quickly generate analytical and numerical expressions for 0νββ rates and to generate a large variety of plots. In this work, we provide examples of possible use along with a detailed code documentation. The code can be accessed through:GitHub: https://github.com/OScholer/nudobeOnline User-Interface: https://oscholer-nudobe-streamlit-4foz22.streamlit.app/

Study of neutrino mass matrices with vanishing trace and one vanishing minor

In this work we carry out a systematic texture study of the neutrino mass matrix with the ansatzes - (i) one vanishing minor and (ii) the zero sum of the mass eigenvalues with the CP phases (henceforth vanishing trace). There are six possible textures of a neutrino mass matrix with one vanishing minor. The viability of each texture is checked with $3\sigma$ values of current neutrino data by drawing scatter plots. In our analysis we are motivated to use the ratio of solar to atmospheric mass-squared differences $R_{\nu}$ for its precise measurement (and also the atmospheric mixing angle $\theta_{23}$) to constrain phenomenologically first the Dirac CP phase $\delta$ in the range of $0^{\degree}-360^{\degree}$ for a given texture with the solutions of the constraint equations. Subsequently we employ this constrained $\delta$ to determine the range of completely unknown Majorana CP Phases ($\alpha$ and $\beta$) for all the viable textures. We also check the neutrinoless double beta decay rate, $|m_{ee}|$ and the Jarlskog invariant, $J_{cp}$ for the textures. Finally the symmetry realization of all the viable textures under the flavor symmetry group $Z_5$ via seesaw mechanism is implemented along with the FN mechanism to determine mass hierarchy structure.

A predictive and testable unified theory of fermion masses, mixing and leptogenesis

We consider a minimal non-supersymmetric SO(10) Grand Unified Theory (GUT) model that can reproduce the observed fermionic masses and mixing parameters of the Standard Model. We calculate the scales of spontaneous symmetry breaking from the GUT to the Standard Model gauge group using two-loop renormalisation group equations. This procedure determines the proton decay rate and the scale of U(1)B−L breaking, which generates cosmic strings and the right-handed neutrino mass scales. Consequently, the regions of parameter space where thermal leptogenesis is viable are identified and correlated with the fermion masses and mixing, the neutrinoless double beta decay rate, the proton decay rate, and the gravitational wave signal resulting from the network of cosmic strings. We demonstrate that this framework, which can explain the Standard Model fermion masses and mixing and the observed baryon asymmetry, will be highly constrained by the next generation of gravitational wave detectors and neutrino oscillation experiments which will also constrain the proton lifetime.

Light sterile neutrinos, left-right symmetry, and 0νββ decay

We investigate neutrinoless double beta (0νββ) decay rates in minimal left-right symmetric models in presence of relatively light right-handed neutrinos. By use of an effective field theory approach, we systematically include all contributions in the model as well as the dependence of the decay amplitude on the masses of right-handed neutrinos. In type-I and type-II seesaw scenarios, we analyze the impact of right-handed neutrinos heavier than about 10 MeV, showing that this effect can lead to a detection of 0νββ decay in the next-generation experiments even for the normal hierarchy and a relatively large right-handed scale set by the mass of hypothetical right-handed gauge bosons. Finally, we comment on a possible connection between light right-handed neutrinos and the strong CP problem.

Left-Right Symmetry and Leading Contributions to Neutrinoless Double Beta Decay.

We study the impact of the mixing (LR mixing) between the standard model W boson and its hypothetical, heavier right-handed parter W_{R} on the neutrinoless double beta decay (0νββ decay) rate. Our study is done in the minimal left-right symmetric model assuming a type-II dominance scenario with charge conjugation as the left-right symmetry. We then show that the 0νββ decay rate may be dominated by the contribution proportional to this LR mixing, which at the hadronic level induces the leading-order contribution to the interaction between two pions and two charged leptons. The resulting long-range pion exchange contribution can significantly enhance the decay rate compared to previously considered short-range contributions. Finally, we find that even if future cosmological experiments rule out the inverted hierarchy for neutrino masses, there are still good prospects for a positive signal in the next generation of 0νββ decay experiments.

Simplest scoto-seesaw mechanism

By combining the simplest (3,1) version of the seesaw mechanism containing a single heavy “right-handed” neutrino with the minimal scotogenic approach to dark matter, we propose a theory for neutrino oscillations. The “atmospheric” mass scale arises at tree level from the seesaw, while the “solar” oscillation scale emerges radiatively, through a loop involving the “dark sector” exchange. Such simple setup gives a clear interpretation of the neutrino oscillation lengths, has a viable WIMP dark matter candidate, and implies a lower bound on the neutrinoless double beta decay rate.

Search for creation of electrons in lab

We examine the physics motivations to search for lepton number violations in the laboratory, in particular by studying the important nuclear transition called neutrinoless double beta decay, which consists in the creation of a pair of electrons. We address some major shortcomings of the Standard Model of electroweak interactions, arguing that most of them can be solved simply within extended models with Majorana neutrinos. At the same time, we discuss the difficulties of obtaining precise predictions for the neutrinoless double beta decay rate and strengthen the case of probing Majorana neutrino masses of about 10 meV.

Naturalness and lepton number/flavor violation in inverse seesaw models

We introduce three right-handed neutrinos and three sterile neutrinos, and consider an inverse seesaw mechanism for neutrino mass generation. From naturalness point of view, their Majorana masses should be small, while it induces a large neutrino Yukawa coupling. Then, a neutrinoless double beta decay rate can be enhanced, and a sizable Higgs mass correction is inevitable. We find that the enhancement rate can be more than ten times compared with a standard prediction from light neutrino contribution alone, and an analytic form of heavy neutrino contributions to the Higgs mass correction. In addition, we numerically analyze the model, and find almost all parameter space of the model can be complementarily searched by future experiments of neutrinoless double beta decay and $\mu \to e$ conversion.

Generalized μ–τ reflection symmetry and leptonic CP violation

We propose a generalized μ–τ reflection symmetry to constrain the lepton flavor mixing parameters. We obtain a new correlation between the atmospheric mixing angle θ23 and the “Dirac” CP violation phase δCP. Only in a specific limit our proposed CP transformation reduces to standard μ–τ reflection, for which θ23 and δCP are both maximal. The “Majorana” phases are predicted to lie at their CP-conserving values with important implications for the neutrinoless double beta decay rates. We also study the phenomenological implications of our scheme for present and future neutrino oscillation experiments including T2K, NOνA and DUNE.

Double beta decay, lepton flavor violation, and collider signatures of left-right symmetric models with spontaneousD-parity breaking

We propose a class of left-right symmetric models (LRSMs) with spontaneous D parity breaking, where SU(2)_R breaks at the TeV scale while discrete left-right symmetry breaks around 10^9 GeV. By embedding this framework in a non-supersymmetric SO(10) Grand Unified Theory (GUT) with Pati-Salam symmetry as the highest intermediate breaking step, we obtain g_R / g_L ~ 0.6 between the right- and left-handed gauge couplings at the TeV scale. This leads to a suppression of beyond the Standard Model phenomena induced by the right-handed gauge coupling. Here we focus specifically on the consequences for neutrinoless double beta decay, low energy lepton flavour violation and LHC signatures due to the suppressed right handed currents. Interestingly, the reduced g_R allows us to interpret an excess of events observed recently in the range of 1.9 TeV to 2.4 TeV by the CMS group at the LHC as the signature of a right handed gauge boson in LRSMs with spontaneous D parity breaking. Moreover, the reduced right-handed gauge coupling also strongly suppresses the non-standard contribution of heavy states to the neutrinoless double beta decay rate as well as the amplitude of low energy lepton flavour violating processes. In a dominant type-II Seesaw mechanism of neutrino mass generation, we find that both sets of observables provide stringent and complimentary bounds which make it challenging to observe the scenario at the LHC.

Relating quarks and leptons with the T7 flavour group

In this letter we present a model for quarks and leptons based on T7 as flavour symmetry, predicting a canonical mass relation between charged leptons and down-type quarks proposed earlier. Neutrino masses are generated through a Type-I seesaw mechanism, with predicted correlations between the atmospheric mixing angle and neutrino masses. Compatibility with oscillation results leads to lower bounds for the lightest neutrino mass as well as for the neutrinoless double beta decay rates, even for normal neutrino mass hierarchy.

Radiative neutrino mass generation linked to neutrino mixing and0νββ-decay predictions

We discuss the connection between the origin of neutrino masses and their mixings, which arises in a class of scenarios with radiatively induced neutrino masses. In these scenarios, the neutrino mass matrix acquires textures with two entries close to zero in the basis where the charged-lepton mass matrix is diagonal. This results in specific constraints on the neutrino mixing parameters, which leads to the prediction of (i) a normal ordering of neutrino masses with the lightest neutrino mass in the $\ensuremath{\sim}\mathrm{meV}$ range and (ii) testable correlations among the various mixing angles, including a nonzero ${\ensuremath{\theta}}_{13}$ angle with its exact value correlated with the values of the atmospheric angle ${\ensuremath{\theta}}_{23}$ and the $CP$ phase $\ensuremath{\delta}$. We quantify the impact of deviations from exact zeroes in the mass matrix texture and connect it to the amount of hierarchy among Yukawa couplings. These scenarios of radiative neutrino mass generation also give rise to new short-range contributions to neutrinoless double beta decay, which dominate over the usual light-neutrino exchange contribution. As a result, this class of models can have a sizable neutrinoless double beta decay rate, in the range of upcoming experiments despite the normal mass ordering of neutrinos.

Neutrinoless double-βdecay of48Ca in the shell model: Closure versus nonclosure approximation

Neutrinoless double-beta decay is a unique process that could reveal physics beyond the Standard Model. Essential ingredients in the analysis of neutrinoless double-beta rates are the associated nuclear matrix elements. Most of the approaches used to calculate these matrix elements rely on the closure approximation. Here we analyze the light neutrino-exchange matrix elements of 48Ca neutrinoless double-beta decay and test the closure approximation in a shell-model approach. We calculate the neutrinoless double-beta nuclear matrix elements for 48Ca using both the closure approximation and a nonclosure approach, and we estimate the uncertainties associated with the closure approximation. We demonstrate that the nonclosure approach has excellent convergence properties which allow us to avoid unmanageable computational cost. Combining the nonclosure and closure approaches we propose a new method of calculation for neutrinoless double-beta decay rates which can be applied to the neutrinoless double-beta decay rates of heavy nuclei, such as 76Ge or 82Se.

Systematic decomposition of the neutrinoless double beta decay operator

We discuss the systematic decomposition of the dimension nine neutrinoless double beta decay operator, focusing on mechanisms with potentially small contributions to neutrino mass, while being accessible at the LHC. We first provide a (d=9 tree-level) complete list of diagrams for neutrinoless double beta decay. From this list one can easily recover all previously discussed contributions to the neutrinoless double beta decay process, such as the celebrated mass mechanism or "exotics", such as contributions from left-right symmetric models, R-parity violating supersymmetry and leptoquarks. More interestingly, however, we identify a number of new possibilities which have not been discussed in the literature previously. Contact to earlier works based on a general Lorentz-invariant parametrisation of the neutrinoless double beta decay rate is made, which allows, in principle, to derive limits on all possible contributions. We furthermore discuss possible signals at the LHC for mediators leading to the short-range part of the amplitude with one specific example. The study of such contributions would gain particular importance if there were a tension between different measurements of neutrino mass such as coming from neutrinoless double beta decay and cosmology or single beta decay.

Left–right models with light neutrino mass prediction and dominant neutrinoless double beta decay rate

In TeV scale left–right symmetric models, new dominant predictions to neutrinoless double beta decay and light neutrino masses are in mutual contradiction because of large contribution to the latter through popular seesaw mechanisms. We show that in a class of left–right models with high-scale parity restoration, these results coexist without any contravention with neutrino oscillation data and the relevant formula for light neutrino masses is obtained via gauged inverse seesaw mechanism. The most dominant contribution to the double beta decay is shown to be via WL−–WR− mediation involving both light and heavy neutrino exchanges, and the model predictions are found to discriminate whether the Dirac neutrino mass is of quark–lepton symmetric origin or without it. We also discuss associated lepton flavor violating decays.

Constraining neutrinoless double β decay matrix elements in 130Te

If a reliable measurement of a neutrinoless double beta decay (0v2β) rate is made, the effective neutrino masses can be determined from the nuclear matrix element. Theoretical calculations of nuclear matrix elements, however, show some disagreement. To test the suitability of various theoretical models, they should be benchmarked against experimentally measured nuclear properties, such as the ground-state distribution of nucleons in the parent-daughter nuclei, and how they change as a result of the decay process. Single neutron-adding reactions have been performed on the 0v2β candidate nucleus, 130Te. The Macfarlane-French sum rules have then been used to determine the single-particle vacancies. Some quasi-random phase approximations (QRPA) can greatly simplify theoretical calculations by describing the ground state of even-even nuclei using a BCS wavefunction. This assumption has been tested using two-neutron removal, (p,t) reactions. The BCS wavefunction appeared to be a valid approximation for valence neutrons.

Dark matter stability from non-Abelian discrete flavor symmetries

We present a mechanism for the dark matter (DM) stability in the framework of a non-Abelian flavour symmetry renormalizable model. The same non-Abelian discrete flavor symmetry which accounts for the observed pattern of neutrino oscillations, spontaneously breaks to a Z2 subgroup which renders DM stable. The simplest scheme leads to a scalar doublet DM potentially detectable in nuclear recoil experiments, inverse neutrino mass hierarchy, hence a neutrinoless double beta decay rate accessible to upcoming searches.

A realistic model of neutrino masses with a large neutrinoless double beta decay rate

The minimal Standard Model extension with the Weinberg operator does accommodate the observed neutrino masses and mixing, but predicts a neutrinoless double beta ($0\nu\beta\beta$) decay rate proportional to the effective electron neutrino mass, which can be then arbitrarily small within present experimental limits. However, in general $0\nu\beta\beta$ decay can have an independent origin and be near its present experimental bound; whereas neutrino masses are generated radiatively, contributing negligibly to $0\nu\beta\beta$ decay. We provide a realization of this scenario in a simple, well defined and testable model, with potential LHC effects and calculable neutrino masses, whose two-loop expression we derive exactly. We also discuss the connection of this model to others that have appeared in the literature, and remark on the significant differences that result from various choices of quantum number assignments and symmetry assumptions. In this type of models lepton flavor violating rates are also preferred to be relatively large, at the reach of foreseen experiments. Interestingly enough, in our model this stands for a large third mixing angle, $\sin^2\theta_{13} \gtrsim 0.008$, when $\mu \rightarrow eee$ is required to lie below its present experimental limit.

Shell model progress on neutrinoless double beta decay: nuclear matrix element uncertainties, neutrino exchange mechanism in seesaw models

We study the neutrinoless double beta decay in the context of the interacting shell model. Firstly, we estimate the uncertainties associated to the different approximations performed in the calculation of the nuclear matrix elements, which are necessary to obtain information about the neutrino masses. We then study the dependence of the nuclear matrix elements on the mass of the exchanged neutrinos and we discuss, within the type I seesaw model, which will be the contribution to the neutrinoless double beta decay rate of the different extra neutrinos, depending on their mass range. We also discuss how seesaw models could reconcile large rates of neutrinoless double beta decay with stringent cosmological bounds on neutrino masses.

Neutrino phenomenology and stable dark matter with [formula omitted

We present a model based on the A4 non-Abelian discrete symmetry leading to a predictive five-parameter neutrino mass matrix and providing a stable dark matter candidate. We found an interesting correlation among the atmospheric and the reactor angles which predicts θ23∼π/4 for very small reactor angle and deviation from maximal atmospheric mixing for large θ13. Only normal neutrino mass spectrum is possible and the effective mass entering the neutrinoless double beta decay rate is constrained to be |mee|>4×10−4 eV.