We investigate neutrinoless double beta decay ($0νββ$) in the presence of sterile neutrinos with Majorana mass terms. These gauge-singlet fields are allowed to interact with Standard-Model (SM) fields via renormalizable Yukawa couplings as well as higher-dimensional gauge-invariant operators up to dimension seven in the Standard Model Effective Field Theory extended with sterile neutrinos. At the GeV scale, we use Chiral effective field theory involving sterile neutrinos to connect the operators at the level of quarks and gluons to hadronic interactions involving pions and nucleons. This allows us to derive an expression for $0νββ$ rates for various isotopes in terms of phase-space factors, hadronic low-energy constants, nuclear matrix elements, the neutrino masses, and the Wilson coefficients of higher-dimensional operators. The needed hadronic low-energy constants and nuclear matrix elements depend on the neutrino masses, for which we obtain interpolation formulae grounded in QCD and chiral perturbation theory that improve existing formulae that are only valid in a small regime of neutrino masses. The resulting framework can be used directly to assess the impact of $0νββ$ experiments on scenarios with light sterile neutrinos and should prove useful in global analyses of sterile-neutrino searches. We perform several phenomenological studies of $0νββ$ in the presence of sterile neutrinos with and without higher-dimensional operators. We find that non-standard interactions involving sterile neutrinos have a dramatic impact on $0νββ$ phenomenology, and next-generation experiments can probe such interactions up to scales of $\mathcal O(100)$ TeV.
Nuclear matrix elements (NME) for exchange of arbitrary mass neutrinos are calculated in the interacting boson model (IBM-2). By combining the NME with the phase space factors (PSF), expected half-lives for neutrinos of mass $m_N$ and coupling $U_{eN}$ are estimated. Limits on sterile neutrinos with masses in the eV, keV, MeV-GeV, and TeV range are given.
Sterile neutrinos of mass up to a few tens of TeV can saturate the present experimental bound of neutrinoless double beta decay process. Due to the updated nuclear matrix elements, the bound on mass and mixing angle is now improved by one order of magnitude. We have performed a detailed analysis of neutrinoless double beta decay for the minimal Type I seesaw scenario. We have shown that in spite of the naive expectation that the light neutrinos give the dominant contribution, sterile neutrinos can saturate the present experimental bound of neutrinoless double beta decay process. However, in or…
The physics potential of neutrinoless double beta decay is discussed. Furthermore, experimental considerations are presented as well as the current status of experiments. Finally an outlook towards the future, work on nuclear matrix elements and alternative processes is given.
In this paper we analyze the neutrinoless double beta decay predictions in some scenarios with admixture of pseudo-Dirac and Majorana neutrinos in the 3 and 3+1 neutrino frameworks. We found that some of the cases can be falsifiable in near-term and future generations of neutrinoless double beta decay experiments even for the normal neutrino mass hierarchy. In the 3+1 framework we consider the sterile neutrino with a mass of the order of 1 eV. The complementarity between cosmological constraints and the future sensitivity for the next generations of the neutrinoless double beta decay searches …
We study possible contribution of the Majorana neutrino mass eigenstate $ν_h$ dominated by a sterile neutrino component to neutrinoless double beta ($0νββ$) decay. From the current experimental lower bound on the $0νββ$-decay half-life of $^{76}$Ge we derive stringent constraints on the $ν_h-ν_e$ mixing in a wide region of the values of $ν_h$ mass. We discuss cosmological and astrophysical status of $ν_h$ in this mass region.
Light sterile neutrinos with masses at the sub-eV or eV scale are hinted by current experimental and cosmological data. Assuming the Majorana nature of these hypothetical particles, we discuss their effects in the neutrinoless double beta decay by exploring the implications of a vanishing effective Majorana neutrino mass. Allowed ranges of neutrino masses, mixing angles and Majorana CP-violating phases are illustrated in some instructive cases for both normal and inverted mass hierarchies of three active neutrinos.
We have studied a flavor symmetry-based extended left-right symmetric model(LRSM) with a dominant type-II seesaw mechanism and have explored the associated neutrino phenomenology. The particle content of the model includes usual quarks, and leptons along with additional sterile fermion per generation in the fermion sector while the scalar content contains Higgs doublets and scalar bidoublet. Realization of this extension of LRSM has been done by using $A_{4}\times Z_{4}$ discrete symmetries. In this work, we have also included the study of sterile neutrino dark matter(DM) phenomenology along w…
We investigate the possibility of producing neutrinoless double beta decay without having an electron neutrino with a mass in the vicinity of 1 eV. We do so by having a much lighter electron neutrino mix with a much heavier (m > 1 GeV) sterile neutrino. We study the constraints on the masses and mixings of such heavy sterile neutrinos from existing laboratory, astrophysical and cosmological information, and discuss the properties it would require in order to produce a detectable signal in current searches for neutrinoless double beta decay.
We make a comparative study of the neutrinoless double beta decay constraints on heavy sterile neutrinos versus other direct and indirect constraints from both lepton number conserving and violating processes, as a sensitive probe of the extent of lepton number violation and possible interference effects in the sterile sector. We introduce a phenomenological parametrisation of the simplified one-generation seesaw model with one active and two sterile neutrino states in terms of experimentally measurable quantities, such as active-sterile neutrino mixing angles, CP phases, masses and mass split…
Recent neutrino experiment results show a preference for the normal neutrino mass ordering. The global efforts to search for neutrinoless double beta decays undergo a broad gap with the approach to the prediction in the three-neutrino framework based on the normal ordering. This research is intended to show that it is possible to find a neutrinoless double beta decay signal even with normal ordered neutrino masses. We propose the existence of a light sterile neutrino as a solution to the higher effective mass of the electron neutrino expected by the current experiments. A few short-baseline os…
The existence of light sterile neutrinos, as predicted in several models, can help to explain a number of observations starting from dark mater to recent anomalies in short baseline experiments. In this paper we consider two models - Left-Right Symmetric Zee model and Extended Seesaw model, that can naturally accommodate the presence of light sterile neutrinos in the eV to MeV mass scale. We perform a detailed study on the neutrinoless double beta decay process which receives major contributions from diagrams involving these light sterile neutrinos. Considering a number of theoretical and expe…
We show that chiral effective field theory (EFT) two-body currents provide important contributions to the quenching of low-momentum-transfer Gamow-Teller transitions, and use chiral EFT to predict the momentum-transfer dependence that is probed in neutrinoless double-beta decay. We then calculate for the first time the neutrinoless double-beta decay operator based on chiral EFT currents and study the nuclear matrix elements at successive orders. The contributions from chiral two-body currents are significant and should be included in all calculations.
Neutrinoless double beta decay is a hypothetical radioactive process which, if observed, would prove the neutrino to be a Majorana fermion: a particle that is its own antiparticle. In this lecture mini-series I discuss the physics of Majorana fermions and the connection between the nature of neutrino mass and neutrinoless double beta decay. We review Dirac and Majorana spinors, discuss methods of distinguishing between Majorana and Dirac fermions, and derive in outline the connection between neutrino mass and double beta decay rates. We conclude by briefly summarizing the experimental landscap…
We assess how well next generation neutrinoless double beta decay and normal neutrino beta decay experiments can answer four fundamental questions. 1) If neutrinoless double beta decay searches do not detect a signal, and if the spectrum is known to be inverted hierarchy, can we conclude that neutrinos are Dirac particles? 2) If neutrinoless double beta decay searches are negative and a next generation ordinary beta decay experiment detects the neutrino mass scale, can we conclude that neutrinos are Dirac particles? 3) If neutrinoless double beta decay is observed with a large neutrino mass el…
Motivated by the capability of the KATRIN experiment to explore the existence of KeV neutrinos in the $[1-18.5]$ KeV mass range, we explore the viability of minimal extensions of the Standard Model involving sterile neutrinos (namely the 3 + $N$ frameworks) and study their possible impact in both the beta energy spectrum and the neutrinoless double beta decay effective mass, for the two possible ordering cases for the light neutrino spectrum. We also explore how both observables can discriminate between motivated low-scale seesaw realizations involving KeV sterile neutrinos. Our study concerns…
Neutrinoless double beta decay has been the subject of intensive theoretical work as it represents the only practical approach to discovering whether neutrinos are Majorana particles or not, and whether lepton number is a conserved quantum number. Available calculations of matrix elements and phase-space factors are reviewed from the perspective of a future large-scale experimental search for neutrinoless double beta decay. Somewhat unexpectedly, a uniform inverse correlation between phase space and the square of the nuclear matrix element emerges. As a consequence, no isotope is either favore…
A measurement of neutrinoless double beta decay in one isotope does not allow to determine the underlying physics mechanism. We discuss the discrimination of mechanisms for neutrinoless double beta decay by comparing ratios of half life measurements for different isotopes. Six prominent examples for specific new physics contributions to neutrinoless double beta decay are analyzed. We find that the change in corresponding ratios of half lives varies from 60% for supersymmetric models up to a factor of 5-20 for extra-dimensional and left-right-symmetric mechanisms.
In this proceeding we present predictions of the effective Majorana mass $|m_{ββ}|$ in neutrinoless double-$β$ decay for the standard $3ν$ mixing case and for the 3+1 neutrino mixing case indicated by the short-baseline anomalies. We have taken into account the uncertainties of the neutrino mixing parameters determined by oscillation experiments. We obtained that the predictions for $|m_{ββ}|$ in the cases of $3ν$ and 3+1 mixing are quite different, in agreement with previous discussions in the literature, and that future measurements of neutrinoless double-$β$ decay and the total mass of the …
We analyze the constraints on neutrino mass spectra with extra sterile neutrinos as implied by the LSND experiment. The various mass related observables in neutrinoless double beta decay, tritium beta decay and cosmology are discussed. Both neutrino oscillation results as well as recent cosmological neutrino mass bounds are taken into account. We find that some of the allowed mass patterns are severely restricted by the current constraints, in particular by the cosmological constraints on the total sum of neutrino masses and by the non-maximality of the solar neutrino mixing angle. Furthermore…
The detection of neutrinoless double-beta decay will establish the Majorana nature of neutrinos. In addition, if the nuclear matrix elements of this process are reliably known, the experimental lifetime will provide precious information about the absolute neutrino masses and hierarchy. I review the status of nuclear structure calculations for neutrinoless double-beta decay matrix elements, and discuss some key issues to be addressed in order to meet the demand for accurate nuclear matrix elements.
Recent $ν_e$ appearance data from the Mini Booster Neutrino Experiment (MiniBooNE) are in support of the excess of events reported by the Liquid Scintillator Neutrino Detector (LSND), which provides an indirect hint for the existence of eV-scale sterile neutrino. As these sterile neutrinos can mix with the standard active neutrinos, in this paper we explore the effect of such active-sterile mixing on the determination of various oscillation parameters by the currently running long-baseline neutrino experiments T2K and NO$ν$A. We find that the existence of sterile neutrino can lead to new kind …
We present a framework to combine data from the latest neutrinoless double-beta decay experiments for multiple isotopes and derive a limit on the effective neutrino mass using the experimental energy distributions. The combined limits on the effective mass range between 130-310 meV, where the spread is due to different model calculations of nuclear matrix elements (NMEs). The statistical consistency (p values) between this result and the signal observation claimed by the Heidelberg-Moscow experiment is derived. The limits on the effective mass are also evaluated in a (3+1) sterile neutrino mod…
We point out that lepton number violation is possible even if neutrinos are Dirac particles. We illustrate this by constructing a simple model that allows for lepton number violation by four units only. As a consequence, neutrinoless double beta decay is forbidden, but neutrinoless quadruple beta decay is possible: $(A,Z) \to (A,Z+4) + 4 e^-$. We identify three candidate isotopes for this decay, the most promising one being Nd-150 due to its high $Q_{0ν4β}$-value of 2 MeV. Analogous processes, such as neutrinoless quadruple electron capture, are also possible. The expected lifetimes are extrem…
We address the impact of sterile fermion states on the anomalous magnetic moment of charged leptons, as well as their contribution to neutrinoless double beta decays. We illustrate our results in a minimal, effective extension of the Standard Model by one sterile fermion state, and in a well-motivated framework of neutrino mass generation, embedding the Inverse Seesaw into the Standard Model. The simple "3+1" effective case succeeds in alleviating the tension related to the muon anomalous magnetic moment, albeit only at the 3$σ$ level, and for light sterile states (corresponding to a }cosmolog…
We review the potential to probe new physics with neutrinoless double beta decay $(A,Z) \to (A,Z+2) + 2 e^-$. Both the standard long-range light neutrino mechanism as well as short-range mechanisms mediated by heavy particles are discussed. We also stress aspects of the connection to lepton number violation at colliders and the implications for baryogenesis.
Heavy neutrino potential for neutrinoless double beta decay is studied with focusing on its statistical property. The existence condition for heavy neutrinos is also presented. In particular sterile neutrinos are possible candidate for heavy nuetrinos. The statistics provide a gross view of understanding amplitude of constitutional components of the nuclear matrix element.
Neutrinoless double beta decay experiments constrain one combination of neutrino parameters, while cosmic surveys constrain another. This complementarity opens up an exciting range of possibilities. If neutrinos are Majorana particles, and the neutrino masses follow an inverted hierarchy, then the upcoming sets of both experiments will detect signals. The combined constraints will pin down not only the neutrino masses but also constrain one of the Majorana phases. If the hierarchy is normal, then a beta decay detection with the upcoming generation of experiments is unlikely, but cosmic surveys…
The variances and covariances associated to the nuclear matrix elements (NME) of neutrinoless double beta decay are estimated within the quasiparticle random phase approximation (QRPA). It is shown that correlated NME uncertainties play an important role in the comparison of neutrinoless double beta decay rates for different nuclei, and that they are degenerate with the uncertainty in the reconstructed Majorana neutrino mass.
We review probes of heavy sterile neutrinos, focusing on direct experimental searches and neutrinoless double beta decay. Working in a phenomenological parametrization, we emphasize the importance of the nature of sterile neutrinos in interpreting neutrinoless double beta decay searches. While current constraints on the active-sterile neutrino mixing are already stringent, we highlight planned future efforts that will probe regimes motivated by the lightness of active neutrinos.
Neutrinoless double beta decay can significantly help to shed light on the issue of non-zero neutrino mass, as observation of this lepton number violating process would imply neutrinos are Majorana particles. However, the underlying interaction does not have to be as simple as the standard neutrino mass mechanism. The entire variety of neutrinoless double beta decay mechanisms can be approached effectively. In this work we focus on a theoretical description of short-range effective contributions to neutrinoless double beta decay, which are equivalent to 9-dimensional effective operators incorp…
Neutrino potential for neutrinoless double beta decay is studied with focusing on its statistical property. The statistics provide a gross view of understanding amplitude of constitutional components of the nuclear matrix element.
The study of neutrinoless double beta decay is of outmost importance for neutrino physics. It is considered to be the gold plated channel to probe the fundamental character of neutrinos and to determine the neutrino mass. From the experimental point about nine different isotopes are explored for the search. After a general introduction follows a short discussion on nuclear matrix element calculations and supportive measurements. The current experimental status of double beta searches is presented followed by a short discussion of the ideas and proposals for large scale experiments.
In a previous article [Phys. Rev. D 79, 053001 (2009)] we estimated the correlated uncertainties associated to the nuclear matrix elements (NME) of neutrinoless double beta decay (0 nu beta beta) within the quasiparticle random phase approximation (QRPA). Such estimates encompass recent independent calculations of NMEs, and can thus still provide a fair representation of the nuclear model uncertainties. In this context, we compare the claim of 0 nu beta beta decay in Ge-76 with recent negative results in Xe-136 and in other nuclei, and we infer the lifetime ranges allowed or excluded at 90% C.…
The experimental rate of neutrinoless double beta decay can be saturated by the exchange of virtual sterile neutrinos, that mix with the ordinary neutrinos and are heavier than 200 MeV. Interestingly, this hypothesis is subject only to marginal experimental constraints, because of the new nuclear matrix elements. This possibility is analyzed in the context of the Type I seesaw model, performing also exploratory investigations of the implications for heavy neutrino mass spectra, rare decays of mesons as well as neutrino-decay search, LHC, and lepton flavor violation. The heavy sterile neutrinos…
In the minimal supersymmetric extension to the Standard Model, a non-zero lepton number violating coupling lambda'_111 predicts both neutrinoless double beta decay and resonant single slepton production at the LHC. We show that, in this case, if neutrinoless double beta decay is discovered in the next generation of experiments, there exist good prospects to observe single slepton production at the LHC. Neutrinoless double beta decay could otherwise result from a different source (such as a non-zero Majorana neutrino mass). Resonant single slepton production at the LHC can therefore discriminat…
The connection of neutrino physics with neutrinoless double beta decay is reviewed. After presenting the current status of the PMNS matrix and the theoretical background of neutrino mass and lepton mixing, we will summarize the various implications of neutrino physics for double beta decay. The influence of light sterile neutrinos and other exotic modifications of the three neutrino picture is also discussed.
To quantitatively assess the impact of an eV-mass sterile neutrino on the neutrinoless double-beta ($0νββ$) decays, we calculate the posterior probability distribution of the relevant effective neutrino mass $|m^\prime_{ee}|$ in the (3+1)$ν$ mixing scenario, following the Bayesian statistical approach. The latest global-fit analysis of neutrino oscillation data, the cosmological bound on the sum of three active neutrino masses from {\it Planck}, and the constraints from current $0νββ$ decay experiments are taken into account in our calculations. Based on the resultant posterior distributions, …
It is firmly believed that a signal of neutrinoless double beta decay can unquestionably confirm the Majorana nature of neutrinos. However we notice that a Majorana neutrino mass induced after some neutrinoless double beta decay processes can be accidentally cancelled by another Majorana neutrino mass induced before any neutrinoless double beta decay processes. This realistic cancellation can simultaneously allow an observable neutrinoless double beta decay and a vanishing Majorana neutrino mass. In consequence a future discovery of neutrinoless double beta decay cannot fully rule out the poss…
We consider perturbative one loop QCD corrections to the light neutrino contribution to neutrinoless double beta decay and find large enhancement to the rate. QCD corrections also generate structures which mimic new physics contributions usually considered. Within some approximations, the net effect seem to almost saturate the experimental limits, and therefore seems to implt that this is all there is to neutrinoless double beta decay.
We study the general phenomenology of neutrinoless double beta decay in seesaw models. In particular, we focus on the dependence of the neutrinoless double beta decay rate on the mass of the extra states introduced to account for the Majorana masses of light neutrinos. For this purpose, we compute the nuclear matrix elements as functions of the mass of the mediating fermions and estimate the associated uncertainties. We then discuss what can be inferred on the seesaw model parameters in the different mass regimes and clarify how the contribution of the light neutrinos should always be taken in…
We investigate the predictions for neutrinoless double beta ($(ββ)_{0 ν}$-) decay effective Majorana mass $\left| \langle \, m \, \rangle \right|$ in the 3+1 and 3+2 schemes with one and two additional sterile neutrinos with masses at the eV scale. The two schemes are suggested by the neutrino oscillation interpretation of the reactor neutrino and Gallium "anomalies" and of the data of the LSND and MiniBooNE experiments. We analyse in detail the possibility of a complete or partial cancellation between the different terms in $\left| \langle \, m \, \rangle \right|$, leading to a strong suppres…
We demonstrate that in the process of deducing the constraint on the electroweak mixing angle $θ_{W}$ in our paper, we have indeed been working with three mass scales while implementing (331) model.
We present accurate predictions of the effective Majorana mass $|m_{ββ}|$ in neutrinoless double-$β$ decay in the standard case of $3ν$ mixing and in the case of 3+1 neutrino mixing indicated by the reactor, Gallium and LSND anomalies. We have taken into account the uncertainties of the neutrino mixing parameters determined by oscillation experiments. It is shown that the predictions for $|m_{ββ}|$ in the cases of $3ν$ and 3+1 mixing are quite different, in agreement with previous discussions in the literature, and that future measurements of neutrinoless double-$β$ decay and of the effective …
Weak interaction in nuclei represents a well-known venue for testing many of the fundamental symmetries of the Standard Model. In particular, neutrinoless double-beta decay offers the possibility to test Beyond Standard Model theories predicting that neutrinos are Majorana fermions and the lepton number conservation is violated. This paper focuses on an effective field theory approach to neutrinoless double-beta decay for extracting information regarding the properties of the Beyond Standard Model Lagrangian responsible for this process. We use shell model nuclear matrix elements and the lates…
A class of discrete flavor-symmetry-based models predicts constrained neutrino mass matrix schemes that lead to specific neutrino mass sum-rules (MSR). We show how these theories may constrain the absolute scale of neutrino mass, leading in most of the cases to a lower bound on the neutrinoless double beta decay effective amplitude.
The neutrinoless double beta decay transition to the first excited 0^+ collective final state is examined for A=76, 82, 100 and 136 nuclei by assuming light and heavy Majorana neutrino exchange mechanisms as well as the trilinear R-parity violating contributions. Realistic calculations of nuclear matrix elements have been performed within the renormalized quasiparticle random phase approximation. Transitions to the first excited two-quadrupole phonon 0^+ state are described within a boson expansion formalism and alternatively by using the operator recoupling method. We present the sensitivity …
In the event of an observation of neutrinoless double beta decay, a relevant question would be: what lepton number violating physics is responsible for the decay? The exchange of Majorana neutrinos and/or supersymmetric particles may contribute. We point out that measurements of supersymmetric signals at the LHC, including single slepton production, could be used to help bound some supersymmetric processes contributing to neutrinoless double beta decay. LHC information about the supersymmetric spectrum could be combined with Bd-Bd bar mixing data in order to bound a competing neutrinoless doub…
A significant signal of neutrinoless double beta decay can be consistent with the existence of light quasi-Dirac neutrinos. To demonstrate this possibility, we consider a realistic model where the neutrino masses and the neutrinoless double beta decay can be simultaneously generated after a Peccei-Quinn symmetry breaking.
The possible existence of an eV-mass sterile neutrino, slightly mixing with ordinary active neutrinos, is not yet excluded by neutrino oscillation experiments. Assuming neutrinos to be Majorana particles, we explore the impact of such a sterile neutrino on the effective neutrino mass of neutrinoless double-beta decays $\langle m \rangle^\prime_{ee} \equiv m^{}_1 |V^{}_{e1}|^2 e^{{\rm i}ρ} + m^{}_2 |V^{}_{e2}|^2 + m^{}_3 |V^{}_{e3}|^2 e^{{\rm i}σ} + m^{}_4 |V^{}_{e4}|^2 e^{{\rm i}ω}$, where $m^{}_i$ and $V^{}_{ei}$ (for $i = 1, 2, 3, 4$) denote respectively the absolute masses and the first-row…
We study the effective operators of the standard model fields which would yield an observable rate of neutrinoless double beta decay. We particularly focus on the possibility that neutrinoless double beta decay is dominantly induced by lepton-number-violating higher dimensional operators other than the Majorana neutrino mass. Our analysis can be applied to models in which neutrinoless double beta decay is induced either by a strong dynamics or by quantum gravity effects at a fundamental scale near the TeV scale as well as the conventional models in which neutrinoless double beta decay is induc…
Neutrinoless double beta decay is one of the most sensitive approaches in non-accelerator particle physics to take us into a regime of physics beyond the standard model. This article is a brief review of the experiments in search of neutrinoless double beta decay from 76Ge. Following a brief introduction of the process of double beta decay from 76Ge, the results of the very first experiments IGEX and Heidelberg-Moscow which give indications of the existence of possible neutrinoless double beta decay mode has been reviewed. Then ongoing efforts to substantiate the early findings are presented a…
We argue three-flavour neutrino mixing. We consider the neutrinos as Majorana particles and see how the neutrinoless double beta decay constrains the neutrino mixing angles. Our formulation is widely valid and is applied to the neutrino oscillation experiment.
In light of recent experimental results, we carefully analyze the effects of interference in neutrinoless double beta decay, when more than one mechanism is operative. We assume a complete cancellation is at work for $^{136}\rm{Xe}$, and find its implications on the half-life of other isotopes, such as $^{76}\rm{Ge}$. For definiteness, we consider the role of light and heavy sterile neutrinos. In this case, the effective Majorana mass parameter can be redefined to take into account all contributions and its value gets suppressed. Hence, larger values of neutrino masses are required for the sam…
