In the type-I seesaw mechanism, both the light Majorana neutrinos (ν_1, ν_2, ν_3) and the heavy Majorana neutrinos (N_1, ..., N_n) can mediate the neutrinoless double-beta (0νββ) decay. We point out that the contribution of ν_i to this 0νββprocess is also dependent on the masses M_k and the mixing parameters R_{ek} of N_k as a direct consequence of the exact seesaw relation, and the effective mass term of ν_i is in most cases dominant over that of N_i. We obtain a new bound |\sum R^2_{ek} M_k| < 0.23 eV (or < 0.85 eV as a more conservative limit) at the 2σlevel, which is much stronger than |\sum R^2_{ek} M^{-1}_k| < 5 \times 10^{-8} GeV^{-1} used in some literature, from current experimental constraints on the 0νββdecay. Taking the minimal type-I seesaw scenario for example, we illustrate the possibility of determining or constraining two heavy Majorana neutrino masses by using more accurate low-energy data on lepton number violation and non-unitarity of neutrino mixing.
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 assume that neutrinoless double beta decay is caused by the exchange of three light Majorana neutrinos. Under this assumption, we obtain, by the method of perturbation, the equation representing the isocontour of effective Majorana mass which is the function of two CP-violating Majorana phases. The equation representing the isocontour (constraint equation between two Majorana phases) is expressed analytically by six parameters: two lepton mixing angles, two kinds of neutrino mass squared differences, lightest neutrino mass scale, and the effective Majorana mass. We discuss how the constrain…
Neutrinoless double beta decay (NDBD) is the only experiment that could probe the Majorana nature of the neutrino. Here we study the theoretical implications of NDBD for models yielding tri-bimaximal lepton mixing like A4 and S4.
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 …
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 probability distribution for the effective Majorana mass as a function of the lightest neutrino mass in the standard three neutrino scheme is computed via a random sampling from the distributions of the involved mixing angles and squared mass diffences. A flat distribution in the [0,2pi] range for the Majorana phases is assumed, and the dependence of small values of the effective mass on the Majorana phases is highlighted. The study is then extended with the addition of the cosmological bound on the sum of the neutrino masses. Finally, the prospects for neutrinoless double beta decay searc…
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…
Usually it is supposed that Majorana neutrino produced in the superposition state $χ_L = ν_L + (ν_L)^c$ and then follows the neutrinoless double beta decay. But since weak interactions are chiral invariant then the neutrino at production has definite helicity (i.e., $ν_L$ and $(ν_L)^c$ neutrinos are separately produced and then neutrino is not in the superposition state). This helicity cannot change after production without any external interactions. Thus we see that for unsuitable helicity the neutrinoless double $β$ decay is not possible even if neutrino is a Majorana particle. Also transiti…
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.
The relation between neutrino oscillation parameters and neutrinoless double beta decay is studied, assuming normal and inverse hierarchies for Majorana neutrino masses. For normal hierarchy the crucial dependence on U_{e3} is explored. The link with tritium beta decay is also briefly discussed.
If the electron neutrino has an effective nonzero Majorana mass, then neutrinoless double beta decay will occur. However, the latter is possible also with a negligible neutrino mass. We show how this may happen in a simple model of scalar diquarks and dileptons. This possibility allows neutrino masses to be small and hierarchical, without conflicting with the possible experimental evidence of neutrinoless double beta decay.
Inspired by the recent HEIDELBERG-MOSCOW double beta decay experiment, we discuss the neutrinoless double beta decay in the supersymmetric seesaw model. Our numerical analysis indicates that we can naturally explain the data of the observed neutrinoless double beta decay, as well as that of the solar and atmospheric neutrino experiments with at least one Majorana-like sneutrino of middle energy scale in the model.
In a class of left-right symmetric models for linear seesaw, a neutrinoless double beta decay induced by the left- and right-handed charged currents together will only depend on the breaking details of left-right and electroweak symmetries. This neutrinoless double beta decay can reach the experimental sensitivities if the right-handed charged gauge boson is below the 100 TeV scale.
Indirect support for the evidence of neutrinoless double beta decay reported recently, is obtained by analysis of other Ge double beta experiments, which yield independent information on the background in the region of Q_(beta-beta). Some statistical features as well as background simulations with GEANT 4 of the HEIDELBERG-MOSCOW experiment are discussed which disprove recent criticism.
A brief overview is given of theoretical analyses with neutrinoless double beta decay experiments. Theoretical bounds on the ``observable'', <m>_betabeta, are presented. By using experimental bounds on <m>_betabeta, allowed regions are obtained on the m_l-cos{2theta_12} plane, where m_l stands for the lightest neutrino mass. It is shown that Majorana neutrinos can be excluded by combining possible results of future neutrinoless double beta decay and {}^3H beta decay experiments. A possibility to constrain one of two Majorana phases is discussed also.
We have examined Lorentz invariance and equivalence principle violations in the neutrino sector as manifested in neutrinoless double beta decay. We conclude that this rare decay cannot provide a useful view of these exotic processes.
We treat 0+ -> 2+ neutrinoless double beta decays taking into account recoil corrections to the nuclear currents. The decay probability can be written as a quadratic form of the effective coupling constants of the right-handed leptonic currents and the effective neutrino mass. We calculate the nuclear matrix elements for the 0+ -> 2+ neutrinoless double beta decays of 76Ge and 100Mo, and demonstrate that the relative sensitivities of 0+ -> 2+ decays to the neutrino mass and the right-handed currents are comparable to those of 0+ -> 0+ decays.
The effective Majorana neutrino mass is evaluated by using the latest results of neutrino oscillation experiments. The problems of the neutrino mass spectrum,absolute mass scale of neutrinos and the effect of CP phases are addressed. A connection to the next generation of the neutrinoless double beta decay (0nbb-decay) experiments is discussed. The calculations are performed for 76Ge, 100Mo, 136Xe and 130Te by using the advantage of recently evaluated nuclear matrix elements with significantly reduced theoretical uncertainty. An importance of observation of the 0nbb-decay of several nuclei is …
One possible probe to physics beyond the standard model is to look for scalar bilinears, which couple to two fermions of the standard model. We point out that the scalar bilinears allow new diagrams contributing to the neutrinoless double beta decay. The upper bound on the neutrinoless double beta decay lifetime would then give new constraints on the ratio of the masses of these scalars to their couplings to the fermions.
We explain excess events near the endpoints of the double beta decay spectra of several elements, using the neutrinoless emission of massless Goldstone bosons. Models with scalars carrying lepton number $-2$ are proposed for this purpose so that ordinary neutrinoless double beta decay is forbidden, and we can raise the scale of global symmetry breaking above the 10 keV scale needed for observable emission of conventional Majorons in double beta decay. The electron spectrum has a different shape, and the rate depends on different nuclear matrix elements, than for the emission of ordinary Majoro…
Motivated by recent intensive experimental efforts on searching for neutrinoless double beta decays, we present a detailed quantitative analysis on the prospect of resolving neutrino mass ordering in the next generation $^{76}$Ge-type experiments.
Neutrinoless double beta decay violates lepton number by two units, a positive observation therefore necessarily implies physics beyond the standard model. Here, three possible contributions to neutrinoless double beta decay are briefly reviewed: (a) The mass mechanism and its connection to neutrino oscillations; (b) Left-right symmetric models and the lower limit on the right-handed W boson mass; and (c) R-parity violating supersymmetry. In addition, the recently published ``extended black box'' theorem is briefly discussed. Combined with data from oscillation experiments this theorem provide…
The problem of Majorana neutrino mass generated in Arkani-Hamed--Dimopoulos-Dvali model with n extra spatial dimensions is discussed. Taking into account constraints on neutrino masses coming from cosmological observations, it is possible to obtain lower limits on the size of extra dimensions as large as 10^{-6} mm. In the case of n=4 it is easy to lower the fundamental scale of gravity from the Planck energy to electroweak scale TeV without imposing any additional constraints. A link between the half-life of neutrinoless double beta decay and the size of extra dimensions is discussed.
Taking account of possible CP violation, we discuss about the constraints on the lepton mixing angles from the neutrinoless double beta decay and from the neutrino oscillation for the three flavour Majorana neutrinos. From the CHORUS oscillation experiment, combined with the data of neutrinoless double beta decay, we show that the large angle solution of (θ_{23}) is improbable if the neutrino mass (m_3) of the third generation is a candidate of hot dark matters.
We study the relation between the Majorana neutrino mass matrices and the neutrinoless double beta decay when CP is not conserved. We give an explicit form of the decay rate in terms of a rephasing invariant quantity and demonstrate that in the presence of CP violation it is impossible to have vanishing neutrinoless double beta decay in the case of two neutrino generations (or when the third generation leptons do not mix with other leptons and hence decouple).
We discuss the relation between lepton number violation at high and low energies, particularly, the constraints on baryogenesis models, which would be implied by an observation of neutrinoless double beta decay. The primordial baryon asymmetry can be washed out by effective lepton number violating operators triggering neutrinoless double beta decay in combination with sphaleron processes. A generic conclusion is that popular models of baryogenesis are excluded if a non-standard mechanism of neutrinoless double beta decay, i.e., other than the standard light neutrino exchange, is observed. Apar…
The neutrinoless double $β$-decay of nuclei is reviewed. We discuss neutrino mixing and 3x3 PMNS neutrino mixing matrix. Basic theory of neutrinoless double $β$-decay is presented in some details. Results of different calculations of nuclear matrix element are discussed. Experimental situation is considered. The Appendix is dedicated to E. Majorana (brief biography and his paper in which the theory of Majorana particles is given)
We illustrate the graphical method that gives the constraints on the parameters appearing in the neutrino oscillation experiments and the neutrinoless double beta decay. This method is applicable in three and four generations. Though this method is valid for more general case, we examine explicitly the cases in which the CP violating factors take $\pm 1$ or $\pm i$ in the neutrinoless double beta decay for illustrative clearance. We also discuss some mass matrix models which lead to the above CP violating factors.
Associated with two TeV-scale leptoquark scalars, a dark matter fermion which is the neutral component of an isotriplet can mediate a testable neutrinoless double beta decay at one-loop level. The dark matter fermion with determined mass and spin-independent scattering can be verified by the future dark matter direct detection experiments. We also discuss the implications on neutrino masses and baryon asymmetry.
The present experimental status in the search for neutrinoless double beta decay is reviewed, with emphasis on the first indication for neutrinoless double beta decay found in the HEIDELBERG-MOSCOW experiment, giving first evidence for lepton number violation and a Majorana nature of the neutrinos. Future perspectives of the field are briefly outlined.
It is shown that, in the framework of the scheme with three-neutrino mixing and a mass hierarchy, the results of neutrino oscillation experiments imply an upper bound of about 10^{-2} eV for the effective Majorana mass in neutrinoless double-beta decay. The schemes with four massive neutrinos are also briefly discussed.
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…
Observation of the neutrinoless double beta decay ($\0n$) has established that there is lepton number violation in nature and the neutrino masses are Majorana in nature. It also gives the absolute mass of the neutrinos and discriminates between different models of neutrino masses. The allowed amount of lepton number violation puts severe constraints on some possible new physics beyond the standard model. The recent results from WMAP are consistent with the consequences of the neutrinoless double beta decay. They improve some of these constraints very marginally, which we shall summarise here. …
Neutrinoless double beta decay data together with information on the absolute neutrino masses obtained from the future KATRIN experiment and/or astrophysical measurements give a chance to find CP violation in the lepton sector with Majorana neutrinos. We derive and discuss necessary conditions which make discovery of such CP violation possible for the future neutrino oscillation and mass measurements data.
The Minimal Supersymmetric Standard Model with gauge mediated supersymmetry breaking and trilinear R-parity violation is applied to the description of neutrinoless double beta decay. A detailed study of limits on the parameter space coming from the B to (X,gamma) processes by using the recent CLEO results is performed. The importance of two-nucleon and pion-exchange realizations of neutrinoless double beta decay together with gluino and neutralino contributions to this process are addressed. We have deduced new limits on the trilinear R-parity breaking parameter lambda_{111}' from the non-obse…
Neutrinoless double beta decay is the most powerful tool to probe not only for Majorana neutrino masses but for lepton number violating physics in general. We discuss relations between lepton number violation, double beta decay and neutrino mass, review a general Lorentz invariant parametrization of the double beta decay rate, highlight a number of different new physics models showing how different mechanisms can trigger double beta decay, and finally discuss possibilities to discriminate and test these models and mechanisms in complementary experiments.
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…
The predictions for the effective Majorana mass |<m>| in neutrinoless double-beta decay in the case of 3-neutrino mixing and massive Majorana neutrinos are reviewed. The physics potential of the experiments, searching for neutrinoless double-beta decay and having sensitivity to $|<m>| \gtap 0.01$ eV, for providing information on the type of the neutrino mass spectrum, on the absolute scale of neutrino masses and on the Majorana CP-violation phases in the PMNS neutrino mixing matrix is also discussed.
The constraints on baryogenesis models obtained from an observation of neutrinoless double beta decay are discussed. The lepton number violating processes, which can underlie neutrinoless double beta decay, would together with sphaleron processes, which are effective in a wide range of energies, wash out any primordial baryon asymmetry of the universe. Typically, if a mechanism of neutrinoless double beta decay other than the standard light neutrino exchange is observed, typical scenarios of high-scale baryogenesis will be excluded. This can be achieved by different methods, e.g. through the o…
We consider the scheme with mixing of three neutrinos and a mass hierarchy. We shown that, under the natural assumptions that massive neutrinos are Majorana particles and there are no unlikely fine-tuned cancellations among the contributions of the different neutrino masses, the results of solar neutrino experiments imply a lower bound for the effective Majorana mass in neutrinoless double-beta decay. We also discuss briefly neutrinoless double-beta decay in schemes with mixing of four neutrinos. We show that one of them is favored by the data.
In this work we show that the implementation of spontaneous breaking of the lepton number in the 3-3-1 model with right-handed neutrinos gives rise to fast neutrino decay with majoron emission and generates a bunch of new contributions to the neutrinoless double beta decay.
We discuss the impact of the observation of neutrinoless double beta decay on the washout of lepton number in the early universe. Neutrinoless double beta decay can be triggered by a large number of mechanisms that can be encoded in terms of Standard Model effective operators which violate lepton number by two units. We calculate the contribution of such operators to the rate of neutrinoless double beta decay and correlate it with the washout of lepton number induced by the same operators in the early universe. We find that the observation of a non-standard contribution to neutrinoless double …
We give predictions for the neutrinoless double beta decay rate in a simple variant of the A_4 family symmetry model. We show that there is a lower bound for the neutrinoless double beta decay amplitude even in the case of normal hierarchical neutrino masses, corresponding to an effective mass parameter |m_{ee}| >= 0.17 \sqrt{Δm^2_{ATM}}. This result holds both for the CP conserving and CP violating cases. In the latter case we show explicitly that the lower bound on |m_{ee}| is sensitive to the value of the Majorana phase. We conclude therefore that in our scheme, neutrinoless double beta dec…
The constraints from the non-observation of neutrinoless double beta decay on the violations of Lorentz invariance (VLI) or violations of the equivalence principle (VEP) have recently been re-examined (hep-ph/9904298) and it was claimed that the constraints are not valid. In this reply we point out that this statement is not correct and prove that the arguments given are wrong.
We discuss a consistency test which makes it possible to discriminate unknown nuclear background lines from neutrinoless double beta decay with only one isotope. By considering both the transition to the ground state and to the first excited $0^+$ state, a sufficiently large detector can reveal if neutrinoless double beta decay or some other nuclear physics process is at work. Such a detector could therefore simultaneously provide a consistency test for a certain range of Majorana masses and be sensitive to lower values of the effective Majorana mass.
We examine the pion realization of the short ranged supersymmetric (SUSY) mechanism of neutrinoless double beta decay. It originates from the R-parity violating quark-lepton interactions of the SUSY extensions of the standard model of the electroweak interactions. We argue that pions are dominant SUSY mediators in neutrinoless double beta decay. The corresponding nuclear matrix elements for various isotopes are calculated within the proton-neutron renormalized quasiparticle random phase approximation. We define those isotopes which are most sensitive to the SUSY signal and outlook the present …
We consider recently observed neutrinoless double beta decay in the context of the minimal supersymmetric standard model with R-parity violating couplings lambda^{'}. We observe that most of the current experimental bounds on the R-parity violating couplings do not exclude the possibility that the neutrinoless double beta decay is caused by R-parity violation. But if we consider K-bar{K} oscillation, we observe that we have to make the R-parity violating couplings generation-dependent to accomodate with the observed neutrinoless double beta decay. And furthermore, we need some mechanism to can…
We show that, in the framework of a general model with mixing of three Majorana neutrinos and a neutrino mass hierarchy, the results of the Bugey and Krasnoyarsk reactor neutrino oscillation experiments imply strong limitations for the effective Majorana mass |<m>| that characterizes the amplitude of neutrinoless double beta decay. We obtain further limitations on |<m>| from the data of the atmospheric neutrino experiments. We discuss the possible implications of the results of the future long baseline neutrino oscillation experiments for neutrinoless double beta decay.
We prove a low-energy theorem valid for any model of weak scale softly broken supersymmetry. It claims that the neutrino Majorana mass, the B-L violating mass of the sneutrino and the neutrinoless double beta decay amplitude are intimately related to each other such that if one of them is non-zero the other two are also non-zero and, vice versa, if one of them vanishes the other two vanish as well. The theorem is a consequence of the underlying supersymmetry and independent of the mechanisms of neutrinoless double beta decay and (s-)neutrino mass generation.
We examine the prospects of detecting an analogous process of neutrinoless double beta decay at a neutrino factory from a high energy muon storage ring. Limits from LEP experiments, neutrinoless double beta decay as well as from global fits have to be incorporated and severely restrict the results. We investigate what limits on light and heavy effective Majorana neutrino masses can be obtained and compare them with existing ones. Discussed are also contributions from right-handed neutrinos and purely right-handed interactions. Other ``new physics'' contributions to the same final state might p…
We discuss the rare decay of the top quark into a pair of same charge leptons (with identical or different flavors), a b quark and a (real or virtual) W-. The above process proceeds only if the exchanged neutrino N is of the Majorana type. This decay is the neutrinoless double b decay of the top. We find measurable values for its rate at the LHC with luminosity of 100 inverse fb. Furthermore, we consider an interaction of charged Higgs bosons with N which leads to lepton number violating processes such as pp to l+ N to l+ l+ H-, exhibiting spectacular events of the type: l+ l+ b b(bar) + 2 jet…
We study the neutrinoless double beta decay in the colored Zee-Babu model. We consider three cases of the colored Zee-Babu model with a leptoquark and a diquark introduced. The neutrino masses are generated at two-loop level, and the constraints given by tree-level flavor violation processes and muon anomalous magnetic moment $(g-2)_μ$ have been considered. In our numerical analysis, we find that the standard light neutrino exchange contribution can be canceled by new physics contribution under certain assumption and condition, leading to a hidden neutrinoless double beta decay. The condition …
The various mechanisms for neutrinoless double beta decay in gauge theories are reviewed and the present experimental data is used to set limits on physics scenarios beyond the standard model. The positive indications for nonzero neutrino masses in various experiments such as those involving solar, atmospheric and accelerator neutrinos are discussed and it is pointed out how some neutrino mass textures consistent with all data can be tested by the ongoing double beta decay experiments. Finally, the outlook for observable neutrinoless double beta decay signal in grand unified theories is discus…
A new mechanism for neutrinoless double beta ($\znbb$) decay based on leptoquark exchange is discussed. Due to the specific helicity structure of the effective four-fermion interaction this contribution is strongly enhanced compared to the well-known mass mechanism of $\znbb$ decay. As a result the corresponding leptoquark parameters are severely constrained from non-observation of $\znbb$-decay. These constraints are more stringent than those derived from other experiments.
From the standard seesaw mechanism of neutrino mass generation, which is based on the assumption that the lepton number is violated at a large (~10exp(+15) GeV) scale, follows that the neutrinoless double-beta decay is ruled by the Majorana neutrino mass mechanism. Within this notion, for the inverted neutrino-mass hierarchy we derive allowed ranges of half-lives of the neutrinoless double-beta decay for nuclei of experimental interest with different sets of nuclear matrix elements. The present-day results of the calculation of the neutrinoless double-beta decay nuclear matrix elements are bri…
Assuming 3-neutrino mixing and massive Majorana neutrinos, we analyze the possibility of establishing the existence of CP-violation associated with Majorana neutrinos in the lepton sector i) by measuring of the effective Majorana mass |<m>| in neutrinoless double beta-decay with a sufficient precision and ii) by measuring of, or obtaining a stringent upper limit on, the lightest neutrino mass m1. Information on m1 can be obtained in the tritium beta decay experiment KATRIN and from astrophysical and cosmological observations. Proving that the indicated CP-violation takes place requires, in par…
