Search

We calculate nuclear matrix elements (NME) of neutrinoless double beta decay in four different candidate nuclei (Ge-76, Se-82, Mo-100, Te-130) within the quasiparticle random phase approximation (QRPA) and its uncertainties. We assume (up to) four coexisting mechanisms for neutrinoless double beta decay, mediated by light Majorana neutrino exchange, heavy Majorana neutrino exchange, R-parity breaking supersymmetry, and squark-neutrino, interfering either constructively or destructively with each other. We find that, unfortunately, current NME uncertainties appear to prevent a robust determination of the relative contribution of each mechanism to the decay amplitude, even assuming accurate measurements of decay lifetimes. The near-degeneracy of the decay mechanisms is analyzed with simple algebraic techniques, which do not involve assumptions about the statistical distribution of errors. We discuss implications of such degeneracy on prospective searches for absolute neutrino masses., Comment: Expanded discussion and bibliography; to appear in Phys. Rev. D

We have investigated neutron-proton (np) pairing in light nuclei (2p-lf shell) using a specialized Hartree-Fock-Bogoliubov (HFB) method. For the pairing interaction we used the constant Kisslinger-Sorensen interaction and the realistic G -matrix obtained by solving the Bethe-Goldstone equation with the Bonn one-boson-exchange potential. Our results show that there are at least two minima of the total energy corresponding to two solutions of the HFB equation. The lower solution shows large np pairing. This is confirmed by a recent empirical determination of the np pairing gap, which turns out to be surprisingly large in agreement with our theoretical result. If one renormalizes the Brueckner reaction matrix elements of the Bonn potential by a factor g np multiplying the neutron-proton particle-particle matrix elements to reproduce the experimental np gaps δ np , one obtains large T = 1 np pairing. Preliminary results indicate that the np pairing increases even more if particle-number projection is included. These effects are expected to affect strongly the double-beta decay. The 2 v double-beta decay in 20 48 Ca 28 → 22 48 Ti 26 is calculated. The Gamow-Teller matrix elements are reduced remarkably by the large np pairing compared to the results without np pairing. The sensitivity of the 2 tv double-beta decay transition on the particle-particle force strength parameter g pp is also reduced compared with the results without np pairing correlations.

It is well known that there exist many mechanisms that may contribute to neutrinoless double beta decay. By exploiting the fact that the associated nuclear matrix elements are target dependent we show that, given definite experimental results on a sufficient number of targets, one can determine or sufficiently constrain all lepton violating parameters including the mass term. As a specific example we show that, assuming the observation of the $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay in three different nuclei, e.g., $\mathrm{G}^{76}\mathrm{e}$, $^{100}\mathrm{Mo}$, and $^{130}\mathrm{Te}$, and just three lepton number violating mechanisms (light- and heavy-neutrino mass mechanisms as well as the $R$-parity breaking supersymmetry mechanism) being active, there are only four different solutions for the lepton violating parameters, provided that they are relatively real. In particular, our analysis shows that the effective neutrino Majorana mass $|{m}_{\ensuremath{\beta}\ensuremath{\beta}}|$ can be almost uniquely extracted by utilizing other existing constraints (cosmological observations and tritium $\ensuremath{\beta}$-decay experiments). We also point out the possibility that the nonobservation of the $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay for some isotopes could be in agreement with a value of $|{m}_{\ensuremath{\beta}\ensuremath{\beta}}|$ in the sub-eV region. We thus suggest that it is important to have at least two different $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$-decay experiments for a given nucleus. We note that obtained results are sensitive to the accuracy of measured half-lives and to uncertainties in calculated nuclear matrix elements.

In the search for the nuclide with the largest probability for neutrinoless double-electron capture, we have determined the ${Q}_{ϵϵ}$ value between the ground states of $^{152}\mathrm{Gd}$ and $^{152}\mathrm{Sm}$ by Penning-trap mass-ratio measurements. The new ${Q}_{ϵϵ}$ value of 55.70(18) keV results in a half-life of ${10}^{26}\text{ }\text{ }\mathrm{yr}$ for a 1 eV neutrino mass. With this smallest half-life among known $0\ensuremath{\nu}ϵϵ$ transitions, $^{152}\mathrm{Gd}$ is a promising candidate for the search for neutrinoless double-electron capture.

The process of neutrinoless double electron capture ($0\nu$ECEC) is revisited for those cases where the two participating atoms are nearly degenerate in mass. The theoretical framework is the formalism of an oscillation of two atoms with different total lepton number (and parity), one of which can be in an excited state so that mass degeneracy is realized. In such a case and assuming light Majorana neutrinos, the two atoms will be in a mixed configuration with respect to the weak interaction. A resonant enhancement of transitions between such pairs of atoms will occur, which could be detected by the subsequent electromagnetic de-excitation of the excited state of the daughter atom and nucleus. Available data of atomic masses, as well as nuclear and atomic excitations are used to select the most likely candidates for such resonant $0\nu$ECEC transitions. Assuming an effective mass for the Majorana neutrino of 1 eV, some half-lives are predicted to be as low as $10^{22}$ years in the unitary limit. It is argued that, in order to obtain more accurate predictions for the $0\nu$ECEC half-lives, precision mass measurements of the atoms involved are necessary, which can readily be accomplished by today's high precision Penning traps. Further advancements also require a better understanding of high-lying excited states of the final nuclei (i.e. excitation energy, angular momentum and parity) and the calculation of the nuclear matrix elements., Comment: 35 pages LaTeX, 2 eps figures, 5 tables; Sect. 3.6 extended, references to recent papers added, replaced with published version

A microscopic state-of-the-art calculation of the nuclear matrix element for neutrinoless double-$\ensuremath{\beta}$ decay of $^{150}\mathrm{Nd}$ with an account for nuclear deformation is performed. The proton-neutron quasiparticle random phase approximation (QRPA) with a realistic residual interaction [the Brueckner $G$ matrix derived from the charge-dependent Bonn (Bonn-CD) nucleon-nucleon potential] is used as the underlying nuclear structure model. The present calculated matrix element is suppressed by about $40%$ as compared with our previous QRPA result for $^{150}\mathrm{Nd}$ obtained with neglect of deformation. By making use of this newest nuclear matrix element, one may conclude that neutrinoless double-$\ensuremath{\beta}$ decay of $^{150}\mathrm{Nd}$, to be measured soon by the SNO$+$ collaboration, provides one of the best probes of the Majorana neutrino mass.

We have constructed a GEANT4-based detailed software model of photon transport in plastic scintillator blocks and have used it to study the NEMO-3 and SuperNEMO calorimeters employed in experiments designed to search for neutrinoless double beta decay. We compare our simulations to measurements using conversion electrons from a calibration source of $\rm ^{207}Bi$ and show that the agreement is improved if wavelength-dependent properties of the calorimeter are taken into account. In this article, we briefly describe our modeling approach and results of our studies., Comment: 16 pages, 10 figures

The development of BiPo detectors is dedicated to the measurement of extremely high radiopurity in (TI)-T-208 and Bi-214 for the SuperNEMO double beta decay source foils. A modular prototype, called BiPo-1, with 0.8 m(2) of sensitive surface area, has been running in the Modane Underground Laboratory since February, 2008. The goal of BiPo-1 is to measure the different components of the background and in particular the surface radiopurity of the plastic scintillators that make up the detector. The first phase of data collection has been dedicated to the measurement of the radiopurity in (TI)-T-208. After more than one year of background measurement, a surface activity of the scintillators of A((TI)-T-208) = 1.5 μBq/m(2) is reported here. Given this level of background, a larger BiPo detector having 12 m(2) of active surface area, is able to qualify the radiopurity of the SuperNEMO selenium double beta decay foils with the required sensitivity of A((TI)-T-208), The authors would like to thank the Modane Underground Laboratory staff for their technical support in running BiPo-1, and the IN2P3 Computing Center in Lyon for its software and computing support. This work was supported by the French Grant ANR-06-BLAN-0299 funded by the Agence Nationale de la Recherche, by the Spanish MICINN for the FPA2007-62833, FPA2008-03456 and FPA2006-12120-003 contracts, part of which comes from FEDER funds, by the Russian RFBR 09-02-00737 Grant and by the UK STFC.

The $2\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$-decay running sums for $^{76}\mathrm{Ge}$ and $^{150}\mathrm{Nd}$ nuclei are calculated within a QRPA approach with account for deformation. A realistic nucleon-nucleon residual interaction based on the Brueckner $G$ matrix (for the Bonn CD force) is used. The influence of different model parameters on the functional behavior of the running sums is studied. It is found that the parameter ${g}_{\mathit{pp}}$ renormalizing the $G$ matrix in the QRPA particle-particle channel is responsible for a qualitative change in behavior of the running sums at higher excitation energies. For realistic values of ${g}_{\mathit{pp}}$ a significant negative contribution to the total $2\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$-decay matrix element is found to come from the energy region of the giant Gamow-Teller resonance. This behavior agrees with results of other authors.

The methods used till now to calculate the neutrinoless double beta decay matrix elements are: the Quasiparticle Random Phase Approximation (QRPA), the Shell Model (SM), the angular momentum projected Hartee-Fock-Bogoliubov approach (HFB) and the Interacting Boson Model (IBM). The different approaches are compared specifically concerning the the angular momenta and parities of the neutron pairs, which are changed into two protons by the $0\nu\beta\beta$ decay. The QRPA and SM involve about the same angular momentum and parity neutron pairs, while the HFB is restricted to $0^{+}, 2^{+}, 4^{+}, ...$, and IBM to $0^{+}$ and $2^{+}$ nucleon pairs. The differences in the seniority contributions for the QRPA and the SM are discussed., Comment: 14 pages, 8 figures, extensively revised to discuss the effect of different seniorities, 1 figure and 2 tables added

The possibility to probe new physics scenarios of light Majorana neutrino exchange and right-handed currents at the planned next generation neutrinoless double beta decay experiment SuperNEMO is discussed. Its ability to study different isotopes and track the outgoing electrons provides the means to discriminate different underlying mechanisms for the neutrinoless double beta decay by measuring the decay half-life and the electron angular and energy distributions., The authors would like to thank H. Pas, M. Hirsch, E. Lisi, V. Rodin and A. Faessler for useful discussions. We acknowledge support by the Grants Agencies of France, the Czech Republic, RFBR (Russia), STFC (UK), MICINN (Spain), NSF, DOE, and DOD (USA). We acknowledge technical support from the staff of the Modane Underground Laboratory (LSM).

The half-life for double-{beta} decay of {sup 150}Nd has been measured by the NEMO-3 experiment at the Modane Underground Laboratory. Using 924.7 days of data recorded with 36.55 g of {sup 150}Nd, we measured the half-life for 2{nu}{beta}{beta} decay to be T{sub 1/2}{sup 2{nu}}=(9.11{sub -0.22}{sup +0.25}(stat.){+-}0.63(syst.))x10{sup 18} yr. The observed limit on the half-life for neutrinoless double-{beta} decay is found to be T{sub 1/2}{sup 0{nu}}>1.8x10{sup 22} yr at 90% confidence level. This translates into a limit on the effective Majorana neutrino mass of

Theories beyond the standard model include a number of new particles some of which might be light and weakly coupled to ordinary matter. Such particles affect equation of state of nuclear matter and can shift admissible masses of neutron stars to higher values. The internal structure of neutron stars is modified provided the ratio between coupling strength and mass squared of a weakly interacting light boson is above $g^2/\mu^2 \sim 25 ~\mathrm{GeV}^{-2}$. We provide limits on the couplings with the strange sector, which cannot be achieved from laboratory experiments analysis. When the couplings to the first family of quarks is considered the limits imposed by the neutron stars are not more stringent than the existing laboratory ones. The observations on neutron stars give evidence that equation of state of the $\beta$-equilibrated nuclear matter is stiffer than expected from many-body theory of nuclei and nuclear matter. A weakly interacting light vector boson coupled predominantly to the second family of the quarks can produce the required stiffening., Comment: 5 pages REVTeX, 2 pdf figures

Using 9.4 g of Zr-96 and 1221 days of data from the NEMO-3 detector corresponding to 0.031 kg yr, the obtained 2vbb decay half-life measurement is [2.35 +/- 0.14(stat) +/- 0.16(syst)] x 10^19 yr. Different characteristics of the final state electrons have been studied, such as the energy sum, individual electron energy, and angular distribution. The 2v nuclear matrix element is extracted using the measured 2vbb half-life and is 0.049 +/- 0.002. Constraints on 0vbb decay have also been set., Published in Nucl.Phys.A (10 pages, 10 figures)

The variances and covariances associated to the nuclear matrix elements of neutrinoless double beta decay ($0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$) are estimated within the quasiparticle random phase approximation. It is shown that correlated nuclear matrix elements uncertainties play an important role in the comparison of $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay rates for different nuclei, and that they are degenerate with the uncertainty in the reconstructed Majorana neutrino mass.

The measured occupancies of valence orbits in 76Ge and 76Se are used as a guideline for modification of the effective mean field energies that results in better description of these quantities. With them, in combination with the self-consistent renormalized quasiparticle random phase approximation (SRQRPA) method that ensures conservation of the mean particle number in the correlated ground state, we show that the resulting 0νββ nuclear matrix element for the 76Ge-->76Se transition is reduced by ~25% compared to the previous QRPA value, and therefore the difference between the present approach and the interacting shell model predictions becomes correspondingly smaller. Analogous modification of the mean field energies for the A=82 system also results in a reduction of 0νββ matrix element for the 82Se-->82Kr transition, making it also closer to the shell model prediction.

In this paper a microscopic approach to calculation of the nuclear matrix element ${M}^{0\ensuremath{\nu}}$ for neutrinoless double-$\ensuremath{\beta}$ decay with an account for nuclear deformation is presented in length and applied for $^{76}\mathrm{Ge}$, $^{150}\mathrm{Nd}$, and $^{160}\mathrm{Gd}$. The proton-neutron quasiparticle random-phase approximation with a realistic residual interaction (the Brueckner $G$ matrix derived from the charge-depending Bonn nucleon-nucleon potential) is used as the underlying nuclear structure model. The effects of the short-range correlations and the quenching of the axial vector coupling constant ${g}_{A}$ are analyzed. The results suggest that neutrinoless double-$\ensuremath{\beta}$ decay of $^{150}\mathrm{Nd}$, to be measured soon by the SNO$+$ Collaboration, may provide one of the best probes of the Majorana neutrino mass. This confirms our preliminary conclusion in Fang et al. [Phys. Rev. C 82, 051301(R) (2010)].

The nuclear matrix elements M0v of the neutrinoless double beta decay (0vββ‐decay) are systematically evaluated using the self‐consistent renormalized quasiparticle random phase approximation (SRQRPA). The residual interaction and the two‐nucleon short‐range correlations are derived from the charge‐dependent Bonn (CD‐Bonn) potential. The importance of further progress in the calculation of the 0vββ‐decay nuclear matrix elements is stressed.

Neutrinos are probably one of the most important structural constituents of the Universe. The Big Bang Theory predicts that the significant component of them is formed by the cosmic neutrino background, an analogues of the big bang relic photons comprising the cosmic microwave background radiation, which has been measured with amazing accuracy. Properties of the relic neutrino background are closely related to the ones of the cosmic microwave radiation. Relic neutrinos pervade space, but their temperature is extremely small, being of the order of 0.1 meV. Although belonging to the most abundant particles of the Universe, the relic neutrinos evade direct detection so far. This is because the low‐energy neutrinos interact only very weakly with matter. In this contribution, we explore the feasibility to detect the cosmic neutrino background by means of β‐decaying (3H and 187Re) and double beta decaying (100Mo) nuclei. In addition, we address the question whether double relic neutrino capture on nuclei can be...

The TGV II (Telescope Germanium Vertical) facility is a low background spectrometer operated in Modane Underground Laboratory (France). It aims at the study of double beta electron capture of 106Cd. The spectrometer is composed of 32 HPGe planar detectors (total mass of Ge ∼3 kg) interleaved with thin-foil samples made of enriched 106Cd. In 2007 the Phase I of the experiment (1 year measurement) was finished and the new limit on half-life for two-neutrino double electron capture (g.s. → g.s.) of 106Cd was obtained as 3.2 × 1020 years. This limit is significantly higher (by almost three orders of magnitude) than those already published. From December 2007 the Phase II of the experiment continues with more enriched material (13.6 grams instead of 8 grams) and with significantly suppressed background of the cryostat.

At the quark level there are basically two types of contributions of $R$-parity violating supersymmetry (${\mathrm{R\ensuremath{\llap{\not\;}}}}_{p}$ SUSY) to neutrinoless double beta decay: the short-range contribution involving only heavy virtual superpartners and the long-range one with the virtual squark and neutrino. Hadronization of the effective operators, corresponding to these two types of contributions, may in general involve virtual pions in addition to close on-mass-shell nucleons. From the previous studies it is known that the short-range contribution is dominated by the pion exchange. In the present paper we show that this is also true for the long-range ${\mathrm{R\ensuremath{\llap{\not\;}}}}_{p}$ SUSY contribution. Therefore, we conclude that the ${\mathrm{R\ensuremath{\llap{\not\;}}}}_{p}$ SUSY contributes to the neutrinoless double beta decay dominantly via charged pion exchange between the decaying nucleons.

We present the relativistic calculation of the beta-decay of tritium in a hadron model. The elementary particle treatment of the transition 3H -> 3He + e^- + nu_e is performed in analogy with the description of the beta-decay of neutron. The effects of higher order terms of hadron current and nuclear recoil are taken into account in this formalism. The relativistic Kurie function is derived and presented in a simple form suitable for the determination of neutrino masses from the shape of the endpoint spectrum. A connection with the commonly used Kurie function is established., 6 pages, 1 figure

We show that, within the quasiparticle random phase approximation (QRPA) and the renormalized QRPA (RQRPA) based on the Bonn-CD nucleon-nucleon interaction, the competition between the pairing and the neutron-proton particle-particle and particle-hole interactions causes contributions to the neutrinoless double-beta decay matrix element to nearly vanish at internucleon distances of more than 2 or 3 fermis. As a result, the matrix element is more sensitive to short-range/high-momentum physics than one naively expects. We analyze various ways of treating that physics and quantify the uncertainty it produces in the matrix elements, with three different treatments of short-range correlations.

The recently proposed Fully-Renormalized QRPA (FR-QRPA), which fullfils the Ikeda sum rule (ISR) exactly, is applied to the two-neutrino double beta decay of 76 Ge, 82 Se, 100 Mo, 116 Cd, 128 Te and 130 Xe. The results obtained are compared with those of other approaches, standard QRPA and self-consistent QRPA (SCQRPA). The similarities and the differences among the methods are discussed. The influence of the restoration of the Ikeda sum rule on the 2���-decay amplitude is analyzed. 21.60.Jz, 23.40.Hc

The status of calculation of the neutrinoless double beta decay (0νββ‐decay) nuclear matrix elements (NME's) is reviewed. The spread of published values of NME's is discussed. The main attention is paid to the recent progress achieved in the evaluation of the 0νββ‐decay NME's in the framework of the quasiparticle random phase approximation (QRPA). The obtained results are compared with those of the nuclear shell model. The problem of reliable determination of the 0νββ‐decay NME's is addressed. The uncertainty in NME's are analyzed and further progress in calculation of the 0νββ‐decay NME's is outlined.

One expects three Cosmic Backgrounds: (1) The Cosmic Microwave Background (CMB) originated 380000 years after the Big Bang (BB). (2) The Neutrino Background decoupled about one second after the BB, while (3) the Cosmic Gravitational Wave Background created by the inflationary expansion decoupled directly after the BB. Only the Cosmic Microwave Background (CMB) has been detected and is well studied. Its spectrum follows Planck's black body radiation formula and shows a remarkable constant temperature of T0γ ≈ 2.7 K independent of the direction. The present photon density is about 370 photons per cm3. The size of the hot spots, which deviates only in the fifth decimal of the temperature from the average value, tells us, that the universe is flat. About 380 000 years after the Big Bang at a temperature of T0γ = 3000 K already in the matter dominated era the electrons combine with the protons and 4He and the photons move freely in the neutral universe and form the CMB. So the temperature and distribution of the photons give us information of the universe 380 000 years after the Big Bang. The Cosmic Neutrino Background (CνB) decoupled from matter already one second after the BB at a temperature of about 1010 K. Today their temperature is ~ 1.95 K and the average density is 56 electron-neutrinos and the total density of all neutrinos about 336 per cm3. Measurement of these neutrinos is an extremely challenging experimental problem which can hardly be solved with the present technologies. On the other hand it represents a tempting opportunity to check one of the key elements of the Big Bang Cosmology and to probe the early stages of the universe. The search for the CνB with the induced beta decay νe+3H → 3He + e− using KATRIN (KArlsruhe TRItium Neutrino experiment) is the topic of this contribution.

The double beta decay of 100Mo to the 0^+_1 and 2^+_1 excited states of 100Ru is studied using the NEMO 3 data. After the analysis of 8024 h of data the half-life for the two-neutrino double beta decay of 100Mo to the excited 0^+_1 state is measured to be T^(2nu)_1/2 = [5.7^{+1.3}_{-0.9}(stat)+/-0.8(syst)]x 10^20 y. The signal-to-background ratio is equal to 3. Information about energy and angular distributions of emitted electrons is also obtained. No evidence for neutrinoless double beta decay to the excited 0^+_1 state has been found. The corresponding half-life limit is T^(0nu)_1/2(0^+ --> 0^+_1) > 8.9 x 10^22 y (at 90% C.L.). The search for the double beta decay to the 2^+_1 excited state has allowed the determination of limits on the half-life for the two neutrino mode T^(2nu)_1/2(0^+ --> 2^+_1) > 1.1 x 10^21 y (at 90% C.L.) and for the neutrinoless mode T^(0nu)_1/2(0^+ --> 2^+_1) > 1.6 x 10^23 y (at 90% C.L.)., 23 pages, 7 figures, 4 tables, submitted to Nucl. Phys

The transition magnetic moments of Majorana neutrinos are calculated in grand unified theory (GUT) constrained Minimal Supersymmetric Standard Model (MSSM) with explicit R-parity violation. It is assumed that neutrinos acquire masses via one-loop (quark-squark and lepton-slepton) radiative corrections. The mixing of squarks, sleptons, and quarks is considered explicitly. The connection between neutrino magnetic moments and the entries of neutrino mass matrix is studied. The current upper limits on neutrino magnetic moments are deduced from the elements of phenomenological neutrino mass matrix, which is reconstructed using the neutrino oscillation data and the lower bound on the neutrinoless double beta decay half-life. Further, the results for transitional magnetic moments of Majorana neutrinos are presented for the cases of inverted and normal hierarchy of neutrino masses and different SUSY scenarios. The largest values are of the order of 10^{-17} in units of Bohr magneton., 12 pages including 1 eps figure

We study the effect of deformation on the two-neutrino double beta decay for ground state to ground state transitions in all the nuclei whose half-lives have been measured. Our theoretical framework is a deformed QRPA based in Woods-Saxon or Hartree-Fock mean fields. We are able to reproduce at the same time the main characteristics of the two single beta branches, as well as the double beta matrix elements. We find a suppression of the double beta matrix element with respect to the spherical case when the parent and daughter nuclei have different deformations.

The NEMO-3 tracking detector is located in the Fr��jus Underground Laboratory. It was designed to study double beta decay in a number of different isotopes. Presented here are the experimental half-life limits on the double beta decay process for the isotopes $^{100}$Mo and $^{82}$Se for different Majoron emission modes and limits on the effective neutrino-Majoron coupling constants. In particular, new limits on "ordinary" Majoron (spectral index 1) decay of $^{100}$Mo ($T_{1/2} > 2.7\cdot10^{22}$ y) and $^{82}$Se ($T_{1/2} > 1.5\cdot10^{22}$ y) have been obtained. Corresponding bounds on the Majoron-neutrino coupling constant are $ < (0.4-1.9) \cdot 10^{-4}$ and $< (0.66-1.7) \cdot 10^{-4}$., 23 pages includind 4 figures, to be published in Nuclear Physics A

Present status of the experiment TGV II which is devoted to the measurement of double-beta decay of 106Cd is given. The low background spectrometer TGV II is installed in the Modane Underground Laboratory and has been running from February 2005 with approx 10 grams of 106Cd enriched at 75%. After an analysis of 3736 hours of experimental data the new improved half-life limit for 2νEC/EC decay of 106Cd (0 g.s. + → 0 g.s. + ) is given as T 1 2/2 > 4.8 × 1019 years (90% CL). The search for 2νEC/EC decay of 106Cd to the excited states of 106Pd allows to determine the limits of the half-lives T 1 2/2 (0 g.s. + → 2 1 + ) > 3.9 × 1019 years (90% CL) and T 1 2/2 (0 g.s. + → 0 1 + ) > 5.8 × 1019 years (90% CL).

Expected event rates for a number of dark matter nuclear targets were calculated in the effective low-energy minimal supersymmetric standard model, provided the lightest neutralino is the dark matter Weakly Interacting Massive Particle (WIMP). These calculations allow direct comparison of sensitivities of different dark matter detectors to intermediate mass WIMPs expected from the measurements of the DArk MAtter (DAMA) experiment., 14 pages, 11 figures, revtex4

We study possible contribution of the Majorana neutrino mass eigenstate $\nu_h$ dominated by a sterile neutrino component to neutrinoless double beta ($0\nu\beta\beta$) decay. From the current experimental lower bound on the $0\nu\beta\beta$-decay half-life of $^{76}$Ge we derive stringent constraints on the $\nu_h-\nu_e$ mixing in a wide region of the values of $\nu_h$ mass. We discuss cosmological and astrophysical status of $\nu_h$ in this mass region., Comment: 6 pages, 1 figure; v2 added comments and references

The NEMO 3 detector, which has been operating in the Frejus underground laboratory since February 2003, is devoted to the search for neutrinoless double beta decay (bb0nu). Half-lives of the two neutrino double beta decays (bb2nu) have been measured for 100Mo and 82Se. After 389 effective days of data collection from February 2003 until September 2004 (Phase I), no evidence for neutrinoless double beta decay was found from ~7kg of 100Mo and ~1 kg of 82Se. The corresponding lower limits for the half-lives are 4.6 x 10^23 years for 100Mo and 1.0 x10^23 years for 82Se (90% C.L.). Depending on the nuclear matrix elements calculation, limits for the effective Majorana neutrino mass are < 0.7-2.8 eV for 100Mo and < 1.7-4.9 eV for 82Se, Comment: 5 pages Submitted to Phys. Rev. Lett

A set of moderately deformed $s-d$ shell nuclei is employed for testing the reliability of the nuclear ground state wave functions which are obtained in the context of a BCS approach and offer a simultaneous consideration of deformation and pairing correlations effects. In this method, the mean field is assumed to be an axially symmetric Woods-Saxon potential and the effective two-body interaction is a monopole pairing force. As quantities of main interest we have chosen the nuclear form factors, the occupancies of the active (surface) orbits and the Fermi sea depletion, which provide quite good tests for microscopic descriptions of nuclei within many body theories. For our comparisons with results emerging from other similar methods, an axially deformed harmonic oscillator field is also utilized., Comment: 20 pages, 12 figures, 2 tables

We have examined the role of proton-neutron pairing on the Quasiparticle Random Phase Approximation (QRPA) by calculating neutrinoless double beta decay matrix elements using the recently proposed full-QRPA, which includes proton-neutron pairing. With this full-QRPA we have performed calculations on the neutrinoless double beta decay matrix elements of the experimentally interesting nuclei A=48, 76, 82, 96, 100, 116, 128, 130 and 136. Using the best presently available experimental limits on the half-time of neutrinoless double beta decay we have extracted new limits on the lepton number violating parameters. We have found that the inclusion of proton-neutron pairing makes the limits on the lepton number non-conserving parameters less stringent.

We study lepton number violating (LNV) process of muon-positron conversion in nuclei mediated by the exchange of light and heavy Majorana neutrinos. Nuclear structure calculations have been carried out for the case of experimentally interesting nucleus 48Ti in the framework of renormalized proton-neutron Quasiparticle Random Phase Approximation. We demonstrate that the imaginary part of the amplitude of light Majorana neutrino exchange mechanism gives an appreciable contribution to the muon-positron conversion rate. This specific feature is absent in the allied case of neutrinoless double beta decay. Using the present neutrino oscillations, tritium beta decay, accelerator and cosmological data we derived the limits on the effective masses of light _{\mu e} and heavy _{\mu e} neutrinos. The expected rates of muon-positron nuclear conversion, corresponding to these limits, were found to be so small that even within a distant future the muon-positron conversion experiments will hardly be able to detect the neutrino signal. Therefore, searches for this LNV process can only rely on the presence of certain physics beyond the trivial extension of the Standard Model by inclusion of massive Majorana neutrinos.

13 pages, 4 tables, 18 figures.-- PACS nrs.: 21.60.Jz; 23.40.Hc; 23.40.Bw., We use a deformed quasiparticle random phase approximation formalism to describe simultaneously the energy distributions of the single β Gamow-Teller strength and the two-neutrino double β decay matrix elements. Calculations are performed in a series of double β decay partners with A=48 , 76, 82, 96, 100, 116, 128, 130, 136, and 150, using deformed Woods-Saxon potentials and deformed Skyrme Hartree-Fock mean fields. The formalism includes a quasiparticle deformed basis and residual spin-isospin forces in the particle-hole and particle-particle channels. We discuss the sensitivity of the parent and daughter Gamow-Teller strength distributions in single β decay, as well as the sensitivity of the double β decay matrix elements to the deformed mean field and to the residual interactions. Nuclear deformation is found to be a mechanism of suppression of the two-neutrino double β decay. The double β decay matrix elements are found to have maximum values for about equal deformations of parent and daughter nuclei. They decrease rapidly when differences in deformations increase. We remark on the importance of a proper simultaneous description of both double β decay and single Gamow-Teller strength distributions. Finally, we conclude that for further progress in the field, it would be useful to improve and complete the experimental information on the studied Gamow-Teller strengths and nuclear deformations., We would like to thank A. A. Raduta for useful discussions. This work was supported by Ministerio de Educación y Ciencia (Spain) under Contract No. BFM2002-03562 and by International Graduiertenkolleg GRK683, by the “Land Baden-Wuerttemberg” within the “Landesforschungsschwerpunkt: Low Energy Neutrinos,” by the DFG under 418SPA112/8/03, the VEGA Grant agency of the Slovac Republic under Contract No. 1/0249/03, and by the EU ILIAS project under Contract No. RII3-CT-2004-506222. One of us (R.A.R.) thanks Ministerio de Educación y Ciencia (Spain) for financial support.

The neutrino masses are generated in grand unified theory (GUT) constrained supersymmetric model with R-parity violation. The neutrinos acquire masses via tree-level neutrino-neutralino mixing as well as via one-loop radiative corrections. The theoretical mass matrix is compared with the phenomenological one, which is reconstructed by using neutrino oscillation and neutrinoless double beta decay data. This procedure allows to obtain significantly stronger constraints on R-parity breaking parameters than those existing in the literature. The implication of normal and inverted neutrino mass hierarchy on the sneutrino expectation values, lepton-Higgs bilinear and trilinear R-parity breaking couplings is also discussed.

We study nuclear {mu}{sup -}-e{sup -} conversion in the general framework of an effective Lagrangian approach without referring to any specific realization of the physics beyond the standard model (SM) responsible for lepton flavor violation (Le {sub f}). We examine the impact of a specific hadronization prescription on the analysis of new physics in nuclear {mu}{sup -}e{sup -} conversion and stress the importance of vector meson exchange between lepton and nucleon currents. A new issue of this mechanism is the presence of the strange quark vector current contribution induced by the {phi} meson. This allows us to extract new limits on the Le {sub f} lepton-quark effective couplings from the existing experimental data.

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 stressed., Comment: 29 pages, 5 figures, EXO (10 t) experiment considered

The recently proposed fully renormalized quasiparticle random-phase approximation (QRPA), which fulfills the Ikeda sum rule exactly, is applied to the two-neutrino double $\ensuremath{\beta}$ decay of $^{76}\mathrm{Ge}$, $^{82}\mathrm{Se}$, $^{100}\mathrm{Mo}$, $^{116}\mathrm{Cd}$, $^{128}\mathrm{Te}$, and $^{130}\mathrm{Xe}$. The results obtained are compared with those of other approaches, standard QRPA and self-consistent QRPA. The similarities and the differences among the methods are discussed. The influence of the restoration of the Ikeda sum rule on the $2\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$-decay amplitude is analyzed.

The nuclear matrix elements M0nu of the neutrinoless double-beta decay (0nubetabeta) are evaluated for 76Ge,100Mo,130Te, and 136Xe within the renormalized quasiparticle random phase approximation (RQRPA) and the simple QRPA. Three sets of single particle level schemes are used, ranging in size from 9 to 23 orbits. When the strength of the particle-particle interaction is adjusted so that the 2nubetabeta decay rate is correctly reproduced, the resulting M0nu values become essentially independent of the size of the basis, and of the form of different realistic nucleon-nucleon potentials. Thus, one of the main reasons for variability of the calculated M0nu within these methods is eliminated.

We examine isovector and isoscalar proton-neutron pairing correlations for the ground state of even-even Ge isotopes with mass number A=64-76 within the deformed BCS approach. For N=Z 64Ge the BCS solution with only T=0 proton-neutron pairs is found. For other nuclear systems (N>Z) a coexistence of a T=0 and T=1 pairs in the BCS wave function is observed. A problem of fixing of strengths of isoscalar and isovector pairing interactions is addressed. A dependence of number of like and unlike pairs in the BCS ground state on the difference between number of neutrons and protons is discussed. We found that for nuclei with N much bigger than Z the effect of proton-neutron pairing is small but not negligible., 24 pages, 6 figures

10 pages, 4 tables, 8 figures.-- PACS nrs.: 23.40.Hc; 21.60.Jz; 27.50.1e.-- ArXiv pre-print available at: http://arxiv.org/abs/nucl-th/0303053v1