Search

It has recently been shown that in the framework of weak-scale softly broken supersymmetry the existence of a Majorana neutrino inevitably implies a finite (B-L)-violating ``Majorana'' mass ${m}_{M}$ for scalar neutrinos, with the effect of splitting the complex sneutrino field into two real fields separated in mass by $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{m}{}_{1}^{2}\ensuremath{-}\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{m}{}_{2}^{2}=2|\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{m}{}_{M}^{2}|$. The existence of a finite Majorana sneutrino mass leads to new processes potentially observable at future colliders. Taking into account existing low-energy constraints, to find positive signals for electron sneutrinos will be very difficult, although not impossible. For muon and tau sneutrinos a dedicated search for Majorana masses has much better prospects.

The modification of the R{sub p}-violating potential in the MSSM when both generation and left-right sfermion mixing are included is discussed. Taking into account squark left-right mixing, decays of charged pions are reexamined in order to derive some new constraints on combinations of {lambda}{sub ijk}{sup {prime}} couplings appearing in the R/{sub p}MSSM. {copyright} {ital 1997} {ital The American Physical Society}

The full setup of the Heidelberg-Moscow double \ensuremath{\beta} decay experiment is presented. This experiment gives at present the most stringent upper bound, improving the neutrino mass limit into the sub-eV range. Out of 19.2 kg of 86% ${\mathrm{enriched}}^{76}$Ge five crystals were grown with a total mass of 11.51 kg. Since February 1995 all five detectors, corresponding to 10.96 kg active mass, are in regular operation in the Gran Sasso underground laboratory, four of them in a common shield. No signal is observed for the neutrinoless double \ensuremath{\beta} decay (0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}). The measured data from the first three enriched detectors with a statistical significance of 13.60 kg yr result in a new half-life limit of ${\mathit{T}}_{1/2}$${(0}^{+}$\ensuremath{\rightarrow}${0}^{+}$)g7.4\ifmmode\times\else\texttimes\fi{}${10}^{24}$ yr (90% C.L.). With this limit a Majorana mass of the neutrinos larger than 0.6 eV (90% C.L.) is excluded. From the data taken in the previously operated setup with three enriched detectors in a common shielding and a statistical significance of 10.58 kg yr new results are extracted for the two neutrino double \ensuremath{\beta} decay (2\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}) ${\mathrm{of}}^{76}$Ge. The procedure of a quantitative and model-independent description of the background via a Monte Carlo simulation is outlined in some detail. The combined result is ${\mathit{T}}_{1/2}^{2\mathrm{\ensuremath{\nu}}}$=[${1.77}_{\mathrm{\ensuremath{-}}0.01}^{+0.01}$${(\mathrm{stat})}_{\mathrm{\ensuremath{-}}0.11}^{+0.13}$(sys)]\ifmmode\times\else\texttimes\fi{}${10}^{21}$ yr. Further on the results concerning new Majoron models and the impact on SUSY parameters are briefly reviewed. Future improvements on the background with the application of digital pulse shape analysis are discussed and an outlook on the future of \ensuremath{\beta}\ensuremath{\beta} research is given.

The sizes of tracks of events of neutrinoless double-beta decay in a Germanium detector depend on particle physics and nuclear physics parameters such as neutrino mass, right-handed current parameters, etc., and nuclear matrix elements. In this paper for the first time Monte Carlo simulations of neutrino-accompanied ($2\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$) and neutrinoless double-beta decay ($0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$) events, and of various kinds of background processes such as multiple and other $\ensuremath{\gamma}$ interactions are reported for a Ge detector. The time history of the evolution of the individual events is followed and the sizes of the events (partial volumes in the detector inside which the energy of the event is released) are investigated. Effects of the angular correlations of the two electrons in $\ensuremath{\beta}\ensuremath{\beta}$ decay, which again depend on the above nuclear and (for $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay) on particle physics parameters, are taken into account and have been calculated for this purpose for the first time on basis of the experimental half-life of $^{76}\mathrm{G}\mathrm{e}$ and of realistic nuclear matrix elements. The sizes determine, together with the location of the events in the detector, the pulse shapes to be observed. It is shown for $\ensuremath{\beta}\ensuremath{\beta}$ decay of $^{76}\mathrm{G}\mathrm{e}$, that $\ensuremath{\beta}\ensuremath{\beta}$ events should be selectable with high efficiency by rejecting large size (high multiplicity) $\ensuremath{\gamma}$ events. Double-escape peaks of similar energy of $\ensuremath{\gamma}$ lines show concerning their sizes similar behavior as $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ events, and in that sense can be of some use for corresponding 'calibration' of pulse shapes of the detector. The possibility to distinguish $\ensuremath{\beta}\ensuremath{\beta}$ events from $\ensuremath{\gamma}$ events is found to be essentially independent of the particle physics parameters of the $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ process. A brief outlook is given on the potential of future experiments with respect to determination of the particle physics parameters $⟨{m}_{\ensuremath{\nu}}⟩,⟨\ensuremath{\lambda}⟩,⟨\ensuremath{\eta}⟩$.

The Weakly Interacting Massive Particle (WIMP) is one of the main candidates for the relic dark matter (DM). In the effective low-energy minimal supersymmetric standard model (effMSSM) the neutralino nucleon spin and scalar cross sections in the low-mass regime were calculated. The calculated cross sections are compared with almost all experimental currently available exclusion curves for spin-dependent WIMP-proton and WIMP-neutron cross sections. It is demonstrated that in general about 2 orders of magnitude improvement of the current DM experiment sensitivities is needed to reach the (effMSSM) supersymmetric (SUSY) predictions. At the current level of accuracy it looks reasonable to safely neglect subdominant spin WIMP nucleon contributions analyzing the data from spin-nonzero targets. To avoid misleading discrepancies between data and SUSY calculations it is, however, preferable to use a mixed spin-scalar coupling approach. This approach is applied to estimate future prospects of experiments with the odd-neutron high-spin isotope $^{\mathrm{73}}\mathrm{G}\mathrm{e}$. It is noticed that the DAMA evidence favors the light Higgs sector in the effMSSM, a high event rate in a $^{\mathrm{73}}\mathrm{G}\mathrm{e}$ detector and relatively high up-going muon fluxes from relic neutralino annihilations in the Earth and the Sun.

Recently, a paper entitled 'The IGEX {sup 76}Ge neutrinoless double-beta decay experiment: Prospects for next generation experiments' has been published [Phys. Rev. D 65, 092007 (2002)]. In view of the recently reported evidence for neutrinoless double-beta decay [Mod. Phys. Lett. A 16, 2409 (2001).; Found. Phys. 31, 1181 (2002); Phys. Lett. B 586, 198 (2004).], it is particularly unfortunate that the IGEX paper is rather incomplete in its presentation. We would like to point out in this Comment that and why it would be highly desirable to make more details about the experimental conditions and the analysis of IGEX available. We list some of the main points, which require further explanation. We also point to an arithmetic mistake in the analysis of the IGEX data, the consequence of which are too high half-life limits given in that paper.

We study the model-building conditions under which a sizeable $0\nu\beta\beta$-decay signal to the recently reported level of~0.4 eV is due to Kaluza--Klein singlet neutrinos in theories with large extra dimensions. Our analysis is based on 5-dimensional singlet-neutrino models compactified on an $S^1/Z_2$ orbifold, where the Standard--Model fields are localized on a 3-brane. We show that a successful interpretation of a positive signal within the above minimal 5-dimensional framework would require a non-vanishing shift of the 3-brane from the orbifold fixed points by an amount smaller than the typical scale (100 MeV)$^{-1}$ characterizing the Fermi nuclear momentum. The resulting 5-dimensional models predict a sizeable effective Majorana-neutrino mass that could be several orders of magnitude larger than the light neutrino masses. Most interestingly, the brane-shifted models with only one bulk sterile neutrino also predict novel trigonometric textures leading to mass scenarios with hierarchical active neutrinos and large $\nu_\mu$-$\nu_\tau$ and $\nu_e$-$\nu_\mu$ mixings that can fully explain the current atmospheric and solar neutrino data., Comment: 33 pages, LaTeX, minor rewordings, references added

We calculate the neutralino relic density within the low-energy effective minimal supersymmetric extension of the standard model (effMSSM) taking into account slepton-neutralino, squark-neutralino and neutralino\char21{}chargino-neutralino coannihilation channels. By including squark (top squark and bottom squark) coannihilation channels we extend our comparative study to all allowed coannihilations and obtain the general result that all of them give sizable contributions to the reduction of the neutralino relic density. Because of these coannihilation processes some models (mostly with large neutralino masses) fall within the cosmologically interesting region for relic density, but other models drop out at this region. Nevertheless, the predictions for direct and indirect dark matter detection rates are not strongly affected by these coannihilation channels in the effMSSM.

Within the low-energy effective Minimal Supersymmetric extension of Standard Model (effMSSM) we calculated the neutralino relic density taking into account slepton-neutralino and neutralino-chargino/neutralino coannihilation channels. We performed comparative study of these channels and obtained that both of them give sizable contributions to the reduction of the relic density. Due to these coannihilation processes some models (mostly with large neutralino masses) enter into the cosmologically interesting region for relic density, but other models leave this region. Nevertheless, in general, the predictions for direct and indirect dark matter detection rates are not strongly affected by these coannihilation channels in the effMSSM.

We investigate the contribution of the minimal supersymmetric extension of the standard model Higgs bosons produced in the neutralino annihilation in the Earth and Sun to the total weakly interacting massive particles detection signal. We find that this contribution is important and results in a lower bound for the muon flux from the Sun of ${10}^{\ensuremath{-}7}--{10}^{\ensuremath{-}8} {\mathrm{m}}^{\ensuremath{-}2} {\mathrm{yr}}^{\ensuremath{-}1}$ for neutralinos heavier than about 200 GeV. We notice that due to the SUSY charged Higgs bosons one can expect an energetic $\ensuremath{\tau}$ neutrino flux from the Sun at a level of ${10}^{2} {\mathrm{m}}^{\ensuremath{-}2} {\mathrm{yr}}^{\ensuremath{-}1}.$

We perform an investigation of the minmal supersymmetric standard model (MSSM) parameter space at the Fermi scale taking into account available accelerator, nonaccelerator and cosmological constraints. Extra assumptions about upper bounds for some of the supersymmetry (SUSY) particles are also imposed. We show that a nonobservation of the SUSY dark matter candidates with a high-accuracy dark matter detector, such as ${}^{73}\mathrm{Ge},$ under the above-mentioned assumptions can exclude large domains of the MSSM parameter space and, for instance, can make especially desirable the collider search for a light SUSY charged Higgs boson.

New results after 0.69 kg yr of measurement with an enriched ${}^{76}\mathrm{Ge}$ detector of the Heidelberg-Moscow experiment with an active mass of 2.758 kg are presented. An energy threshold of 9 keV and a background level of 0.042 cts/(kg d keV) in the energy region between 15 keV and 40 keV was reached. The derived limits on the weakly interacting massive particles--nucleon cross section are the most stringent limits on spin-independent interactions obtained to date by using essentially raw data without background subtraction.

Direct dark matter detection is considered in the next-to-minimal supersymmetric standard model (NMSSM). The effective neutralino-quark Lagrangian is obtained and event rates are calculated for the ${}^{73}\mathrm{Ge}$ isotope. Accelerator and cosmological constraints on the NMSSM parameter space are included. By means of scanning the parameter space at the Fermi scale we show that the lightest neutralino could be detected in dark matter experiments with a sizable event rate.