We discuss the systematic decomposition of all dimension-7 (d=7) lepton number violating operators. These d=7 operators produce momentum enhanced contributions to the long-range part of the neutrinoless double beta decay amplitude and thus are severely constrained by existing half-live limits. In our list of possible models one can find contributions to the long-range amplitude discussed previously in the literature, such as the left-right symmetric model or scalar leptoquarks, as well as some new models not considered before. The d=7 operators generate Majorana neutrino mass terms either at tree-level, 1-loop or 2-loop level. We systematically compare constraints derived from the mass mechanism to those derived from the long-range double beta decay amplitude and classify our list of models accordingly. We also study one particular example decomposition, which produces neutrino masses at 2-loop level, can fit oscillation data and yields a large contribution to the long-range double beta decay amplitude, in some detail.
We study the corrections to the determination of sin(2 beta) from the time dependent CP asymmetry of B^0 to J/Psi K_S which arise in the standard model. Although a precise prediction of these corrections is not possible we find that they are indeed extremely small, of the order of less than a per mil of the observed value. This means in turn that any deviation visible at the B factories will be a clear signal for new physics.
We critically reexamine the prospects for the observation of the $ΔL=2$ lepton-number-violating process $\eeWW$ using the $e^-e^-$ option of a high-energy $e^+e^-$ collider (NLC). We find that, except in the most contrived scenarios, constraints from neutrinoless double beta decay render the process unobservable at an NLC of $\sqrt{s}<2$ TeV. Other $ΔL=2$ processes such as $\ggllww$, $\egnllw$, $\eennll$ ($\ell=μ,τ$), and $\egeww$, which use various options of the NLC, require a $\sqrt{s}$ of at least 4 TeV for observability.
We point out that in the minimal supersymmetric standard model terms from the mixing of Higgs and Goldstone bosons which are connected to the renormalization of tan(beta) via Slavnov-Taylor identities give rise to corrections that do not vanish in the limit where the supersymmetric particles are much heavier than the Higgs bosons. These additional contributions have important phenomenological implications as they can lead to potentially large supersymmetric effects in DeltaM_d and to a significant increase of DeltaM_s relative to the standard model prediction for a light pseudoscalar Higgs A0.…
We apply the effective field theory definition of Minimal Flavour Violation (MFV) to the MSSM. We explicitly show how, by this definition, the new sources of flavour and CP violation present in the MSSM become functions of the SM Yukawa couplings, and cannot be simply set to zero, as is common wisdom in phenomenological MSSM studies that assume MFV. We apply our approach to the MSSM Delta B = 2 Hamiltonian at low tan(beta). The limit of MFV amounts to a striking increase in the predictivity of the model. In particular, SUSY corrections to meson-antimeson mass differences Delta M(d,s) are alway…
We study the performance of gamma = 100 Beta-Beam setups based on the decays of 8B and 8Li as a function of the achievable production fluxes and compare them with the standard setups based on 18Ne and 6He decays. For the standard setup we also investigate the physics potential for reduced 18Ne fluxes, since it seems experimentally challenging to achieve the baseline numbers. We find that, contrary to the standard setup, setups based in 8B and 8Li can be sensitive to the mass hierarchy down to values of sin^2 2theta_{13} > 10^-2 by themselves, due to the stronger matter effects granted by the h…
We revisit the process of inverse neutrino-less double beta decay (e e -> W W) at future linear colliders. The cases of Majorana neutrino and Higgs triplet exchange are considered. We also discuss the processes e mu -> W W and mu mu -> W W, which are motivated by the possibility of muon colliders. For heavy neutrino exchange and center-of-mass energies larger than 1 TeV, we show that masses up to 10^6 (10^5) GeV could be probed for e-e and e-mu machines, respectively. The stringent limits for mixing of heavy neutrinos with muons render mu mu -> W W less promising, even though this process is n…
The background in the region of the Q-value for neutrinoless double beta decay of 76Ge has been investigated by different methods: Simulation with GEANT 4 of the HEIDELBERG-MOSCOW experiment, analysis of other Ge double beta experiments.Statistical features of the analysis at very low count rates are discussed.
We update the upper bound on the lightest CP even Higgs mass in the NMSSM, which is given as a function of tan(beta) and lambda. We include the available one and two loop corrections to the NMSSM Higgs masses, and constraints from the absence of Landau singularities below the GUT scale as well as from the stability of the NMSSM Higgs potential. For m_top varying between 171.4 and 178 GeV, squark masses of 1 TeV and maximal mixing the upper bound is assumed near tan(beta) ~ 2 and varies between 139.9 and 141.4 GeV.
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 investigate neutrino flux induced double beta transitions in targets built of Cd112, Cd114, Cd116 and O18 isotopes. In addition to known beta^- beta^- channel we consider new beta^- beta^+ and beta^- beta^+ gamma modes of the neutrino induced double beta process. A possibility of detection of the solar neutrinos via the induced double beta transitions of interest is discussed. We note that the beta^- part of the solar neutrino induced beta^- beta^+ process in O18 was already discussed in Ref. [9,10] in connection with a possible influence of high energy electron production of this origin on…
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 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.
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.
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.
We discuss the relation between the absolute neutrino mass scale, the effective mass measured in neutrinoless double beta decay, and the Majorana CP phases. Emphasis is placed on estimating the upper bound on the nuclear matrix element entering calculations of the double beta decay half life. Consequently, one of the Majorana CP phases can be constrained when combining the claimed evidence for neutrinoless double beta decay with the neutrino mass bound from cosmology.
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…
We revise the radiative corrections to double-Dalitz decays ($P\to\ell\bar{\ell}\ell'\bar{\ell}'$), completing the full next-to-leading order calculation in QED as compared to existing calculations. As a result, we find mild differences with respect to previous studies, that might be relevant for extracting information about the mesons transition form factors. The latter play an important role in determining the hadronic light-by-light contribution to the anomalous magnetic moment of the muon. Finally, we outline an ongoing extension of this work to the $e^+e^-\to e^+e^- P$ processes.
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…
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.
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.
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.
The dynamics of two heavy quarks inside the same hadron is probed against the double charm baryon results of SELEX. This can be seen as a part of the mechanism to bind tetraquarks with two heavy quarks and two light antiquarks. In the framework of potential models, it is possible to test the role of different effects: relativistic corrections, confinement, hyperfine forces, etc. It is conjectured that an additional interaction rescaled from the nucleon--nucleon system and acting between light quarks only, can help in bringing extra, possibly required, binding in tetraquarks.
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.
The decay rate of neutrinoless double beta decay could be dominated by short-range diagrams involving heavy scalar particles ("topology-II" diagrams). Examples are diagrams with diquarks, leptoquarks or charged scalars. Here, we compare the discovery potential for lepton number violating signals at the LHC with constraints from dijet and leptoquark searches and the sensitivity of double beta decay experiments, using three example models. We note that already with 20/fb the LHC will test interesting parts of the parameter space of these models, not excluded by current limits on double beta deca…
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.
We propose formulas of the nuclear beta-decay rate that are useful in a practical calculation. The decay rate is determined by the product of the lepton and hadron current densities. A widely used formula relies upon the fact that the low-energy lepton wave functions in a nucleus can be well approximated by a constant and linear to the radius for the $s$-wave and $p$-wave wave functions, respectively. We find, however, the deviation from such a simple approximation is evident for heavy nuclei with large $Z$ by numerically solving the Dirac equation. In our proposed formulas, the neutrino wave …
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 examine the constraints on the MNS lepton mixing matrix =66rom the present and future experimental data of the neutrino oscillation, tritium beta decay, and neutrinoless double beta decay for Majorana neutrinos. We show that the small mixing angle solutions for solar neutrino problem are disfavored for small averaged mass ($<m_ν>$) of neutrinoless double beta decay ($\leq 0.01$ eV) in the inverse neutrino mass hierarchy scenario. This is the case even in the normal mass hierarchy scenario except for very restrictive value of the averaged neutrino mass ($\bar{m_ν}$) of single beta decay. The…
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.
The search for neutrinoless double beta decay and WIMP dark matter has a broad potential to test particle physics beyond the standard model. During the last years, the analysis of various contributions to the double beta decay rate by the Heidelberg group led, besides the most restrictive limit on the effective Majorana neutrino mass, to bounds on left-right-symmetric models, leptoquarks and supersymmetry. In a general framework bounds on arbitrary lepton number violating theories can be derived. Using double beta technology for direct dark matter detection, stringent limits on the spin-indepe…
Double parton scattering (DPS) is studied at the example of $J/ψ$ pair-production in the LHCb and ATLAS experiments of the Large Hadron Collider (LHC) at centre-of-mass energies of $\sqrt{S}=$ 7, 8, and 13 TeV. We report theoretical predictions delivered to the LHCb and ATLAS collaborations adjusted for the fiducial volumes of the corresponding measurements during Run I and provide new predictions at 13 TeV collision energy. It is shown that DPS can lead to noticeable contributions in the distributions of longitudinal variables of the di-$J/ψ$ system, especially at 13 TeV. The increased DPS ra…
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…
We re-derive the renormalization group equation for the effective coupling of the dimension five operator which corresponds to a Majorana mass matrix for the Standard Model neutrinos. We find a result which differs somewhat from earlier calculations, leading to modifications in the evolution of leptonic mixing angles and CP phases. We also present a general method for calculating beta-functions from counterterms in MS-like renormalization schemes, which works for tensorial quantities.
We discuss the potential of neutrinoless double beta decay for testing Lorentz invariance and the weak equivalence principle as well as contributions from dilaton exchange gravity in the neutrino sector. While neutrino oscillation bounds constrain the region of large mixing of the weak and gravitational eigenstates, we obtain new constraints on violations of Lorentz invariance and the equivalence principle from neutrinoless double beta decay, applying even in the case of no mixing. Double beta decay thus probes a totally unconstrained region in the parameter space.
This paper is addressed to the analysis of the set of observables of the bound-state beta-decay, which can be used for the experimental investigation of contributions of i) interactions beyond the Standard Model (SM) and of ii) the left-handed polarisation state of antineutrinos. For this aim we calculate the branching ratio, probabilities and angular distributions of probabilities of hydrogen in the hyperfine states and of the proton-electron pair in different spinorial states, induced by left-handed and right-handed hadronic and leptonic currents. The branching ratio of the bound-state beta-…
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.
The current situation of the double beta decay direct counting experiments is briefly reviewed. A comparison with the theoretical predictions in some representative nuclear models is presented.
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 …
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…
We examine the constraints from the recent HEIDELBERG-MOSCOW double beta decay experiment. It leads us to the almost degenerate or inverse hierarchy neutrino mass scenario. In this scenario, we obtain possible upper bounds for the Majorana CP violating phase in the lepton sector by incorporating the data from the neutrino oscillation, the single beta decay experiments, and from the astrophysical observation. We also predict the neutrino mass that may be measurable in the future beta decay experiments.
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).
Assuming equal tree-level Majorana masses for the standard-model neutrinos, either from the canonical seesaw mechanism or from a heavy scalar triplet, I discuss how their radiative splitting may be relevant to neutrinoless double beta decay and neutrino oscillations.
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 detection of solar-neutrinos of different origin via induced beta beta process of Mo100 is investigated. The particular counting rates and energy distributions of emitted electrons are presented. A discussion in respect to solar-neutrino detector consisting of 10 tones of Mo100 is included. Both the cases of the standard solar model and neutrino oscillation scenarios are analyzed. Moreover, new beta^- beta^+ and beta^-/EC channels of the double-beta process are introduced and possibilities of their experimental observation are addressed.
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…
The effect of Majorana neutrinos in the MeV mass range on the double beta decay of various isotopes is studied on pure phenomenological arguments. By using only experimental half life data, limits on the mixing parameter $U_{eh}^2$ of the order 10$^{-7}$ can be derived. Also the possible achievements of upcoming experiments and some consequences are outlined.
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 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…
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…
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. …
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…
