Majoron Decay Research Articles

Pseudo-Goldstone dark matter in a radiative inverse seesaw scenario

We consider a scale-invariant inverse seesaw model with dynamical breaking of gauge symmetry and lepton number. In some regions of the parameter space, the Majoron — the pseudo-Goldstone of lepton number breaking — is a viable dark matter candidate. The bound on the Majoron decay rate implies a very large dilaton vacuum expectation value, which also results in a suppression of other dark matter couplings. Because of that, the observed dark matter relic abundance can only be matched via the freeze-in mechanism. The scalar field which gives mass to heavy neutrinos can play the role of the inflaton, resulting in a tensor-to-scalar ratio r ≲ 0.01 for metric inflation and r ≲ 0.21 for Palatini gravity.

Search for Majoron-emitting modes of Xe136 double beta decay with the complete EXO-200 dataset

A search for Majoron-emitting modes of the neutrinoless double-beta decay of $^{136}$Xe is performed with the full EXO-200 dataset. This dataset consists of a total $^{136}$Xe exposure of 234.1 kg$\cdot$yr, and includes data with detector upgrades that have improved the energy threshold relative to previous searches. A lower limit of T$_{1/2}^{\rm{^{136}Xe}}>$4.3$\cdot$10$^{24}$ yr at 90\% C.L. on the half-life of the spectral index $n=1$ Majoron decay was obtained, a factor of 3.6 more stringent than the previous limit from EXO-200, corresponding to a constraint on the Majoron-neutrino coupling constant of $|\langle g_{ee}^{M}\rangle|$$<(0.4$-$0.9)\cdot10^{-5}$. The lower threshold and the additional data taken resulted in a factor 8.4 improvement for the $n=7$ mode compared to the previous EXO search. This search provides the most stringent limits to-date on the Majoron-emitting decays of $^{136}$Xe with spectral indices $n=1,2,3,$ and 7.

On the MSW-like neutrino mixing effects in atomic weak interactions and double beta decays

Matter effects on the mixing of the neutrinos mass eigenstates, also known as the Mikheyev–Smirnov–Wolfenstein effect, seem to be well established in describing the propagation of the neutrino from the source to detecting devices. These effects were mostly considered in bulk matter, but not inside the atoms. Here we consider the effect of the high electron densities existing in the atomic nuclei. We investigate if these effects can affect the known neutrino phenomenology. It was reported that the mixing of the neutrinos in high density matter, such as inside a supernova, can affect the Majoron decay probabilities. We investigate if the neutrino mixing effects in the high electron density inside the atomic nuclei can change the neutrinoless double beta decay half-life formula. In both cases we found that the standard results stand. The results look simple, but the road to them is complex and it opens the possibility that the neutrino mixing in atomic nuclei may affect other observables, such as the neutrinoless double beta Majoron decays.

Detecting a secondary cosmic neutrino background from Majoron decays in neutrino capture experiments

We consider theories in which the generation of neutrino masses is associated with the breaking of an approximate global lepton number symmetry. In such a scenario the spectrum of light states includes the Majoron, the pseudo-Nambu Goldstone boson associated with the breaking of the global symmetry. For a broad range of parameters, the Majoron decays to neutrinos at late times, after the cosmic neutrinos have decoupled from the thermal bath, resulting in a secondary contribution to the cosmic neutrino background. We determine the current bounds on this scenario, and explore the possibility of directly detecting this secondary cosmic neutrino background in experiments based on neutrino capture on nuclei. For Majoron masses in the eV range or below, the neutrino flux from these decays can be comparable to that from the primary cosmic neutrino background, making it a promising target for direct detection experiments. The neutrinos from Majoron decay are redshifted by the cosmic expansion, and exhibit a characteristic energy spectrum that depends on both the Majoron mass and its lifetime. For Majoron lifetimes of order the age of the universe or larger, there is also a monochromatic contribution to the neutrino flux from Majoron decays in the Milky Way that can be comparable to the diffuse extragalactic flux. We find that for Majoron masses in the eV range, direct detection experiments based on neutrino capture on tritium, such as PTOLEMY, will be sensitive to this scenario with 100 gram-years of data. In the event of a signal, the galactic and extragalactic components can be distinguished on the basis of their distinct energy distributions, and also by using directional information obtained by polarizing the target nuclei.

Phase-space factors and half-life predictions for Majoron-emittingβ−β−decay

A complete calculation of phase space factors (PSF) for Majoron emitting $0\nu\beta^-\beta^-$ decay modes is presented. The calculation makes use of exact Dirac wave functions with finite nuclear size and electron screening and includes life-times, single electron spectra, summed electron spectra, and angular electron correlations. Combining these results with recent interacting boson nuclear matrix elements (NME) we make half-life predictions for the the ordinary Majoron decay (spectral index $n$=1). Furthermore, comparing theoretical predictions with the obtained experimental lower bounds for this decay mode we are able to set limits on the effective Majoron-neutrino coupling constant $\langle g_{ee}^M\rangle$.

Search for Majoron-emitting modes of double-beta decay ofXe136with EXO-200

EXO-200 is a single phase liquid xenon detector designed to search for neutrinoless double-beta decay of $^{136}$Xe. Here we report on a search for various Majoron-emitting modes based on 100 kg$\cdot$yr exposure of $^{136}$Xe. A lower limit of $T^{^{136}Xe}_{1/2} >1.2 \cdot 10^{24}$ yr at 90% C.L. on the half-life of the spectral index = 1 Majoron decay was obtained, corresponding to a constraint on the Majoron-neutrino coupling constant of $|< g^{M}_{ee} >|<$ (0.8-1.7)$\cdot$10$^{-5}$.

Electroweak scale neutrinos and decaying Majorons

We study the Higgs phenomenology of a model of electroweak scale neutrinos that incorporates the presence of a lepton number violating singlet scalar. In order to verify its viability, we perform an analysis of the pseudoscalar-Majoron field. In particular we study the Majoron decay J → vv and use the bounds on the Majoron mass and width obtained in a modified Majoron Decaying Dark Matter scenario.

Electroweak scale neutrinos and decaying dark matter

We explore the scalar phenomenology of a model of electroweak scale neutrinos that incorporates the presence of a lepton number violating singlet scalar. An analysis of the pseudoscalar-Majoron field associated to this singlet field is carried out in order to verify the viability of the model and to restrict its parameter space. In particular we study the Majoron decay J→νν and use the bounds on the Majoron mass and width obtained in a modified Majoron decaying dark matter scenario.

Limits on different majoron decay modes of 100Mo and 82Se for neutrinoless double beta decays in the NEMO-3 experiment

The NEMO-3 tracking detector is located in the Fréjus 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 100Mo and 82Se 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 100Mo ( T 1 / 2 > 2.7 × 10 22 yr ) and 82Se ( T 1 / 2 > 1.5 × 10 22 yr ) have been obtained. Corresponding bounds on the majoron–neutrino coupling constant are 〈 g e e 〉 < ( 0.4 – 1.8 ) × 10 −4 and < ( 0.66 – 1.9 ) × 10 −4 .

A combined treatment of neutrino decay and neutrino oscillations

Neutrino decay in vacuum has often been considered as an alternative to neutrino oscillations. Because non-zero neutrino masses imply the possibility of both neutrino decay and neutrino oscillations, we present a model-independent formal treatment of these combined scenarios. For that, we show for the example of Majoron decay that in many cases decay products are observable and may even oscillate. Furthermore, we construct a minimal scenario where we study the physical implications of neutrino oscillations with intermediate decays.

Majoron decay in matter

It is well known that matter can significantly alter the picture of neutrino oscillation [1] or neutrino decay [2]. Here we show that the presence of dense matter induces also the decay of massless majoron, a Goldstone boson associated with the spontaneous lepton number violation, into a couple of neutrinos with the same (or in some cases also opposite) helicities. We calculate the rates of such matter induced majoron decays in various cases, depending on the neutrino type and the chemical content of the medium, and analyse their properties.

New limits on double beta decay of 136Xe

A Xenon TPC with an active volume of 180 liters has been built to study the neutrinoless double beta decay in 136Xe. Data were taken in the Gotthard Underground Laboratory with 5 atm of xenon enriched to 62% in 136Xe. A total of 7647 hours of data has been taken. New limits on neutrino mass and majoron decay are presented.

New limits on double beta decay of 136Xe

A Xenon TPC with an active volume of 207 liters has been built to study the neutrinoless double beta decay in 136Xe. Data were taken in the Gotthard Underground Laboratory with 5 atm of xenon enriched to 62.5% in 136Xe. A total of 6830 hours of data has been taken. New limits on neutrino mass and majoron decay are presented.

Majoron decay of neutrinos in matter.

Using an helicity formalism for Majorana neutrino fields, we calculate the decay rates for the helicity-flipping and helicity-conserving Majoron decays of neutrinos propagating in dense media. We discuss the subtlety involved in the neutrino mixing in matter in a quantum-field-theoretical approach to clarify previous misunderstandings in the calculation of Majoron decays. General formulas, derived in a model-independent approach, can be applied to any number of neutrino generations and to the decay with production of any massless pseudoscalar boson. In particular, we discuss the two-generation case and show that in matter the helicity-flipping decays are dominant over the helicity-conserving decays. The implications of the Majoron decay for the neutrinos from astrophysical objects are also briefly discussed.

Neutrino decay and spontaneous violation of lepton number

The orders of magnitude of decay rates for relatively light neutrinos are studied in the framework of the SU(2)\ifmmode\times\else\texttimes\fi{}U(1) gauge group. The assumption is made that a hierarchy parameter $\ensuremath{\epsilon}(\ensuremath{\approx}(\mathrm{muon}\mathrm{mass})\textdiv{}[\mathrm{some}\mathrm{new}\mathrm{mass}\mathrm{scale}(\mathrm{possibly}\mathrm{much}\mathrm{smaller}\mathrm{than}\mathrm{the}\mathrm{grand}\mathrm{unification}\mathrm{scale})])$ plays a meaningful role in the full theory. For orientation it is first noted that the traditional $\ensuremath{\nu}\ensuremath{\gamma}$ decay channel as well as the $3\ensuremath{\nu}$ decay channel give neutrino lifetimes which for "typical" parameters are substantially longer than the age of the universe. Then we examine in detail some recent proposals which are claimed to result in greatly speeded-up decays into $\ensuremath{\nu}$+Majoron, where the Majoron is a true Goldstone boson associated with spontaneous breakdown of lepton number. In a theory in which the usual Higgs doublet is augmented by a complex singlet (1-2 model) it is noted that the decay width into $\ensuremath{\nu}$+Majoron actually vanishes to order ${\ensuremath{\epsilon}}^{5}$. In a theory where the doublet is augmented by a complex triplet (2-3 model) this decay is shown to vanish exactly, neglecting radiative corrections. A more general Majoron theory (1-2-3 model) is constructed and shown to also yield a vanishing tree-level decay rate for $\ensuremath{\nu}$+Majoron decay to order ${\ensuremath{\epsilon}}^{5}$. Finally, the tree amplitudes in the 1-2 and 1-2-3 models are shown to give decay widths for $\ensuremath{\nu}$+Majoron of order ${\ensuremath{\epsilon}}^{9}$ which correspond to lifetimes much greater than the age of the universe.