Singlet Majoron Model Research Articles

Precision CMB constraints on eV-scale bosons coupled to neutrinos

The cosmic microwave background (CMB) has proven to be an invaluable tool for studying the properties and interactions of neutrinos, providing insight not only into the sum of neutrino masses but also the free streaming nature of neutrinos prior to recombination. The CMB is a particularly powerful probe of new eV-scale bosons interacting with neutrinos, as these particles can thermalize with neutrinos via the inverse decay process, nu bar{nu } rightarrow X, and suppress neutrino free streaming near recombination – even for couplings as small as lambda _{nu } sim {mathcal {O}}(10^{-13}). Here, we revisit CMB constraints on such bosons, improving upon a number of approximations previously adopted in the literature and generalizing the constraints to a broader class of models. This includes scenarios in which the boson is either spin-0 or spin-1, the number of interacting neutrinos is either N_{textrm{int}} = 1,2 or 3, and the case in which a primordial abundance of the species is present. We apply these bounds to well-motivated models, such as the singlet majoron model or a light U(1)_{L_{mu }-L_{tau }} gauge boson, and find that they represent the leading constraints for masses m_Xsim 1, {textrm{eV}}. Finally, we revisit the extent to which neutrino-philic bosons can ameliorate the Hubble tension, and find that recent improvements in the understanding of how such bosons damp neutrino free streaming reduces the previously found success of this proposal.

Cosmology of an axion-like majoron

We propose a singlet majoron model that defines an inverse seesaw mechanism in the ν sector. The majoron ϕ has a mass mϕ ≈ 0.5 eV and a coupling to the τ lepton similar to the one to neutrinos. In the early universe it is initially in thermal equilibrium, then it decouples at T ≈ 500 GeV and contributes with just ΔN eff = 0.026 during BBN. At T = 26 keV (final stages of BBN) a primordial magnetic field induces resonant γ ⟷ ϕ oscillations that transfer 6% of the photon energy into majorons, implying ΔN eff = 0.55 and a 4.7% increase in the baryon to photon ratio. At T ≈ mϕ the majoron enters in thermal contact with the heaviest neutrino and it finally decays into νν̅ pairs near recombination, setting ΔN eff = 0.85. The boost in the expansion rate at later times may relax the Hubble tension (we obtain H 0 = (71.4 ± 0.5) km/s/Mpc), while the processes νν̅ ⟷ ϕ suppress the free streaming of these particles and make the model consistent with large scale structure observations. Its lifetime and the fact that it decays into neutrinos instead of photons lets this axion-like majoron avoid the strong bounds that affect other axion-like particles of similar mass and coupling to photons.

Radiative seesaw dark matter

The singlet majoron model of seesaw neutrino mass is appended by one dark Majorana fermion singlet $\chi$ with $L=2$ and one dark complex scalar singlet $\zeta$ with $L=1$. This simple setup allows $\chi$ to obtain a small radiative mass anchored by the same heavy right-handed neutrinos, whereas the one-loop decay of the standard-model Higgs boson to $\chi \chi + \bar{\chi} \bar{\chi}$ provides the freeze-in mechanism for $\chi$ to be the light dark matter of the Universe.

Leptogenesis from oscillations and dark matter

An extension of the Standard Model with Majorana singlet fermions in the 1–100 GeV range can explain the light neutrino masses and give rise to a baryon asymmetry at freeze-in of the heavy states, via their CP-violating oscillations. In this paper we consider extending this scenario to also explain dark matter. We find that a very weakly coupled B-L gauge boson, an invisible QCD axion model, and the singlet majoron model can simultaneously account for dark matter and the baryon asymmetry.

Massive Majorons and constraints on the Majoron-neutrino coupling

We revisit a singlet Majoron model in which neutrino masses arise from the spontaneous violation of lepton number. If the Majoron obtains a mass of order MeV, it can play the role of dark matter. We discuss constraints on the couplings of the massive Majoron with masses of order MeV to neutrinos from supernova data. In the dense supernova core, Majoron-emitting neutrino annihilations are allowed and can change the signal of a supernova. Based on the observation of SN1987A, we exclude a large range of couplings from the luminosity and the deleptonization arguments, taking the effect of the background medium into account. If the Majoron mass does not exceed the Q-value of the experiment, the neutrino-Majoron couplings allow for neutrinoless double beta decay with Majoron emission. We derive constraints on the couplings for a Majoron mass of order MeV based on the phase space suppression and the diminishing signal-to-background ratio due to the Majoron mass. The combination of constraints from astrophysics and laboratory experiments excludes a large range of neutrino-Majoron couplings in the mass range of intererest for Majoron dark matter.

Two-field cosmological phase transitions and gravitational waves in the singlet Majoron model

In the singlet Majoron model, we study cosmological phase transitions (PTs) and their resulting gravitational waves (GWs), in the two-field phase space, without freezing any of the field directions. We first calculate the effective potential, at one loop and at finite temperature, of the Standard Model Higgs doublet together with one extra Higgs singlet. We make use of the public available Python package ‘CosmoTransitions’ to simulate the two-dimensional (2D) cosmological PTs and evaluate the gravitational waves generated by first-order PTs. With the full 2D simulation, we are able not only to confirm the PTs’ properties previously discussed in the literature, but also we find new patterns, such as strong first-order PTs tunneling from a vacuum located on one axis to another vacuum located on the second axis. The two-field phase space analysis presents a richer panel of cosmological PT patterns compared to analysis with a single-field approximation. The PTGW amplitudes turn out to be out of the reach for the space-borne gravitational wave interferometers such as LISA, DECIGO, BBO, TAIJI and TianQin when constraints from colliders physics are taken into account.

LSZ-reduction, resonances and non-diagonal propagators: Gauge fields

We analyze in the Landau gauge mixing of bosonic fields in gauge theories with exact and spontaneously broken symmetries, extending to this case the Lehmann–Symanzik–Zimmermann (LSZ) formalism of the asymptotic fields. Factorization of residues of poles (at real and complex values of the variable p2) is demonstrated and a simple practical prescription for finding the “square-rooted” residues, necessary for calculating S-matrix elements, is given. The pseudo-Fock space of asymptotic (in the LSZ sense) states is explicitly constructed and its BRST-cohomological structure is elucidated. Usefulness of these general results, obtained by investigating the relevant set of Slavnov–Taylor identities, is illustrated on the one-loop examples of the Z0-photon mixing in the Standard Model and the GZ-Majoron mixing in the singlet Majoron model.

Renormalization group study of the minimal Majoronic dark radiation and dark matter model

We study the 1-loop renormalization group equation running in the simplest singlet Majoron model constructed by us earlier to accommodate the dark radiation and dark matter content in the universe. A comprehensive numerical study was performed to explore the whole model parameter space. A smaller effective number of neutrinos △ Neff∼ 0.05, or a Majoron decoupling temperature higher than the charm quark mass, is preferred. We found that a heavy scalar dark matter, ρ, of mass 1.5–4 TeV is required by the stability of the scalar potential and an operational type-I see-saw mechanism for neutrino masses. A neutral scalar, S, of mass in the 10–100 GeV range and its mixing with the standard model Higgs as large as 0.1 is also predicted. The dominant decay modes are S into bb̄ and/or ωω. A sensitive search will come from rare Z decays via the chain Z → S+ ff̄, where f is a Standard Model fermion, followed by S into a pair of Majoron and/or b-quarks. The interesting consequences of dark matter bound state due to the sizable Sρ ρ-coupling are discussed as well. In particular, shower-like events with an apparent neutrino energy at Mρ could contribute to the observed effective neutrino flux in underground neutrino detectors such as IceCube.

Minimal model of Majoronic dark radiation and dark matter

We extend the singlet Majoron model of dark radiation by adding another singlet scalar of unit lepton charge. The spontaneous breaking of global $U(1{)}_{L}$ connects dark radiation with neutrino mass generation via the type-I seesaw mechanism. The model naturally has a stable scalar dark matter field. It also predicts the existence of a light scalar of mass less than 1 GeV that mixes with the Standard Model Higgs boson. We perform a numerical analysis of the parameters of the model by imposing constraints from giving correct relic abundance and satisfying bounds from direct dark matter detection, rare decays of the $B$ meson, and invisible width of the Higgs boson. The viability of the model in accommodating the gamma rays from the Galactic center is discussed as well. The model gives rise to new rare Higgs boson decays such as four-muon final states with displaced vertices. Another unique signal is two muons and missing energy recoil against the muon pair. Our result also shows that such a bridge between dark radiation and the seesaw mechanism will put the seesaw scale in the range of 1--100 TeV.

Signals of an invisibly decaying Higgs boson in a scalar dark matter scenario: A study for the Large Hadron Collider

We consider the collider phenomenology of a singlet Majoron model with softly broken lepton number. Lepton number is spontaneously broken when the real part of a new singlet scalar develops vacuum expectation value. With the additional soft terms violating lepton numbers, the imaginary part of this singlet scalar becomes a massive pseudo-Majoron which can account for the dark matter. In presence of the coupling of the pseudo-Majoron with the Standard Model (SM) Higgs, the SM Higgs mostly decays into a pair of pseudo-Majorons, giving rise to missing transverse energy signals at a hadron collider. Since the Higgs visible decay branching fractions get reduced in presence of this invisible decay mode, the bounds on the SM Higgs mass from the LEP and Tevatron experiments get diluted and the invisible decay channel of the Higgs become important for the discovery of low mass Higgs at the Large Hadron Collider.

Leptogenesis bound on spontaneous symmetry breaking of global lepton number

We propose a new class of leptogenesis bounds on the spontaneous symmetry breaking of global lepton number. These models have a generic feature of inducing new lepton number violating interactions, due to the presence of the Majorons. We analyzed the singlet Majoron model with right-handed neutrinos and find that the lepton number should be broken above 10^5 GeV to realize a successful leptogenesis because the annihilations of the right-handed neutrinos into the massless Majorons and into the standard model Higgs should go out of equilibrium before the sphaleron process is over. We then argue that this type of leptogenesis constraint should exist in the singlet-triplet Majoron models as well as in a class of R-parity violating supersymmetric Majoron models.

Pseudo-Majoron as dark matter

We consider the singlet Majoron model with softly broken lepton number. This model contains three right-handed neutrinos and a singlet scalar besides the standard model fields. The real part of the singlet scalar develops a vacuum expectation value to generate the lepton number violation for seesaw and leptogenesis. The imaginary part of the singlet scalar becomes a massive pseudo-Majoron to be a dark matter candidate with testability by colliders, direct detection experiments and neutrino observations.

Electroweak resonant leptogenesis in the singlet Majoron model

We study resonant leptogenesis at the electroweak phase transition in the singlet Majoron model with right-handed neutrinos. We consider a scenario where the SM gauge group and the lepton number break down spontaneously during a second-order electroweak phase transition. We calculate the flavor- and temperature-dependent leptonic asymmetries, by including the novel contributions from the transverse polarizations of the ${W}^{\ifmmode\pm\else\textpm\fi{}}$ and $Z$ bosons. The required resummation of the gauge-dependent, off-shell, heavy-neutrino self-energies is consistently treated within the gauge-invariant framework of the pinch technique. Taking into consideration the freeze-out dynamics of sphalerons, we delineate the parameter space of the model that is compatible with successful electroweak resonant leptogenesis. The phenomenological and astrophysical implications of the model are discussed.

BOUNDS ON THE COUPLING CONSTANTS OF THE MAJORON TO TWO NEUTRINOS IN EXTRA DIMENSIONS FROM Z → νν(J) DECAY

We give an overview for the bounds of Majoron-neutrino coupling constants from supernova and accelerators. Using the accurate known value for the invisible partial width for Z boson we obtained constraints on the coupling of the Majoron to two neutrinos, for singlet Majoron model, in case of 3+1 dimensions as well as in extra dimensions, where we assumed the singlet Majoron can propagate in higher dimensions. We found that the predicted coupling constants are far below these upper bounds if a natural see-saw is adopted. Also, the expected increase in Z partial width due to many Kaluza-Klein excitations has been suppressed due to the decrease of the coupling constants.

Superheavy dark matter and parametric resonance

We propose a new scenario to produce the superheavy dark matter based on the inflationary universe. In our scenario, the inflaton couples to both a boson and a stable fermion. Although the fermion is produced by the inflaton decay after inflation, almost energy density of the inflaton is transmitted into the radiation by parametric resonance which causes the explosively copious production of the boson. We show that the fermion produced by the inflaton decay can be the superheavy dark matter, whose abundance in the present universe coincides with the critical density. We also present two explicit models as examples in which our scenario can be realized. One is the softly broken supersymmetric theory. The other is the “singlet majoron model” with an assumed neutrino mass matrix. The latter example can simultaneously explain the neutrino oscillation data and the observed baryon asymmetry in the present universe through the leptogenesis scenario.

Radiative corrections to neutrino-Majoron couplings

The coupling of a Majoron to neutrinos is calculated at the one loop level in various models, including the singlet Majoron model and the Zee model with a Majoron. When the respective corrections to the mass matrix are taken into account, the would-be nondiagonal terms in the neutrino-Majoron coupling are rotated away. It is pointed out that the coincidence between neutrino mass matrices and neutrino-Majoron couplings is a general consequence of N\"other's theorem.

Doublet-singlet oscillations and dark matter neutrinos

We examine the “singlet majoron model” first introduced by Chikashige, Mohapatra and Peccei as a simple extension of the standard model with massive Majorana neutrinos. We can explain both the solar and the atmospheric neutrino deficits by the oscillations between electroweak doublet and singlet neutrions without flavor mixing. Furthermore, while some light neutrinos can be the hot dark matter, tau neutrinos with a mass of 8.9–2.4 MeV can be the cold dark matter through the interaction with the majoron. Thus, we can simultaneously explain the solar neutrino deficit, the atmospheric neutrino anomaly, and the cold and hot dark matters only with the Majorana neutrinos.

Damping rate of neutrinos in the singlet Majoron model

The damping rate and free path of neutrinos in primordial plasma have been calculated in the singlet Majoron model including both finite temperature and symmetry breaking effects. The behaviour of right- and left-handed fermions are found inherently different. While the damping rates of the left-handed leptons are essentially model independent, e.g. directly applicable to the Standard Model, for the right-handed particles the rates are crucially sensitive to parameters of the scalar sector. In general, the damping rates are fairly large. The possibility of the right-handed neutrinos to penetrate deep into the broken phase in the electroweak phase transition still remains, however, for some parts of the parameter space.

R-parity breaking phase transition in the SUSY singlet majoron model

We consider thermal properties of the SUSY singlet majoron model. We compute the critical temperature T c and the subsequent reheating temperature T RH for R-parity breaking. Successful baryogenesis constrains the parameter space via the requirements that T c and T RH are lower than the electroweak phase transition temperature. A further constraint is provided by requiring that the gauge singlet should be kinematically allowed to decay, in order not to have a matter dominated universe at the time of nucleosynthesis. We have made a detailed study of the parameter space and find an upper limit for the SUSY breaking scalar mass m 0 ≲ 750 (900) GeV if m gluino = 100 (1000) GeV, which is valid except for certain special values of the singlet sector parameters.

CP violation and the baryonic asymmetry of the universe

The physics of electroweak baryogenesis is described with the aim of making the essentials clear to non-experts. Several models for the source of the necessary CP violation are discussed: CKM phases as in the minimal standard model, general two higgs doublet models, the supersymmetric standard model, Z condensates, and the singlet majoron model. In a more technical section, a strategy is introduced for consistently treating quark dynamics in the neighborhood of the bubble wall, where both local and non-local interactions are important. This provides a method for deciding whether gluonic corrections wash out the elecroweak contribution to the baryonic asymmetry in the minimal standard model.