Inverse Seesaw Scenario Research Articles

Dynamical origin of neutrino masses and dark matter from a new confining sector

A dynamical mechanism, based on a confining non-Abelian dark symmetry, which generates Majorana masses for hyperchargeless fermions, is proposed. We apply it to the inverse seesaw scenario, which allows us to generate light neutrino masses from the interplay of TeV-scale pseudo-Dirac mass terms and a small explicit breaking of lepton number. A single generation of vectorlike dark quarks, transforming under a SU(3)D gauge symmetry, is coupled to a real singlet scalar, which serves as a portal between the dark quark condensate and three generations of heavy sterile neutrinos. Such a dark sector and the Standard Model (SM) are kept in thermal equilibrium with each other via sizable Yukawa couplings to the heavy neutrinos. In this framework, the lightest dark baryon, which has spin 3/2 and is stabilized at the renormalizable level by an accidental dark baryon number symmetry, can account for the observed relic density via thermal freeze-out from annihilations into the lightest dark mesons. These mesons, in turn, decay to heavy neutrinos, which produce SM final states upon decay. This model may be probed by next generation neutrino telescopes via neutrino lines produced from dark matter annihilations. Published by the American Physical Society 2024

Modular flavor models with positive modular weights: a new lepton model building

We propose an interesting assignment of positive modular weights for fields in a modular non-Abelian discrete flavor symmetry. By this assignment, we can construct inverse seesaw and linear seesaw models without any additional symmetries which possess good testability in current experiments. At first, we discuss possibilities for positive modular weights from a theoretical point of view. Then we show concrete examples of inverse seesaw and linear seesaw scenarios applying modular A4 symmetry as examples and demonstrate some predictions as well as consistency with experimental results such as neutrino masses and mixings.

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.

A radiatively induced inverse seesaw model with hidden U(1) gauge symmetry

We propose an inverse seesaw scenario under hidden U(1) gauge symmetry, having rather natural hierarchies among neutral fermion mass scales. The hierarchies are derived from theory and experimental constraints. The theory requires Majorana exotic masses have to be induced at one-loop level. The experimental side requests that the Dirac mass terms has to be highly suppressed to satisfy the constraints from the lepton flavor violations (LFVs) such as mu rightarrow egamma . In order to induce such a small Majorana exotic masses we introduce exotic fermions and bosons that also provide us additional intriguing phenomenologies such as muon anomalous magnetic moment, dark matter candidate as well as LFVs and deviations in leptonic Z decays. We analyze these phenomenologies including neutrino oscillation data numerically, and show allowed region. Finally, we discuss the DM candidate in both the cases of fermion and scalar boson, where we focus on rather lighter range that is equal or less than 10 GeV. The dominant contributions originate from interactions of hidden gauge sector, and we show allowed ranges for both cases.

A full parametrization of the 9 × 9 active-sterile flavor mixing matrix in the inverse or linear seesaw scenario of massive neutrinos

The inverse and linear seesaw scenarios are two typical extensions of the canonical seesaw mechanism, which contain much more sterile degrees of freedom but can naturally explain the smallness of three active neutrino masses at a sufficiently low energy scale (e.g., the TeV scale). To fully describe the mixing among three active neutrinos, three sterile neutrinos and three extra gauge-singlet neutral fermions in either of these two seesaw paradigms, we present the first full parametrization of the 9×9 flavor mixing matrix in terms of 36 rotation angles and 36 CP-violating phases. The exact inverse and linear seesaw formulas are derived, respectively; and possible deviations of the 3×3 active neutrino mixing matrix from its unitary limit are discussed by calculating the effective Jarlskog invariants and unitarity nonagons.

Inverse Seesaw, dark matter and the Hubble tension

We consider the inverse Seesaw scenario for neutrino masses with the approximate Lepton number symmetry broken dynamically by a scalar with Lepton number two. We show that the Majoron associated to the spontaneous symmetry breaking can alleviate the Hubble tension through its contribution to Delta N_text {eff} and late decays to neutrinos. Among the additional fermionic states required for realizing the inverse Seesaw mechanism, sterile neutrinos at the keV-MeV scale can account for all the dark matter component of the Universe if produced via freeze-in from the decays of heavier degrees of freedom.

Pair production of heavy neutrinos in next-to-leading order QCD at the hadron colliders in the inverse seesaw framework

The explanation of the small neutrino mass can be depicted using some handsome models like type-I and inverse seesaw where the Standard Model gauge singlet heavy right-handed neutrinos are deployed. The common thing in these two models is a lepton number violating parameter, however, its order of magnitude creates a striking difference between them making the nature of the right-handed heavy neutrinos a major play factor. In the type-I seesaw a large lepton number violating parameter involves the heavy right-handed neutrinos in the form of Majorana fermions while a small lepton number violating parameter being involved in the inverse seesaw demands the pseudo-Dirac nature of the heavy right-handed neutrinos. Such heavy neutrinos are accommodated in these models through the sizable mixings with the Standard Model light neutrinos. In this paper we consider the purely inverse seesaw scenario to study the pair production of the pseudo-Dirac heavy neutrinos followed by their various multilepton decay modes through the leading branching fraction at the leading order and next-to-leading order QCD at the LHC with a center-of-mass energy of 13 TeV and a luminosity of 3000 fb[Formula: see text]. We also consider a prospective 100 TeV hadron collider with luminosities of 3000 fb[Formula: see text] and 30,000 fb[Formula: see text], respectively to study the process. Using anomalous multilepton search performed by the CMS at the 8 TeV with 19.5 fb[Formula: see text] luminosity we show prospective search reaches of the mixing angles for the three lepton and four lepton events at the 13 TeV LHC and 100 TeV hadron collider.

Looking for minimal inverse seesaw scenarios at the LHC with jet substructure techniques

Simple extensions of the standard model (SM) with additional right handed neutrinos (RHNs) can elegantly explain the existence of small neutrino masses and their flavor mixings. Collider searches for sterile neutrinos are being actively pursued currently. Heavy RHNs may dominantly decay into after being produced at the LHC. In this paper, we consider collider signatures of heavy pseudo-Dirac neutrinos in the context of the inverse seesaw scenario, with a sizable mixing with the SM neutrinos under two different flavor structures, viz. flavor diagonal and flavor non-diagonal (FND) scenarios. For the latter scenario we use a general parametrization for the model parameters by introducing an arbitrary orthogonal matrix and nonzero Dirac and Majorana phases. We then perform a parameter scan to identify allowed parameter regions which satisfy all experimental constraints. As an alternative channel to the traditional trilepton signature, we propose the opposite-sign di-lepton signature in the final state, in association with a fat jet from the hadronic decay of the boosted . We specifically consider a fat jet topology and explore the required enhancements from exploiting the characteristics of the jet substructure techniques. We perform a comprehensive collider analysis to demonstrate the effectiveness of this channel in both of the scenarios, significantly enhancing the bounds on the RHN mass and mixing angles at the 13 TeV LHC. Interestingly the FND scenario can reach up to a 5-σ limit under the presence of the general parametrization at the high luminosity LHC.

Common origin of inverse seesaw and baryon asymmetry

In the inverse seesaw scenario, several fermion singlets have a small Majorana mass term. We show such Majorana masses can be suppressed by some heavy fermion and/or Higgs singlets after a global symmetry is spontaneously broken. These interactions can also accommodate a leptogenesis mechanism to explain the cosmic baryon asymmetry if there are two or more heavy fermion and/or Higgs singlets.

Probing sterile neutrinos in the framework of inverse seesaw mechanism through leptoquark productions

We consider an extension of the Standard Model (SM) augmented by two neutral singlet fermions per generation and a leptoquark. In order to generate the light neutrino masses and mixing, we incorporate inverse seesaw mechanism. The right handed neutrino production in this model is significantly larger than the conventional inverse seesaw scenario. We analyze the different collider signatures of this model and find that the final states associated with three or more leptons, multi jet and at least one b-tagged and (or) $\tau$-tagged jet can probe larger RH neutrino mass scale. We have also proposed a same-sign dilepton signal region associated with multiple jets and missing energy that can be used to distinguish the the present scenario from the usual inverse seesaw extended SM.

A neutrinophilic 2HDM as a UV completion for the inverse seesaw mechanism

In Neutrinophilic Two Higgs Doublet Models, Dirac neutrino masses are obtained by forbidding a Majorana mass term for the right-handed neutrinos via a symmetry. We study a variation of such models in which that symmetry is taken to be a local U(1), leading naturally to the typical Lagrangian of the inverse seesaw scenario. The presence of a new gauge boson and of an extended scalar sector result in a rich phenomenology, including modifications to Z, Higgs and kaon decays as well as to electroweak precision parameters, and a pseudoscalar associated to the breaking of lepton number.

Right handed sneutrino dark matter in inverse and linear seesaw scenarios

We consider supersymmetric models in which the right–handed sneutrino is a viable WIMP dark matter candidate. These are either simple extensions of the Minimal Supersymmetric Standard Model or models with the addition of an extra U(1) group. All of them can explain small neutrino masses, through either the Inverse or the Linear Seesaw mechanism. We investigate the properties of the dark matter candidate naturally arising in these scenarios. We check for phenomenological bounds, such as correct relic abundance, consistency with direct detection cross section limits and laboratory constraints. Especially, we comment on limitations of the model space due to lepton flavour violating charged lepton decays.

Inverse seesaw neutrino signatures at the LHC and ILC

We study the collider signature of pseudo-Dirac heavy neutrinos in the inverse seesaw scenario, where the heavy neutrinos with mass at the electroweak scale can have sizable mixings with the Standard Model neutrinos, while providing the tiny light neutrino masses by the inverse seesaw mechanism. Based on a simple, concrete model realizing the inverse seesaw scenario, we fix the model parameters so as to reproduce the neutrino oscillation data and to satisfy other experimental constraints, assuming two typical flavor structures of the model and the different types of hierarchical light neutrino mass spectra. For completeness, we also consider a general parametrization for the model parameters by introducing an arbitrary orthogonal matrix and the nonzero Dirac and Majorana phases. We perform a parameter scan to identify an allowed parameter region which satisfies all experimental constraints. With the fixed parameters, we analyze the heavy neutrino signal at the LHC through trilepton final states with large missing energy and at the ILC through a single lepton plus dijet with large missing energy. We find that in some cases, the heavy neutrino signal can be observed with a large statistical significance via different flavor charged lepton final states.

Two radiative inverse seesaw models, dark matter, and baryogenesis.

The inverse seesaw mechanism allows the neutrino masses to be generated by new physics at an experimentally accessible scale, even with \U0001d4aa(1) Yukawa couplings. In the inverse seesaw scenario, the smallness of neutrino masses is linked to the smallness of a lepton number violating parameter. This parameter may arise radiatively. In this paper, we study the cosmological implications of two contrasting radiative inverse seesaw models, one due to Ma and the other to Law and McDonald. The former features spontaneous, the latter explicit lepton number violation. First, we examine the effect of the lepton-number violating interactions introduced in these models on the baryon asymmetry of the universe. We investigate under what conditions a pre-existing baryon asymmetry does not get washed out. While both models allow a baryon asymmetry to survive only once the temperature has dropped below the mass of their heaviest fields, the Ma model can create the baryon asymmetry through resonant leptogenesis. Then we investigate the viability of the dark matter candidates arising within these models, and explore the prospects for direct detection. We find that the Law/McDonald model allows a simple dark matter scenario similar to the Higgs portal, while in the Ma model the simplest cold dark matter scenario would tend to overclose the universe.

Triplet scalar dark matter and leptogenesis in an inverse seesaw model of neutrino mass generation

We propose a UV completion of the inverse see-saw scenario using fermion SU(2) triplet representations. Within this framework, a variation of the standard thermal leptogenesis is achievable at the O(TeV) scale, owing to the presence of a viable dark matter candidate. This baryogenesis scenario is ruled out if a triplet fermion is observed at the LHC. The dark matter is given by the lightest neutral component of a complex scalar SU(2) triplet, with mass in the TeV range. The scalar sector, which is enriched in order to account for the small neutrino masses, is treated in detail and shows potentially sizable Higgs boson h \to \gamma \gamma\ rates together with large h invisible branching ratios.

Neutrino mass from higher thand=5effective operators in supersymmetry, and its test at the LHC

We discuss neutrino masses from higher than d=5 effective operators in a supersymmetric framework, where we explicitly demonstrate which operators could be the leading contribution to neutrino mass in the MSSM and NMSSM. As an example, we focus on the d=7 operator L L H_u H_u H_d H_u, for which we systematically derive all tree-level decompositions. We argue that many of these lead to a linear or inverse see-saw scenario with two extra neutral fermions, where the lepton number violating term is naturally suppressed by a heavy mass scale when the extra mediators are integrated out. We choose one example, for which we discuss possible implementations of the neutrino flavor structure. In addition, we show that the heavy mediators, in this case SU(2) doublet fermions, may indeed be observable at the LHC, since they can be produced by Drell-Yan processes and lead to displaced vertices when they decay. However, the direct observation of lepton number violating processes is on the edge at LHC.

Phenomenological consequences of sub-leading terms in see-saw formulas

Several aspects of next-to-leading (NLO) order corrections to see-saw formulas are discussed and phenomenologically relevant situations are identified. We generalize the formalism to calculate the NLO terms developed for the type I see-saw to variants like the inverse, double or linear see-saw, i.e., to cases in which more than two mass scales are present. In the standard type I case with very heavy fermion singlets the sub-leading terms are negligible. However, effects in the percent regime are possible when sub-matrices of the complete neutral fermion mass matrix obey a moderate hierarchy, e.g. weak scale and TeV scale. Examples are cancellations of large terms leading to small neutrino masses, or inverse see-saw scenarios. We furthermore identify situations in which no NLO corrections to certain observables arise, namely for mu-tau symmetry and cases with a vanishing neutrino mass. Finally, we emphasize that the unavoidable unitarity violation in see-saw scenarios with extra fermions can be calculated with the formalism in a straightforward manner.

TeV scale see-saw mechanisms of neutrino mass generation, the Majorana nature of the heavy singlet neutrinos and (ββ)0ν-decay

It is shown that the Majorana nature of the heavy neutrinos N j having masses in the range of M j ~ (100 - 1000) GeV and present in the TeV scale type I and inverse see-saw scenarios of neutrino mass generation, is unlikely to be observable in the currently operating and future planned accelerator experiments (including LHC) due to the existence of very strong constraints on the parameters and couplings responsible for the corresponding ∣ΔL∣= 2 processes, L being the total lepton charge. If the heavy Majorana neutrinos N j are observed and they are associated only with the type I or inverse see-saw mechanisms and no additional TeV scale “new physics”, they will behave like Dirac fermions to a relatively high level of precision, being actually pseudo-Dirac particles. The observation of effects proving the Majorana nature of N j would imply that these heavy neutrinos have additional relatively strong couplings to the Standard Model particles (as, e.g. in the type III see-saw scenario), or that light neutrino masses compatible with the observations are generated by a mechanism other than see-saw (e.g., radiatively at one or two loop level) in which the heavy Majorana neutrinos N j are nevertheless involved.

Calculable neutrino masses in an inverse see-saw scenario and DM candidates

Within the supersymmetric inverse seesaw mechanism we provide a scenario where naturally small and calculable neutrino masses arise from a supersymmetry breaking renormalization-group-induced vacuum expectation value. In such a scenario the sneutrino can be the lightest supersymmetric particle potentially viable as WIMP dark matter.

Neutrino masses from higher thand= 5 effective operators

We discuss the generation of small neutrino masses from effective operators higher than dimension five, which open new possibilities for low scale see-saw mechanisms. In order to forbid the radiative generation of neutrino mass by lower dimensional operators, extra fields are required, which are charged under a new symmetry. We discuss this mechanism in the framework of a two Higgs doublet model. We demonstrate that the tree level generation of neutrino mass from higher dimensional operators often leads to inverse see-saw scenarios in which small lepton number violating terms are naturally suppressed by the new physics scale. Furthermore, we systematically discuss tree level generalizations of the standard see-saw scenarios from higher dimensional operators. Finally, we point out that higher dimensional operators can also be generated at the loop level. In this case, we obtain the TeV scale as new physics scale even with order one couplings.