Neutrino Mass Generation Research Articles

Explaining the Bd,s→K∗K¯∗\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {B}_{d,s}\ o {K}^{\\left(\\ast \\right)}{\\overline{K}}^{\\left(\\ast \\right)} $$\\end{document} non-leptonic puzzle and charged-current B-anomalies via scalar leptoquarks

We present a model based on S1 scalar leptoquarks to solve the tension observed in the recently proposed non-leptonic optimized observables LK∗K¯∗\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {L}_{K^{\\ast }{\\overline{K}}^{\\ast }} $$\\end{document} and LKK¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {L}_{K\\overline{K}} $$\\end{document}. These observables are constructed as ratios of U-spin related decays based on Bd,s0→K∗0K¯∗0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {B}_{d,s}^0\ o {K}^{\\left(\\ast \\right)0}{\\overline{K}}^{\\left(\\ast \\right)0} $$\\end{document}. The model gives a one-loop contribution to the Wilson coefficient of the chromomagnetic dipole operator needed to explain the tension in both non-leptonic observables, while naturally avoiding large contributions to the corresponding electromagnetic dipoles. The necessary chiral enhancement comes from an O(1) Yukawa coupling with a TeV-scale right-handed neutrino running in the loop. We endow the model with a U(2) flavor symmetry, necessary to protect light-family flavor observables that otherwise would be in tension. Furthermore, we show that the same S1 scalar leptoquark is capable of simultaneously explaining the hints of lepton flavor universality violation observed in charged-current B-decays. The model therefore provides a potential link between two puzzles in B-physics and TeV-scale neutrino mass generation. Finally, the combined explanation of the B-physics puzzles unavoidably results in an enhancement of BB→Kνν¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{B}\\left(B\ o K\ u \\overline{\ u}\\right) $$\\end{document}, yielding a value close to present bounds.

Linear seesaw mechanism from dark sector

We propose a minimal model where a dark sector seeds neutrino mass generation radiatively within the linear seesaw mechanism. Neutrino masses are calculable, since tree-level contributions are forbidden by symmetry. They arise from spontaneous lepton number violation by a small Higgs triplet vacuum expectation value. Lepton flavour violating processes e.g. μ → eγ can be sizeable, despite the tiny neutrino masses. We comment also on dark-matter and collider implications.

Light neutrinophilic dark matter from a scotogenic model

We present a minimal sub-GeV thermal Dark Matter (DM) model where the DM primarily interacts with neutrinos and participates in neutrino mass generation through quantum loop corrections at one-loop level. We discuss the challenges in achieving this in the scotogenic framework and identify a viable variant. Due to minimality and the interplay between obtaining the correct DM relic abundance and neutrino oscillation data, the model predicts (i) a massless lightest neutrino, (ii) enhanced rate of 0νββ decay due to loop corrections involving light DM exchange, and (iii) testable lepton flavor-violating signal μ→eγ. Detecting monoenergetic neutrinos from DM annihilation in next-generation neutrino detectors offers a promising way to test this scenario.

Connecting (g − 2)μ to neutrino mass in the extended neutrinophilic 2HDM

One simple way to lower the scale of the seesaw mechanism that generates neutrino masses is to attribute part of their smallness to a suppressed vacuum expectation value of a second Higgs doublet as in the neutrinophilic 2HDM or in the type IB seesaw model. On that structure we add one charged singlet scalar to induce a chirally enhanced contribution to (g – 2)μ with the same righthanded neutrinos of the seesaw. We discuss the interplay of generating the necessary contribution to the latter with lepton flavor violation which is also necessarily brought to low scale. We show that it is possible to explain (g –2)μ even for heavy neutrino masses of order of a few TeV.

Nu Electroweak baryogenesis: the scalar singlet strikes back

We perform a comprehensive scan of the parameter space of a general singlet scalar extension of the Standard Model to identify the regions which can lead to a strong first-order phase transition, as required by the electroweak baryogenesis mechanism. We find that taking into account bubble nucleation is a fundamental constraint on the parameter space and present a conservative and fast estimate for it so as to enable efficient parameter space scanning. The allowed regions turn out to be already significantly probed by constraints on the scalar mixing from Higgs signal strength measurements. We also consider the addition of new neutrino singlet fields with Yukawa couplings to both scalars and forming heavy (pseudo)-Dirac pairs, as in the linear or inverse Seesaw mechanisms for neutrino mass generation. We find that their inclusion does not alter the allowed parameter space from early universe phenomenology in a significant way. Conversely, there are allowed regions of the parameter space where the presence of the neutrino singlets would remarkably modify the collider phenomenology, yielding interesting new signatures in Higgs and singlet scalar decays.

Phenomenology of the simplest linear seesaw mechanism

The linear seesaw mechanism provides a simple way to generate neutrino masses. In addition to Standard Model particles, it includes quasi-Dirac leptons as neutrino mass mediators, and a leptophilic scalar doublet seeding small neutrino masses. Here we review its associated physics, including restrictions from theory and phenomenology. The model yields potentially detectable μ → eγ rates as well as distinctive signatures in the production and decay of heavy neutrinos (Ni) and the charged Higgs boson (H±) arising from the second scalar doublet. We have found that production processes such as e+e−→ NN, e−γ → NH− and e+e−→ H+H− followed by the decay chain {H}^{pm}to {ell}_i^{pm }N , Nto {ell}_j^{pm }{W}^{mp } leads to striking lepton number violation signatures at high energies which may probe the Majorana nature of neutrinos.

Neutrino masses and self-interacting dark matter with mass mixing Z − Z′ gauge portal

New light gauge bosons can affect several low-energy experiments, such as atomic parity violation or colliders. Here, we explore the possibility that a dark sector is charged under a new U(1) gauge symmetry, and the portal to the Standard Model is through a Z − Z′ mass mixing. In our approach, breaking the new gauge symmetry is crucial to generate neutrino masses. We investigate the parameter space to reproduce neutrino masses, the correct dark matter relic abundance, and to produce the observed core-like DM distribution in galactic centers.

Neutrino physics: Experimental and theoretical challenges

The existence of massive neutrinos is the first solid evidence of physics beyond the standard model of particle physics. A remarkable progress has been achieved in solar, atmospheric, reactor, and accelerator neutrino experiments during the last decades. On the theoretical side, several questions are being addressed, namely the Dirac or Majorana nature of neutrinos, the mechanisms for neutrino mass generation, and the relation between neutrinos and the matter–antimatter asymmetry observed in the Universe, among others. This article provides a brief overview on some of the current experimental and theoretical aspects in neutrino physics.

An alternate left-right symmetric model with Dirac neutrinos

We study a different variant of left-right symmetric model, incorporating Dirac type neutrinos. In the absence of the bi-doublet scalars, the possibility of a universal seesaw type of mass generation mechanism for all the Standard Model charged fermions have been discussed. The model has been constructed by extending the Standard Model particle spectrum with heavy vector-like fermions as well as different scalar multiplets. We have shown that this model can generate non zero neutrino mass through loop mediated processes. The parameters which are involved in neutrino mass generation mechanism can satisfy the neutrino oscillation data for both normal and inverted hierarchy. The lightest charged Higgs plays a crucial role in neutrino mass generation mechanism and can have mass of {mathcal {O}}[text {GeV}]. We have systematically studied different constraints which are relevant for the charged Higgs phenomenology. In addition to that we also briefly discuss discovery prospects of the charged Higgs at different colliders.

Implications on cosmology from Dirac neutrino magnetic moments

The mechanism for generating neutrino masses remains a puzzle in particle physics. If neutrino masses follow from a Dirac mass term, then neutrino states exist with opposite chirality compared to their weakly-interacting counterparts. These inactive states do not interact with their active counterparts at measurable scales in the standard model. However, the existence of these states can have implications for cosmology as they contribute to the radiation energy density at early times, and the matter energy density at late times. How Dirac neutrinos may populate thermal states via an anomalous magnetic moment operator is the focus of this work. A class of models where all neutrinos have a magnetic moment independent of flavor or chirality is considered. Subsequently, the cross sections for neutrinos scattering on background plasma particles are calculated so that the relic inactive neutrino energy is derived as a function of plasma temperature. To do so, one needs cross sections for scattering on all electrically charged standard-model particles. Therefore, the scattering cross section between a neutrino and $W$-boson via the magnetic moment vertex is derived. Current measurements put a constraint on the size of the neutrino magnetic moment from the cosmological parameter $N_{\rm eff}$ and light-element primordial abundances. Finally, how the extra Dirac states contribute to the matter energy density at late times is investigated by examining neutrino free-streaming.

Leptogenesis in Majoron models without domain walls

The emergence of domain walls is a well-known problem in Majoron models for neutrino mass generation. Here, we present extensions of the Majoron model by right-handed doublets and triplets that prevent domain walls from arising. These extensions are highly interesting in the context of Leptogenesis as they impact the conversion of a lepton asymmetry to a baryon asymmetry by Sphaleron processes.

Type-II seesaw Complex Triplet Model: Phase Transition and Global Fit Analysis

The type-II seesaw model can explain neutrino masses and address the baryon asymmetry problem of the Universe simultaneously. In this letter, we explore its phase transition and the resulting gravitational wave signals. We find a strong first-order electroweak phase transition generically prefers a relatively light triplet in the 300∼500GeV range, which is ideal for collider searches and can generate gravitational waves within the sensitivity reach of BBO and Ultimate-DECIGO. While above ∼1TeV where a future 100 TeV pp collider will play a key role in model discovery, we integrate out the triplet and perform a global fit analysis of this model at various future colliders. A lower bound in the 10−3∼10−2eV range on the triplet vacuum expectation value is obtained, which is comparable or even better than that from current μ→eγ experiments depending on the first generation neutrino mass.

Third-family quark-lepton Unification and electroweak precision tests

We analyze the compatibility of the hypothesis of third-family quark-lepton unification at the TeV scale with electroweak precision data, lepton flavor universality tests, and high-pT constraints. We work within the framework of the UV complete flavor non-universal 4321 gauge model, which is matched at one loop to the Standard Model Effective Field Theory. For consistency, all electroweak precision observables are also computed at one loop within the effective field theory. At tree level, the most sizeable corrections are to W → τντ and Z → ντντ due to integrating out a pseudo-Dirac singlet fermion required by the model for neutrino mass generation. At loop level, the new colored states of the model generate large flavor-universal contributions to the electroweak precision observables via leading- and next-to-leading log running effects, yielding a significant improvement in the electroweak fit (including an increase in the W-boson mass). These effects cannot be decoupled if the model addresses the charged-current B-meson anomalies. Overall, we find good compatibility between the data sets, while simultaneously satisfying all low- and high-energy constraints.

Dark matter in the scotogenic model with spontaneous lepton number violation

Scotogenic models constitute an appealing solution to the generation of neutrino masses and to the dark matter mystery. In this work we consider a version of the Scotogenic model that breaks lepton number spontaneously. At this scope, we extend the particle content of the Scotogenic model with an additional singlet scalar which acquires a non-zero vacuum expectation value and breaks a global lepton number symmetry. As a consequence, a massless Goldstone boson, the majoron, appears in the particle spectrum. We discuss how the presence of the majoron modifies the phenomenology, both in flavor and dark matter observables. We focus on the fermionic dark matter candidate and analyze its relic abundance and prospects for both direct and indirect detection.

PeV-scale leptogenesis, gravitational waves, and black holes from a SUSY-breaking phase transition

Supersymmetry is a highly motivated theoretical framework, whose scale of breaking may be at PeV energies, to explain null searches at the Large Hadron Collider. SUSY breaking through a first order phase transition may have occurred in the early universe, leading to potential gravitational wave signals. Constructing a realistic model for gauge-mediated supersymmetry breaking, we show that such a transition can also induce masses for heavy right-handed neutrinos and sneutrinos, whose CP-violating decays give leptogenesis at the PeV scale, and a novel mechanism of neutrino mass generation at one loop. For the same models we predict the possible gravity wave signals, and we study the possibility of production of primordial black holes during the phase transition.

Latest progress of PandaX-III neutrinoless double beta decay experiment

Neutrinoless double beta decay experiments are one of the most promising approaches to resolving the puzzle of neutrino mass generation. PandaX-III experiment searches the neutrinoless double beta decay of 136Xe with a high-pressure gaseous time projection chamber. A total amount of 140 kg enriched 136Xe under 10 bar will be loaded in the detector. Micromegas is used for charge collection with a high spatial resolution. Benefitting from the long event track in the gaseous detector, identification algorithms can significantly suppress the background rate. In this proceeding, the design and construction of the detector is presented, whose technologies have been successfully demonstrated by a prototype detector. The event classification algorithms were developed, suppressing the background events at a rate of about 300. Based on the result, we expect an exclusion sensitivity of 2.7×1026 yr (90% C.L.) for decay half life after 5 years’ exposure.

Exploring the vacuum structure of gravitationally induced neutrino masses

In this work, we explore the proposed mechanism in which the gravitational $\ensuremath{\theta}$ anomaly generates neutrino masses. We highlight that the leading renormalizable interactions of the neutrino condensate forbid the possibility of generating hierarchical masses consistent with observation. This conclusion still holds when Standard Model loop corrections are accounted for. We show that higher-dimensional operators can alleviate this problem. The higher-dimensional operators could be generated from the gravitational anomaly itself, but there is no clear way to know without a deeper understanding of the low-energy description of this mechanism. Because of that, we explore the possibility of new particles generating neutrino mass splittings. We show that both new particles that alter the scalar potential of the condensate or new particles in loops for the neutrino self-energy can solve this problem.

A new viable mass region of dark matter and dirac neutrino mass generation in a scotogenic extension of SM

In this paper, we propose a scotogenic extension of the Standard Model (SM) which can provide a scalar dark matter (DM) candidate in the new, theoretically previously unaddressed, intermediate region ([Formula: see text][Formula: see text]GeV) and also generate light Dirac neutrino masses. In this framework, the SM is extended by three gauge singlet fermions, two singlet scalar fields and one additional scalar doublet along with a continuous global symmetry [Formula: see text] and discrete symmetries [Formula: see text] and [Formula: see text]. These additional symmetries prevent the singlet fermions from obtaining Majorana mass terms along with providing the stability to the DM candidate. It is known that in the case of the scalar singlet DM model, the only region which is not yet excluded is a narrow region close to the Higgs resonance [Formula: see text] — others ruled out from different experimental and theoretical bounds. In the case of the inert doublet model, the mass region ([Formula: see text]–80[Formula: see text]GeV) and the high-mass region (heavier than 550[Formula: see text]GeV) are allowed. This motivates us to explore a parameter range in the intermediate-mass region [Formula: see text][Formula: see text]GeV, which we do in a scotogenic extension of SM with a scalar doublet and scalar singlets. The DM in our model is a mixture of singlet and doublet scalars, in the freeze-out scenario. We constrain the allowed parameter space of the model using the Planck bound on present DM relic abundance, neutrino mass and the latest bound on spin-independent DM-nucleon scattering cross-section from the XENON1T experiment. Further, we constrain the DM parameters from the indirect detection bounds arising from the global analysis of the Fermi-LAT observations of dwarf spheroidal satellite (dSphs) galaxies, Higgs invisible decay and Electroweak Precision Test (EWPT) as well. We find that our model findings may provide a viable DM candidate satisfying all the constraints on DM parameters in the new, previously unexplored mass range ([Formula: see text][Formula: see text]GeV). This new window for the DM candidate could be searched in future experiments along with an explanation of the Dirac mass of neutrinos since so far there is no strong evidence in support of the Majorana nature of neutrino mass.

Vacuum stability and radiative symmetry breaking of the scale-invariant singlet extension of type II seesaw model

The questions of the origin of electroweak symmetry breaking and neutrino mass are two major puzzles in particle physics. Neutrino mass generation requires new physics beyond the Standard Model and also suggests reconsideration of physics of symmetry breaking. The aim of this paper is to study radiative symmetry breaking in the singlet scalar extension of type II seesaw neutrino mass model. We derive bounded-from-below conditions for the scalar potential of the model in full generality for the first time. The Gildener–Weinberg approach is utilised in minimising the multiscalar potential. Upon imposing the bounded-from-below and perturbativity conditions, as well as experimental constraints from colliders, we find the parameter space of scalar quartic couplings that can radiatively realise electroweak symmetry breaking at one-loop level. To satisfy all the constraints, the masses of the heavy triplet-like Higgs bosons must be nearly degenerate. The evolution of the Higgs doublet quartic coupling lambda _{H} can be prevented from being negative up to the Planck scale.

Texture-zero patterns of lepton mass matrices from modular symmetry

Texture zeros in fermion mass matrices have been widely considered in tackling the Standard Model flavour puzzle. In this work, we perform a systematic analysis of texture zeros in lepton mass matrices in the framework of {Gamma}_3^{prime}cong {T}^{prime } modular symmetry. Assuming that the lepton fields transform as irreducible representations of T′, we obtain all possible texture-zero patterns for both charged-lepton and neutrino mass matrices which can be achieved from T′ modular symmetry. We provide representative models for the phenomenologically-viable textures which can accommodate the experimental data. The predictions for lepton mixing angles, CP-violating phases, light neutrino masses and effective neutrino mass relevant for neutrinoless double beta decay, are discussed. We find that the minimal viable lepton model depends on only 7 real free parameters including the modulus τ (the corresponding charged-lepton mass matrix contains 4 vanishing entries, and the neutrino mass matrix has 1 texture zero). Finally, we study in detail three benchmark models, one for each neutrino mass generation mechanism considered (Dirac, Majorana via Weinberg operator and Majorana via minimal type-I seesaw mechanism).