Search

In the model [J. Ganguly and R. S. Hundi, Chinese Phys. C 46, 103101 (2022).], the neutrino mixing has been explained in a type II seesaw scenario with generalized CP symmetries. The neutrino mass matrix has μ − τ symmetric nature. As neutrino oscillation data suggests neutrino mixing can deviate from μ − τ symmetry, in this work, deviation from μ − τ symmetric mass matrix is shown by breaking the generalized CP symmetry explicitly by a small amount in the Yukawa Lagrangian which actually shows that atmospheric mixing angle can deviate from maximal value. As a phenomenological implication, branching ratios of the lepton flavor violating decays have been studied, which occurs by the triplet Higgs, by writing down the full scalar potential and then finding the mass eigenstates of the scalars. We have studied the implications of neutrinoless double beta decay within our model. [ABSTRACT FROM AUTHOR]

In this paper we investigate how well the nature of heavy neutral leptons can be determined at a future lepton collider, after its potential discovery. Considered in a simplified model are prompt decays of the neutrino in the mass range from 100 GeV to 10 TeV. We study event selection and application of multivariate analyses to determine whether such a newly discovered particle is of the Dirac or Majorana nature. Combining lepton charge and kinematic event variables, we find that the nature of a heavy neutrino, whether it is a Dirac or a Majorana particle, can be determined at 95% C.L. almost in the whole discovery range. We will briefly speculate about other than the studied channels and the robustness of this statement in more general models of heavy neutral leptons, particularly on the complementarity of high-energy electron-positron vs. muon colliders on resolving the flavor structure of heavy neutrinos. [ABSTRACT FROM AUTHOR]

We study lepton flavour universality violation in SM boson decays in low-scale seesaw models of neutrino mass generation, also addressing other electroweak precision observables. We compute the electroweak next-to-leading order corrections, which turn out to be important – notably in the case of the invisible decay width of the Z boson, for which the corrections can be as large as the current experimental uncertainty. As a well-motivated illustrative study case, we choose a realisation of the Inverse Seesaw mechanism, and discuss the complementary role of lepton flavour conserving, lepton flavour violating and precision observables, both in constraining and in probing such models of neutrino mass generation. Our findings suggest that invisible Z decays are especially important, potentially at the origin of the most stringent constraints for certain regimes of the Inverse Seesaw (while complying with charge lepton flavour violation and other electroweak precision tests). We also discuss the probing power of the considered observables in view of the expected improvement in experimental precision at FCC-ee. [ABSTRACT FROM AUTHOR]

Searches for new physics (NP) at particle colliders typically involve multivariate analysis of kinematic distributions of final state particles produced in a decay of a hypothetical NP resonance. Since the pair-production cross-sections mediated by such resonances are strongly suppressed by the NP scale, this analysis becomes less relevant for NP searches for masses of the BSM resonance above 1 TeV. On the other hand, t-channel processes are less sensitive to the mass of the virtual mediator and therefore larger phase-space can be potentially probed as well as the couplings between the NP particles and the Standard Model fields. The fact that transitions between different generations of quarks and leptons may exist, the potential of the search presented in this article can be used, as a reference guide, to enlarge significantly the scope of searches performed at the LHC to flavour off-diagonal channels, in a theoretically consistent approach. In this work, we study non-resonant production of scalar leptoquarks which have been proposed in the literature to provide a potential avenue for radiative generation of neutrino masses, accommodating as well the existing flavour physics data. Final states involving just two muons at the LHC (μ+μ−), are used as a well-motivated case study. [ABSTRACT FROM AUTHOR]

We propose a tri-hypercharge (TH) extension of the Standard Model (SM) in which a separate gauged weak hypercharge is associated with each fermion family. In this way, every quark and lepton multiplet carries unique gauge quantum numbers under the extended gauge group, providing the starting point for a theory of flavour. If the Higgs doublets only carry third family hypercharge, then only third family renormalisable Yukawa couplings are allowed. However, non-renormalisable Yukawa couplings may be induced by the high scale Higgs fields (hyperons) which break the three hypercharges down to the SM hypercharge, providing an explanation for fermion mass hierarchies and the smallness of CKM quark mixing. Following a similar methodology, we study the origin of neutrino masses and mixing in this model. Due to the TH gauge symmetry, the implementation of a seesaw mechanism naturally leads to a low scale seesaw, where the right-handed neutrinos in the model may be as light as the TeV scale. We present simple examples of hyperon fields which can reproduce all quark and lepton (including neutrino) masses and mixing. After a preliminary phenomenological study, we conclude that one of the massive Z′ bosons can be as light as a few TeV, with implications for flavour-violating observables, LHC physics and electroweak precision observables. [ABSTRACT FROM AUTHOR]

We discuss sensitivities to lepton flavor violating (and conserving) interactions at future muon colliders, especially at μ+μ+ colliders. Compared with the searches for rare decays of μ and τ, we find that the TeV-scale future colliders have better sensitivities depending on the pattern of hierarchy in the flavor mixings. As an example, we study the case with the type-II seesaw model, where the flavor mixing parameters have direct relation to the neutrino mass matrix. At a μ+μ+ collider, the number of events of the μ+μ+ → μ+τ+ process can be larger than O 100 with the center of mass energy s = 2 TeV, and with an integrated luminosity L = 1 ab−1, while satisfying bounds from rare decays of μ and τ. We discuss impacts of the overall mass scale of neutrinos as well as CP violating phases to the number of expected events. [ABSTRACT FROM AUTHOR]

The neutrinoless double beta decay is studied in the framework of left-right symmetric model. The coexistence of left and right handed currents induces rather complicated interactions between the lepton and hadron sectors, called < λ > mechanism and < η > mechanism in addition to the conventional effective neutrino mass < mν > mechanism. In this letter, we study the possible magnification of < η > mechanism and the relatively vanishing of < λ > mechanism. The importance to survey 0νββ decay of different nuclei for specifying new physics beyond the Standard Model is also discussed. [ABSTRACT FROM AUTHOR]

The future high-energy muon colliders, featuring both high energy and low background, could play a critical role in our searches for new physics. The smallness of neutrino mass is a puzzle of particle physics. Broad classes of solutions to the neutrino puzzles can be best tested by seeking the partners of SM light neutrinos, dubbed as heavy neutral leptons (HNLs), at muon colliders. We can parametrize HNLs in terms of the mass mN and the mixing angle with ℓ-flavor Uℓ. In this work, we focus on the regime mN> O(100) GeV and study the projected sensitivities on the |Uℓ|2 − mN plane with the full-reconstructable HNL decay into a hadronic W and a charged lepton. The projected reach in |Uℓ|2 leads to the best sensitivities in the TeV realm. [ABSTRACT FROM AUTHOR]

Heavy neutrinos are usually introduced to accommodate tiny neutrino masses via seesaw mechanism, or to alleviate the cosmology problem, and there may exist charged Higgs which couple to the leptons with different flavors. These two features can appear in the Twin Higgs models. What interests us is that such new particles and interactions may lead to new contributions to the lepton flavor violating processes ℓ i → ℓ j γ and ℓ i → ℓ j ℓ k ℓ l . We find that current experimental data can constrain the parameter spaces and certain lepton flavor violating processes can possibly be tested by the next generation experiments. [ABSTRACT FROM AUTHOR]

The SUSY SO(10) GUT is in severe tension with the experimental bounds on proton partial lifetimes because proton decay mediated by colored Higgsinos (dimension-five proton decay) is too rapid. In this paper, we pursue the possibility that a texture of the Yukawa coupling matrices in a renormalizable SUSY SO(10) GUT model suppresses dimension-five proton decay. We focus on a general renormalizable SUSY SO(10) GUT model which contains 10 + 126 + 126 ¯ + 120 representation fields and where the Yukawa coupling matrices of the 16 matter fields with the 10, 126 ¯ , 120 fields, Y10, Y126, Y120, provide the quark and lepton Yukawa couplings and Majorana mass of the singlet neutrinos. We find that if components in certain flavor bases, Y 10 u R d R , Y 126 u R d R , Y 10 u R s R , Y 126 u R s R , Y 10 u L d L , Y 126 u L d L , Y 10 u L s L , Y 126 u L s L , Y 10 u L u L , Y 126 u L u L , are all on the order of the up quark Yukawa coupling, dimension-five proton decay can be suppressed while the Yukawa coupling matrices still reproduce the realistic quark and lepton masses and flavor mixings. We numerically obtain specific Yukawa coupling matrices satisfying the above conditions, calculate proton partial lifetimes from them and evaluate how dimension-five proton decay is suppressed when these conditions are met. [ABSTRACT FROM AUTHOR]

We present a neutrino mass model based on modular symmetry with the fewest input parameters to date, which successfully accounts for the 12 lepton masses and mixing parameters through 6 real free parameters including the modulus. The neutrino masses are predicted to be normal ordering, the atmospheric angle θ23 is quite close to maximal value and the Dirac CP phase δCP is about 1.34π. We also study the soft supersymmetry breaking terms due to the modulus F-term in this minimal model, which are constrained to be the non-holomorphic modular forms. The radiative lepton flavor violation process μ → eγ is discussed. [ABSTRACT FROM AUTHOR]

Many beyond the Standard Model signatures predict new physics phenomena that lead to final states containing both leptons and jets. The latest search results for massive particles or lepton flavor violation using the full Run 2 dataset recorded by the ATLAS experiment are presented. A particular focus is given to searches for leptoquarks, that offer an attractive potential explanation for the lepton flavor anomalies observed at B -physics factories; searches for heavy leptons, such as the ones appearing in Type-III seesaw model that can explain the smallness of neutrino masses; and lepton flavor violating Z decays, which is an excellent probe for new physics that predict direct lepton flavor violating processes. [ABSTRACT FROM AUTHOR]

We analyse the effects of Dirac and Majorana neutrinos on leptonic decays of muon and tau leptons using the most general four-lepton effective interaction Hamiltonian of dimension six. We calculate the specific energy and angular distribution of the final charged lepton, including the polarizations of the initial and final charged leptons. We discuss the new generalized Michel parameters and focus on the effects of the heavy neutrino masses that would lead to sizable contributions on scenarios where the new sterile neutrinos have non-negligible mixing. Specifically, the most promising scenario is found for the case of τ decay with one heavy final-state neutrino with a mass around 102 − 103 MeV, where the linear term suppression could be of order 10−4, low enough to be measured in current and forthcoming experiments. [ABSTRACT FROM AUTHOR]

We extend the contents of the standard model (SM) by introducing TeV-scale scalar leptoquarks to generate neutrino masses and explain some current observed deviations from the SM predictions, including the anomalous magnetic moments of charged leptons (electron and muon) and B-physics anomalies ( R K (∗) and R D (∗) ). The model consists of SU (2) L singlet leptoquark S 1 ∼ (3 ¯ , 1 , 1 / 3) , doublet leptoquark R ~ 2 ∼ (3 , 2 , 1 / 6) and triplet leptoquark S 3 ∼ (3 ¯ , 3 , 1 / 3) . We combine the constraints arising from the low-energy lepton flavor violation, meson decay and mixing observables. We perform a detailed phenomenological analysis and identify the minimized texture of leptoquark Yukawa matrices to accommodate a unified explanation of the anomalies and neutrino oscillation data. [ABSTRACT FROM AUTHOR]

Charged Lepton Flavour Violating (cLFV) decays constrain the relationship between the neutrino and the scalar sectors of the Grimus-Neufeld model (GNM), an appealing minimal model of neutrino masses. It turns out, that in the scenario, where the seesaw scale is lower than the electroweak one, cLFV is completely defined by the new Yukawa interactions between the additional single heavy Majorana neutrino, the second Higgs doublet and the lepton doublets. Therefore, we derive a useful parameterization for the Yukawa couplings which reproduces by construction the correct PMNS matrix and the correct neutrino masses for both Normal and Inverted ordering at one-loop level. We embed this scenario in the FlexibleSUSY spectrum-generator generator to perform parameter scans. Focusing on the tiny seesaw scale, we show that current μ → eγ limits provide significant constraints on the scalar sector, and we evaluate the impact of future cLFV τ-decay searches for the cases of discovery or non-discovery. The tiny seesaw scale makes the neutrino sector and the cLFV processes in the GNM similar to the scotogenic and the scoto-seesaw models, so we provide constraints for these models as well. [ABSTRACT FROM AUTHOR]

In this work, by using the machine learning methods, we study the sensitivities of heavy pseudo-Dirac neutrino N in the inverse seesaw at the high-energy hadron colliders. The production process for the signal is pp → ℓ → 3ℓ + E T miss , while the dominant background is pp → WZ → 3ℓ + E T miss . We use either the Multi-Layer Perceptron or the Boosted Decision Tree with Gradient Boosting to analyse the kinematic observables and optimize the discrimination of background and signal events. It is found that the reconstructed Z boson mass and heavy neutrino mass from the charged leptons and missing transverse energy play crucial roles in separating the signal from backgrounds. The prospects of heavy-light neutrino mixing |VℓN|2 (with ℓ = e, μ) are estimated by using machine learning at the hadron colliders with s = 14 TeV, 27 TeV, and 100 TeV, and it is found that |VℓN|2 can be improved up to O (10−6) for heavy neutrino mass mN = 100 GeV and O (10−4) for mN = 1 TeV. [ABSTRACT FROM AUTHOR]

The neutrino mass and dark matter (DM) problems are addressed in a Standard Model extension where the type-II seesaw and scotogenic mechanisms coexist. The model features a flavour 풵8 discrete symmetry which is broken down to a 풵2, stabilising the (scalar or fermion) DM particle. Spontaneous CP violation is implemented through the complex vacuum expectation value of a singlet scalar field, inducing observable CP-violating effects in the lepton sector. The structure of the effective neutrino mass matrix leads to constraints on the low-energy neutrino observables, namely the atmospheric neutrino mixing angle θ23, the Dirac CP-violating phase δ and the absolute neutrino mass scale mlightest. In particular, in most cases, the model selects one θ23 octant with δ ≃ 3π/2. Moreover, the obtained lower bounds on mlightest are typically in the range probed by cosmology. We also analyse the constraints imposed on the model by current experimental limits on charged lepton flavour violating (cLFV) processes, as well as future projected sensitivities. It is shown that the Higgs triplet and scotogenic contributions to cLFV never overlap and that the interplay among Yukawa couplings, dark charged scalar masses and mixing leads to a wide parameter-space region compatible with current experimental bounds. We investigate the scalar and fermion DM parameter space of our model by considering relic density, direct-detection (DD) and collider constraints. For scalar DM the mass interval 68 GeV ≲ mDM ≲ 90 GeV is viable and will be probed by future DD searches. In the fermion DM case, correct relic density is always obtained for mDM ≳ 45 GeV thanks to dark fermion-scalar coannihilation channels. [ABSTRACT FROM AUTHOR]

We show that the anomalous magnetic moment experimental data of muon and electron (g - 2) μ , e can be explained simultaneously in simple extensions of the 3-3-1 models consisting of new heavy neutrinos and a singly charged Higgs boson. The heavy neutrinos generate active neutrino masses and mixing through the general seesaw mechanism. They also have non-zero Yukawa couplings with singly charged Higgs bosons and right-handed charged leptons, which result in large one-loop contributions known as chirally-enhanced ones. Numerical investigation confirms a conclusion indicated previously that these contributions are the key point to explain the large (g - 2) μ , e data, provided that the inverse seesaw mechanism is necessary to allow both conditions that heavy neutrino masses are above few hundred GeV and non-unitary part of the active neutrino mixing matrix must be large enough. [ABSTRACT FROM AUTHOR]

Neutrino masses are evidence of lepton flavor violation, but no violation in the interactions among the charged leptons has been observed yet. Many models of Physics Beyond the Standard Model (BSM) predict Charged Lepton Flavor Violation (CLFV) in a wide spectrum of processes with rates in reach of upcoming experiments. The experimental searches that provide the current best limits on the CLFV searches are reviewed, with a particular emphasis on the muon-based experiments that give the most stringent constraints on the BSM parameter space. The next generation of muon-based experiments (MEG-II, Mu2e, COMET, Mu3e) aims to reach improvements by many orders of magnitude with respect to the current best limits, thanks to several technological advancements. We review popular heavy BSM theories, and we present the calculations of the predicted CLFV branching ratios, focusing on the more sensitive μ → e sector. [ABSTRACT FROM AUTHOR]

In this paper, we present a model which employs CP × Z 3 symmetries where quark mixing and charged leptons masses are explained by following some texture. To achieve neutrino mass and mixing, we write a nonrenormalizable Lagrangian using type II seesaw mechanism by assuming (1) couplings predicting no CP violation. Then, we calculate the value of the couplings for both normal and inverted ordering of neutrino masses. We propose a mechanism of ultraviolet (UV) completion that motivates the higher-dimensional Lagrangian in the neutrino sector. We also calculate the branching fraction of lepton flavor violating decays driven by triplet scalar for the model. Later, it is shown that the model can also accommodate maximal CP violation by breaking the CP symmetry spontaneously. [ABSTRACT FROM AUTHOR]

Experimental hints for lepton-flavor universality violation in the muon's magnetic moment as well as neutral- and charged-current B-meson decays require Standard-Model extensions by particles such as leptoquarks that generically lead to unacceptably fast rates of charged lepton flavor violation and proton decay. We propose a model based on a gauged U (1) L μ - L τ that eliminates all these unwanted decays by symmetry rather than finetuning and efficiently explains (g - 2) μ , R K (∗) , R D (∗) , and neutrino masses. The U (1) L μ - L τ furthermore acts as a stabilizing symmetry for dark matter and the light Z ′ gauge boson mediates velocity-dependent dark-matter self-interactions that resolve the small-scale structure problems. Lastly, even the Hubble tension can be ameliorated via the light Z ′ contribution to the relativistic degrees of freedom. [ABSTRACT FROM AUTHOR]

We make an investigation of modular Î" 5 ′ ≃ A 5 ′ group in inverse seesaw framework. Modular symmetry is advantageous because it reduces the usage of extra scalar fields significantly. Moreover, the Yukawa couplings are expressed in terms of Dedekind eta functions, which also have a q expansion form, generally utilized to achieve numerical simplicity. Our proposed model includes six heavy fermion superfields i.e., N R i , S L i and a weighton. The study of neutrino phenomenology becomes simplified and effective by the usage of A 5 ′ modular symmetry, which provides us a well defined mass structure for the lepton sector. Here, we observe that all the neutrino oscillation parameters, as well as the effective electron neutrino mass in neutrinoless double beta decay can be successfully accommodated in this model. We also briefly discuss the lepton flavor violating decays â„" i â†' â„" j Îł, the collider bound on Z ′ mass and comment on non-unitarity of lepton mixing matrix. [ABSTRACT FROM AUTHOR]

We summarize the potential charged lepton flavor violation (LFV) from neutrino mass relevant models, for instance the seesaw mechanisms. In particular, we study, in a model-dependent way, the LFV signals at the high-energy hadron and lepton colliders originating from the beyond standard model (BSM) neutral scalar H, doubly charged scalar H ± ± , heavy neutrino N, heavy W R boson, and the Z ′ boson. For the neutral scalar, doubly charged scalar and Z ′ boson, the LFV signals originate from the (effective) LFV couplings of these particles to the charged leptons, while for the heavy neutrino N and W R boson, the LFV effects are from flavor mixing in the neutrino sector. We consider current limits on these BSM particles and estimate their prospects at future high-energy hadron and lepton colliders. [ABSTRACT FROM AUTHOR]

S U (2) L -invariance links charged dilepton and dineutrino couplings. Phenomenological implications are worked out for flavor changing neutral currents involving strange, charm, beauty and top quark transitions in a model-independent way. We put forward novel tests of lepton universality and lepton flavor conservation in | Δ c | = | Δ u | = 1 and | Δ b | = | Δ q | = 1 , q = d , s , transitions suitable for the experiments Belle II and BES III. Single top production plus dileptons uniquely probes semileptonic four-fermion | Δ t | = | Δ q ′ | = 1 , q ′ = u , c , couplings and further study at the LHC is encouraged. Tests with single top production associated with dileptons and missing energy are suitable for study at future e + e - or muon colliders. [ABSTRACT FROM AUTHOR]

General U (1) extension of the Standard Model (SM) is a well motivated beyond the Standard Model (BSM) scenario where three generations of right handed neutrinos (RHNs) are introduced to cancel gauge and mixed gauge-gravity anomalies. After the U (1) X is broken, RHNs participate in the seesaw mechanism to generate light neutrino masses satisfying neutrino oscillation data. In addition to that, a neutral gauge boson Z ′ is evolved which interacts with the left and right handed fermions differently manifesting chiral nature of the model which could be probed in future collider experiments. As a result, if we consider μ + e − and μ + μ + collisions in μ TRISTAN experiment Z ′ mediated 2 → 2 scattering will appear in t − and u -channels depending on the initial and final states being accompanied by the photon and Z mediated interactions. This will result well motivated resulting forward dominant scenarios giving rise to sizable left-right asymmetry. Estimating constraints on general U (1) coupling from LEP-II and LHC for different U (1) X charges, we calculate differential and integrated scattering cross section and left-right asymmetry for μ + e − → μ + e − and μ + μ + → μ + μ + processes which could be probed at μ TRISTAN experiment further enlightening the interaction between Z ′ and charged leptons and the U (1) X breaking scale. [ABSTRACT FROM AUTHOR]

We propose a quark-lepton model via leptoquarks and modular A 4 symmetry. Since the neutrino mass is induced at one-loop level mediated by down quarks as well as leptoquarks, we have to explain lepton and quark masses and mixings with a single modulus τ . Here, we find predictions for lepton and quark sectors with unified modulus τ , and show several constraints originating from leptoquarks. [ABSTRACT FROM AUTHOR]

We propose a simple model to simultaneously explain four observed flavor anomalies while generating the neutrino mass at the one-loop level. Specifically, we address the measured anomalous magnetic dipole moments of the muon, ∆aμ, and electron, ∆ae, the observed anomaly of b → sl+l− in the B-meson decays, and the Cabibbo-angle anomaly. The model consists of four colorful new degrees of freedom: three scalar leptoquarks with the Standard Model quantum numbers (3, 3, −1/3), (3, 2, 1/6), and (3, 1, 2/3), and one pair of down-quark-like vector fermion in (3, 1, −1/3). The baryon number is assumed to be conserved for simplicity. Phenomenologically viable solutions with the minimal number of real parameters can be found to accommodate all the above-mentioned anomalies and produce the approximate, close to 1σ, neutrino oscillation pattern at the same time. From general consideration, the model robustly predicts: (1) neutrino mass is of the normal hierarchy type, and (2) M ee ν ≲ 3 × 10−4 MeV. The possible UV origin to explain the flavor pattern of the found viable parameter space is briefly discussed. The parameter space can be well reproduced within a simple split fermion toy model. [ABSTRACT FROM AUTHOR]

The search for lepton flavor violation in charged lepton decays is a highly sensitive tool to look for physics beyond the Standard Model. Among the possible processes, μ-decays are considered to have the largest discovery potential in most of the standard model extensions. Many searches have been performed in the past, but no evidence has been found so far. In this paper, we have reviewed the current theoretical and experimental status of the field of muon to electron decay and its potential to search for new physics beyond the Standard Model. Future prospects of experiments for further progress in this field are also discussed. [ABSTRACT FROM AUTHOR]

Motivated by the intriguing discrepancies in b → sℓℓ transitions, the fermion mass problem, and a desire to preserve the accidental symmetries of the Standard Model (SM), we extend the SM by an anomalous U(1)X gauge symmetry where X = Y3 + a(Lμ− Lτ)/6. The heavy Z′ boson associated with spontaneously breaking U(1)X at the TeV scale mediates the b → sℓℓ anomalies via O 9 μ ~ 1 Λ 2 s ¯ γ ρ P L b μ ¯ γ ρ μ . We show that this model, which features mixed gauge anomalies involving U(1)X and hypercharge, can be made anomaly-free for any a ∈ ℤ by integrating in a pair of charged fermions whose masses naturally reside somewhere between 1 and 30 TeV. The gauge symmetry permits only the third family Yukawas at the renormalisable level, and so the light quark masses and mixings are controlled by accidental U(2)3 flavour symmetries which we assume are minimally broken alongside U(1)X. The lepton sector is not governed by U(2) symmetries, but rather one expects a nearly diagonal charged lepton Yukawa with me,μ « mτ. The model does not explain the hierarchy me « mμ, but it does possess high quality lepton flavour symmetries that are robust to the heavy physics responsible for generating me,μ. We establish the viability of these models by checking agreement with the most important experimental constraints. We comment on how the model could also explain neutrino masses and the muon g − 2. [ABSTRACT FROM AUTHOR]

We propose a leptoquark model with two scalar leptoquarks S 1 3 ¯ 1 1 3 and R ˜ 2 3 2 1 6 to give a combined explanation of neutrino masses, lepton flavor mixing and the anomaly of muon g − 2, satisfying the constraints from the radiative decays of charged leptons. The neutrino masses are generated via one-loop corrections resulting from a mixing between S1 and R ˜ 2 . With a set of specific textures for the leptoquark Yukawa coupling matrices, the neutrino mass matrix possesses an approximate μ-τ reflection symmetry with (Mν)ee = 0 only in favor of the normal neutrino mass ordering. We show that this model can successfully explain the anomaly of muon g − 2 and current experimental neutrino oscillation data under the constraints from the radiative decays of charged leptons. [ABSTRACT FROM AUTHOR]

We analyse the experimental limits on the breaking scale of Pati-Salam extensions of the Standard Model. These arise from the experimental limits on rare-meson decay processes mediated at tree-level by the vector leptoquark in the model. This leptoquark ordinarily couples to both left- and right-handed SM fermions and therefore the meson decays do not experience a helicity suppression. We find that the current limits vary from O (80–2500) TeV depending on the choice of matrix structure appearing in the relevant three-generational charged-current interactions. We extensively analyse scenarios where additional fermionic degrees of freedom are introduced, transforming as complete Pati-Salam multiplets. These can lower the scales of Pati-Salam breaking through mass-mixing within the charged-lepton and down-quark sectors, leading to a helicity suppression of the meson decay widths which constrain Pati-Salam breaking. We find four multiplets with varying degrees of viability for this purpose: an SU(2)L/R bidoublet, a pair of SU(4) decuplets and either an SU(2)L or SU(2)R triplet all of which contain heavy exotic versions of the SM charged leptons. We find that the Pati-Salam limits can be as low as O (5–150) TeV with the addition of these four multiplets. We also identify an interesting possible connection between the smallness of the neutrino masses and a helicity suppression of the Pati-Salam limits for three of the four multiplets. [ABSTRACT FROM AUTHOR]

We study the charged lepton flavour violation in a popular neutrino mass model with A 4 discrete symmetry. This symmetry requires the presence of multiple Higgs doublets in the model and it also dictates the flavour violating Yukawa couplings of the additional neutral scalars of the model. Such couplings lead to the decays of the neutral mesons, the top quark and the τ lepton into charged leptons of different flavours at tree level. The A 4 symmetry of the model leads to certain characteristic signatures in these decays. We discuss these signatures and predict the rates for the most favourable charged lepton flavour violating modes. [ABSTRACT FROM AUTHOR]

We propose a renormalizable gauge U (1) B − L extension of the Standard Model (SM) based on Q 4 symmetry and an auxiliary Z 4 symmetry which can explain the observed quark and lepton masses and mixing angles associated to normal neutrino mass ordering through type-I seesaw mechanism. The relation between the atmospheric mixing angle 𝜃 2 3 and the effective parameters in neutrino sector is analyzed. Two Majorana phases are predicted to be α 2 1 = 0 and α 3 1 = − 1. 9 3 8 5 rad and the model also predicts the effective neutrino mass parameters of m β = 6. 6 8 5 meV , 〈 m e e 〉 = 6. 7 6 7 meV which is well consistent with the planning of future experiments. In the quark sector, the model is predictive since it has ten effective parameters that allow to successfully reproduce the experimental values of the experimental values of the ten physical observables of the quark sector. [ABSTRACT FROM AUTHOR]

Sum rules in the lepton sector provide an extremely valuable tool to classify flavour models in terms of relations between neutrino masses and mixing parameters testable in a plethora of experiments. In this manuscript we identify new leptonic sum rules arising in models with modular symmetries with residual symmetries. These models simultaneously present neutrino mass sum rules, involving masses and Majorana phases, and mixing sum rules, connecting the mixing angles and the Dirac CP-violating phase. The simultaneous appearance of both types of sum rules leads to some non-trivial interplay, for instance, the allowed absolute neutrino mass scale exhibits a dependence on the Dirac CP-violating phase. We derive analytical expressions for these novel sum rules and present their allowed parameter ranges as well as their predictions at upcoming neutrino experiments. [ABSTRACT FROM AUTHOR]

We propose a theory of quark and lepton mass and mixing with non-universal Z′ couplings based on a 5d Standard Model with quarks and leptons transforming as triplets under a new gauged SO(3) isospin. In the 4d effective theory, the SO(3) isospin is broken to U(1)′, through a S1/(ℤ2× ℤ 2 t ) orbifold, then subsequently dynamically broken, resulting in a massive Z′. Quarks and leptons in the 5d bulk appear as massless modes, with zero Yukawa couplings to the Higgs on the brane, and zero couplings to Z′, at leading order, due to the U(1)′ symmetry. However, after the U(1)′ breaking, both Yukawa couplings and non-universal Z′ couplings are generated by heavy Kaluza-Klein exchanges. Hierarchical quark and lepton masses result from a hierarchy of 5d Dirac fermion masses. Neutrino mass and mixing arises from a novel type Ib seesaw mechanism, mediated by Kaluza-Klein Dirac neutrinos. The non-universal Z′ couplings may contribute to semi-leptonic B decay ratios which violate μ − e universality. In this model such couplings are related to the corresponding quark and lepton effective Yukawa couplings. [ABSTRACT FROM AUTHOR]

We discuss the modular A4 invariant model of leptons combining with the generalized CP symmetry. In our model, both CP and modular symmetries are broken spontaneously by the vacuum expectation value of the modulus τ. The source of the CP violation is a non-trivial value of Re[τ] while other parameters of the model are real. The allowed region of τ is in very narrow one close to the fixed point τ = i for both normal hierarchy (NH) and inverted ones (IH) of neutrino masses. The CP violating Dirac phase δCP is predicted clearly in [98°, 110°] and [250°, 262°] for NH at 3 σ confidence level. On the other hand, δCP is in [95°, 100°] and [260°, 265°] for IH at 5 σ confidence level. The predicted ∑mi is in [82, 102] meV for NH and ∑mi = [134, 180] meV for IH. The effective mass 〈mee〉 for the 0νββ decay is predicted in [12.5, 20.5] meV and [54, 67] meV for NH and IH, respectively. [ABSTRACT FROM AUTHOR]

We investigate a model based on hidden U(1)X gauge symmetry in which neutrino mass is induced at one-loop level by effects of interactions among particles in hidden sector and the Standard Model leptons. Neutrino mass generation is also associated with U(1)X breaking scale which is taken to be low to suppress neutrino mass. Then we formulate neutrino mass matrix, lepton flavor violating processes and muon g − 2 which are induced via interactions among Standard Model leptons and particles in U(1)X hidden sector that can be sizable in our scenario. Carrying our numerical analysis, we show expected ratios for these processes when generated neutrino mass matrix can fit the neutrino data. [ABSTRACT FROM AUTHOR]

We consider the one-loop radiative corrections to the light-neutrino mass matrix and their consequences for the predicted branching ratios of the five lepton-flavour-violating decays ℓ 1 − → ℓ 2 − ℓ 3 + ℓ 3 − in a two-Higgs-doublet model furnished with the type-I seesaw mechanism and soft lepton-flavour violation. We find that the radiative corrections are very significant; they may alter the predicted branching ratios by several orders of magnitude and, in particular, they may help explain why BR (μ− → e−e+e−) is strongly suppressed relative to the branching ratios of the decays of the τ−. We conclude that, in any serious numerical assessment of the predictions of this model, it is absolutely necessary to take into account the one-loop radiative corrections to the light-neutrino mass matrix. [ABSTRACT FROM AUTHOR]

Asymmetric tri-bi-maximal mixing is a recently proposed, grand unified theory (GUT) based, flavor mixing scheme. In it, the charged lepton mixing is fixed by the GUT connection to down-type quarks and a 𝒯 1 3 flavor symmetry, while neutrino mixing is assumed to be tri-bi-maximal (TBM) with one additional free phase. Here we show that this additional free phase can be fixed by the residual flavor and CP symmetries of the effective neutrino mass matrix. We discuss how those residual symmetries can be unified with 𝒯 1 3 and identify the smallest possible unified flavor symmetries, namely (ℤ 1 3 × ℤ 1 3) ⋊ D 1 2 and (ℤ 1 3 × ℤ 1 3) ⋊ S 4 . Sharp predictions are obtained for lepton mixing angles, CP violating phases and neutrinoless double beta decay. [ABSTRACT FROM AUTHOR]

We investigate neutrino mass generation scenarios where the lepton number breaking new physics does not interact with Standard Model (SM) quarks and couples only to the SM right-handed charged lepton chirality. The lowest-order lepton number violating effective operator which describes this framework is a unique dimension nine operator involving SM gauge fields, O 9 . We find that there are two possible classes of new physics scenarios giving rise to this O 9 operator. In these scenarios neutrino masses are induced radiatively via dark matter interactions, linking the dark matter to a natural explanation for the smallness of neutrino masses compared to the electroweak scale. We discuss the phenomenology and existing constraints in the different neutrino mass models within each class. In particular, we analyze the important interplay between neutrino mixing and neutrinoless double β-decay in order to predict characteristic signatures and disfavour certain scenarios. [ABSTRACT FROM AUTHOR]

Neutrino oscillations are precision probes of new physics. Apart from neutrino masses and mixings, they are also sensitive to possible deviations of low-energy interactions between quarks and leptons from the Standard Model predictions. In this paper we develop a systematic description of such non-standard interactions (NSI) in oscillation experiments within the quantum field theory framework. We calculate the event rate and oscillation probability in the presence of general NSI, starting from the effective field theory (EFT) in which new physics modifies the flavor or Lorentz structure of charged-current interactions between leptons and quarks. We also provide the matching between the EFT Wilson coefficients and the widely used simplified quantum-mechanical approach, where new physics is encoded in a set of production and detection NSI parameters. Finally, we discuss the consistency conditions for the standard NSI approach to correctly reproduce the quantum field theory result. [ABSTRACT FROM AUTHOR]

In this work, we propose new five texture zeros for the mass matrices in the lepton sector in order to predict neutrino masses. In our approach, we extend beyond the standard model (SM) by assuming Dirac masses for the neutrinos, a feature which allows us to make a theoretical prediction for the lightest neutrino mass in the normal ordering. The textures that were analyzed have enough free parameters to adjust the VPMNS mixing matrix including the CP-violating phase, the neutrino mass squared differences , and the three charged lepton masses. In order to obtain reliable results, we used two different procedures that are based on the weak basis transformation, a well known technique to analyze textures and their implications for flavor physics. The first method was based on a least-squares analysis to theoretically fit the lepton masses and the mixing parameters to their corresponding experimental values; for this case, the best fit obtained for the lightest neutrino mass was eV. The second approach was algebraic, resulting in a lightest neutrino mass consistent with the experimental values and the restrictions arising from the five texture zeros of the mass matrices, and the lightest neutrino mass obtained was (3.5 ± 0.9) × 10−3 eV. [ABSTRACT FROM AUTHOR]

We propose a renormalizable B - L Standard Model (SM) extension based on S 3 symmetry which successfully accommodates the observed fermion mass spectra and flavor mixing patterns as well as the CP violating phases. The small masses for the light active neutrinos are generated through a type I seesaw mechanism. The obtained physical parameters in the lepton sector are well consistent with the global fit of neutrino oscillations (Esteban et al. in J High Energy Phys 01:106, 2019) for both normal and inverted neutrino mass orderings. The model also predicts effective neutrino mass parameters of ⟨ m ee ⟩ = 1.02 × 10 - 2 eV , m β = 1.25 × 10 - 2 eV for normal hierarchy (NH) and ⟨ m ee ⟩ = 5.03 × 10 - 2 eV , m β = 5.05 × 10 - 2 eV for inverted hierarchy (IH) which are all well consistent with the future large and ultra-low background liquid scintillator detectors which has been discussed in Ref. (Zhao et al. in Chin Phys C 41(5):053001, 2017) or the limit of the effective neutrino mass can be reached by the planning of future experiments. The model results are consistent with and successfully accommodate the recent experimental values of the physical observables of the quark sector, including the six quark masses, the quark mixing angles and the CP violating phase in the quark sector. [ABSTRACT FROM AUTHOR]

We propose and discuss a new Littlest Seesaw model, realized in the tri-direct CP approach, in which the couplings of the two right-handed neutrinos to the lepton doublets are proportional to (0, −1, 1) and (1,5/2, −1/2) respectively with the relative phase η = −π/2. This model can give an excellent description of lepton flavour mixing, including an atmospheric neutrino mixing angle in the second octant, in terms of only two input parameters. We show that the observed baryon asymmetry can be generated for the lightest right-handed neutrino mass M1 = 1.176 × 1011 GeV in SM and M1 = 3.992 × 1010 GeV in MSSM with. We construct an explicit Littlest Seesaw model based on the flavour symmetry S4 × Z5 × Z8 in which the desired alignments and the phase η = −π/2 are achieved. [ABSTRACT FROM AUTHOR]

We present a purely linear seesaw mechanism in a mirror left-right symmetric framework and then realize a novel leptogenesis scenario for parametrizing the cosmic baryon asymmetry by the charged lepton masses, the light Majorana neutrino mass matrix and the heavy mirror charged lepton masses. Through the same Yukawa couplings, the lepton-number-conserving decays of the mirror charged leptons can generate three individual lepton asymmetries stored in the ordinary lepton flavors, while the lepton-number-violating processes for the Majorana neutrino mass generation can wash out part of these lepton asymmetries. The remnant lepton asymmetries then can be partially converted to a baryon asymmetry by the sphaleron processes. [ABSTRACT FROM AUTHOR]

Recently a new model of "Affleck-Dine inflation" was presented, that produces the baryon asymmetry from a complex inflaton carrying baryon number, while being consistent with constraints from the cosmic microwave background. We adapt this model such that the inflaton carries lepton number, and communicates the lepton asymmetry to the standard model baryons via quasi-Dirac heavy neutral leptons (HNLs) and sphalerons. One of these HNLs, with mass < ~ 4.5 GeV, can be (partially) asymmetric dark matter (DM), whose asymmetry is determined by that of the baryons. Its stability is directly related to the vanishing of the lightest neutrino mass. Neutrino masses are generated by integrating out heavy sterile neutrinos whose mass is above the inflation scale. The model provides an economical origin for all of the major ingredients missing from the standard model: inflation, baryogenesis, neutrino masses, and dark matter. The HNLs can be probed in fixed-target experiments like SHiP, possibly manifesting N − N ¯ oscillations. A light singlet scalar, needed for depleting the DM symmetric component, can be discovered in beam dump experiments and searches for rare decays, possibly explaining anomalous events recently observed by the KOTO collaboration. The DM HNL is strongly constrained by direct searches, and could have a cosmologically interesting self-interaction cross section. [ABSTRACT FROM AUTHOR]

We perform a complete analysis of the consistency of the singlet-triplet scotogenic model, where both dark matter and neutrino masses can be explained. We determine the parameter space that yields the proper thermal relic density been in agreement with neutrino physics, lepton flavor violation, direct and indirect dark matter searches. In particular, we calculate the dark matter annihilation into two photons, finding that the corresponding cross-section is below the present bounds reported by the Fermi-LAT and H.E.S.S. collaborations. We also determine the spin-dependent cross-section for dark matter elastic scattering with nucleons at one-loop level, finding that the next generation of experiments as LZ and DARWIN could test a small region of the parameter space of the model. [ABSTRACT FROM AUTHOR]

SHiP is a proposed high-intensity beam dump experiment set to operate at the CERN SPS. It is expected to have an unprecedented sensitivity to a variety of models containing feebly interacting particles, such as Heavy Neutral Leptons (HNLs). Two HNLs or more could successfully explain the observed neutrino masses through the seesaw mechanism. If, in addition, they are quasi-degenerate, they could be responsible for the baryon asymmetry of the Universe. Depending on their mass splitting, HNLs can have very different phenomenologies: they can behave as Majorana fermions — with lepton number violating (LNV) signatures, such as same-sign dilepton decays — or as Dirac fermions with only lepton number conserving (LNC) signatures. In this work, we quantitatively demonstrate that LNV processes can be distinguished from LNC ones at SHiP, using only the angular distribution of the HNL decay products. Accounting for spin correlations in the simulation and using boosted decision trees for discrimination, we show that SHiP will be able to distinguish Majorana-like and Dirac-like HNLs in a significant fraction of the currently unconstrained parameter space. If the mass splitting is of order 10−6 eV, SHiP could even be capable of resolving HNL oscillations, thus providing a direct measurement of the mass splitting. This analysis highlights the potential of SHiP to not only search for feebly interacting particles, but also perform model selection. [ABSTRACT FROM AUTHOR]

We implement a symmetry violation guideline into a two-Higgs-doublet model embedded with three right-handed neutrinos, and exploit the generic Yukawa structures of the model via a hypothetical symmetry restoration of a global U Q (1) 3 × U L (1) 3 symmetry. We then apply a mass-powered parametrization to construct the phenomenologically motivated Yukawa interactions, which enables us to incorporate correlatively the neutrino mass, dark matter, as well as the lepton-flavor universality violations in R K (∗) and R D (∗) . Specifically, two atmospheric-scale neutrino masses are generated by a low-scale seesaw mechanism, while the much lighter one, being of O (10 - 6) eV , is fixed by a 7.1 keV sterile neutrino dark matter produced primordially by the freeze-in mechanism. On the other hand, the neutrino and the charged-lepton mass hierarchies encoded in the mass-powered textures can naturally account for the R K (∗) and the R D (∗) anomalies, respectively. As a further application, a milder discrepancy of the muon g - 2 is observed, which has also been implied by the recently refined lattice results. [ABSTRACT FROM AUTHOR]

Since its inception, no decisive departure from the predictions of the standard model (SM) has been reported. However, recently various experiments have observed a few hints of possible departure from SM predictions in lepton flavor universality observables such as , , muon (g–2), , etc. Many of these are observable where deviation from the SM in the range of (2–4)σ is observed related to the muon (μ) lepton. So these deviations may hint at a possible new physics (NP) in the muon sector. In this work we extend the SM by introducing two SM singlet heavy charged leptons (Fe, Fμ), whose left-handed components are charged under a new U(1)F gauge symmetry, one color triplet lepto-quark (ϕQ) doublet under SU(2)L, one inert Higgs doublet (ϕl), and three very heavy Majorana neutrinos (NiR), all of which are odd under a Z2 discrete symmetry. One more scalar (ϕ) charged only under the U(1)F, whose VEV gives masses to the U(1)F gauge boson as well as the heavy leptons. With these new particles, we show that the observed anomalies in the muon sector as well as small neutrino masses can be explained taking into account all the other experimental and theoretical constraints to date. [ABSTRACT FROM AUTHOR]