Search

We propose a three loop radiative neutrino mass scenario with an isolated doubly charged singlet scalar k±± without couplings to the charged leptons, while two other singly charged scalars h±1 and h±2 attach to them. In this setup, the lepton flavor violation originating from k±± exchanges is suppressed and the model is less constrained, where some couplings can take sizable values. As reported in our previous work [1], the loop suppression factor at the three loop level would be too strong and realized neutrino masses in a three loop scenario could be smaller than the observed minuscule values. The sizable couplings can help us to enhance neutrino masses without drastically large scalar trilinear couplings appearing in a neutrino mass matrix, which tends to drive the vacuum stability to become jeopardized at the one loop level. Now the doubly charged scalar k±± has less constraint via lepton flavor violation and the vacuum can be quite stable, and thus a few hundred GeV mass in k±± is possible, which is within the LHC reach and this model can be tested in the near future. Note that the other h±1 and h±2 should be heavy at least around a few TeV. We suitably arrange the charges of an additional global U(1) symmetry, where the decay constant of the associated Nambu-Goldstone boson can be around a TeV scale consistently. Also, this model is indirectly limited through a global analysis on results of the LHC Higgs search and issues on a dark matter candidate, the lightest Majorana neutrino. After h±1 and h±2 are decoupled, this particle couples to the standard model particles only through two charge parity even scalars in theory and thus information on this scalar sector is important. Consistent solutions are found, but a part of them is now on the edge. [ABSTRACT FROM AUTHOR]

Recent observations of high-energy neutrinos in the IceCube experiment suggests the existence of superheavy dark matter beyond the PeV scale. We identify the parent particles of neutrinos as two degenerated right-handed neutrinos, assuming the dark matter is the heaviest right-handed neutrino. The O(Vcb) ~ O(10-2) flavor symmetry breaking accounts for the O(10-4) mass degeneracy of right-handed neutrinos, which is a sizable scale to explain the successful resonant leptogenesis at the PeV scale. At the same time, nonthermal production of the heaviest right-handed neutrino gives the right amount of dark matter for TRH ~ 10 PeV. The footprint of flavor symmetry is left in the degenerated mass spectra of the extra Higgs multiplet and colored Higgs multiplet, which may be testable at the LHC or future colliders. [ABSTRACT FROM AUTHOR]

We propose a two-loop induced Zee-Babu-type neutrino mass model at the TeV scale. Although there is no dark matter candidate in the original Zee-Babu model, our model can include the dark matter by introducing an unbroken discrete Z2 symmetry. The discrepancy between the experimental value of the muon anomalous magnetic moment (muon g - 2) and its prediction in the standard model can be explained by contributions from additional vectorlike charged leptons which are necessary to give nonzero neutrino masses. The mass of vectorlike leptons to be slightly above 300 GeV is favored and allowed from the muon g - 2 and the current LHC data. We find that from the structure of the neutrino mass matrix, doubly charged scalar bosons in our model can mainly decay into the same-sign and same-flavor dilepton plus missing transverse momentum. By measuring an excess of these events at the LHC, our model can be distinguished from the other models including doubly charged scalar bosons. [ABSTRACT FROM AUTHOR]

We study a three-loop-induced radiative neutrino model with global U(1) symmetry at the TeV scale, in which we consider two-component dark matter particles. We explain the x-ray line signal at about 3.55 keV recently reported by the XMM-Newton X-ray Observatory using the data of various galaxy clusters and the Andromeda Galaxy. Subsequently, we also discuss and show that a sizable muon anomalous magnetic moment, a discrepancy of the effective number of neutrino species δNeff ≈ 0.39, and a scattering cross section detected by direct detection searches can be derived. [ABSTRACT FROM AUTHOR]

We revisit our previous model proposed by Okada and Yagyu [Phys. Rev. D 89, 053008 (2014)], in which lepton masses, except the tauon mass, are generated at the one-loop level in TeV-scale physics. Although in the previous work, rather large Yukawa coupling constants, i.e., greater than about 3, are required to reproduce the muon mass, we do not need to introduce such large 0 ( 1 ) couplings. In our model, masses for neutrinos (charged leptons) are generated by higher-dimensional operators with two isospin triplet (singlet and doublet) scalar fields, which are introduced at the one-loop level. Thus, the mass hierarchy between neutrinos and charged leptons can be naturally described by the difference in the number of vacuum expectation values of the triplet fields which must be much smaller than the vacuum expectation values of the doublet field due to the constraint from the electroweak rho parameter. Furthermore, the discrepancy in the measured muon anomalous magnetic moment (g - 2) from the prediction in the standard model is explained by new particle contributions at the one-loop level. The collider phenomenology is discussed, especially focusing on a signature from doubly charged scalar bosons at the LHC. [ABSTRACT FROM AUTHOR]

We propose a leptoquark model simultaneously to explain anomalies of muon anomalous magnetic dipole moment and b→sμ̅μ in light of experimental reports very recently. Here, we satisfy several stringent constraints such as μ→eγ and meson mixings. In addition, we find these leptoquarks also play an role in generating tiny neutrino masses at one-loop level without introducing any additional symmetries. We have numerical analysis and show how degrees our parameter space is restricted. [ABSTRACT FROM AUTHOR]

In the modular invariant flavor model of A4, we study the hierarchical structure of lepton/quark flavors at nearby fixed points of τ=i and τ=ω of the modulus, which are in the fundamental domain of PSL(2,Z). These fixed points correspond to the residual symmetries ZS2={I,S} and ZST3={I,ST,(ST)²} of A4, where S and T are generators of the A4 group. The infinite τ=i∞ also preserves the residual symmetry of the subgroup ZT3={I,T,T²} of A4. We study typical two-type mass matrices for charged leptons and quarks in terms of modular forms of weights 2, 4, and 6, while the neutrino mass matrix with the modular forms of weight 4 through the Weinberg operator. Linear modular forms are obtained approximately by performing Taylor expansion of modular forms around fixed points. By using them, the flavor structure of the lepton and quark mass matrices are examined at nearby fixed points. The hierarchical structure of these mass matrices is clearly shown in the diagonal base of S, T, and ST. The observed Pontecorvo-Maki-Nakagawa-Sakata and Cabibbo-Kobayashi-Maskawa mixing matrices can be reproduced at nearby fixed points in some cases of mass matrices. By scanning model parameters numerically at nearby fixed points, our discussion are confirmed for both the normal hierarchy and the inverted one of neutrino masses. Predictions are given for the sum of neutrino masses and the CP violating Dirac phase of leptons at each nearby fixed point. [ABSTRACT FROM AUTHOR]

We propose an extension to the Standard Model accommodating two families of Dirac neutral fermions and Majorana fermions under additional U(1)e-µ×Z3×Z2 symmetries where U(1)e-µ is a flavor dependent gauge symmetry related to the first and second family of the lepton sector, which features a two-loop induced neutrino mass model. The two families are favored by minimally reproducing the current neutrino oscillation data and two mass difference squares and canceling the gauge anomalies at the same time. As a result, we have a prediction for neutrino masses. The lightest Dirac neutral fermion is a dark matter candidate with tree-level interaction restricted to electron, muon and neutrinos, which makes it difficult to detect in direct dark matter search as well as indirect search focusing on the τ-channel, such as through γ-rays. It may however be probed by search for dark matter signatures in electron and positron cosmic rays, and allows interpretation of a structure appearing in the CALET electron+positron spectrum around 350-400 GeV as its signature, with a boost factor ~40 Breit-Wigner enhancement of the annihilation cross section. [ABSTRACT FROM AUTHOR]

We analyze the allowed region of the muon anomalous magnetic moment (muon g - 2) satisfying lepton flavor violations, Z boson decays, and collider physics, in a framework of multicharged particles. Then we explore the typical size of the muon g - 2 and discuss which mode dominantly affects the muon g - 2. [ABSTRACT FROM AUTHOR]

We propose a one-loop induced radiative seesaw model applying a modular S3 flavor symmetry, which is known as the minimal non-Abelian discrete group. In this scenario, dark matter (DM) candidate is correlated with neutrinos and lepton flavor violations (LFVs). We show several predictions of mixings and phases satisfying LFVs, observed relic density, and neutrino oscillation data. [ABSTRACT FROM AUTHOR]

We propose a seesaw model with a hidden gauge symmetry SU(2)H×U(1)X in which two types of standard model singlet fermions in realizing a seesaw mechanism are organized into an SU(2)H doublet. Then, we formulate scalar and gauge sector, neutrino mass matrix, and lepton flavor violations. In our gauge sector, Z-Z′ mixing appears after spontaneous symmetry breaking, and we investigate the constraint from the ρ parameter. In addition, we discuss Z′ production at the large hadron collider via Z-Z′ mixing, in which Z′ tends to dominantly decay into heavy neutrinos. [ABSTRACT FROM AUTHOR]

We propose a natural realization of a linear seesaw model with hidden gauge symmetry in which SU(2)L triplet fermions and one extra Higgs singlet, doublet, and quartet scalar are introduced. Small neutrino mass can be realized by two suppression factors that are the small vacuum expectation value of a quartet scalar and the inverse of a Dirac mass for the triplet. After formulating the neutrino mass matrix, we discuss the collider phenomenology of the model, focusing on signals from exotic charged particles production at the LHC. [ABSTRACT FROM AUTHOR]

We propose a new kind of inverse seesaw model without any additional symmetries. Instead of the symmetries, we introduce several fermions and bosons with higher SU(2)L representations. After formulating the Higgs sector and neutrino sector, we show that the cutoff energy, which is valid for our model, is at around the TeV scale by examining behavior of SU(2)L gauge coupling. Then we show the validity of our model for testing at collider physics. [ABSTRACT FROM AUTHOR]

We extend the Zee-Babu model, introducing local U(1)Lμ-Lτ symmetry with several singly charged bosons. We find a predictive neutrino mass texture in a simple hypothesis in which mixings among singly charged bosons are negligible. Also, lepton-flavor violations are less constrained compared with the original model. Then, we explore the testability of the model, focusing on doubly charged boson physics at the LHC and the International Linear Collider. [ABSTRACT FROM AUTHOR]

We propose a neutrinophilic two-Higgs-doublet model with hidden local U(1) symmetry, where active neutrinos are Dirac type, and a fermionic dark matter (DM) candidate is naturally induced as a result of remnant symmetry even after the spontaneous symmetry breaking. In addition, a physical Goldstone boson arises as a consequence of two types of gauge singlet bosons and contributes to the DM phenomenologies as well as an additional neutral gauge boson. Then, we analyze the relic density of DM within the safe range of direct detection searches and show the allowed region of dark matter mass. [ABSTRACT FROM AUTHOR]

We propose a radiative neutrino-mass model by introducing 3 generations of fermion pairs E-(N+1)/2E+(N+1)/2 and a couple of multicharged bosonic doublet fields ΦN/2,ΦN/2+1, where N=1, 3, 5, 7, 9. We show that the models can satisfy the neutrino masses and oscillation data, and are consistent with lepton-flavor violations, the muon anomalous magnetic moment, the oblique parameters, and the beta function of the U(1)Y hypercharge gauge coupling. We also discuss the collider signals for various N, namely, multicharged leptons in the final state from the Drell-Yan production of E-(N+1)/2E+(N+1)/2. In general, the larger the N the more charged leptons will appear in the final state. [ABSTRACT FROM AUTHOR]

We study a neutrino model introducing an additional nontrivial gauged lepton symmetry where the neutrino masses are induced at two-loop level, while the first and second charged-leptons of the standard model are done at one-loop level. As a result of the model structure, we can predict one massless active neutrino, and there is a dark matter candidate. Then we discuss the neutrino mass matrix, muon anomalous magnetic moment, lepton flavor violations, oblique parameters, and relic density of dark matter, taking into account the experimental constraints. [ABSTRACT FROM AUTHOR]

We propose a minimally extended gauge symmetry model with U(1)R, where only the right-handed fermions have nonzero charges in the fermion sector. To achieve both anomaly cancellations and minimality, three right-handed neutrinos are naturally required, and the standard model Higgs has to have nonzero charge under this symmetry. Then we find that its breaking scale(Λ) is restricted by precise measurement of neutral gauge boson in the standard model; therefore, O(10) TeV≲Λ. We also discuss its testability of the new gauge boson and discrimination of U(1)R model from U(1)B-L one at collider physics such as LHC and ILC. [ABSTRACT FROM AUTHOR]

We propose an extension of the standard model introducing large SU(2)L multiplet fields which are quartet and septet scalars and quintet Majorana fermions. These multiplets can induce the neutrino masses via interactions with the SU(2) doublet leptons. We then find the neutrino masses are suppressed by a small vacuum expectation value of the quartet/septet and an inverse of the quintet fermion mass, relaxing the Yukawa hierarchies among the standard model fermions. We also discuss collider physics at the Large Hadron Collider, considering the production of charged particles in these multiplets, and due to the effects of violating the custodial symmetry, some specific signatures can be found. Then, we discuss the detectability of these signals. [ABSTRACT FROM AUTHOR]

We propose a model with a two-Higgs doublet, where quark and charged-lepton masses in the first and second families are induced at one-loop level, and neutrino masses are induced at the two-loop level. In our model, we introduce an extra U(1)R gauge symmetry that plays a crucial role in achieving desired terms in no conflict with anomaly cancellation. We show the mechanism to generate fermion masses, the resultant mass matrices, and Yukawa interactions in mass eigenstates, and we discuss several interesting phenomenologies such as the muon anomalous magnetic dipole moment and the dark matter candidate that arise from this model. [ABSTRACT FROM AUTHOR]

We study a simple one-loop induced neutrino mass model that contains both bosonic and fermionic dark matter candidates and has the capacity to explain the muon anomalous magnetic moment anomaly. We perform a comprehensive analysis by taking into account the relevant constraints of charged lepton flavor violation, electric dipole moments, and neutrino oscillation data. We examine the constraints from lepton flavor-changing Z boson decays at the one-loop level, particularly when the involved couplings contribute to the muon g - 2. It is found that BR (Z → μ τ) ≃ (10-7 - 10-6) while BR (τ → μ γ) ≲ 10-11 in the fermionic dark matter scenario. The former can be probed by the precision measurement of the Z boson at future lepton colliders. [ABSTRACT FROM AUTHOR]

We propose a loop-induced neutrino mass model, in which we introduce several exotic fermions and bosons with an SU(2)L multiplet, and discuss various phenomenologies such as lepton flavor violations, the muon anomalous magnetic moment, nonstandard interacting neutrinoless double beta decay, the relic density of dark matter, and the possibility of the spin-independent direct detection searches, imposing the constraints of oblique parameters. And we show a benchmark point to satisfy all the constraints and discuss our predictions. [ABSTRACT FROM AUTHOR]

A two-loop induced radiative neutrino model is proposed as an extension of our previous work in which the first- and second-generation standard model fermion masses are generated at the one-loop level in both quark and lepton sectors. Then we discuss the current neutrino oscillation data, lepton flavor violations, muon anomalous magnetic moment, and a bosonic dark matter candidate, for both the normal and inverted neutrino mass hierarchy. Our numerical analysis shows that fewer hierarchical Yukawa coupling constants can fit the experimental data with TeV-scale dark matter. [ABSTRACT FROM AUTHOR]

We study the extended colored Zee-Babu model introducing a vectorlike quark and singlet scalar. The active neutrino mass matrix and muon anomalous magnetic moment, which can be fitted to experimental data satisfying the constraints from the flavor-changing neutral current, are analyzed. Then, we discuss the constraint from hSM→γγ, the implication of an exotic diphoton resonance as a signature of the model, and the stability of the scalar potential. In addition, we discuss the signature of our model via vectorlike quark production. [ABSTRACT FROM AUTHOR]

We study a radiative neutrino model with a SU(2) septet scalar with hypercharge Y=2 where active neutrino mass is induced at a one-loop level. Calculating a one-loop diagram, mass matrices for an active neutrino are derived. We also analyze lepton flavor violations, the anomalous magnetic moment of a muon, and the flavor-violating Higgs decay h→μτ. Then, sizable muon gâ?'2 and ∼1% of BR(h→μτ) could be obtained in our setup. Furthermore, the collider signature of the septet is discussed, and we focus on the quadratically charged scalar at the LHC 14 TeV. We find that it could be discovered up to 1.5 TeV mass by searching multicharged lepton signal events. [ABSTRACT FROM AUTHOR]

We study a one-loop induced radiative neutrino model with an inert isospin triplet scalar field in the general framework of U(1)Y, in which we discuss current neutrino oscillation data, lepton flavor violations, a muon anomalous magnetic moment, and a dark matter candidate depending on the number of hypercharges. We show global analysis combining all the constraints and discuss the model. [ABSTRACT FROM AUTHOR]

The primordial lithium abundance inferred from spectroscopic observations of metal-poor stars is ~3 times smaller than the theoretical prediction in the standard big bang nucleosynthesis (BBN) model. We assume a simple model composed of standard model particles and a sterile neutrino vH with mass of O(10) MeV which decays long after BBN. We then investigate cosmological effects of a sterile neutrino decay, and check if a sterile neutrino can reduce the primordial lithium abundance. We formulate the injection spectrum of nonthermal photon induced by the vH decay. We take into account the generation of electrons and positrons, e±s, and active neutrinos at the vH decay, the primary photon production via the inverse Compton scattering of cosmic background radiation (CBR) by energetic e±, and electromagnetic cascade showers induced by the primary photons. The steady state injection spectrum is then derived as a function of the vH mass and the photon temperature. The vH decay produces energetic active neutrinos which are not thermalized, and e±'s which are thermalized. We then derive formulas relevant to the vH decay rates and formulas for the baryon-to-photon ratio ɳ and effective neutrino number Neff. The initial abundance, mass, and lifetime of vH are taken as free parameters. We then consistently solve (1) the cosmic thermal history, (2) nonthermal nucleosynthesis induced by the nonthermal photons, (3) the ɳ value, and (4) the Neff value. We find that an effective 7Be destruction can occur only if the sterile neutrino decays at photon temperature T = O(1) keV. Amounts of energy injection at the vH decay are constrained from limits on primordial D and 7Li abundances, the Neff value, and the CBR energy spectrum. We find that 7Be is photodisintegrated and the Li problem is partially solved for the lifetime 104--105 s and the mass >14 MeV. 7Be destruction by more than a factor of 3 is not possible because of an associated D overdestruction. In the parameter region, the ɳ value is decreased slightly, while the Neff value is increased by a factor of ***. In this study, errors in photodisintegration cross sections of 7Be(y, a)³He and 7Li(&#947, a)³H that have propagated through the literature are corrected, and new functions are derived based on recent nuclear experiments. It is found that the new photodisintegration rates are 2.3 to 2.5 times smaller than the old rates. The correct cross sections thus indicate significantly smaller efficiencies of 7Be and 7Li photodisintegration. Abundances of sterile neutrino necessary for the 7Li reduction are much smaller than thermal freeze-out abundances. The relic sterile neutrino, therefore, must be diluted between the freeze-out and BBN epochs by some mechanism. [ABSTRACT FROM AUTHOR]

We investigate a model of dark sector based on non-Abelian SU(2)D gauge symmetry. This dark gauge symmetry is broken into discrete Z2 via vacuum expectation values of two real triplet scalars, and an SU(2)D doublet Dirac fermion becomes Z2--odd particles whose lighter component makes stable dark matter candidate. The standard model and dark sector can be connected via the scalar mixing and the gauge kinetic mixing generated by higher dimensional operators. We then discuss relic density of dark matter and implications to collider physics in the model. The most unique signatures of this model at the LHC would be the dark scalar (Φ(')1) productions where it subsequently decays into: (1) a fermionic dark matter (χl) and a heavy dark fermion (χh) pair, Φ(')1→χ̄lχh(χ̄hχl), followed by χh decays into χl and non-Abelian dark gauge bosons (Xi's) which decays into SM fermion pair fSMf̄SM resulting in the reaction pp→Φ(')1→χ̄hχl(χ̄lχh)→fSMf̄SMχlχ̄l, (2) a pair of Xi's followed by Xi decays into a DM pair or the SM fermions resulting in the reaction, pp→Φ(')1→XiXi→χ̄lχlfSMf̄SM or even number of fSMf̄SM pairs. [ABSTRACT FROM AUTHOR]

We propose an inverse seesaw model based on hidden global symmetry U(1)H in which we realize tiny neutrino masses with rather natural manner taking into account relevant experimental bounds. The small Majorana mass for inverse seesaw mechanism is induced via the small vacuum expectation value of a triplet scalar field whose Yukawa interactions with standard model fermions are controlled by U(1)H. We discuss the phenomenology of the exotic particles present in the model, including the Goldstone boson coming from breaking of the global symmetry, and explore testability at the Large Hadron Collider experiments. [ABSTRACT FROM AUTHOR]

We propose an inverse seesaw model based on hidden global symmetry U(1)H in which we realize tiny neutrino masses with rather natural manner taking into account relevant experimental bounds. The small Majorana mass for inverse seesaw mechanism is induced via the small vacuum expectation value of a triplet scalar field whose Yukawa interactions with standard model fermions are controlled by U(1)H. We discuss the phenomenology of the exotic particles present in the model, including the Goldstone boson coming from breaking of the global symmetry, and explore testability at the Large Hadron Collider experiments. [ABSTRACT FROM AUTHOR]

A possibility of explaining the anomalies in the semileptonic B-meson decay B→K*μμ̄ has been explored in the framework of the gauged U(1)μ-τ symmetry. Apart from the muon anomalous magnetic moment and neutrino sector, we formulate the model starting with a valid Lagrangian and consider the constraints from the neutral meson mixings, the bounds on direct detection and the relic density of the bosonic dark matter candidate augmented to collider constraints. We search the parameter space, which accommodate the size of the anomaly of the B→K*μμ̄ decay, to satisfy all experimental constraints. We found the allowed region on the plane of the dark matter and Z' masses is rather narrow compared to the previous analysis. [ABSTRACT FROM AUTHOR]

We investigate origins of predictive one-zero neutrino mass textures in a systematic way. Here, we search Abelian continuous(discrete) global symmetries, and non-Abelian discrete symmetries, and show how to realize these neutrino masses. We then propose a concrete model involving a dark matter candidate and an extra gauge boson and show their phenomenologies. [ABSTRACT FROM AUTHOR]