Search

Scalar leptoquarks naturally arise within unified theories, offering a promising avenue for addressing one of the most significant challenges of the Standard Model–the existence of non-zero neutrino masses. In this work, we present a unified theory based on the SU(5) gauge group, where neutrino mass appears at the two-loop level via the propagation of scalar leptoquarks. Due to the unified framework, the charged fermion and neutrino masses and mixings are entangled and determined by a common set of Yukawa couplings. These exotic particles not only shed light on the neutrino mass generation mechanism but also help to achieve the unification of gauge couplings and are expected to lead to substantial lepton flavor violating rates, offering tangible opportunities for experimental verification. Reproducing the observed neutrino mass scale necessitates that a set of leptoquarks reside a few orders of magnitude below the unification scale–a specific feature of the proposed scenario. Moreover, maximizing the unification scale implies TeV scale new physics states, making them accessible at colliders. The diverse roles that leptoquarks play highlight the elegance and predictive ability of the proposed unified model. [ABSTRACT FROM AUTHOR]

Small neutrino masses confirmed in the neutrino oscillation experiments indicate the need for new physics beyond the standard model. Seesaw mechanism is an interesting way to extend the standard model for explaining the neutrino masses. In a low-scale type-I seesaw mechanism, the tiny masses of neutrinos can be explained by heavy Majorana neutrino masses. Heavy Majorana neutrinos can lead to lepton-number-violating processes and the induced CP violation can contribute to the baryon asymmetry in the Universe. Heavy Majorana neutrinos can also lead to lepton-number-conserving processes and in this paper, we study the CP violation in lepton-number-conserving processes through heavy Majorana neutrinos at future lepton colliders. New possible observations of CP violation can also be connected to evidences of new physics beyond the standard model. [ABSTRACT FROM AUTHOR]

This paper's novelty lies in introducing a hybrid scoto-seesaw model rooted in A 4 discrete modular symmetry leading to several interesting phenomenological implications. The scoto-seesaw framework leads to generation of one mass square difference (Δ m atm 2) using the type-I seesaw mechanism at the tree level. Additionally, the scotogenic contribution is vital in obtaining the other mass square difference (Δ m sol 2) at the loop level, thus providing a clear interpretation of the two different mass square differences. The non-trivial transformation of Yukawa couplings under the A 4 modular symmetry helps to explore neutrino phenomenology with a specific flavor structure of the mass matrix. In addition to predictions for neutrino mass ordering, mixing angles and CP phases, this setup leads to precise predictions for ∑ m i as well as | m e e |. In particular, the model predicts ∑ m i ∈ (0.073 , 0.097) eV and | m e e | ∈ (3.15 , 6.66) × 10 − 3 eV range; within reach of upcoming experiments. Furthermore, our model is also promising for addressing lepton flavor violations, i.e., ℓ α → ℓ β γ , ℓ α → 3 ℓ β and μ − e conversion rates while staying within the realm of current experimental limits. [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 simple interpretation of the γγ excesses reported by both CMS and ATLAS groups at 95 GeV together with the LEP excess in the Z b b ¯ channel around the same mass in terms of a neutral scalar field in the minimal left-right symmetric model (LRSM). We point out that the scalar field which implements the seesaw mechanism for neutrino masses has all the right properties to explain these observations, without introducing any extra fields. The key point is that this scalar particle is hardly constrained because it couples only to heavy right-handed particles. As a result, the diphoton decay mode receives contributions from both mixing with the Standard Model (SM) Higgs and the heavy charged bosons in the LRSM. The latter depends on the S U (2) R × U (1) B − L symmetry breaking scale v R. The complete allowed parameter space for explaining the 95 GeV excesses in this model can be probed with the high-precision measurements of the SM Higgs mixing with other scalars at the high-luminosity LHC and future Higgs factories. [ABSTRACT FROM AUTHOR]

We discuss radiative neutrino mass models with a general lepton flavor dependent U (1) gauge symmetry. The scotogenic model is adopted for neutrino mass generation in which Z 2 odd singlet fermions and an inert scalar doublet are introduced. A lepton flavor dependent local U (1) symmetry is applied to realize two-zero texture of a Majorana mass matrix of Z 2 odd singlet fermions where we explore minimal construction choosing U (1) charges of the standard model fermions and singlet fermions. Then we investigate neutrino mass matrix and show some predictions for constructed models, and discuss some phenomenological implications. [ABSTRACT FROM AUTHOR]

Our analysis involves enhancing the Δ (54) flavor symmetry model with Inverse Seesaw mechanism along with two SM Higgs through the incorporation of distinct flavons. Additionally, we introduce supplementary Z 2 ⊗ Z 3 ⊗ Z 4 symmetries to eliminate any undesirable components within our investigation. The exact tri-bimaximal neutrino mixing pattern undergoes a deviation as a result of the incorporation of extra flavons, leading to the emergence of a non-zero reactor angle θ 13 that aligns with the latest experimental findings. It was found that for our model the atmospheric oscillation parameter occupies the lower octant for normal hierarchy case. We also examine the parameter space of the model for normal hierarchy to explore the Dirac CP (δ C P), Jarlskog invariant parameter (J) and the Neutrinoless double-beta decay parameter (m β β) and found it in agreement with the neutrino latest data. Hence our model may be testable in the future neutrino experiments. [ABSTRACT FROM AUTHOR]

It is well known that energy fluxes will produce gravitational wave memory. The gravitational wave memory produced by background including cosmic microwave background (CMB), cosmic neutrino background (C ν B), and gravitational wave background is investigated in this work. We construct a theory relating the gravitational wave memory strength to the energy flux of a stochastic background. We find that the resulted gravitational wave memory behaves as a constantly varying metric tensor. Such a varying metric tensor will introduce a quadrupole structure to the universe expansion. The gravitational wave memory due to the CMB is too small to be detected. But the gravitational wave memory due to the C ν B and the gravitational wave background is marginally detectable. Interestingly, such detection can be used to estimate the neutrino masses and the properties of the gravitational wave background. [ABSTRACT FROM AUTHOR]

We propose a Majoron-like extension of the Standard Model with an extra global U (1) X -symmetry where neutrino masses are generated through an inverse seesaw mechanism at the 1-loop level. In contrast to the tree-level inverse seesaw, our framework contains dark matter (DM) candidates stabilized by a residual Z 2 -symmetry surviving spontaneous breaking of the U (1) X -group. We explore the case in which the DM is a Majorana fermion. Furthermore, we provide parameter space regions allowed by current experimental constraints coming from the dark matter relic abundance, (in)direct detection, and charged lepton flavor violation. [ABSTRACT FROM AUTHOR]

We investigate neutrino non-radiative two-body decay in vacuum, in relation to SN1987A. In a full 3 ν decay framework, we perform a detailed likelihood analysis of the 24 neutrino events from SN1987A observed by Kamiokande-II, IMB, and Baksan. We consider both normal and inverted neutrino mass orderings, and the possibility of strongly hierarchical and quasi-degenerate neutrino mass patterns. The results of the likelihood analysis show that the sensitivity is too low to derive bounds in the case of normal mass ordering. On the contrary, in the case of inverted mass ordering we obtain the bound τ / m ≥ 2.4 × 10 5 s/eV (1.2 × 10 5) s/eV at 68% (90%) CL on the lifetime-to-mass ratio of the mass eigenstates ν 2 and ν 1. [ABSTRACT FROM AUTHOR]

We present a mechanism which drives Dirac neutrino masses to tiny values along the Renormalization Group flow, starting from an asymptotically safe ultraviolet completion of the third generation of the Standard Model including quantum gravity. At the same time, the mechanism produces a mass-splitting between the neutrino and the quark sector and also generates the mass splitting between top and bottom quark. The mechanism hinges on the hypercharges of the fermions and produces a tiny neutrino Yukawa coupling, because the right-handed neutrino is sterile and does not carry hypercharge. [ABSTRACT FROM AUTHOR]

It has recently been speculated that the NANOGrav observations point towards a first-order phase transition in the dark sector at the GeV scale [1]. Here, we show that such a phase transition might already have been predicted in the Hot New Early Dark Energy model (Hot NEDE) [2,3]. There, it was argued that two dark sector phase transitions are the signature of neutrino mass generation through the inverse seesaw mechanism. In particular, an IR phase transition serves a double purpose by resolving the Hubble tension through an energy injection and generating the Majorana mass entry in the inverse seesaw mixing matrix. This usual NEDE phase transition is then accompanied by a UV counterpart, which generates the heavy Dirac mass entry in the inverse seesaw mass matrix of a right-handed neutrino. Here, we investigate if the UV phase transition of the Hot NEDE model can occur at the GeV scale in view of the recent NANOGrav observations. [ABSTRACT FROM AUTHOR]

We assess the potential of using presupernova neutrino signals at the Jiangmen Underground Neutrino Observatory (JUNO) to probe the yet-unknown neutrino mass hierarchy. Using models for stars of 12, 15, 20, and 25 M ⊙ , we find that if the ν ¯ e signals from such a star can be predicted precisely and the star is within ≈440–880 pc, the number of ν ¯ e + p → n + e + events detected within one day of its explosion allows to determine the hierarchy at the ≳ 95 % confidence level. For determination at this level using such signals from Betelgeuse, which is at a distance of ≈222 pc, the uncertainty in the predicted number of signals needs to be ≲14–30%. In view of more realistic uncertainties, we discuss and advocate a model-independent determination using both ν e and ν ¯ e signals from Betelgeuse. This method is feasible if the cosmogenic background for ν - e scattering events can be reduced by a factor of ∼2.5–10 from the current estimate. Such reduction might be achieved by using coincidence of the background events, the exploration of which for JUNO is highly desirable. [ABSTRACT FROM AUTHOR]

Results from neutrino mass and oscillation experiments now set the mass of the muon neutrino to less than 2 eV/c2. This fact, together with our former measurement of the muon momentum in pion decay at rest, p μ + = (29.792 00 ± 0.000 11) MeV/c, allows us to directly determine the charged pion mass with 1 ppm precision which constitutes the most precise value of the charged pion mass to date, m π + = (139.570 21 ± 0.000 14) MeV / c 2. This value is within 1.44 σ of the Particle Data Group's compilation of the charged pion mass value, m π ± = (139.570 61 ± 0.000 24) MeV/c2. From p μ + we derive the kinetic energy of the muon, T μ + = (4.119 84 ± 0.000 03) MeV and the mass difference, m π + − m μ + = (33.911 84 ± 0.000 14) MeV/c2. From our new m π + value, assuming CPT invariance (m π − = m π + ) and our measured mass difference D π = m π − − m π 0 = (4.593 64 ± 0.000 48) MeV/c2 we obtain a new value for the neutral pion mass, m π 0 = (134.976 57 ± 0.000 50) MeV/c2. One also obtains a new quantitative measure of CPT invariance in the pion sector: (m π + − m π − ) / m π (av) = (− 2.9 ± 2.0) ⋅ 10 − 6 , an improvement by two orders of magnitude. [ABSTRACT FROM AUTHOR]

We propose that the fermionic part of the action in the framework of the noncommutative description of the Standard Model is spectral, in an analogous way to the bosonic part of the action that is customary considered as being spectral. We then discuss the terms that appear in the asymptotic expansion of the fermionic spectral action. [ABSTRACT FROM AUTHOR]

Motivated by the interesting features of Two Higgs Doublet Models (2HDM) we present a 2HDM extension where the stability of dark matter, neutrino masses and the absence of flavor changing interactions are explained by promoting baryon and lepton number to gauge symmetries. Neutrino masses are addressed within the usual type I seesaw mechanism. A vector-like fermion acts as dark matter and it interacts with Standard Model particles via the kinetic and mass mixings between the neutral gauge bosons. We compute the relevant observables such as the dark matter relic density and spin-independent scattering cross section to outline the region of parameter space that obeys current and projected limits from collider and direct detection experiments via thermal and non-thermal dark matter production. [ABSTRACT FROM AUTHOR]

The heavy singlet Majorana neutrinos are introduced to generate the neutrino mass in the so-called phenomenological type-I seesaw mechanism. The phenomena induced by the heavy Majorana neutrinos are important to search for new physics. In this paper, we explore the heavy Majorana neutrino production and decay at future e − p colliders. The corresponding cross sections via W and photon fusion are predicted for different collider energies. Combined with the results of the heavy Majorana neutrino production via single W exchange, this work can provide helpful information to search for heavy Majorana neutrinos at future e − p colliders. [ABSTRACT FROM AUTHOR]

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 0 ν β β decay due to loop corrections involving light DM exchange, and (iii) testable lepton flavor-violating signal μ → e γ. Detecting monoenergetic neutrinos from DM annihilation in next-generation neutrino detectors offers a promising way to test this scenario. [ABSTRACT FROM AUTHOR]

The density of relic neutrinos is expected to be enhanced due to clustering in our local neighbourhood at Earth. We introduce a novel analytical technique to calculate the neutrino overdensity, based on kinetic field theory. Kinetic field theory is a particle-based theory for cosmic structure formation and in this work we apply it for the first time to massive neutrinos. The gravitational interaction is expanded in a perturbation series and we take into account the first-order contribution to the local density of relic neutrinos. For neutrino masses that are consistent with cosmological neutrino mass bounds, our results are in excellent agreement with state-of-the-art calculations. [ABSTRACT FROM AUTHOR]

In this letter, we perform a perturbative analysis by the lightest singular value m D 1 of the Dirac mass matrix m D in the type-I seesaw mechanism. A mass relation M 1 = m D 1 2 / | (m ν) 11 | is obtained for the lightest mass M 1 of the right-handed neutrino ν R 1 and the mass matrix of the left-handed neutrinos m ν in the diagonal basis of m D. This relation is rather stable under renormalization because it is gauge-invariant in the SM and associates with the approximate chiral symmetry of ν R 1. If diagonalization of the Yukawa matrices of leptons Y ν , e has only small mixings, the value (m ν) 11 is close to the effective mass m e e of the neutrinoless double beta decay. By assuming m D 1 ≃ m u , e ≃ 0.5 MeV, the lightest mass is about M 1 ≳ O (100) TeV in the normal hierarchy and M 1 ∼ O (10) TeV in the inverted hierarchy. Such a ν R 1 with a tiny Yukawa coupling y ν 1 ∼ O (10 − 5) can indirectly influence various observations. On the other hand, the famous bound of the thermal leptogenesis M 1 ≳ 10 9 GeV that requires m D 1 ≳ 30 MeV seems to be difficult to reconcile with a simple unified theory without a special condition. [ABSTRACT FROM AUTHOR]

We present two models where the familiar leptonic symmetry L e − L μ − L τ is a gauge symmetry. We show how anomaly cancellation constrains the allowed theories, with one of them requiring a fourth sequential chiral standard model fermion generation and a second one with three generations, requiring gauging of (L e − L μ − L τ) − (B 1 − B 2 − B 3) with B a representing the baryon number of the a th generation quarks. Unlike global L e − L μ − L τ models which always leads to inverted mass hierarchy for neutrinos, the gauged version can lead to normal hierarchy. We show how to construct realistic models in both the cases and discuss the dark matter candidate in both. In our model, the breaking of U (1) L e − L μ − L τ is responsible for neutrino mass via type-I mechanism whereas the real part of U (1) L e − L μ − L τ breaking scalar field (called ϕ here) plays the role of freeze-in dark matter candidate. Since ϕ is unstable, for it to qualify as dark matter, its lifetime must be larger than the age of the Universe, implying that the relic of ϕ is generated through freeze-in mechanism and its mass must be less than an MeV. We also discuss the possibility of explaining both muon and electron g − 2 while being consistent with the DM relic density and lifetime constraints. [ABSTRACT FROM AUTHOR]

We propose a minimal model where a dark sector, odd under a Z 2 discrete symmetry, is the seed of lepton number violation in the neutrino sector at the loop level, in the context of the linear seesaw mechanism. Neutrino mass suppression stems from a naturally small scalar potential coupling which breaks the lepton number symmetry softly. The fact that we consider (dark) Dirac vector-like neutral leptons, prevents the appearance of other mass terms that could contribute to neutrino masses via alternative mechanisms. We study the dark-matter phenomenology of the model, focusing on the case in which the stable particle is the lightest neutral scalar arising from the dark scalar sector. Prospects for testing our framework with the results of current and future lepton flavour violation searches are also discussed. [ABSTRACT FROM AUTHOR]

In the limit of an approximate μ − τ symmetry in the neutrino mass matrix, we explore deviations to the Tri-Bi-Maximal mixing pattern in the neutrino sector. We consider two different ansatzes for the corrected pattern to predict the current values of neutrino mixing parameters. We show that it is possible to constrain the Majorana CP phases by studying their correlation to the mixing parameters and we study their effects on neutrinoless double beta decay observables. These predictions are sharp for the quasi-degenerate ordering and can be tested in upcoming experiments. [ABSTRACT FROM AUTHOR]

The standard model of quarks and leptons is extended to include the gauge symmetry U (1) χ which comes from S O (10) → S U (5) × U (1) χ. The radiative generation of Dirac neutrino masses through dark matter is discussed in two examples. One allows for light Dirac fermion dark matter. The other allows for self-interacting scalar dark matter with a light scalar mediator which decays only to two neutrinos. [ABSTRACT FROM AUTHOR]

We construct phenomenologically viable models of lepton masses and mixing based on modular A 4 invariance broken to residual symmetries Z 3 T or Z 3 S T and Z 2 S respectively in the charged lepton and neutrino sectors. In these models the neutrino mixing matrix is of trimaximal mixing form. In addition to successfully describing the charged lepton masses, neutrino mass-squared differences and the atmospheric and reactor neutrino mixing angles θ 23 and θ 13 , these models predict the values of the lightest neutrino mass (i.e., the absolute neutrino mass scale), of the Dirac and Majorana CP violation (CPV) phases, as well as the existence of specific correlations between i) the values of the solar neutrino mixing angle θ 12 and the angle θ 13 (which determines θ 12), ii) the values of the Dirac CPV phase δ and of the angles θ 23 and θ 13 , iii) the sum of the neutrino masses and θ 23 , iv) the neutrinoless double beta decay effective Majorana mass and θ 23 , and v) between the two Majorana phases. [ABSTRACT FROM AUTHOR]

2-Higgs Doublet Models (2HDMs) typically need to invoke an ad-hoc discrete symmetry to avoid severe flavor bounds and in addition feature massless neutrinos, thus falling short of naturally complying with existing data. However, when augmented by an Abelian gauge symmetry naturally incorporating neutrino masses via a type-I seesaw mechanism while at the same time escaping flavor changing interactions, such enlarged 2HDMs become very attractive phenomenologically. In such frameworks, the distinctive element is the Z ′ gauge boson generated by the spontaneous breaking of the Abelian group U (1) X. In this work, we derive updated collider bounds on it. Several theoretical setups are possible, each with different and sometimes suppressed couplings to quarks and leptons. Thus, complementary data from dijet and dilepton resonance searches need to be considered to fully probe these objects. We employ the corresponding datasets as obtained at the Large Hadron Collider (LHC) at the 13 TeV CMs energy for L = 12 , 36 and 300 fb−1 of luminosity. Moreover, we present the potential sensitivity to such Z ′ s of the High Luminosity LHC (HL-LHC) and High Energy LHC (HE-LHC). [ABSTRACT FROM AUTHOR]

Abstract We obtain a phenomenologically acceptable PMNS matrix in a flipped SU(5) model, possessing the Z 4 R discrete symmetry, from the compactification of heterotic string E 8 × E 8 ′. To analyze the Jarlskog determinant efficiently, we include the simple Kim-Seo form for the Pontecorbo-Maki-Nakagawa-Sakata matrix. We also noted that | δ PMNS | ≲ 63 o for the normal hierarchy of neutrino masses with the PDG book parametrization. [ABSTRACT FROM AUTHOR]

Abstract Neutrinos may be the harbingers of new dark sectors, since the renormalizable neutrino portal allows for their interactions with hidden new physics. We propose here to use this fact to connect the generation of neutrino masses to a light dark sector, charged under a new U (1) D dark gauge symmetry. We introduce the minimal number of dark fields to obtain an anomaly free theory with spontaneous breaking of the dark symmetry, and obtain automatically the inverse seesaw Lagrangian. In addition, the so-called μ -term of the inverse seesaw is dynamically generated and technically natural in this framework. As a bonus, the new light dark gauge boson can provide a possible explanation to the MiniBooNE anomaly. [ABSTRACT FROM AUTHOR]

Abstract Compactifying the SM down to 3D or 2D one may obtain AdS vacua depending on the neutrino mass spectrum. It has been recently shown that, by insisting in the absence of these vacua, as suggested by Weak Gravity Conjecture (WGC) arguments, intriguing constraints on the value of the lightest neutrino mass and the 4D cosmological constant are obtained. For fixed Yukawa coupling one also obtains an upper bound on the EW scale 〈 H 〉 ≲ Λ 4 1 / 4 / Y ν i , where Λ 4 is the 4D cosmological constant and Y ν i the Yukawa coupling of the lightest (Dirac) neutrino. This bound may lead to a reassessment of the gauge hierarchy problem. In this letter, following the same line of arguments, we point out that the SM without a Higgs field would give rise to new AdS lower dimensional vacua. Absence of latter would require the very existence of the SM Higgs. Furthermore one can derive a lower bound on the Higgs vev 〈 H 〉 ≳ Λ QCD which is required by the absence of AdS vacua in lower dimensions. The lowest number of quark/lepton generations in which this need for a Higgs applies is three, giving a justification for family replication. We also reassess the connection between the EW scale, neutrino masses and the c.c. in this approach. The EW fine-tuning is here related to the proximity between the c.c. scale Λ 4 1 / 4 and the lightest neutrino mass m ν i by the expression Δ H H ≲ (a Λ 4 1 / 4 − m ν i ) m ν i . We emphasize that all the above results rely on the assumption of the stability of the AdS SM vacua found. [ABSTRACT FROM AUTHOR]

Abstract Central jet vetoes are powerful tools for reducing QCD background in measurements and searches for electroweak and colorless, new physics processes in hadron collisions. In this letter, we report the key findings of a new philosophy to designing searches for such phenomena at hadron colliders, one designed and centered around a dynamical jet veto instead of a static veto applied independently of other selection criteria. Specifically, we investigate the theoretical and phenomenological consequences of setting the jet veto scale to the transverse momentum (p T) of the leading charged lepton ℓ in multi-lepton processes on an event-by-event basis. We consider the case of a TeV-scale heavy neutrino N decaying to the trilepton final state and find the following: (i) Perturbative uncertainties associated with the veto greatly reduce due to tying the veto scale to the hard process scale. (ii) The signal efficiency for passing the veto jumps to ≳ 95 % and exhibits little-to-no dependence on the neutrino mass scale. (iii) Top quark and "fake" lepton rejection capabilities also improve compared to only vetoing heavy flavor-tagged jets above a fixed p T. This results in an increased sensitivity to active–sterile neutrino mixing by approximately an order of magnitude over the LHC's lifetime. For a Dirac neutrino with mass m N = 150 – 1000 GeV and the representative active–sterile mixing hypothesis | V e 4 | = | V τ 4 | with | V μ 4 | = 0 , we find that LHC experiments can probe | V e 4 | 2 , | V τ 4 | 2 ≲ 6 × 10 − 4 – 8 × 10 − 3 , surpassing the global upper limit for m N < 450 GeV, with L = 3 ab−1 of data at s = 14 TeV. Due to the color structures of the heavy N production mechanisms considered, we argue that our results hold broadly for other color-singlet processes. [ABSTRACT FROM AUTHOR]

Abstract The appealing feature of inverse seesaw models is that the Standard Model (SM) neutrino mass emerges from the exchange of TeV scale singlets with sizable Yukawa couplings, which can be tested at colliders. However, the tiny Majorana mass splitting between TeV singlets, introduced to accommodate small neutrino masses, is left unexplained. Moreover, we argue that these models suffer from a structural limitation that prevents a successful leptogenesis if one insists on having unsuppressed Yukawa couplings and TeV scale singlets. In this work we propose a hybrid seesaw model, where we replace the mass splitting with a coupling to a high scale seesaw module including a TeV scalar. We show that this structure achieves the goal of filling both the above gaps with couplings of order unity. The necessary structure automatically arises embedding the seesaw mechanism in composite Higgs models, but may also be enforced by new gauge symmetries in a weakly-coupled theory. Our hybrid seesaw models have distinguishing features compared to the standard high scale type-I seesaw and inverse seesaw. Firstly, they have much richer phenomenology. Indeed, they generally predict new TeV scale physics (including scalars) potentially accessible at present and future colliders, whereas weakly-coupled versions may also have cosmological signature due to the presence of a light Nambu–Goldstone boson coupled to neutrinos. Secondly, our scenario features an interesting interplay between high scale and TeV scale physics in leptogenesis and enlarges the range of allowed high scale singlet masses beyond the usual ∼ 10 9 – 10 15 GeV , without large hierarchies in the Yukawa couplings nor small mass splitting among the singlets. [ABSTRACT FROM AUTHOR]

Abstract We consider tomography of the Earth's interior using the neutrino pair beam which has recently been proposed. The beam produces a large amount of neutrino and antineutrino pairs from the circulating partially stripped ions and provides the possibility to measure precisely the energy spectrum of neutrino oscillation probability together with a sufficiently large detector. It is shown that the pair beam gives a better sensitivity to probe the Earth's crust compared with the neutrino sources at present. In addition we present a method to reconstruct a matter density profile by means of the analytic formula of the oscillation probability in which the matter effect is included perturbatively to the second order. [ABSTRACT FROM AUTHOR]

Abstract Motivated by the latest neutrino oscillation data which is consistent with maximal atmospheric mixing and maximal leptonic CP violation, we review various results in μτ symmetry, then include several new observations and clarifications, including identifying a new general form of neutrino mass matrix with μτ symmetry. We then apply the new results to the neutrino mass matrix associated with the Littlest Seesaw model, and show that it approximately satisfies the new general form with μτ symmetry, and that this is responsible for its approximate predictions of maximal atmospheric mixing and maximal CP violation in the lepton sector. [ABSTRACT FROM AUTHOR]

Abstract The minimal gauge group extension to the standard model (SM) by the local U (1) B − L (MBLSM) is well known as the minimal model to understand neutrino mass origins via the seesaw mechanism, following the gauge principle. This “small” symmetry also has deep implication to another big thing, dark matter (DM) stability. We demonstrate it in the framework of minimal dark matter (MDM), which aims at addressing two basic questions on DM, stability and the nature of interactions. However, stability and perturbativity may only allow the fermionic quintuplet. The situation is very different in the MBLSM, which leaves the subgroup of U (1) B − L , the matter parity (− 1) 3 (B − L) , unbroken; it is able to stabilize all of the MDM candidates after assigning a proper U (1) B − L charge. For the candidates with nonzero hypercharge, the phenomenological challenge comes from realizing the inelastic DM scenario thus evading the very strict DM direct detention bounds. We present two approaches that can slightly split the CP-even and -odd parts of the neutral components: 1) using the dimension 5 operators, which works for the U (1) B − L spontaneously breaking at very high scale; 2) mixing with other fields having zero hypercharge, which instead works for a low U (1) B − L breaking scale. [ABSTRACT FROM AUTHOR]

We perform such a calculation in quantum field theory, where we include simultaneously the source, detector, and neutrino fields in the Hamiltonian. Within the appropriate limits associated with current neutrino oscillation experiments, we recover the standard oscillation formula. On the other hand, we find that the dominant contributions to the amplitude are associated with different neutrino mass eigenstates being emitted at different times, such that they arrive at the detector at the same time. This is contrary to the neutrino wave packet picture, where they are emitted simultaneously and separate as they travel to the detector. This has direct consequences regarding the mechanisms that lead to a damping of neutrino oscillations for very long baselines. Our analysis also provides a pedagogical example of a measurement process in quantum mechanics. [ABSTRACT FROM AUTHOR]

We propose a model of neutrino mass matrix with large S U ( 2 ) multiplets and gauged U ( 1 ) L μ − L τ symmetry, in which we introduce S U ( 2 ) quartet scalar and quintet fermions with nonzero L μ − L τ charge. Then we investigate the neutrino mass structure and explore phenomenologies of large multiplet fields at the collider, particularly, focusing on doubly- and singly- charged exotic leptons from the quintet. [ABSTRACT FROM AUTHOR]

Neutrinos are the most elusive particles known. Heavier sterile neutrinos mixing with the standard neutrinos might solve the mystery of the baryon asymmetry of the universe. In this letter, we show that among all future energy frontier accelerators, muon colliders will provide the farthest search reach for such neutrinos for mass ranges above the Z pole into the multi-TeV regime, becoming the optimal machine for this kind of studies. We compare the performance of muon with electron colliders of the same machine energy and briefly discuss the complementarity in flavor space between the two types of accelerators. [ABSTRACT FROM AUTHOR]

The Zee model provides a simple model for one-loop Majorana neutrino masses. The new scalars can furthermore explain the long-standing deviation in the muon's magnetic moment and the recent CDF measurement of the W -boson mass. Together, these observations yield predictions for lepton flavor violating processes that are almost entirely testable in the near future. The remaining parameter space makes testable predictions for neutrino masses. [ABSTRACT FROM AUTHOR]

In the present letter, a Dirac neutrino mass model is presented in the view of the new result on W boson mass of m W C D F − I I = 80.4335 ± 0.0094 GeV, recently reported by the CDF-II experimental collaboration. The newly measured value of the W mass anomaly shows a 7- σ deviation from that predicted by the standard model. The model explains the CDF-II W boson mass anomaly by extending the standard model with hypercharge zero vector-like fermion triplet. Symmetry is amended with a global U (1) B − L which is broken with an hypercharge zero electroweak triplet. It is demonstrated that the model can successfully explain CDF-II result, Dirac neutrino mass origin, while satisfying standard model precision constraints and collider constraints with scalar and fermion triplet masses in the ranger 1.4 TeV−5.2 TeV and 100 TeV − 10 13 GeV, respectively. [ABSTRACT FROM AUTHOR]

We present the Sommerfeld enhanced Dark Matter (DM) annihilation into gamma ray for a class of three-loop radiative neutrino mass models with large electroweak multiplets where the DM mass is in O(TeV) range. We show that in this model, the DM annihilation rate becomes more prominent for larger multiplets and it is already within the reach of currently operating Imaging Atmospheric Cherenkov telescopes (IACTs), High Energy Stereoscopic System (H.E.S.S.). Furthermore, Cherenkov Telescope Array (CTA), which will begin operating in 2030, will improve this sensitivity by a factor of O ( 10 ) and may exclude a large portion of parameter space of this radiative neutrino mass model with larger electroweak multiplet. This implies that the only viable option is the model with lowest electroweak multiplets i.e. singlets of S U ( 2 ) L where the DM annihilation rate is not Sommerfeld enhanced and hence it is not yet constrained by the indirect detection limits from H.E.S.S. or future CTA. [ABSTRACT FROM AUTHOR]

We propose a flavored U ( 1 ) e μ neutrino mass and dark matter (DM) model to explain the recent DArk Matter Particle Explorer (DAMPE) data, which feature an excess on the cosmic ray electron plus positron flux around 1.4 TeV. Only the first two lepton generations of the Standard Model are charged under the new U ( 1 ) e μ gauge symmetry. A vector-like fermion ψ , which is our DM candidate, annihilates into e ± and μ ± via the new gauge boson Z ′ exchange and accounts for the DAMPE excess. We have found that the data favors a ψ mass around 1.5 TeV and a Z ′ mass around 2.6 TeV, which can potentially be probed by the next generation lepton colliders and DM direct detection experiments. [ABSTRACT FROM AUTHOR]

We analyze the non-cyclic geometric phase for neutrinos. We find that the geometric phase and the total phase associated to the mixing phenomenon provide a theoretical tool to distinguish between Dirac and Majorana neutrinos. Our results hold for neutrinos propagating in vacuum and through the matter. We feed the values of the experimental parameters in our formulas in order to make contact with experiments. Although it remains an open question how the geometric phase of neutrinos could be detected, our theoretical results may open new scenarios in the investigation of the neutrino nature. [ABSTRACT FROM AUTHOR]

An extra S U ( 2 ) D gauge factor is added to the well-known left-right extension of the standard model (SM) of quarks and leptons. Under S U ( 2 ) L × S U ( 2 ) R × S U ( 2 ) D , two fermion bidoublets ( 2 , 1 , 2 ) and ( 1 , 2 , 2 ) are assumed. The resulting model has an automatic dark U ( 1 ) symmetry, in the same way that the SM has automatic baryon and lepton U ( 1 ) symmetries. Phenomenological implications are discussed, as well as the possible theoretical origins of this proposal. [ABSTRACT FROM AUTHOR]

The DArk Matter Particle Explorer (DAMPE) has reported a measurement of the flux of high energy cosmic ray electrons plus positrons (CREs) in the energy range between 25 GeV and 4.6 TeV . With unprecedented high energy resolution, the DAMPE data exhibit an excess of the CREs flux at an energy of around 1.4 TeV . In this letter, we discuss how the observed excess can be understood in a minimal framework where the Standard Model (SM) is supplemented by a stable SM singlet scalar as dark matter (DM) and type II seesaw for generating the neutrino mass matrix. In our framework, a pair of DM particles annihilates into a pair of the SM SU(2) triplet scalars (Δs) in type II seesaw, and the subsequent Δ decays create the primary source of the excessive CREs around 1.4 TeV . The lepton flavor structure of the primary source of CREs has a direct relation with the neutrino oscillation data. We find that the DM interpretation of the DAMPE excess determines the pattern of neutrino mass spectrum to be the inverted hierarchy type, taking into account the constraints from the Fermi-LAT observations of dwarf spheroidal galaxies. [ABSTRACT FROM AUTHOR]

We discuss a new class of neutrino mass models generated in two loops, and explore specifically three new physics scenarios: (A) doubly charged scalar, (B) dark matter, and (C) leptoquark and diquark, which are verifiable at the 14 TeV LHC Run-II. We point out how the different Higgs insertions will distinguish our two-loop topology with others if the new particles in the loop are in the simplest representations of the SM gauge group. [ABSTRACT FROM AUTHOR]

Contrary to the see-saw models, extended Higgs sectors leading to radiatively-induced neutrino masses do require the extra particles to be at the TeV scale. However, these new states have often exotic decays, to which experimental LHC searches performed so far, focused on scalars decaying into pairs of same-sign leptons, are not sensitive. In this paper we show that their experimental signatures can start to be tested with current LHC data if dedicated multi-region analyses correlating different observables are used. We also provide high-accuracy estimations of the complicated Standard Model backgrounds involved. For the case of the Zee–Babu model, we show that regions not yet constrained by neutrino data and low-energy experiments can be already probed, while most of the parameter space could be excluded at the 95% C.L. in a high-luminosity phase of the LHC. [ABSTRACT FROM AUTHOR]

We propose a Standard Model extension with underlying A 4 flavour symmetry where small Dirac neutrino masses arise from a Type-II seesaw mechanism. The model predicts the “golden” flavour-dependent bottom-tau mass relation, requires an inverted neutrino mass ordering and non-maximal atmospheric mixing angle. Using the latest neutrino oscillation global fit [1] we derive restrictions on the oscillation parameters, such as a correlation between δ C P and m ν lightest . [ABSTRACT FROM AUTHOR]

We revisit the relation between the neutrino masses and the spontaneous breaking of the B – L gauge symmetry. We discuss the main scenarios for Dirac and Majorana neutrinos and point out two simple mechanisms for neutrino masses. In this context the neutrino masses can be generated either at tree level or at quantum level and one predicts the existence of very light sterile neutrinos with masses below the eV scale. The predictions for lepton number violating processes such as μ → e and μ → e γ are discussed in detail. The impact from the cosmological constraints on the effective number of relativistic degree of freedom is investigated. [ABSTRACT FROM AUTHOR]

We propose new mechanisms for small neutrino masses based on clockwork mechanism. The Standard Model neutrinos and lepton number violating operators communicate through the zero mode of clockwork gears, one of the two couplings of the zero mode is exponentially suppressed by clockwork mechanism. Including all known examples for the clockwork realization of the neutrino masses, different types of models are realized depending on the profile and chirality of the zero mode fermion. Each type of realization would have phenomenologically distinctive features with the accompanying heavy neutrinos. [ABSTRACT FROM AUTHOR]