Search

The next generation of water Cherenkov neutrino telescopes in the Mediterranean Sea are under construction offshore France (KM3NeT/ORCA) and Sicily (KM3NeT/ARCA). The KM3NeT/ORCA detector features an energy detection threshold which allows to collect atmospheric neutrinos to study flavour oscillation. This paper reports the KM3NeT/ORCA sensitivity to this phenomenon. The event reconstruction, selection and classification are described. The sensitivity to determine the neutrino mass ordering was evaluated and found to be 4.4 σ if the true ordering is normal and 2.3 σ if inverted, after 3 years of data taking. The precision to measure Δ m 32 2 and θ 23 were also estimated and found to be 85. 10 - 6 eV 2 and (- 3.1 + 1.9) ∘ for normal neutrino mass ordering and, 75. 10 - 6 eV 2 and (- 7.0 + 2.0) ∘ for inverted ordering. Finally, a unitarity test of the leptonic mixing matrix by measuring the rate of tau neutrinos is described. Three years of data taking were found to be sufficient to exclude event rate variations larger than 20% at 3 σ level. [ABSTRACT FROM AUTHOR]

Recent measurements at LHC have inspired searches for TeV scale left–right gauge theory originating from grand unified theories. We show that inclusion of Planck-scale induced effects due to dim . 5 operator not only does away with all the additional intermediate symmetries, but also it predicts the minimal set of light Higgs scalars tailored after neutrino masses and dilepton, or trilepton signals. The heavy-light neutrino mixings are predicted from charged fermion mass fits in SO ( 10 ) and LFV constraints which lead to new predictions for dilepton or trilepton production signals. Including fine-structure constant matching and two-loop, and threshold effects predict M W R = g 2 R 10 4.3 ± 1.5 ± 0.2 GeV and proton lifetime τ p = 10 36.15 ± 5.8 ± 0.2 yrs with W R gauge boson coupling g 2 R = 0.56 – 0.57 . Predictions on lepton flavour and lepton number violations are accessible to ongoing experiments. Current CMS data on di-electron excess at s = 8 TeV are found to be consistent with W R gauge boson mass M W R ≥ 1.9 – 2.2 TeV which also agrees with the values obtained from dijet resonance production data. We also discuss plausible explanations for diboson production excesses observed at LHC and make predictions expected at s = 14 TeV . [ABSTRACT FROM AUTHOR]

Abstract: We investigate a model in which tiny neutrino masses are generated at the two-loop level by using scalar leptoquark and diquark multiplets. The diquark can be singly produced at the LHC, and it can decay into a pair of leptoquarks through the lepton number violating interaction. Subsequent decays of the two leptoquarks can provide a clear signature of the lepton number violation, namely two QCD jets and a pair of same-signed charged leptons without missing energy. We show that the signal process is not suppressed while neutrino masses are appropriately suppressed. [Copyright &y& Elsevier]

Abstract: We constrain the masses of scalar-tops (stop) by analyzing the new precision Tevatron measurement of the W-boson mass and the LHC/Tevatron indications of a Higgs boson of mass . Our study adopts Natural SUSY with low fine-tuning, which has multi-TeV first- and second-generation squarks and a light Higgsino mixing parameter . An effective Lagrangian calculation is made of to 3 loops using the H3m program with weak scale SUSY parameters obtained from RGE evolution from the GUT scale in the Natural SUSY scenario. The SUSY radiative corrections to the Higgs mass imply maximal off-diagonal elements of the stop mass matrix and a mass splitting of the two stops larger than 400 GeV. [Copyright &y& Elsevier]

Abstract: The couplings of the low scale type I see-saw model are severely constrained by the requirement of reproducing the correct neutrino mass and mixing parameters, by the non-observation of lepton number and charged lepton flavour violating processes and by electroweak precision data. We show that all these constraints still allow for the possibility of an exotic Higgs decay channel into a light neutrino and a heavy neutrino with a sizable branching ratio. We also estimate the prospects to observe this decay at the LHC and discuss its complementarity to the indirect probes of the low scale type I see-saw model from experiments searching for the decay. [Copyright &y& Elsevier]

Bilinear R-parity violation provides an attractive origin for neutrino masses and mixings. In such schemes the gravitino is a viable decaying dark matter particle whose R-parity violating decays lead to monochromatic photons with rates accessible to astrophysical observations. We determine the parameter region allowed by gamma-ray line searches, dark matter relic abundance, and neutrino oscillation data, obtaining a limit on the gravitino mass mG ≲ 1-10 GeV corresponding to a relatively low reheat temperature TR ≲ few X 107-108 GeV. Neutrino mass and mixing parameters may be reconstructed at accelerator experiments like the Large Hadron Collider. [ABSTRACT FROM AUTHOR]

We explore some aspects of the phenomenology of the Higgs sector in a model that includes right-handed neutrinos, with a mass of the order of the electroweak scale. In this model all scales arise from spontaneous symmetry breaking, thus the Higgs sector includes an extra Higgs singlet, in addition to the Standard Model Higgs doublet. The scalar spectrum includes two neutral CP-even states (h and H, with mh < mH) and a neutral CP-odd state (σ) that can be identified as a pseudo-Majoron. The parameter of the Higgs potential are constrained using a perturbativity criteria, which amounts to solve the corresponding RGE. The relevant Higgs branching ratios and some cross-sections are discussed, with special emphasis on the detection of the invisible Higgs signal at the LHC. [ABSTRACT FROM AUTHOR]

Abstract: A wide class of Higgs sectors is investigated in supersymmetric standard models. When the lightest Higgs boson (h) looks the standard model one, the mass () and the triple Higgs boson coupling (the hhh coupling) are evaluated at the one-loop level in each model. While is at most 120–130 GeV in the minimal supersymmetric standard model (MSSM), that in models with an additional neutral singlet or triplet fields can be much larger. The hhh coupling can also be sensitive to the models: while in the MSSM the deviation from the standard model prediction is not significant, that can be 30–60% in some models such as the MSSM with the additional singlet or with extra doublets and charged singlets. These models are motivated by specific physics problems like the μ-problem, the neutrino mass, the scalar dark matter and so on. Therefore, when h is found at the CERN Large Hadron Collider, we can classify supersymmetric models by measuring and the hhh coupling accurately at future collider experiments. [Copyright &y& Elsevier]

I argue that LHC may shed light on the nature of neutrino mass through the probe of the seesaw mechanism. The smoking gun signature is lepton number violation through the production of same sign lepton pairs, a collider analogy of the neutrinoless double beta decay. I discuss this in the context of left-right symmetric theories, which led originally to neutrino mass and the seesaw mechanism. A WR gauge boson with a mass in a few TeV region could easily dominate neutrinoless double beta decay, and its discovery at LHC would have spectacular signatures of parity restoration and lepton number violation. Moreover, LHC can measure the masses of the right-handed neutrinos and the right-handed leptonic mixing matrix, which could in turn be used to predict the rates for neutrinoless double decay and lepton flavor violating violating processes. The LR scale at the LHC energies offers great hope of observing these low energy processes in the present and upcoming experiments. [ABSTRACT FROM AUTHOR]

Abstract: We establish a hybrid seesaw mechanism to explain small neutrino masses and predict cold dark matter candidate in the context of the gauge symmetry extension of the Standard Model. In this model a new scalar doublet and two new fermion singlets are introduced at loop-level beyond the minimal Type I seesaw. The lightest particle inside the loop can be dark matter candidate. We study in detail the constraints from neutrino oscillation data, lepton flavor violating processes and cosmological observation. We also explore the predictions of the decays of the new charged scalars in each spectrum of neutrino masses and show the most optimistic scenarios to distinguish the spectra. We consider the pair production of the stable fermion associated with two observable SM charged leptons at the LHC, which occurs in a two-step cascade decay of the new gauge boson and the new charged scalars stand as intermediate particles. The masses of missing dark matter and its parent particle can be well determined in such production topology. [Copyright &y& Elsevier]

The existing data appear to provide hints of an underlying high scale theory. These arise from the gauge coupling unification, from the smallness of the neutrino masses, and via a nonvanishing muon anomaly. An overview of high scale models is given with a view to possible tests at the Large Hadron Collider. Specifically we discuss here some generic approaches to deciphering their signatures. We also consider an out of the box possibility of a four-generation model where the fourth generation is a mirror generation rather than a sequential generation. Such a scenario can lead to some remarkably distinct signatures at the LHC. [ABSTRACT FROM AUTHOR]

Abstract: We present a new model of radiative neutrino mass generation wherein TeV scale leptoquark scalars induce tiny neutrino masses as two-loop radiative corrections. The neutrino oscillation parameter is predicted to be close to the current experimental limit within the model. Rare lepton flavor violating processes mediated by leptoquarks have an interesting pattern: may be suppressed, while and conversion in nuclei are within reach of the next generation experiments. New CP violating contributions to mixing via leptoquark box diagrams are in a range that can explain the recently reported discrepancy with the standard model. decays mediated by leptoquarks brings theory and experiment closer, removing an observed 2σ anomaly. Muon receives new positive contributions, which can resolve the discrepancy between theory and experiment. The leptoquarks of the model are accessible to the LHC, and their decay branching ratios probe neutrino oscillation parameters. [Copyright &y& Elsevier]

Abstract: We present a new approach for generating tiny neutrino masses. The Dirac neutrino mass matrix gets contributions from two new Higgs doublets with their vevs at the electroweak (EW) scale. Neutrino masses are tiny not because of tiny Yukawa couplings, or very heavy () right-handed neutrinos. They are tiny because of a cancellation in the Dirac neutrino mass matrix (fine tuning). After fine tuning to make the Dirac neutrino mass matrix at the scale, light neutrino masses are obtained in the correct scale via the see-saw mechanism with the right-handed neutrino at the EW scale. The proposal links neutrino physics to collider physics. The Higgs search strategy is completely altered. For a wide range of Higgs masses, the Standard Model Higgs decays dominantly to mode giving rise to the final state , or . This can be tested at the LHC, and possibly at the Tevatron. [Copyright &y& Elsevier]

Abstract: I discuss the implications of the observed masses and mixings of neutrinos for unification beyond the standard model and point out the important role that ongoing searches for the remaining mixing angle , neutrinoless double beta decay as well as possible searches for a at LHC can play in this discussion. [Copyright &y& Elsevier]

Abstract: We propose a model of neutrino mass generation in extra dimension. Allowing a large lepton number violation on a distant brane spatially separated from the standard model brane, a small neutrino mass is naturally generated due to an exponential suppression of the messenger field in the 5D bulk. The model accommodates a large Yukawa coupling with the singlet neutrino () which may change the standard Higgs search and can simultaneously accommodate visible lepton number violation at the electroweak scale, which leads to very interesting phenomenology at the CERN Large Hadron Collider. [Copyright &y& Elsevier]

Abstract: We investigate non-standard neutrino interactions (NSIs) in the Zee–Babu model. The size of NSIs predicted by this model is obtained from a full scan over the parameter space, taking into account constraints from low-energy experiments such as searches for lepton flavor violation (LFV) and the requirement to obtain a viable neutrino mass matrix. The dependence on the scale of new physics as well as on the type of the neutrino mass hierarchy is discussed. We find that NSIs at the source of a future neutrino factory may be at an observable level in the and/or channels. In particular, if the doubly charged scalar of the model has a mass in reach of the LHC and if the neutrino mass hierarchy is inverted, a highly predictive scenario is obtained with observable signals at the LHC, in upcoming neutrino oscillation experiments, in LFV processes, and for NSIs at a neutrino factory. [Copyright &y& Elsevier]

Abstract: The properties of light leptoquarks predicted in the context of a simple grand unified theory and their observability at the LHC are investigated. The symmetry of the theory implies that the leptoquark couplings to matter are related to the neutrino mass matrix. We study the resulting connection between neutrino masses and mixing parameters and the leptoquark decays, and show that different light neutrino hierarchies imply distinctive leptoquark decay signatures. We also discuss low-energy constraints implied by searches for charged lepton flavour violation, studies of meson decays, and electroweak precision data. We perform a detailed parton-level study of the leptoquark signals and the Standard Model backgrounds at the LHC. With the clean final states containing a di-lepton plus two jets, the QCD production of the leptoquark pair can be observed for a leptoquark mass of one TeV and beyond. By examining the lepton flavor structure of the observed events, one could further test the model predictions related to the neutrino mass spectrum. In particular, b-flavor tagging will be useful in distinguishing the neutrino mass pattern and possibly probing an unknown Majorana phase in the Inverted Hierarchy or the Quasi-Degenerate scenario. Electroweak associated production of the leptoquark doublet can also be useful in identifying the quantum numbers of the leptoquarks and distinguishing between the neutrino mass spectra, even though the corresponding event rates are smaller than for QCD production. We find that with only the clean channel of , one could expect an observable signal for a leptoquark masses of about 600 GeV or higher. [Copyright &y& Elsevier]

Abstract: In pursuit of a balance between theoretical naturalness and experimental testability, we propose two classes of multiple seesaw mechanisms at the TeV scale to understand the origin of tiny neutrino masses. They are novel extensions of the canonical and double seesaw mechanisms, respectively, by introducing even and odd numbers of gauge-singlet fermions and scalars. It is thanks to a proper implementation of the global symmetry that the overall neutrino mass matrix in either class has a suggestive nearest-neighbor-interaction pattern. We briefly discuss possible consequences of these TeV-scale seesaw scenarios, which can hopefully be explored in the upcoming Large Hadron Collider and precision neutrino experiments, and present a simple but instructive example of model building. [Copyright &y& Elsevier]

Abstract: Recently, there are two hints arising from physics beyond the standard model. One is a possible energy loss mechanism due to emission of very weakly interacting light particles from white dwarf stars, with a coupling strength , and another is the high energy positrons observed by the PAMELA satellite experiment. We construct a supersymmetric flipped-SU(5) model, with appropriate additional symmetries, , such that these are explained by a very light electrophilic axion of mass 0.5 meV from the spontaneously broken and two component cold dark matters from parity. We show that in the flipped-SU(5) there exists a basic mechanism for allowing excess positrons through the charged SU(5) singlet leptons, but not allowing antiproton excess due to the absence of the SU(5) singlet quarks. We show the discovery potential of the charged SU(5) singlet E at the LHC experiments by observing the electron and positron spectrum. With these symmetries, we also comment on the mass hierarchy between the top and bottom quarks. [Copyright &y& Elsevier]

I argue that TeV neutrino physics might become an exciting frontier of particle physics in the era of the Large Hadron Collider (LHC). The origin of non-zero but tiny masses of three known neutrinos is probably related to the existence of some heavy degrees of freedom, such as heavy Majorana neutrinos or heavy Higgs bosons, via a TeV-scale seesaw mechanism. I take a few examples to illustrate how to get a balance between theoretical naturalness and experimental testability of TeV seesaws. Besides possible collider signatures at the LHC, new and non-unitary CP-violating effects are also expected to show up in neutrino oscillations for type-I, type-(I+II) and type-III seesaws at the TeV scale. [ABSTRACT FROM AUTHOR]

Abstract: We discuss the scenario with TeV-scale right-handed neutrinos, which are accessible at future colliders, while holding down tiny seesaw-induced masses and sizable couplings to the standard-model particles. The signal with tri-lepton final states and large missing transverse energy is appropriate for studying collider signatures of the scenario with extra spatial dimensions. We show that the LHC experiment generally has a potential to discover the signs of extra dimensions and the origin of small neutrino masses. [Copyright &y& Elsevier]

Abstract: We propose a simple renormalizable left–right theory where R-parity is spontaneously broken and neutrino masses are generated through the Type I seesaw mechanism and R-parity violation. In this theory R-parity and the gauge symmetry are broken by the sneutrino vacuum expectation values and there is no Majoron problem. The and R-parity violation scales are determined by the SUSY breaking scale making the model very predictive. We discuss the spectrum and possible tests of the theory through the neutralinos, charginos, and decays at the Large Hadron Collider. [Copyright &y& Elsevier]

Abstract: We study thermal leptogenesis from decays of the electroweak triplets that mediate neutrino masses in type-II and type-III see-saw. We find that Sommerfeld corrections reduce the baryon asymmetry by ∼30%, and that successful leptogenesis needs triplets heavier than 1.6 TeV, beyond the discovery reach of LHC. [Copyright &y& Elsevier]

Abstract: Models of type I seesaw can be implemented at the electroweak scale in a natural way provided that the heavy neutrino singlets are quasi-Dirac particles. In such case, their contribution to light neutrino masses has the suppression of a small lepton number violating parameter, so that light neutrino masses can arise naturally even if the seesaw scale is low and the heavy neutrino mixing is large. We implement the same mechanism with fermionic triplets in type III seesaw, deriving the interactions of the new quasi-Dirac neutrinos and heavy charged leptons with the SM fermions. We then study the observability of heavy Dirac neutrino singlets (seesaw I) and triplets (seesaw III) at LHC. Contrarily to common wisdom, we find that heavy Dirac neutrino singlets with a mass around 100 GeV are observable at the 5σ level with a luminosity of 13 fb−1. Indeed, in the final state with three charged leptons , not previously considered, Dirac neutrino signals can be relatively large and backgrounds are small. In the triplet case, heavy neutrinos can be discovered with a luminosity of 1.5 fb−1 for a mass of 300 GeV in the same channel. [Copyright &y& Elsevier]

The NEMO-3 detector has been taking data in the Fréjus underground laboratory (LSM, France) since February 2003 and is devoted to the search for neutrinoless double-beta decay (0 νββ). After 389 effective days of data collection from February 2003 until September 2004 (Phase I), no evidence for neutrinoless double-beta decay was found from ∼7 kg of 100Mo and ∼1 kg of 82Se. The corresponding limits for the half-lives are T 1/2(0 νββ) > 4.6 × 1023 yr for 100Mo and T 1/2(0 νββ) > 1.0 × 1023 yr for 82Se (90% C.L.). They lead to the following limits for the effective Majorana neutrino mass: 〈 m ν〉 < 0.7–2.8 eV for 100Mo and 〈 m ν〉 < 1.8–4.9 eV for 82Se. The half-lives of the two-neutrino double-beta decay (2 νββ) have been measured for 100Mo, 82Se, 116Cd, 150Nd, and 96Zr and reported here as well. [ABSTRACT FROM AUTHOR]

The main goal of the NEMO-3 experiment is to search for neutrinoless double-beta decay and thus to investigate physics beyond the Standard Model. The expected sensitivity for the effective Majorana neutrino mass is on the order of 0.1 eV. The NEMO-3 detector has been completely installed in the Modane Underground Laboratory (LSM), France, and has been taking data since February 2003. In this paper, a brief description of the NEMO-3 detector and some performances of the initial runs are presented. The first preliminary results for both two-neutrino (2β2ν) and neutrinoless double-beta decay (2β0ν) of 100Mo, 82Se, 116Cd, and 150Nd are given.© 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]