Invisible Higgs decays and neutrino physics

A wide class of neutrino physics motivated models are characterized by the spontaneous violation of a global U(1) lepton number symmetry at or below the electroweak scale by an SU(2)⊗U(1) singlet vacuum expectation value 〈σ〉 ≲ O(1) TeV. In all these models the main Higgs decay channel is likely to be ¿invisible¿, e.g. h → JJ, where J denotes the associated weakly interacting pseudoscalar Goldstone boson ¿ the majoron. This leads to events with large missing energy that could be observable at LEP and affect the Higgs mass bounds obtained, as well as lead to novel ways to search for Higgs bosons and high-energy supercolliders such as the LHC/SSC

Bilarge neutrino mixing and Abelian flavor symmetry

We explore two bilarge neutrino mixing Anzatze within the context of Abelian flavor symmetry theories: (BL1) sin theta(12) similar to lambda, sin theta(13) similar to lambda, sin theta(23) similar to lambda, and (BL2) sin theta(12) similar to lambda, sin theta(13) similar to lambda, sin theta(23) similar to 1 ¿ lambda. The first pattern is proposed by two of us and is favored if the atmospheric mixing angle theta(23) lies in the first octant, while the second one is preferred for the second octant of theta(23). In order to reproduce the second texture, we find that the flavor symmetry should be U(1) x Z(m), while for the first pattern the flavor symmetry should be extended to U(1) x Z(m) x Z(n) with m and n of different parity. Explicit models for both mixing patterns are constructed based on the flavor symmetries U(1) x Z(3) x Z(4) and U(1) x Z(2). The models are extended to the quark sector within the framework of SU(5) grand unified theory in order to give a successful description of quark and lepton masses and mixing simultaneously. Phenomenological implications are discussed

Underlying A(4) symmetry for the neutrino mass matrix and the quark mixing matrix

The discrete non-Abelian symmetry A4, valid at some high-energy scale, naturally leads to degenerate neutrino masses, without spoiling the hierarchy of charged-lepton masses. Realistic neutrino mass splittings and mixing angles (one of which is necessarily maximal and the other large) are then induced radiatively in the context of softly broken supersymmetry. The quark mixing matrix is also calculable in a similar way. The mixing parameter Ue3 is predicted to be imaginary, leading to maximal CP violation in neutrino oscillations. Neutrinoless double beta decay and τ→μγ should be in the experimentally accessible range

Is charged lepton flavor violation a high energy phenomenon?

Searches for rare processes such as μ-> e gamma put stringent limits on lepton flavor violation expected in many beyond-the-Standard-Model physics scenarios. This usually precludes the observation of flavor violation at high energy colliders such as the LHC. We here discuss a scenario where right-handed neutrinos are produced via a Z' portal but which can only decay via small flavor violating couplings. Consequently, the process rate is unsuppressed by the small couplings and can be visible despite unobservably small μ-> e gamma rates

Radiative neutrino mass in 3-3-1 scheme

We propose a new radiative mechanism for neutrino mass generation based on the SU(3)(c) circle times SU(3)(L) circle times U(1)(X) electroweak gauge group. Lepton number is a symmetry of the Yukawa sector which is spontaneously broken in the gauge sector. As a result light Majorana masses arise from neutral gauge boson exchanges at the one-loop level. In addition to the isosinglet neutrinos that may be produced at the LHC through the extended gauge boson portals, the model contains new quarks which can also lie at the TeV scale, and which can provide a plethora of accessible collider phenomena

Lepton asymmetries and primordial hypermagnetic helicity evolution

The hypermagnetic helicity density at the electroweak phase transition (EWPT) exceeds many orders of magnitude the galactic magnetic helicity density. Together with previous magnetic helicity evolution calculations after the EWPT and hypermagnetic helicity conversion to the magnetic one at the EWPT, the present calculation completes the description of the evolution of this important topological feature of cosmological magnetic fields. It suggests that if the magnetic field seeding the galactic dynamo has a primordial origin, it should be substantially helical. This should be taken into account in scenarios of galactic magnetic field evolution with a cosmological seed

The Low-Scale Approach to Neutrino Masses

In this short review we revisit the broad landscape of low-scale SU(3)(C) circle times SU(2)(L) circle times U(1)(Y) models of neutrino mass generation, with view on their phenomenological potential. This includes signatures associated to direct neutrino mass messenger production at the LHC, as well as messenger-induced lepton flavor violation processes. We also briefly comment on the presence of WIMP cold dark matter candidates

A White Paper on keV sterile neutrino Dark Matter

We present a comprehensive review of keV-scale sterile neutrino Dark Matter, collecting views and insights from all disciplines involved - cosmology, astrophysics, nuclear, and particle physics - in each case viewed from both theoretical and experimental/observational perspectives. After reviewing the role of active neutrinos in particle physics, astrophysics, and cosmology, we focus on sterile neutrinos in the context of the Dark Matter puzzle. Here, we first review the physics motivation for sterile neutrino Dark Matter, based on challenges and tensions in purely cold Dark Matter scenarios. We then round out the discussion by critically summarizing all known constraints on sterile neutrino Dark Matter arising from astrophysical observations, laboratory experiments, and theoretical considerations. In this context, we provide a balanced discourse on the possibly positive signal from X-ray observations. Another focus of the paper concerns the construction of particle physics models, aiming to explain how sterile neutrinos of keV-scale masses could arise in concrete settings beyond the Standard Model of elementary particle physics. The paper ends with an extensive review of current and future astrophysical and laboratory searches, highlighting new ideas and their experimental challenges, as well as future perspectives for the discovery of sterile neutrinos

Updated global analysis of the atmospheric neutrino data in terms of neutrino oscillations

A global analysis of all the available atmospheric neutrino data is presented in terms of neutrino oscillations in the nu_mu -> nu_tau and nu_mu -> nu_s channels, where nu_s denotes a sterile neutrino. We perform our analysis of the contained events data as well as the upward-going neutrino-induced muon fluxes. In addition to the previous data samples of Frejus, Nusex, IMB and Kamioka experiments, we include the full data set of the 52 kton-yr of Super-Kamiokande, the recent 4.6 kton-yr contained events of Soudan2 and the results on upgoing muons from the MACRO and Baksan detectors. From the statistical analysis it emerges that the nu_mu -> nu_tau channel provides the best agreement with the combined data, with a best fit point of sin^2(2 theta) = 0.99 and Delta m^2 = 3.0 * 10^{-3} eV^2. Although somehow disfavoured, the nu_mu -> nu_s channels cannot be ruled out on the basis of the global fit to the full set of observables

Gravitino dark matter and neutrino masses with bilinear R-parity violation

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 m_{\tilde G} \lsim 1-10 GeV corresponding to a relatively low reheat temperature T_R \lsim few ×107−108 GeV. Neutrino mass and mixing parameters may be reconstructed at accelerator experiments like the Large Hadron Collider