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Rocha-Moran, P., & Vicente, A. (2016). Lepton Flavor Violation in the singlet-triplet scotogenic model. J. High Energy Phys., 07(7), 078–25pp.
Abstract: We investigate lepton flavor violation (LFV) in the the singlet-triplet scotogenic model in which neutrinos acquire non-zero masses at the 1-loop level. In contrast to the most popular variant of this setup, the singlet scotogenic model, this version includes a triplet fermion as well as a triplet scalar, leading to a scenario with a richer dark matter phenomenology. Taking into account results from neutrino oscillation experiments, we explore some aspects of the LFV phenomenology of the model. In particular, we study the relative weight of the dipole operators with respect to other contributions to the LFV amplitudes and determine the most constraining observables. We show that in large portions of the parameter space, the most promising experimental perspectives are found for LFV 3-body decays and for coherent mu-e conversion in nuclei.
Keywords: Neutrino Physics; Beyond Standard Model
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Farzan, Y., & Tortola, M. (2018). Neutrino oscillations and non-standard Interactions. Front. Physics, 6, 10–34pp.
Abstract: Current neutrino experiments are measuring the neutrino mixing parameters with an unprecedented accuracy. The upcoming generation of neutrino experiments will be sensitive to subdominant neutrino oscillation effects that can in principle give information on the yet-unknown neutrino parameters: the Dirac CP-violating phase in the PMNS mixing matrix, the neutrino mass ordering and the octant of.23. Determining the exact values of neutrino mass and mixing parameters is crucial to test various neutrino models and flavor symmetries that are designed to predict these neutrino parameters. In the first part of this review, we summarize the current status of the neutrino oscillation parameter determination. We consider the most recent data from all solar neutrino experiments and the atmospheric neutrino data from Super-Kamiokande, IceCube, and ANTARES. We also implement the data from the reactor neutrino experiments KamLAND, Daya Bay, RENO, and Double Chooz as well as the long baseline neutrino data from MINOS, T2K, and NO.A. If in addition to the standard interactions, neutrinos have subdominant yet-unknown Non-Standard Interactions (NSI) with matter fields, extracting the values of these parameters will suffer from new degeneracies and ambiguities. We review such effects and formulate the conditions on the NSI parameters under which the precision measurement of neutrino oscillation parameters can be distorted. Like standard weak interactions, the non-standard interaction can be categorized into two groups: Charged Current (CC) NSI and Neutral Current (NC) NSI. Our focus will bemainly on neutral current NSI because it is possible to build a class of models that give rise to sizeable NC NSI with discernible effects on neutrino oscillation. These models are based on new U(1) gauge symmetry with a gauge boson of mass. 10 MeV. The UV complete model should be of course electroweak invariant which in general implies that along with neutrinos, charged fermions also acquire new interactions on which there are strong bounds. We enumerate the bounds that already exist on the electroweak symmetric models and demonstrate that it is possible to build viable models avoiding all these bounds. In the end, we review methods to test these models and suggest approaches to break the degeneracies in deriving neutrino mass parameters caused by NSI.
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Abada, A., De Romeri, V., Lucente, M., Teixeira, A. M., & Toma, T. (2018). Effective Majorana mass matrix from tau and pseudoscalar meson lepton number violating decays. J. High Energy Phys., 02(2), 169–57pp.
Abstract: An observation of any lepton number violating process will undoubtedly point towards the existence of new physics and indirectly to the clear Majorana nature of the exchanged fermion. In this work, we explore the potential of a minimal extension of the Standard Model via heavy sterile fermions with masses in the [0.1-10] GeV range concerning an extensive array of “neutrinoless” meson and tau decay processes. We assume that the Majorana neutrinos are produced on-shell, and focus on three-body decays. We conduct an update on the bounds on the active-sterile mixing elements, vertical bar U-l alpha 4,U-l beta 4 vertical bar, taking into account the most recent experimental bounds (and constraints) and new theoretical inputs, as well as the effects of a finite detector, imposing that the heavy neutrino decay within the detector. This allows to establish up-to-date comprehensive constraints on the sterile fermion parameter space. Our results suggest that the branching fractions of several decays are close to current sensitivities (likely within reach of future facilities), some being already in conflict with current data (as is the case of K-broken vertical bar -> l(alpha)(broken vertical bar)+l(beta)(+)pi(-), and tau(-)->mu(broken vertical bar)pi(-)pi(-)). We use these processes to extract constraints on all entries of an enlarged definition of a 3 x 3 “effective” Majorana neutrino mass matrix m(v)(alpha beta).
Keywords: Beyond Standard Model; Neutrino Physics
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Helo, J. C., Hirsch, M., & Ota, T. (2018). Proton decay and light sterile neutrinos. J. High Energy Phys., 06(6), 047–15pp.
Abstract: Within the standard model, non-renormalizable operators at dimension six (d = 6) violate baryon and lepton number by one unit and thus lead to proton decay. Here, we point out that the proton decay mode with a charged pion and missing energy can be a characteristic signature of d = 6 operators containing a light sterile neutrino, if it is not accompanied by the standard pi(0)e(+) final state. We discuss this effect first at the level of effective operators and then provide a concrete model with new physics at the TeV scale, in which the lightness of the active neutrinos and the stability of the proton are related.
Keywords: Beyond Standard Model; Neutrino Physics
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Helo, J. C., Hirsch, M., & Wang, Z. S. (2018). Heavy neutral fermions at the high-luminosity LHC. J. High Energy Phys., 07(7), 056–23pp.
Abstract: Long-lived light particles (LLLPs) appear in many extensions of the standard model. LLLPs are usually motivated by the observed small neutrino masses, by dark matter or both. Typical examples for fermionic LLLPs (a.k.a. heavy neutral fermions, HNFs) are sterile neutrinos or the lightest neutralino in R-parity violating supersymmetry. The high luminosity LHC is expected to deliver up to 3/ab of data. Searches for LLLPs in dedicated experiments at the LHC could then probe the parameter space of LLLP models with unprecedented sensitivity. Here, we compare the prospects of several recent experimental proposals, FASER, CODEX-b and MATHUSLA, to search for HNFs and discuss their relative merits.s
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