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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Feruglio, F., Gherardi, V., Romanino, A., & Titov, A. (2021). Modular invariant dynamics and fermion mass hierarchies around tau = i. J. High Energy Phys., 05(5), 242–26pp.
Abstract: We discuss fermion mass hierarchies within modular invariant flavour models. We analyse the neighbourhood of the self-dual point tau = i, where modular invariant theories possess a residual Z(4) invariance. In this region the breaking of Z(4) can be fully described by the spurion epsilon approximate to tau – i, that flips its sign under Z(4). Degeneracies or vanishing eigenvalues of fermion mass matrices, forced by the Z(4) symmetry at tau = i, are removed by slightly deviating from the self-dual point. Relevant mass ratios are controlled by powers of vertical bar epsilon vertical bar. We present examples where this mechanism is a key ingredient to successfully implement an hierarchical spectrum in the lepton sector, even in the presence of a non-minimal Kahler potential.
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Bazzocchi, F., Morisi, S., Peinado, E., Valle, J. W. F., & Vicente, A. (2013). Bilinear R-parity violation with flavor symmetry. J. High Energy Phys., 01(1), 033–16pp.
Abstract: Bilinear R-parity violation (BRPV) provides the simplest intrinsically supersymmetric neutrino mass generation scheme. While neutrino mixing parameters can be probed in high energy accelerators, they are unfortunately not predicted by the theory. Here we propose a model based on the discrete flavor symmetry Lambda(4) with a single R-parity violating parameter, leading to (i) correct Cabbibo mixing given by the Gatto-Sartori-Tonin formula, and a successful unification-like b-tau mass relation, and (ii) a correlation between the lepton mixing angles theta(13) and theta(23) in agreement with recent neutrino oscillation data, as well as a (nearly) massless neutrino, leading to absence of neutrinoless double beta decay.
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Merle, A., Platscher, M., Rojas, N., Valle, J. W. F., & Vicente, A. (2016). Consistency of WIMP Dark Matter as radiative neutrino mass messenger. J. High Energy Phys., 07(7), 013–17pp.
Abstract: The scotogenic scenario provides an attractive approach to both Dark Matter and neutrino mass generation, in which the same symmetry that stabilises Dark Matter also ensures the radiative seesaw origin of neutrino mass. However the simplest scenario may suffer from inconsistencies arising from the spontaneous breaking of the underlying Z(2) symmetry. Here we show that the singlet-triplet extension of the simplest model naturally avoids this problem due to the presence of scalar triplets neutral under the Z(2) which affect the evolution of the couplings in the scalar sector. The scenario offers good prospects for direct WIMP Dark Matter detection through the nuclear recoil method.
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Alekhin, S. et al, & Hernandez, P. (2016). A facility to search for hidden particles at the CERN SPS: the SHiP physics case. Rep. Prog. Phys., 79(12), 124201–137pp.
Abstract: This paper describes the physics case for a new fixed target facility at CERN SPS. The SHiP (search for hidden particles) experiment is intended to hunt for new physics in the largely unexplored domain of very weakly interacting particles with masses below the Fermi scale, inaccessible to the LHC experiments, and to study tau neutrino physics. The same proton beam setup can be used later to look for decays of tau-leptons with lepton flavour number non-conservation, tau -> 3 μand to search for weakly-interacting sub-GeV dark matter candidates. We discuss the evidence for physics beyond the standard model and describe interactions between new particles and four different portals-scalars, vectors, fermions or axion-like particles. We discuss motivations for different models, manifesting themselves via these interactions, and how they can be probed with the SHiP experiment and present several case studies. The prospects to search for relatively light SUSY and composite particles at SHiP are also discussed. We demonstrate that the SHiP experiment has a unique potential to discover new physics and can directly probe a number of solutions of beyond the standard model puzzles, such as neutrino masses, baryon asymmetry of the Universe, dark matter, and inflation.
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