Portillo-Sanchez, D., Escribano, P., & Vicente, A. (2023). Ultraviolet extensions of the Scotogenic model. J. High Energy Phys., 08(8), 023–35pp.
Abstract: The Scotogenic model is a popular scenario that induces radiative Majorana neutrino masses and includes a weakly-interacting dark matter candidate. We classify all possible ultraviolet extensions of the Scotogenic model in which (i) the dark DOUBLE-STRUCK CAPITAL Z(2) parity emerges at low energies after the spontaneous breaking of a global U(1)(L) lepton number symmetry, and (ii) the low-energy effective theory contains a naturally small lepton number breaking parameter, suppressed by the mass of a heavy mediator integrated out at tree-level. We find 50 such models and discuss two of them in detail to illustrate our setup. We also discuss some general aspects of the phenomenology of the models in our classification, exploring possible lepton flavor violating signals, collider signatures and implications for dark matter. The phenomenological prospects of these scenarios are very rich due to the presence of additional scalar states, including a massless Goldstone boson.
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Batra, A., Bharadwaj, P., Mandal, S., Srivastava, R., & Valle, J. W. F. (2023). Phenomenology of the simplest linear seesaw mechanism. J. High Energy Phys., 07(7), 221–48pp.
Abstract: The linear seesaw mechanism provides a simple way to generate neutrino masses. In addition to Standard Model particles, it includes quasi-Dirac leptons as neutrino mass mediators, and a leptophilic scalar doublet seeding small neutrino masses. Here we review its associated physics, including restrictions from theory and phenomenology. The model yields potentially detectable μ-> e gamma rates as well as distinctive signatures in the production and decay of heavy neutrinos ( N-i) and the charged Higgs boson (H-+/-) arising from the second scalar doublet. We have found that production processes such as e(+) e(-) -> NN, e- gamma -> NH- and e(+) e(-) -> H (+) H- followed by the decay chain H-+/--> l(+/-) (i) N, N -> l`(+/-) (j) W (-/+) leads to striking lepton number violation signatures at high energies which may probe the Majorana nature of neutrinos.
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Dreiner, H. K., Koay, Y. S., Kohler, D., Martin Lozano, V., Montejo Berlingen, J., Nangia, S., et al. (2023). The ABC of RPV: classification of R-parity violating signatures at the LHC for small couplings. J. High Energy Phys., 07(7), 215–52pp.
Abstract: We perform a classification of all potential supersymmetric R-parity violating signatures at the LHC to address the question: are existing bounds on supersymmetric models robust, or are there still signatures not covered by existing searches, allowing LHCscale supersymmetry to be hiding? We analyze all possible scenarios with one dominant RPV trilinear coupling at a time, allowing for arbitrary LSPs and mass spectra. We consider direct production of the LSP, as well as production via gauge-cascades, and find 6 different experimental signatures for the LL <overline> E -case, 6 for the LQ <overline> D -case, and 5 for the <overline> U <overline> D <overline> D -case; together these provide complete coverage of the RPV-MSSM landscape. This set of signatures is confronted with the existing searches by ATLAS and CMS. We find all signatures have been covered at the LHC, although not at the sensitivity level needed to probe the direct production of all LSP types. For the case of a dominant LL <overline> E -operator, we use CheckMATE to quantify the current lower bounds on the supersymmetric masses and find the limits to be comparable to or better than the R-parity conserving case. Our treatment can be easily extended to scenarios with more than one non-zero RPV coupling.
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Fischer, O., Pattnaik, B., & Zurita, J. (2023). Testing Heavy Neutral Leptons in Cosmic Ray Beam Dump experiments. J. High Energy Phys., 07(7), 193–24pp.
Abstract: In this work, we discuss the possibility to test Heavy Neutral Leptons (HNLs) using “Cosmic Ray Beam Dump” experiments. In analogy with terrestrial beam dump experiments, where a beam first hits a target and is then absorbed by a shield, we consider high-energy incident cosmic rays impinging on the Earth's atmosphere and then the Earth's surface. We focus here on HNL production from atmospherically produced kaon, pion and D-meson decays, and discuss the possible explanation of the appearing Cherenkov showers observed by the SHALON Cherenkov telescope and the ultra-high energy events detected by the neutrino experiment ANITA. We show that these observations can not be explained with a long-lived HNL, as the relevant parameter space is excluded by existing constraints. Then we propose two new experimental setups that are inspired by these experiments, namely a Cherenkov telescope pointing at a sub-horizontal angle and shielded by the mountain cliff at Mount Thor, and a geostationary satellite that observes part of the Sahara desert. We show that the Cherenkov telescope at Mount Thor can probe currently untested HNL parameter space for masses below the kaon mass. We also show that the geostationary satellite experiment can significantly increase the HNL parameter space coverage in the whole mass range from 10 MeV up to 2 GeV and test neutrino mixing |U-& alpha;4|(2) down to 10(-11) for masses around 300 MeV.
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ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cantero, J., et al. (2023). Search for direct pair production of sleptons and charginos decaying to two leptons and neutralinos with mass splittings near the W-boson mass in root s=13 TeV pp collisions with the ATLAS detector. J. High Energy Phys., 06(6), 031–59pp.
Abstract: A search for the electroweak production of pairs of charged sleptons or charginos decaying into two-lepton final states with missing transverse momentum is presented. Two simplified models of R-parity-conserving supersymmetry are considered: direct pairproduction of sleptons ( (l) over tilde (l) over tilde), with each decaying into a charged lepton and a (x) over tilde (+/-)(0)(1) neutralino, and direct pair-production of the lightest charginos ( (x) over tilde (+/-)(1) (x) over tilde (-/+)(1)), with each decaying into a W-boson and a (x) over tilde (0)(1). The lightest neutralino ( (x) over tilde (0)(1)) is assumed to be the lightest supersymmetric particle (LSP). The analyses target the experimentally challenging mass regions where m( (l) over tilde)- m( (x) over tilde (0)(1)) and m( (x) over tilde (+/-)(1))- m((x) over tilde (0)(1)) are close to the W-boson mass ('moderately compressed' regions). The search uses 139 fb(-1) of root s = 13TeV proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider. No significant excesses over the expected background are observed. Exclusion limits on the simplified models under study are reported in the ((l) over tilde , (x) over tilde (0)(1)) and ( (x) over tilde (+/-) (1), (x) over tilde (0)(1)) mass planes at 95% confidence level (CL). Sleptons with masses up to 150 GeV are excluded at 95% CL for the case of a mass-splitting between sleptons and the LSP of 50 GeV. Chargino masses up to 140 GeV are excluded at 95% CL for the case of a mass-splitting between the chargino and the LSP down to about 100 GeV.
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