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Search for long-lived heavy neutrinos at the LHC with a VBF trigger
(Springer, 2020-07-01)
Abstract The charged current production of long-lived heavy neutrinos at the LHC can use a prompt charged lepton for triggering the measurement of the process. However, in order to fully characterize the heavy neutrino interactions, it is necessary to also probe Higgs or Z mediated neutral current production. In this case the charged lepton is not available, so other means of triggering are required. In this work, we explore the possibility of using a vector boson fusion trigger in the context of a GeV-scale Type I Seesaw model. We consider a minimal model, where both Higgs and Z-mediated contributions produce one heavy neutrino, as well as an extended model where the Higgs can decay into two heavy ones. Both scenarios are tested through displaced dilepton and displaced multitrack jet searches.
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Resolving a challenging supersymmetric low-scale seesaw scenario at the ILC
(American Physical Society, 2021-06-01)
We investigate a scenario inspired by natural supersymmetry, where neutrino data is explained within a low-scale seesaw scenario. For this the minimal supersymmetric Standard Model is extended by adding light right-handed neutrinos and their superpartners, the R-sneutrinos. Moreover, we consider the lightest neutralinos to be Higgsino-like. We first update a previous analysis and assess to which extent does existing LHC data constrain the allowed slepton masses. Here we find scenarios where sleptons with masses as low as 175 GeV are consistent with existing data. However, we also show that the upcoming run will either discover or rule out sleptons with masses of 300 GeV, even for these challenging scenarios. We then take a scenario which is on the borderline of observability of the upcoming LHC run assuming a luminosity of $300\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$. We demonstrate that a prospective international ${e}^{+}{e}^{\ensuremath{-}}$ linear collider with a center of mass energy of 1 TeV will be able to discover sleptons in scenarios which are difficult for the LHC. Moreover, we also show that a measurement of the spectrum will be possible within 1--3 percent accuracy.
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Assessment of the dimension-5 seesaw portal and impact of exotic Higgs decays on non-pointing photon searches
(Springer Science and Business Media Deutschland GmbH, 2022-09-01)
The Dimension-5 Seesaw Portal is a Type-I Seesaw model extended byd= 5 operators involving the sterile neutrino states, leading to new interactions between all neutrinos and the Standard Model neutral bosons. In this work we focus primarily on the implications of these new operators at the GeV-scale. In particular, we recalculate the heavy neutrino full decay width, up to three-body decays. We also review bounds on the dipole operator, and revisit LEP constraints on its coefficient. Finally, we turn to heavy neutrino pair production from Higgs decays, where the former are long-lived and disintegrate into a photon and a light neutrino. We probe this process by recasting two ATLAS searches for non-pointing photons, showing the expected event distribution in terms of arrival timetγand pointing variable|∆zγ|.
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Bounding the dimension-5 seesaw portal with non-pointing photon searches
(Springer Science and Business Media Deutschland GmbH, 2024-04-01)
The addition of d = 5 operators to the Seesaw model leads to the Dimension-5 Seesaw Portal. Here, two new operators provide interactions for the heavy sterile neutrinos. In particular, the Higgs boson can have a large branching ratio into two heavy neutrinos, meaning that these states can be searched for at the LHC. Moreover, the heavy neutrinos can now decay dominantly into light neutrinos and photons. If the heavy neutrinos are long-lived, then searches for delayed, non-pointing photons can constrain the model. In this work, we carry out a detailed recast of an ATLAS search for such displaced photons, triggered by a charged lepton produced in association to the Higgs, placing bounds on the branching ratio for Higgs decay into two heavy neutrinos as low as 2%.
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On the Sensitivity Reach of LQ Production with Preferential Couplings to Third Generation Fermions at the LHC
(Institute for Ionics, 2023-11-01)
Leptoquarks (LQ s) are hypothetical particles that appear in various extensions of the Standard Model (SM), that can explain observed differences between SM theory predictions and experimental results. The production of these particles has been widely studied at various experiments, most recently at the Large Hadron Collider (LHC), and stringent bounds have been placed on their masses and couplings, assuming the simplest beyond-SM (BSM) hypotheses. However, the limits are significantly weaker for LQ models with family non-universal couplings containing enhanced couplings to third-generation fermions. We present a new study on the production of a LQ at the LHC, with preferential couplings to third-generation fermions, considering proton-proton collisions at s=13TeV and s=13.6TeV . Such a hypothesis is well motivated theoretically and it can explain the recent anomalies in the precision measurements of B -meson decay rates, specifically the RD(∗) ratios. Under a simplified model where the LQ masses and couplings are free parameters, we focus on cases where the LQ decays to a τ lepton and a b quark, and study how the results are affected by different assumptions about chiral currents and interference effects with other BSM processes with the same final states, such as diagrams with a heavy vector boson, Z ′ . The analysis is performed using machine learning techniques, resulting in an increased discovery reach at the LHC, allowing us to probe new physics phase space which addresses the B -meson anomalies, for LQ masses up to 5.00TeV , for the high luminosity LHC scenario.
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From WIMPs to FIMPs With Low Reheating Temperatures
(Cornell University, 2023-06-26)
Weakly- and Feebly-Interacting Massive Particles (WIMPs and FIMPs) are among the best-motivated dark matter (DM) candidates. In this paper, we investigate the production of DM through the WIMP and FIMP mechanisms during inflationary reheating. We show that the details of the reheating, such as the inflaton potential and the reheating temperature, have a strong impact on the genesis of DM. The strong entropy injection caused by the inflaton decay has to be compensated by a reduction of the portal coupling in the case of WIMPs, or by an increase in the case of FIMPs. We pinpoint the smooth transition between the WIMP and the FIMP regimes in the case of low reheating temperature. As an example, we perform a full numerical analysis of the singlet-scalar DM model; however, our results are generic and adaptable to other particle DM candidates. Interestingly, in the singlet-scalar DM model with low-reheating temperature, regions favored by the FIMP mechanism are already being tested by direct detection experiments such as LZ and XENONnT.
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Can SUSY Relax Lepton Number Violation Constraints Coming from Loop Corrections to Light Neutrino Masses on the Low-Scale Seesaw Mechanism?
(American Physical Society, 2023-06-01)
Heavy neutrinos from the type-I seesaw model can have a large mixing with active states, motivating their search at collider experiments. However, loop corrections to light neutrino masses constrain the heavy neutrinos to appear in pseudo-Dirac pairs, leading to a potential suppression of lepton number violating parameters. In this work we perform a detailed review of a proposal to relax constraints on lepton number violation by adding supersymmetry (SUSY). We define the conditions necessary to maximize the SUSY screening effect, with the objective of allowing a larger mass splitting between low-scale heavy neutrino masses. We find that the sole addition of SUSY does not guarantee a screening, and that favorable cases have some degree of fine-tuning.
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Opening the parameter space of sub-GeV inelastic dark matter through parity violation
(Springer Nature, 2026-04-01)
A bstract Sub-GeV dark matter (DM) has emerged as a particularly compelling target in light of the persistent null results from conventional DM searches. While s -wave annihilating DM candidates with masses below the GeV are strongly constrained by indirect-detection bounds, inelastic scenarios can naturally evade these limits. In this work, we show that parity violation can play an important role in inelastic DM models featuring long-lived excited states by inducing small diagonal couplings that significantly relax experimental constraints. A precise determination of the excited-state abundance is essential for assessing the phenomenology of such models. To this end, we solve the integrated Boltzmann equation, fully accounting for up- and down-scattering with electrons and positrons as well as dark-sector conversion processes. Using the resulting abundance, we update the viable parameter space in light of the most recent experimental constraints and demonstrate that parity-violating interactions can reopen broad regions of parameter space that would otherwise be excluded. Moreover, the forthcoming LDMX experiment will probe a significant portion of the parameter space. The framework developed in this work can be readily applied to other exothermic sub-GeV DM scenarios.
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