arXiv subjects

Snehashis Parashar

Publications and source records attributed to Snehashis Parashar.

7 recordsLinked to original sources

arXiv2026

Light Leptoquarks in a Dark Sector: Scalar Dark Matter, Neutrino Mass, and Collider Signatures

We investigate the dark matter (DM) phenomenology and subsequent collider signatures of a dark leptoquark (LQ) model containing dark vector-like quarks (VLQs) and a scalar singlet. The dark LQs and VLQs participate in the radiative generation of Majorana neutrino masses at one loop. Since the coloured LQs and VLQs cannot serve as viable DM candidates, a $\mathbb{Z}_2$-odd singlet scalar is introduced as the DM candidate. The $\mathbb{Z}_2$-odd nature of the LQs forbids their conventional decays into a quark and a lepton, allowing them to evade the standard LHC constraints that apply to visible LQ signatures. This framework therefore offers the distinctive possibility of sub-TeV dark LQs coexisting with TeV-scale dark VLQs. These sub-TeV dark LQs help in achieving the observed relic abundance of the singlet through co-annihilation. We analyse the resulting DM phenomenology and assess the prospects for probing this scenario at a future muon collider.

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arXiv2025

Dark clouds to silver linings over the hyperchargeless scalar triplets

A real scalar triplet with zero hypercharge offers a minimal non-trivial extension of the Standard Model (SM) with a charged Higgs and a possible dark matter or custodial symmetry breaking signature. The $Z_2$-odd inert triplet model (ITM) provides a dark matter, while the non-inert Higgs triplet model (HTM) breaks the custodial symmetry, enabling rich collider signatures. Both these models also promise the viability of a first-order phase transition (FOPT). This letter revisits both models under various theoretical and current experimental constraints, revealing a trade-off between DM and FOPT viability, and explores the resulting gravitational wave signals and collider prospects.

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arXiv2024

Probing a scalar singlet-triplet extension of the Standard Model via VBF at the Muon Collider

In this article, we investigate the $Y=0$ $SU(2)$ scalar triplet and $Z_2$-odd scalar singlet extension of the Standard Model (SM). Here, the triplet charged Higgs boson decays to $ZW^\pm$, breaking the custodial symmetry at the tree-level, proportional to the triplet vev, while the singlet provides the dark matter (DM) relic. The triplet neutral Higgs ($T^0$) can decay fully invisibly owing to the triplet-singlet portal coupling $\lambda_{st}$. The other SM Higgs portal couplings $\lambda_{ht}, \lambda_{hs}$ are constrained by the Higgs to di-photon observations, and the dark matter relic and direct searches as well as invisible Higgs decay bounds, respectively. For a cleaner signature, we indulge in a futuristic multi-TeV muon collider (MuC) to probe both the triplet scalars ($T^\pm, T^0 $) via vector boson fusion with Forward muon tagging, at the centre-of-mass energies of 3 TeV and 10 TeV. The analysis is comprised of a traditional cut-based approach and a BDT classifier, where the latter is more effective for lower energies. With large missing energy contributions to the final states from combinations of DM mass and $\lambda_{st}$, The 3 TeV MuC is projected to probe triplet scalar masses of 450 GeV with the BDT classifier. The 10 TeV MuC can pinpoint the custodial symmetry breaking $T^\pm \to ZW^\pm \to 3$-lepton decay up to 800 GeV of triplet scalar mass from cut-based analysis, with $\lambda_{st}$ as low as 1.5 being adequate.

hep-ph↗

arXiv2024

Probing Inert Triplet Model at a multi-TeV muon collider via vector boson fusion with forward muon tagging

This study investigates the potential of a multi-TeV Muon Collider (MuC) for probing the Inert Triplet Model (ITM), which introduces a triplet scalar field with hypercharge $Y=0$ to the Standard Model. The ITM stands out as a compelling Beyond the Standard Model scenario, featuring a neutral triplet $T^0$ and charged triplets $T^\pm$. Notably, $T^0$ is posited as a dark matter (DM) candidate, being odd under a $Z_2$ symmetry. Rigorous evaluations against theoretical, collider, and DM experimental constraints corner the triplet scalar mass to a narrow TeV-scale region, within which three benchmark points are identified, with $T^\pm$ masses of 1.21 TeV, 1.68 TeV, and 3.86 TeV, for the collider study. The ITM's unique $TTVV$ four-point vertex, differing from fermionic DM models, facilitates efficient pair production through Vector Boson Fusion (VBF). This characteristic positions the MuC as an ideal platform for exploring the ITM, particularly due to the enhanced VBF cross-sections at high collision energies. To address the challenge of the soft decay products of $T^\pm$ resulting from the narrow mass gap between $T^\pm$ and $T^0$, we propose using Disappearing Charged Tracks (DCTs) from $T^\pm$ and Forward muons as key signatures. We provide event counts for these signatures at MuC energies of 6 TeV and 10 TeV, with respective luminosities of 4 ab$^{-1}$ and 10 ab$^{-1}$. Despite the challenge of beam-induced backgrounds contaminating the signal, we demonstrate that our proposed final states enable the MuC to achieve a $5\sigma$ discovery for the identified benchmark points, particularly highlighting the effectiveness of the final state with one DCT and one Forward muon.

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arXiv2023

Interplay of inert doublet and vector-like lepton triplet with displaced vertices at the LHC/FCC and MATHUSLA

We study the interaction between the inert Higgs doublet (IDM) dark matter and a vector-like $SU(2)$ triplet lepton (VLL), both of which are $Z_2$-odd. The vector current of the VLL with the $Z$-boson rules out a fermionic or two-component dark matter scenario. However, a compressed mass spectrum and a sufficiently small Yukawa coupling allows co-annihilation and late decay of the VLL into the IDM sector, affecting the relic density of the pseudoscalar dark matter. The same two factors enable displaced decay of the VLL states, providing novel signatures involving hadronically quiet displaced multi-lepton final states. Such signatures to probe the model are studied at the 14 and 27 TeV LHC, as well as the 100 TeV FCC-hh. In addition to being detectable at the CMS/ATLAS experiments, if the new particles have sub-100 GeV masses, signals can also be seen at the proposed MATHUSLA detector.

hep-ph↗

arXiv2023

Phenomenology of Scalar Leptoquarks at the LHC in Explaining the Radiative Neutrino Mass, Muon $g-2$ and Lepton Flavour Violating Observables

We study the phenomenology of a particular leptoquark extension of the Standard Model (SM), namely the doublet-singlet scalar leptoquark extension of the SM (DSL-SM). Besides generating Majorana mass for neutrinos, these leptoquarks contribute to muon and electron $(g-2)$ and various lepton flavour violating processes. Collider signatures of the benchmark points (BPs), consistent with the neutrino oscillation data, anomalous muon/electron magnetic moments, experimental bounds on the charged lepton flavour violation observables, etc., are studied at the LHC/FCC with centre-of-mass energies of 14, 27 and 100 TeV. While the two $-1/3$ charged colored scalars from singlet and doublet leptoquark mix with each other, the charge $2/3$ colored scalar from the doublet leptoquark remains pure. With a near-degenerate mass spectrum, the pure and mixed leptoquark states are shown to be distinguishable from multiple finalstates, while discerning between the two mixed states remain very challenging.

hep-ph↗

arXiv2022

Distinguishing signatures of scalar leptoquarks at hadron and muon colliders

While the hunt for new states beyond the standard model (SM) goes on for various well motivated theories, the leptoquarks are among the most appealing scenarios at recent times due to a series of tensions observed in $B$-meson decays. We consider $SU(2)$ singlet and triplet scalar leptoquarks separately, which contribute to charged and neutral current $B$-meson decays. Focusing on the single production of these two scalar leptoquarks, we perform a PYTHIA-based simulation considering all the dominant SM backgrounds at the current and future setups of the Large Hadron Collider (LHC). The mono-$b$-jet + $\ptmiss$ finalstate gives the strongest signal for the singlet leptoquark at the 30 TeV LHC or Future Circular Collider (FCC), with a possibility of $5σ$ signal significance with $\gtrsim 1000$ \fbi of integrated luminosity, for the chosen benchmark scenarios. The finalstate consisting of a $c$-jet and two $τ$-jets provides highest reach for the singlet leptoquark, probing an $\mathcal{O}(10^{-1})$ value of the Yukawa-type couplings for up to $3.0$ TeV leptoquark mass. For the triplet leptoquark, $1-{\rm jet}+2μ+ \ptmiss$ topology is the most optimistic signature at the LHC, probing leptoquark couplings to fermions at $\mathcal{O}(10^{-1})$ value for the leptoquark mass range up to $ 4.0$ TeV. The invariant mass edge distribution is found to be instrumental in determination of the leptoquark mass scale at the LHC. We also perform the analysis at the proposed multi-TeV muon collider, where an $\mathcal{O}(10^{-1})$ leptoquark Yukawa coupling can be probed for a $5.0$ TeV leptoquark mass.

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