arXiv subjects

Vicky Singh Thounaojam

Publications and source records attributed to Vicky Singh Thounaojam.

8 recordsLinked to original sources

arXiv2026

Signature of GW from the Hidden Sector in light of the Recent LZ Event

The LZ collaboration has recently reported a single nuclear-recoil event at $E_R=248\pm23_\text{stat}\pm23_\text{sys}$ keV, observed in a 2.84 tonne-year exposure with a local significance of $3.4σ$, pointing towards an inelastic dark matter (DM) interpretation. We explain this event within a gauged $U(1)_X$ hidden-sector model, spontaneously broken by a singlet scalar whose vacuum expectation value (VEV) gives rise to: \textit{(i)} gauge boson mass, \textit{(ii)} a small Majorana mass for the vector-like singlet fermion, the DM candidate, charged under the new symmetry, which splits the fermion into two pseudo-Dirac states (mass splitting proportional to the scalar VEV) thus resulting in a purely off-diagonal vector current, \textit{(iii)} the frequency and the amplitude of the GW signal arising from the hidden sector symmetry breaking via first-order phase transition (FOPT). The symmetry-breaking scale thus provides a multi-messenger probe connecting terrestrial direct-detection kinematics at the LZ and early-universe FOPT thermodynamics while obtaining thermal DM relic abundance. We delineate the viable parameter space compatible with the LZ event, correct relic density, and detectable GW signals in the low frequency regimes at future interferometers like $μ{\rm ARES}$ and THEIA while satisfying existing cosmological, astrophysical, and terrestrial bounds.

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arXiv2026

Dark Phoenix: dark matter relic from its own decay

We propose a novel mechanism for generating correct relic of dark matter (DM) which otherwise gets thermally overproduced from the conventional freeze-out mechanism. The mechanism, dubbed as {\it Dark Phoenix}, relies on a transient decay window for DM after its freeze-out which brings its relic within observed limits. Due to finite-temperature effects on masses, DM $ψ$ becomes heavier than its dark sector partner $ϕ$ in this window allowing it to decay. The decay of DM then stops after $ϕ$ gets a sudden jump in its mass from a first-order phase transition (FOPT) driven by another scalar $η$. The dark sector partner $ϕ$, assumed to be a charged scalar, undergoes sufficient pair annihilation during this epoch such that its late decay into DM does not overproduce the latter again. While direct-detection rates of DM remains suppressed due to small couplings, the charged scalar $ϕ$ can have interesting signatures like long-lived charged track at colliders. The associated FOPT can also lead to observable gravitational waves at future experiments like LISA.

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arXiv2026

Anatomy of RHN DM relic in the vanilla scotogenic neutrino mass model

The scotogeneic neutrino mass models are very popular choices to generate light neutrino masses via radiative mechanism. In these models, the particles running in the loop are distinguished from the standard model due to an imposed $\mathcal{Z}_2$ symmetry under which the loop particles are odd. Therefore, the lightest particle running in the loop can be a viable dark matter candidate. In this paper, we revisit the minimal scotogenic neutrino mass model and study the anatomy of right handed neutrino (RHN) DM relic, taking into account contributions from self-annihilation, co-annihilation, conversion-driven processes, as well as production via the freeze-in mechanism. We impose the constraints from direct detection and collider searches of DM including anomalous magnetic moment of muon, charged lepton flavor violation and low-energy neutrino oscillation data to show that the lightest RHN can be a viable DM in the mass range: $M_{h}/2\lesssim M_{\rm DM}\lesssim2000 {\rm GeV}$ (thermal DM) and $0.1 ~{\rm GeV}\lesssim M_{\rm DM}\lesssim 1000 {\rm GeV}$ (non-thermal DM), where $M_h$ denotes the Standard Model Higgs mass and $M_{\rm DM}$ is the RHN dark matter mass. We also find the displaced vertex signatures of long lived particles which can be probed at future colliders.

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arXiv2025

Light thermal dark matter models in the light of DAMIC-M 2025 constraints

We study the viability of light thermal dark matter (DM) in sub-GeV mass range in view of the stringent new DAMIC-M limits on DM-electron scattering. Considering a Dirac fermion singlet DM charged under a new Abelian gauge symmetry $U(1)$, we outline two possibilities: (i) family non-universal $U(1)$ gauge coupling with resonantly enhanced DM annihilation into standard model (SM) fermions and (ii) family universal dark $U(1)$ gauge symmetry where relic is set by DM annihilation into light gauge bosons. As an illustrative example of the first class of models, we consider a gauged $L_μ-L_τ$ extension of the SM having interesting detection prospects at several experiments. While both of these class of models lead to observed DM relic and consistency with DAMIC-M together with other experimental limits, the second class of models also lead to strong DM self-interactions, potentially solving the small-scale structure issues of cold dark matter. While a vast part of the parameter space in both the models is already ruled out, the current allowed region of parameter space can be further probed at ongoing or future experiments keeping the models testable.

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arXiv2025

Self-interacting dark matter with observable $ΔN_{\rm eff}$

We propose a GeV-scale self-interacting dark matter (SIDM) candidate within a dark $U(1)_D$ gauged extension of the Standard Model (SM), addressing small-scale structure issues in $Λ$CDM while predicting an observable contribution to $ΔN_{\rm eff}$ in the form of dark radiation. The model introduces a fermionic DM candidate $χ$ and a scalar $ϕ$, both charged under an unbroken $U(1)_D$ gauge symmetry. The self-interactions of $χ$ are mediated by a light vector boson $X^μ$, whose mass is generated via the Stueckelberg mechanism. The relic abundance of $χ$ is determined by thermal freeze-out through annihilations into $X^μ$, supplemented by a non-thermal component from the late decay of $ϕ$. Crucially, $ϕ$ decays after the Big Bang Nucleosynthesis (BBN) but before the Cosmic Microwave Background (CMB) epoch, producing additional $χ$ and a dark radiation species ($ν_S$). This late-time production compensates for thermal underabundance due to efficient annihilation into light mediators, while remaining consistent with structure formation constraints. The accompanying dark radiation yields a detectable $ΔN_{\rm eff}$, compatible with Planck 2018 bounds and within reach of next-generation experiments such as SPT-3G, CMB-S4, and CMB-HD.

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arXiv2024

New realisation of light thermal dark matter with enhanced detection prospects

Light dark matter (DM) with mass around the GeV scale faces weaker bounds from direct detection experiments. If DM couples strongly to a light mediator, it is possible to have observable direct detection rate. However, this also leads to a thermally under-abundant DM relic due to efficient annihilation into light mediators. We propose a novel scenario where a first-order phase transition (FOPT) occurring at MeV scale can restore GeV scale DM relic by changing the mediator mass sharply at the nucleation temperature. The MeV scale FOPT predicts stochastic gravitational waves with nano-Hz frequencies within reach of pulsar timing array (PTA) based experiments like NANOGrav. In addition to enhancing direct detection rate, the light mediator can also give rise to the required DM self-interactions necessary to solve the small scale structure issues of cold dark matter. The existence of light scalar mediator and its mixing with the Higgs keep the scenario verifiable at different particle physics experiments.

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arXiv2024

Self Interacting Dark Matter and Dirac neutrinos via Lepton Quarticity

In this paper, we put forward a connection between the self-interacting dark matter and the Dirac nature of neutrinos. Our exploration involves a $Z_4 \otimes Z_4'$ discrete symmetry, wherein the Dirac neutrino mass is produced through a type-I seesaw mechanism. This symmetry not only contributes to the generation of the Dirac neutrino mass but also facilitates the realization of self-interacting dark matter with a light mediator that can alleviate small-scale anomalies of the $Λ{\rm CDM}$ while being consistent with the latter at large scales, as suggested by astrophysical observations. Thus the stability of the DM and Dirac nature of neutrinos are shown to stem from the same underlying symmetry. The model also features additional relativistic degrees of freedom $ΔN_{\rm eff}$ of either thermal or non-thermal origin, within the reach of cosmic microwave background (CMB) experiment providing a complementary probe in addition to the detection prospects of DM.

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arXiv2023

Self-interacting dark matter and the GRB221009A event

In this work, we explore the intriguing possibility of connecting self-interacting dark matter (SIDM) with the recently observed exceptionally bright and long-duration Gamma Ray Burst (GRB221009A). The proposed minimal scenario involves a light scalar mediator, simultaneously enabling dark matter (DM) self-interaction and explaining the observed very high energy (VHE) photons from GRB221009A reported by LHAASO's data. The scalar's mixing with the standard model (SM) Higgs boson allows for its production at the GRB site, which will then propagate escaping attenuation by the extra-galactic background light (EBL). These scalars, if highly boosted, have the potential to explain LHAASO's data. Moreover, the same mixing also facilitates DM-nucleon or DM-electron scatterings at terrestrial detectors, linking SIDM phenomenology to the GRB221009A events. This manuscript presents the parameter space meeting all constraints and offers an exciting opportunity to explore SIDM in future direct search experiments using insights from the GRB observation.

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