arXiv subjects

Narendra Sahu

Publications and source records attributed to Narendra Sahu.

At least 37 records · Page 2Linked to original sources

arXiv2026

Verifiable type-III seesaw and dark matter in a gauged $\boldsymbol{U(1)_{\rm B-L}}$ symmetric model

We propose a new extension of the Standard Model that incorporates a gauged $ U(1)_{\rm B-L} $ symmetry and the type-III seesaw mechanism to explain neutrino mass generation and provide a viable dark matter (DM) candidate. Unlike the type-I seesaw, the type-III seesaw extension under $ U(1)_{\rm B-L} $ is not automatically anomaly-free. We show that these anomalies can be canceled by introducing additional chiral fermions, which naturally emerge as DM candidates in the model. We thoroughly analyze the DM phenomenology, including relic density, direct and indirect detection prospects, and constraints from current experimental data. Furthermore, we explore the collider signatures of the model, highlighting the enhanced production cross-section of the triplet fermions mediated by the $ \rm B-L $ gauge boson, as well as the potential disappearing track signatures. Additionally, we investigate the gravitational wave signals arising from the first-order phase transition during $ \rm B-L $ symmetry breaking, offering a complementary cosmological probe of the framework.

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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

Lepton parity dark matter and naturally unstable domain walls

We propose a simple and predictive setup that connects neutrino masses, dark matter (DM), and gravitational waves. A minimal lepton parity DM scenario is considered where the residual symmetry $(-1)^L$ from the type I seesaw acts as the dark parity $D=(-1)^{L+2j}$, ensuring DM stability without imposing any new symmetry. A singlet Majorana fermion $S$ with even lepton parity serves as the DM candidate, interacting via a real scalar $σ$ which is also even lepton parity. The scalar potential possesses an accidental $\mathcal{Z}_2$ symmetry, whose spontaneous breaking gives rise to unstable domain walls (DW) in the presence of explicit $\mathcal{Z}_2$ breaking terms allowed by the lepton parity. The subsequent DW annihilation generates a stochastic gravitational wave (GW) background potentially observable at different GW experiments.

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arXiv2025

Anatomy of singlet-doublet dark matter relic: annihilation, co-annihilation, co-scattering, and freeze-in

The singlet-doublet vector-like fermion dark matter model has been extensively studied in the literature over the past decade. An important parameter in this model is the singlet-doublet mixing angle ($\sinθ$). All the previous studies have primarily focused on annihilation and co-annihilation processes for obtaining the correct dark matter relic density, assuming that the singlet and doublet components decouple at the same epoch. In this work, we demonstrate that this assumption holds only for larger mixing angles with a dependency on the mass of the dark matter. However, it badly fails for the mixing angle $\sinθ<0.05$. We present a systematic study of the parameter space of the singlet-doublet dark matter relic, incorporating annihilation, co-annihilation, and, for the first time, co-scattering processes. Additionally, non-thermal productions via the freeze-in and SuperWIMP mechanism are also explored. We found that due to the inclusion of co-scattering processes, the correct relic density parameter space is shifted towards the detection sensitivity range of the LHC and MATHUSLA via displaced vertex signatures.

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arXiv2025

Effective theory of light Dirac neutrino portal dark matter with observable ${ΔN_{\rm eff}}$

We study the possibility of light Dirac neutrino portal dark matter (DM) in an effective field theory setup. Dirac nature of light neutrino automatically includes its right chiral part $ν_R$ which, in our setup, also acts like a portal between DM and the standard model (SM) particles. Considering a Dirac fermion singlet DM stabilized by an unbroken $Z_2$ symmetry, we write down all possible dimension-6 effective operators involving DM-$ν_R$ as well as $ν_R$-SM which conserve $Z_2$, global lepton number and SM gauge symmetries. DM thermalization also ensures the thermalization of $ν_R$, leading to enhanced effective relativistic degrees of freedom $N_{\rm eff}$, within reach of future cosmic microwave background (CMB) experiments. We study the complementarity among DM and CMB related observations for different Lorentz structures of effective operators. We also propose a UV complete gauged $\rm B-L$ symmetric model with Dirac neutrino portal dark matter.

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arXiv2025

Super heavy dark matter origin of the PeV neutrino event: KM3-230213A

The recent observation of the ultrahigh-energy neutrino event KM3-230213A by the KM3NeT experiment offers a compelling avenue to explore physics beyond the Standard Model (SM). In this paper, we explore a simplest possibility that this event originates from the decay of a super-heavy dark matter (SHDM). We consider a minimal scenario where the SHDM decays to neutrino and SM Higgs. We derive constraints on the DM lifetime as a function of DM mass, ensuring consistency with IceCube, Auger upper limits, and the observed KM3-230213A event, along with the gamma-ray constraints. We find that KM3-230213A gives stringent constraint on the DM mass ranging from $1.5\times10^8$ GeV to $5.2\times10^9$ GeV with lifetime in the range: $1.42\times10^{30}$ s to $5.4\times10^{29}$ s. Remarkably, in our SHDM scenario, the apparent tension between the KM3NeT observation and the nonobservation of this event by IceCube and Auger can be reduced to below $1.2σ$. Our results are applicable to any neutrinophilic SHDM models while evading gamma-ray constraints.

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arXiv2025

Thermal leptogenesis, dark matter, and gravitational waves from an extended canonical seesaw scenario

In a canonical type-I seesaw scenario, the Standard Model is extended with three singlet right-handed neutrinos (RHNs) $N_i, i=1,2,3$ with masses $M_i, i=1,2,3$ to simultaneously explain sub-eV masses of light neutrinos and baryon asymmetry of the Universe at high scales. In this paper, we show that a relatively low-scale thermal leptogenesis accompanied by gravitational wave signatures is possible when the type-I seesaw is extended with a singlet fermion ($S$) and a singlet scalar ($ρ$), where $S$ and $ρ$ are odd under a discrete $Z_2$ symmetry. We also add a vectorlike fermion doublet $Ψ$ and impose a $Z^\prime_2$ symmetry under which both $N_1$ and $Ψ$ are odd while all other particles are even. This gives rise to a singlet-doublet Majorana fermion dark matter in our setup. At a high scale, the $Z_2$ symmetry is broken spontaneously by the vacuum expectation value of $ρ$ and leads to (i) mixing between RHNs ($N_2, N_3$) and $S$, and (ii) formation of Domain walls (DWs). In the former case, the final lepton asymmetry is generated by the out-of-equilibrium decay of $S$, which dominantly mixes with $N_2$. We show that the scale of thermal leptogenesis can be lowered to $M_S \sim 2 \times 10^6$ GeV, which is \textit{3} orders of magnitude lower than the thermal leptogenesis in canonical type-I seesaw. In the latter case, the disappearance of the DWs gives observable gravitational wave signatures, which can be probed at LISA, DECIGO, ${\rm μARES}$ etc.

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arXiv2025

Light thermal dark matter via type-I seesaw portal

We propose a minimal scenario for light thermal dark matter (DM) in sub-GeV to GeV range by incorporating a scalar singlet DM in a type-I seesaw scenario extended by an additional Higgs doublet $ϕ_2$. The latter permits efficient annihilation of light scalar DM into leptonic final states including right-handed neutrinos (RHN). We keep the charged fermion as well as neutral fermion final states in forbidden regime to avoid bounds from indirect search as well as cosmic microwave background (CMB) data. After studying the purely forbidden DM scenario with neutral and charged fermion final states separately, we discuss the interplay of forbidden and non-forbidden channels in generating light thermal DM relic by considering neutral fermions in non-forbidden mode due to relatively weaker constraints. The model can also explain the anomalous magnetic moment of muon, W-mass anomaly and saturate experimental bounds on charged lepton flavour violation and DM direct detection while offering tantalising detection prospects of RHN, the mass of which is kept approximately in the same range as DM.

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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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arXiv2025

Asymmetric long-lived dark matter and leptogenesis from type-III seesaw framework

We propose a simple model in the type-III seesaw framework to explain the neutrino mass, asymmetric dark matter (ADM), and baryon asymmetry of the Universe. We extend the standard model with a vector-like singlet lepton ($χ$) and a hypercharge zero scalar triplet ($Δ$) in addition to three hypercharge zero triplet fermions($Σ_i~,i=1,2,3$). A $Z_2$ symmetry is imposed under which $χ$ and $Δ$ are odd, while all other particles are even. As a result, the lightest $Z_2$ odd particle $χ$ behaves as a candidate of DM. In the early Universe, the $CP$-violating out-of-equilibrium decay of heavy triplet fermions to the Standard Model lepton ($L$) and Higgs ($H$) generate a net lepton asymmetry, while that of triplet fermions to $χ$ and $Δ$ generate a net asymmetric DM. The lepton asymmetry is converted to the required baryon asymmetry of the Universe via the electroweak sphalerons, while the asymmetry in $χ$ remains as a DM relic that we observe today. We introduce a singlet scalar $Φ$, with mass $M_ϕ< M_χ$, which not only assists to deplete the symmetric component of $χ$ through the annihilation process: $\barχ χ\to ΦΦ$ but also paves a path to detect DM $χ$ at direct search experiments through $Φ-H$ mixing. The electro-weak symmetry breaking induces a non-zero vacuum expectation value to $Δ$, which leads to an unstable asymmetric DM ranging from a few MeV to hundreds of GeV. We then explore the displaced vertex signatures of the charged components of the scalar triplet $Δ$ at colliders.

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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

Asymmetric self-interacting dark matter with a canonical seesaw model

We study the possibility of generating dark matter (DM) and baryon asymmetry of the Universe (BAU) simultaneously in an asymmetric DM framework, which also alleviates the small-scale structure issues of cold DM. While the thermal relic of such self-interacting DM remains under-abundant due to efficient annihilation into light mediators, a nonzero asymmetry in the dark sector can lead to the survival of the required DM in the Universe. The existence of a light mediator leads to the required self-interactions of DM at small scales while keeping DM properties similar to cold DM at large scales. It also ensures that the symmetric DM component annihilates away, leaving the asymmetric part in the spirit of cogenesis. The particle physics implementation is done in canonical seesaw models of light neutrino mass, connecting it to the origin of DM and BAU. In particular, we consider type-I and type-III seesaw origin of neutrino mass for simplicity and minimality of the field content. We show that the desired self-interactions and relic of DM together with BAU while satisfying relevant constraints lead to strict limits on DM mass $\mathcal{O}({\rm GeV}) \lesssim M_{\rm DM} \lesssim460 $ GeV. In spite of being a high-scale seesaw, the models remain verifiable in different experiments, including direct and indirect DM searches as well as colliders.

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arXiv2024

Singlet-doublet fermion dark matter with Dirac neutrino mass, $(g-2)_μ$ and $ΔN_{\rm eff}$

We study the possibility of generating light Dirac neutrino mass via scotogenic mechanism where singlet-doublet fermion dark matter (DM) plays non-trivial role in generating one-loop neutrino mass, anomalous magnetic moment of muon $(g-2)_μ$ as well as additional relativistic degrees of freedom $Δ{N_{\rm eff}}$ within reach of cosmic microwave background (CMB) experiments. We show that the Dirac nature of neutrinos can bring interesting correlations within the parameter space satisfying the $\left(g-2\right)_μ$ anomaly and DM relic density and the effective relativistic degrees of freedom $Δ{N_{\rm eff}}$. While we stick to thermal singlet doublet DM with promising detection prospects, both thermal and non-thermal origin of $Δ{N_{\rm eff}}$ have been explored. In addition to detection prospects at DM, $(g-2)$ and other particle physics experiments, the model remains verifiable at future CMB experiments like CMB-S4, SPT-3G.

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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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arXiv2024

Scotogenic $U(1)_{L_μ-L_τ}$ origin of $(g-2)_μ$, W-mass anomaly and 95 GeV excess

We study a scotogenic extension of the minimal gauged $L_μ-L_τ$ model, including three right-handed singlet fermions and a scalar doublet all odd under an in-built $Z_2$ symmetry to explain the anomalous magnetic moments of the muon, CDF-II W-mass anomaly, and the 95 GeV excess reported by the CMS collaboration. While the minimal model can successfully explain the muon $(g-2)$ and CDF-II W-mass anomalies, the required diphoton signal strength for the 95 GeV scalar, together with that of the SM Higgs, can not be obtained in the minimal model. The same can, however, be explained by incorporating one additional scalar doublet whose only role is to contribute radiatively to diphoton decay modes of the light, neutral scalars. Due to the scotogenic extension, the model remains consistent with the observed properties of light neutrinos and dark matter in the Universe.

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arXiv2023

A new realisation of light thermal self-interacting dark matter and detection prospects

Light dark matter (DM) in the GeV ballpark faces weaker constraint from direct detection experiments. If such DM also has sufficient self-interactions due to a light mediator, it can alleviate the small-scale problems of the cold dark matter (CDM) paradigm while being consistent with the latter at large scales, as suggested by astrophysical observations. However, generating correct thermal relic for such light DM is challenging. While GeV scale CDM typically leads to thermal overproduction due to the absence of sufficient annihilation channels, self-interacting dark matter (SIDM) typically has under-abundant thermal relic due to its large annihilation rates into mediator particles. In this letter, we propose a minimal realisation of GeV scale SIDM with correct thermal relic, where one of the three singlet fermions, responsible for seesaw origin of light neutrino masses, assists in generating correct SIDM relic density via freeze-out. The setup thereby encompasses astrophysical as well as cosmological aspects of light DM while simultaneously providing a solution to the origin of light neutrino mass. Due to such connection to several frontiers, there exist exciting discovery prospects in terms of direct and indirect search of DM, laboratory and cosmology based dark photon signatures and effective light neutrino mass.

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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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