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Ujjal Kumar Dey

Publications and source records attributed to Ujjal Kumar Dey.

At least 19 recordsLinked to original sources
arXiv2026

Gravitational lensing of neutrinos through the lens of decoherence

We propose a new source of neutrino decoherence arising from stochastic gravitational lensing by unresolved mass substructure. Unlike traditional models that treat the lensing potential as smooth and deterministic, we decompose the lensing potential into a smooth component and a stochastic population of compact clumps. The substructure induced fluctuations of the lensing potential generate stochastic corrections to the neutrino time delay, thereby producing random relative phases between different neutrino mass eigenstates. Averaging over the clump ensemble converts these phase fluctuations into an effective dampening of flavour coherence. This framework connects stochastic gravitational lensing with neutrino phenomenology and offers a novel route to probe dark matter substructure through astrophysical neutrino flavour transitions.

hep-ph↗
arXiv2026

High-redshift supermassive black hole population from core-collapse in self-interacting dark matter halos

Self-interactions between dark matter (DM) particles facilitate the inter-particle redistribution of energy within the central region of DM halos. Recent studies of dark matter spikes around massive black holes, and the diversity in rotation curves of dark matter rich low-mass galaxies motivate the exploration of self-interaction cross-section $\mathcal{O}(10)\,\rm cm^2/gm$. At such high scattering rates, DM can lead to the formation of supermassive black hole seeds, through the gravothermal collapse of halo cores, under certain cosmological conditions. Quasars near cosmic dawn are powerful probes for examining the formation scenario of high redshift supermassive black holes, and their connection to structure formation. In this work we point out the favorable initial cosmological conditions that are likely to provide the black hole seeds resulting in supermassive black holes, mediated by core-collapse in self-interacting dark matter halos. Employing a semi-analytic prescription of core formation, and realistic mass accretion and halo merger histories, we compare the existing observations of high-redshift supermassive black holes with those predicted for our core-collapse framework. We find the median values of velocity-dependent self-interacting dark matter parameter space $σ/m_χ\sim 56\, \rm cm^2/gm$, and $ω=101\,\rm km/s$, assuming an Eddington accretion rate of unity. Sub-leading values are also presented for sub and super-Eddington accretion rates. We also report the derived self-interacting dark matter model parameters to account for the observed binned supermassive black hole mass functions at high-redshifts.

astro-ph.GA↗
arXiv2026

Enlightening dark moments of neutrino with superradiance

Neutrinos can acquire electromagnetic moments either within the Standard Model through higher order radiative corrections or within the domain of new physics. In this study we focus on probing these beyond the standard model neutrino moments through quenched superradiance of black holes where fermionic pairs can be produced from the superradiant bosonic cloud. We consider the production of dark photons from black hole superradiance and quenching occurs through the production of neutrino-antineutrino pairs from the dark photons. The efficiency of the pair production depends on the effective coupling between the dark photons and neutrinos, i.e., the dark electromagnetic moments. We also discuss bounds on primordial black hole abundance from neutrino background arising from this quenched superradiance mechanism.

hep-ph↗
arXiv2026

Gravitational Wave Probe of Singlet-Doublet Dark Matter Induced Radiative Neutrino Mass

We investigate an one loop radiative neutrino mass model, where the loop particles, notably a singlet fermion ($χ$), a doublet fermion ($Ψ$) and three generations of singlet scalars ($ϕ_i, i=\{1,2,3\}$) are assumed to be odd under an additional $\mathcal{Z}_2$-symmetry. In this setup, the singlet fermion mixes with the neutral component of the doublet to give rise singlet-doublet Majorana dark matter. The addition of $\mathcal{Z}_2$ odd scalars in the model provides rich phenomenological implications. We find that the quartic interaction terms between the SM Higgs and $ϕ_i$s play a significant role in modifying the scalar potential to have a first-order phase transition (FOPT) leading to observable gravitational waves (GWs) spectra. We also examine the non-trivial role played by the singlet-doublet fermion DM and the scalars in loop-induced neutrino mass, $(g-2)_μ$, and lepton flavor violation. We find that the model is predictive due to the combined constraints and can be verified at different terrestrial experiments.

hep-ph↗
arXiv2026

Asymmetric Cannibal Dark Matter: Constraints from Neutron Star

Asymmetric dark matter can be efficiently captured by neutron stars via elastic scattering with nucleons and dark matter self scattering. The accumulated dark matter thermalizes and concentrates in the stellar interior, forming a dark matter core. In this work, we propose a novel framework in which a $\mathbb{Z}_3$ symmetry allows for number-changing self-interactions of the form $3 \rightarrow 2$ within the dark sector. These cannibalistic reactions become increasingly efficient at high dark matter densities, leading to a significant depletion of the dark matter population in the stellar core. This number depletion heats up the neutron star above the standard cooling expectations, yielding observable thermal signatures in relatively old, isolated neutron stars, potentially detectable via future infrared telescopes. We show that even in the presence of other heating mechanisms, e.g. dark matter annihilation and kinetic heating, the cannibal heating dominates for certain parameter space. We demonstrate that the cannibal heating can predict detectable heating signatures in old neutron stars, thereby allowing a broader range of viable dark matter masses and couplings to the Standard Model.

hep-ph↗
arXiv2026

Stodolsky effect in the framework of Generalised Neutrino Interactions

We study the Stodolsky effect utilizing the most general form of neutrino interactions with electrons below the electroweak scale by considering all possible Lorentz invariant operators respecting SU(3)$\otimes$U(1) symmetry. We perform our calculation for both Dirac and Majorana neutrinos and find that in the most general setting, only the non-standard neutrino interactions and the tensor interaction terms provide a non-zero contribution, apart from the Standard Model contribution. We investigate the implications for the possible detection of the cosmic neutrino background (C$ν$B) by analysing the energy shifts that are characteristic of the Stodolsky effect. We also discuss the implication of considerable asymmetry in the C$ν$B on the present scenario.

hep-ph↗
arXiv2026

Majorana CP Violation Insights from Decaying Neutrinos

It is well-known that within the standard three flavor neutrino oscillation formalism, the Majorana phases appearing in the neutrino mixing matrix cannot have any effect on neutrino oscillation probabilities thereby evading testability at neutrino oscillation experiments. We consider an effective non-Hermitian Hamiltonian describing three flavor neutrino oscillations with the possibility of neutrino decay and demonstrate that the two Majorana phases can entangle with the off-diagonal decay terms and appear at the level of oscillation probabilities. Using the Cayley-Hamilton theorem, we derive approximate analytical expressions for three flavor neutrino oscillation probabilities in the presence of neutrino decay, taking into account matter effects. In the context of a long baseline neutrino experiment, we then analyse the impact of Majorana phases on the oscillation probabilities for different channels as well as on observables related to CP violation effects in neutrino oscillations. Finally, we discuss the effect of Majorana phases on the parameter degeneracies in the neutrino oscillation framework.

hep-ph↗
arXiv2025

Radiative symmetry breaking in a gauged Zee-Babu model and its gravitational wave imprints

We construct a classically scale invariant version of the Zee-Babu model governed by an $U(1)_{B-L}$ gauge symmetry wherein three right handed neutrinos with identical gauge charges are present. A $\mathbb{Z}_2$ symmetry is additionally imposed such that the lightest right handed neutrino becomes a dark matter candidate. A spontaneous breakdown of the $U(1)_{B-L}$ gauge group is triggered radiatively through renormalisation group effects and the dimensionful parameters thus emerging are proportional to the corresponding breaking scale $v_{BL}$. We demonstrate in this study how the same $v_{BL}$ controls the dynamics of neutrino mass generation, lepton flavour violation and dark matter phenomenology. It is revealed that the scenario can simultaneously accommodate the observed neutrino masses and mixings, an appropriately low lepton flavour violation and the observed dark matter relic density for 10 TeV $\lesssim v_{BL} \lesssim$ 55 TeV. In addition, the very radiative nature of the set-up signals a strong first order phase transition in the presence of a non-zero temperature. Stochastic gravitational waves stemming from this phase transition are within the reach of detectors such as LISA and BBO. The scenario therefore emerges as a concrete platform to test classical scale invariance that is tied to neutrino masses and dark matter, through gravitational waves.

hep-ph↗
arXiv2025

Superradiant and dynamical spin-down of neutron stars with gravitational wave implications

Neutron stars such as pulsars and magnetars lose angular momentum primarily through electromagnetic dipole radiation, gravitational waves, $r$-mode oscillation, and also affected by fallback accretion processes. However, anomalous spin variations, particularly sudden enhanced spin-down rates, indicate additional spin-down mechanisms. We propose superradiant spin-down as a potential explanation for these events. By modelling the interplay between conventional and superradiant spin-down channels, we evaluate their impact on neutron star rotational evolution. We also discuss gravitational-wave emission produced by quadrupole deformation, $r$-mode oscillations, and axion-induced bosonic clouds around an isolated neutron star, highlighting their potential as distinct multimessenger probes in upcoming detectors.

astro-ph.HE↗
arXiv2025

Neutrino Decoherence via Modified Dispersion

We study in detail the effect of quantum decoherence in neutrino oscillations. We adopt a phenomenological approach that allows us to parametrize the energy dependence of the decoherence effects resulting from the modification of the neutrino dispersion relation. Using the open quantum system framework we derive decoherence parameters, which are usually connected to quantum gravitational effects. Furthermore, we study the sensitivity of decoherence on high-energy astrophysical neutrinos among all possible initial source compositions. We find that variation in the flux composition at neutrino telescopes can be a good probe to test such effects. Additionally, we show that a simple extension with heavy sterile neutrino decoherence produces verifiable signatures.

hep-ph↗
arXiv2025

Bounds on Exotic Couplings from a New $ν$-Background

We propose a hitherto unexplored neutrino background emerging from the mechanism of quenched superradiance of rotating primordial black holes. The quenching of the phenomenon happens through fermionic production, in our case neutrino production, from the boson cloud formed due to superradiance. The couplings involved in these interactions are bounded from above through several studies. In this work we put lower bounds on such scalar and vector couplings.

hep-ph↗
arXiv2025

Multi-messenger Astronomy with Quenched Superradiance

We propose a novel method to study the ultra-light bosons, where compact rotating objects undergo the phenomenon of quenched superradiance to create gravitational waves and neutrino flux signals. The neutrino flux results from appropriate coupling between the ultra-light bosons and the neutrinos. We consider a heavy sterile neutrino generation from ultralight scalar, which later results in active neutrino flux through neutrino oscillations, whereas we consider active neutrino generation directly from the vector bosons. We study the intertwining of gravitational waves and neutrino flux signals produced from a single source and elaborate if and when the signals can be detected in existing and upcoming experiments in a direct manner.

hep-ph↗
arXiv2025

Primordial Black Holes and Gravitational Waves in Extensions of the Standard Model

We investigate the phenomenology of a Standard Model extension incorporating an inert scalar doublet and a gauged $U(1)_{B-L}$ symmetry. Our analysis reveals regions of the parameter space that support strong first-order phase transitions, including cases featuring two successive transitions. Each transition can generate a stochastic gravitational wave background within the sensitivity reach of upcoming experiments. Remarkably, the high-scale transition may also produce primordial black holes with appreciable abundance.

hep-ph↗
arXiv2024

Primordial Black Holes and Gravitational Waves in the $U(1)_{B-L}$ Extended Inert Doublet Model: A First-Order Phase Transition Perspective

We conduct an analysis of a $U(1)_{B-L}$ extended inert doublet model and obtained the parameter space allowing strong first order phase transitions. We show that a large part of the parameter space can cause double first-order phase transitions. Whereas both of these phase transitions can generate a detectable stochastic gravitational wave background, one of them can create primordial black holes with appreciable abundance. The primordial black holes generated at the high scale transition can account for the dark matter maintaining the correct relic abundance. We also show specific benchmark cases and their consequences from the aspect of primordial black holes and gravitational waves.

hep-ph↗
arXiv2024

Spinning Primordial Black Holes from First Order Phase Transition

We conduct a novel study to obtain the initial spin of the primordial black holes created during a first-order phase transition due to delayed false vacuum decay. Remaining within the parameter space consistent with observational bounds, we express the abundance and the initial spin of the primordial black holes as functions of the phase transition parameters. The abundance of the primordial black holes is extremely sensitive to the phase transition parameters. We also find that the initial spin weakly depends on all parameters except the transition temperature.

gr-qc↗
arXiv2024

Gravitational Wave Probe of Primordial Black Hole Origin via Superradiance

In this article we have used stochastic gravitational wave background as a unique probe to gain insight regarding the creation mechanism of primordial black holes. We have considered the cumulative gravitational wave background which consists of the primary part coming from the creation mechanism of the primordial black holes and the secondary part coming from the different mechanisms the primordial black holes go through. We have shown that in the presence of light or ultra light scalar bosons, superradiant instability generates the secondary part of the gravitational wave background which is the most detectable. In order to show the unique features of the cumulative background, we have considered the delayed vacuum decay during a first order phase transition as the origin of primordial black holes. We have shown the dependence of the features of the cumulative background, such as the mass of the relevant light scalars, peak frequencies, etc. on the transition parameters. We have also generated the cumulative background for a few benchmark cases to further illustrate our claim.

gr-qc↗
arXiv2024

PTOLEMY's test of generalized neutrino interactions: unveiling challenges and constraints

Unanswered questions surrounding neutrinos have motivated investigations into physics beyond the standard model (SM) of particle physics. In particular, generalized neutrino interactions (GNI) provide a broader framework for studying these effects compared to the commonly studied non-standard neutrino interactions. These interactions are described by higher dimensional operators while maintaining the gauge symmetries of the SM. Furthermore, the cosmic neutrino background, a predicted component of the SM and standard cosmology, has yet to be directly detected. To shed light on this elusive phenomenon, we conduct a comprehensive analysis of the relevant GNI, specifically focusing on their implications for the proposed cosmic neutrino detector PTOLEMY. We make an attempt to see the capabilities and the limitations of PTOLEMY in sensing GNI while remaining optimistic regarding PTOLEMY's experimental resolution. These interactions play a significant role in modifying the electron spectrum resulting from the capture of cosmic neutrinos on radioactive tritium. This work also explores how the presence of these interactions influences the differential electron spectrum, taking into account factors such as finite experimental resolution, the mass of the lightest neutrino eigenstate, the strength of the interactions, and the ordering of neutrino mass.

hep-ph↗