arXiv subjects

Ranjan Laha

Publications and source records attributed to Ranjan Laha.

At least 19 recordsLinked to original sources

arXiv2026

Not so good $\nu$s for Higgsino dark matter as LZ excess: stringent limits from Super-Kamiokande and IceCube

The LUX-ZEPLIN (LZ) collaboration has recently reported a single nuclear recoil event at a high recoil energy of about 250 keV. This has been interpreted as inelastic scattering of dark matter that is a supersymmetric Higgsino with a mass splitting between the neutral states of a few 100 keV. Such dark matter may be captured at high recoil in the Sun through scattering on heavy elements in it, and annihilate to $W^+W^-$ and $ZZ$, in turn giving rise to a neutrino flux detectable on Earth. Using measurements of atmospheric electron- and muon-neutrino fluxes by Super-Kamiokande and IceCube, we constrain thermal and non-thermal Higgsino dark matter, excluding inter-state mass splittings $\lesssim 557$ keV. This disfavors Higgsino-like interpretations of the LZ event for standard halo velocities.

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arXiv2026

Dive deeper with SUBMARINE: SUB-Mev dArk matter diRect detectIon using bilayer grapheNE

Novel target materials with anisotropic response will play a key role in detecting low-mass dark matter in upcoming experiments. Bilayer graphene is one such material that has been proposed for the detection of sub-MeV mass dark matter particles via electronic excitations. In this work, we calculate scattering rate via a massive mediator in bilayer graphene. With an exposure as small as $\sim$ 0.5 mg-year, bilayer graphene can probe new regions of the parameter space. The anisotropic response function of bilayer graphene leads to a sidereal-day modulation in the scattering rate, depending on its orientation with respect to the Galactic dark matter wind. We find significant modulation in the scattering rate for sub-MeV mass dark matter, demonstrating bilayer graphene's promise for a future experiment. We hope that our work will motivate the community to investigate bilayer graphene as a novel target material, and that it may lead us to discover the particle nature of dark matter.

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arXiv2026

Lights, Camera, Axion: Tracing Axions from Supernovae in the Diffuse $γ$-ray Sky

Axions produced copiously in core-collapse supernovae can convert into photons as they propagate through various astrophysical magnetic fields. The cumulative emission from the cosmic population of supernovae can therefore generate a diffuse gamma-ray signal through axion-photon conversion. In this work, we develop a comprehensive framework to compute the diffuse gamma-ray flux by modeling axion production in supernovae and, \textit{for the first time}, consistently accounting for their conversion into photons across all relevant magnetic field environments - progenitor, host galaxy, intergalactic medium, and the Milky Way - together with an updated cosmic star formation rate. Using measurements of the diffuse gamma-ray sky from COMPTEL, EGRET, and \textit{Fermi}-LAT, we derive competitive constraints on the axion-photon coupling over a wide range of axion masses. We further forecast the sensitivity of upcoming MeV gamma-ray telescopes to this diffuse signal using a Fisher forecast analysis.

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arXiv2025

Dark Recipe for the First Giants: From Population III Stars to Early Supermassive Black Holes via Dark Matter Capture

The presence of supermassive black holes (SMBHs) at high redshifts ($z>5$), as revealed by James Webb Space Telescope (JWST), challenges standard black hole (BH) formation scenarios. We propose a mechanism in which non-annihilating dark matter (DM) with non-gravitational interactions with the Standard Model (SM) particles accumulates inside Population III (Pop III) stars, inducing their premature collapse into BH seeds having the same mass as the parent star. Owing to their early formation, these seeds can accrete for longer periods and grow into the SMBHs observed at early cosmic times. Focusing on spin-dependent (SD) DM-proton interactions, we identify regions of parameter space that account for the observed high-redshift SMBH population, their mass function, and the SMBH-stellar mass relation. Portions of this parameter space are testable by forthcoming direct detection experiments. The scenario may lead to distinctive gravitational wave (GW) signatures from SMBH mergers, accessible to Laser Interferometer Space Antenna (LISA) and pulsar timing array (PTA) observations.

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arXiv2025

Possible $ν$ Source Class: 3-sigma Detection of High-Energy Neutrinos from Supermassive Black Hole Binary Candidates

Identifying the sources of high-energy (TeV-PeV) astrophysical neutrinos is crucial for studies in both astrophysics and particle physics. Despite extensive searches for more than a decade, which revealed several individual potential sources and only one potential source class, the origins of these neutrinos remain largely unresolved; thus, more source classes should be investigated. In this work, we conduct the first search for high-energy neutrino emission from a new source class, supermassive black hole binaries (SMBHBs), which are also theoretically motivated. We perform an unbinned maximum-likelihood-ratio analysis on our constructed catalog of 693 SMBHB candidates and 10 years of IceCube public data. Our results show positive correlations, with higher significance in more physically motivated scenarios and the highest significance at 3.0$σ$. In addition, we also study potential connections between SMBHBs' high-energy neutrino and nano-Hz gravitational-wave emissions, the latter being the main target of pulsar timing arrays. Our results provide the first evidence of SMBHBs being high-energy neutrino emitters.

astro-ph.HE↗

arXiv2025

Galaxy Mergers Collectively Illuminate the $γ$-Ray Sky

The origin and acceleration mechanism of cosmic rays (CRs) remain fundamental open questions. Galaxy mergers are proposed as very high-energy CR accelerators, which are expected to produce high-energy (HE) $γ$ rays and neutrinos through interactions with the ambient gas and low-energy background radiation fields. For the first time, we systematically study the HE $γ$-ray emission from galaxy mergers utilising 16.7 years of Fermi Large Area Telescope (Fermi-LAT) data with the sample list compiled from eight survey catalogs. Our analysis finds 8 galaxy mergers that exhibit $γ$-ray emission with significance $\gtrsim5σ$ in the 1-500 GeV energy range. A stacking analysis of the remaining faint galaxy mergers yields a combined $γ$-ray emission detected at $\sim 35σ$ significance, a best-fit spectral index of $Γ\approx 2.07$, and an energy flux of $\sim \rm 2\times10^{-14}~erg~cm^{-2}~s^{-1}$. We compare the stacked spectral energy distributions of the galaxy mergers with the projected sensitivity of the upcoming $γ$-ray telescope Cherenkov Telescope Array (CTA). Furthermore, we find that 18 previously unassociated Fermi-LAT sources are spatially coincident with galaxy mergers. Our findings establish galaxy mergers as a new class of HE $γ$-ray sources. Future neutrino and $γ$-ray observatories will be crucial to discover the particle acceleration mechanism in these newly identified CR sources.

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arXiv2025

Dark Secrets of Baryons: Illuminating Dark Matter-Baryon Interactions with JWST

The James Webb Space Telescope (JWST) has discovered bright galaxies at high redshifts ($z\approx 10-14$) and various galaxy candidates extending to even higher redshifts ($z\approx 15-30$). Many astrophysical and beyond the Standard Model physics scenarios have been proposed to explain these observations. We investigate, {\it for the first time}, the implications of dark matter (DM) scattering with baryons (protons and electrons) in light of the JWST UV luminosity function (UVLF) observations. These interactions suppress structure formation on galactic scales, which may have an observable effect on the UVLF measurements at high redshifts. Using a recent galaxy formation model designed to explain high redshift observations, we obtain strong upper limits on DM-baryon scattering cross-sections and explore new regions of the parameter space. For DM-proton scattering with cross-section $\propto v^{-2}$ velocity dependence, we obtain the strongest limit for DM masses of $\sim$ 1 -- 500 MeV. For other cases that we study (DM-proton scattering cross-section $\propto v^{0},\,v^{-4}$ and DM-electron scattering cross-section $\propto v^{0},\,v^{-2},\,v^{-4}$, our limits are competitive with those obtained from other cosmological observables. Our study highlights the potential of JWST observations as a novel and powerful probe of non-gravitational interactions of DM.

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arXiv2025

Hunting Primordial Black Hole Dark Matter in Lyman-$α$ Forest

A very pressing question in contemporary physics is the identity of Dark Matter (DM). Primordial Black Holes (PBHs) are one of the most well-motivated DM candidates. Light PBHs have been constrained by either the non-detection of their Hawking radiation itself, or by the non-observation of any measurable effects of this radiation on astrophysical and cosmological observables. We constrain the PBH contribution to the DM density by non-detection of their Hawking radiation's effect on the intergalactic medium (IGM) temperature evolution. We use the latest deductions of IGM temperature from Lyman-$α$ forest observations. We put constraints on the fraction of DM as PBHs with masses $5 \times 10^{15}$ g - $10^{17}$ g, separately for spinning and non-spinning BHs. We derive constraints by dealing with the heating effects of the astrophysical reionization sources on the IGM in two ways. In one way, we completely neglect this heating due to astrophysical sources, thus giving us weaker constraints, but completely robust to the reionization history of the universe. In the second way, we utilise some modelling of the ionization and temperature history, and use it to derive more stringent constraints. We find that for non-spinning PBHs of mass $10^{16}$ g, the current measurements can constrain the PBH-density to be $\lesssim$ 0.1\% of the total DM. We find that these constraints are competitive, and hence provide a new observable to probe the nature of PBH DM. The systematics affecting Lyman-$α$ forest measurements are different from other constraining observations, and thus this is a complementary probe.

astro-ph.CO↗

arXiv2025

LHAASO Galactic Plane $\gamma$-rays Strongly Constrain Heavy Dark Matter

LHAASO, a ground-based observatory, is unveiling new frontiers in our understanding of high-energy $\gamma-$rays and cosmic rays. It has recently observed high energy diffuse $\gamma-$rays from the Galactic plane in the TeV-PeV range. For the first time, we analyze this data to search for signatures of heavy decaying and annihilating dark matter in the mass range $10^{5}-10^{11}$ GeV. We compute the expected photon flux from both Galactic and extragalactic dark matter, incorporating attenuation due to photon pair production. For the Galactic contribution, we include both prompt photons and secondary photons produced via inverse Compton scattering, accounting for electron/positron propagation. For the extragalactic component, in addition to the prompt and inverse Compton contributions, we also include cascade photons arising from inverse Compton scattering of pair-produced electrons and positrons. By combining all these contributions, we derive constraints on the dark matter parameter space. Our bounds for various two body Standard Model final states are strongest to date. This underscore LHAASO's capability to discover the nature of heavy dark matter.

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arXiv2025

Neutrinos from the Sun can discover dark matter-electron scattering

We probe dark matter-electron scattering using high-energy neutrino observations from the Sun. Dark matter (DM) interacting with electrons can get captured inside the Sun. These captured DM may annihilate to produce different Standard Model (SM) particles. Neutrinos produced from these SM states can be observed in IceCube and DeepCore. Although there is no excess of neutrinos in the solar direction, we find that the current datasets of IceCube and DeepCore set the strongest constraint on the DM-electron scattering cross section in the DM mass range $10$\,GeV to $10^5$\,GeV. Therefore our work implies that future observations of the Sun by neutrino telescopes have the potential to discover the DM-electron interaction.

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arXiv2025

Road through Dark$ν$ess: Probing dark matter-neutrino interactions using KM3-230213A

KM3NeT has recently reported an event where a muon of energy $120^{+110}_{-60}$ PeV was observed at its ARCA detector, which can stem from a very high-energy neutrino interaction in the vicinity of the detector. Besides revolutionizing our understanding of high-energy neutrino sources, this event can serve as a valuable probe for studying Beyond the Standard Model (BSM) interactions of neutrinos. In this work, we study the dark matter (DM)-neutrino interaction by assuming the neutrino for the event KM3-230213A is originated from a blazar. The flux of such neutrinos, traveling through DM distributed across astrophysical and cosmological scales, can get attenuated due to DM interactions. The detection of such event by KM3NeT allows us to place constraints on the interaction cross section at highest-ever neutrino energy. We derive both conservative constraints-neglecting flux attenuation from the host halo-and optimistic ones by including host halo contributions. Our results show that the energy-independent constraints are weaker than previous bounds. For energy-dependent case, the extreme energy of the event allows us to set some of the strongest limits on scattering cross sections. In future, more such neutrino events with well-understood origin will be essential in constraining or potentially discovering DM-neutrino interactions.

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arXiv2025

First Search for High-Energy Neutrino Emission from Galaxy Mergers

The exact sources of high-energy neutrinos detected by the IceCube neutrino observatory still remain a mystery. For the first time, this work explores the hypothesis that galaxy mergers may serve as sources for these high-energy neutrinos. Galaxy mergers can host very high-energy hadronic and photohadronic processes, which may produce very high-energy neutrinos. We perform an unbinned maximum-likelihood-ratio analysis utilizing the galaxy merger data from six catalogs and 10 years of public IceCube muon-track data to quantify any correlation between these mergers and neutrino events. First, we perform the single source search analysis, which reveals that none of the considered galaxy mergers exhibit a statistically significant correlation with high-energy neutrino events detected by IceCube. Furthermore, we conduct a stacking analysis with three different weighting schemes to understand if these galaxy mergers can contribute significantly to the diffuse flux of high-energy astrophysical neutrinos detected by IceCube. We find that upper limits (at $95\%$ CL) of the all flavor high-energy neutrino flux, associated with galaxy mergers considered in this study, at $100$ TeV with spectral index $Γ=-2$ are $1.11\times 10^{-18}$, $3.69 \times 10^{-19}$ and $1.02 \times 10^{-18}$ $\rm GeV^{-1}\,cm^{-2}\,s^{-1}\,sr^{-1}$ for the three weighting schemes. This work shows that these selected galaxy mergers do not contribute significantly to the IceCube detected high energy neutrino flux. We hope that in the near future with more data, the search for neutrinos from galaxy mergers can either discover their neutrino production or impose more stringent constraints on the production mechanism of high-energy neutrinos within galaxy mergers.

astro-ph.HE↗

arXiv2025

Shedding Infrared Light on QCD Axion and ALP Dark Matter with JWST

James Webb Space Telescope (JWST) has opened up a new chapter in infrared astronomy. Besides the discovery and a deeper understanding of various astrophysical sources, JWST can also uncover the non-gravitational nature of dark matter (DM). If DM is QCD axion or an eV-scale Axion-like particle (ALP), it can decay into two photons in the infrared band. This will produce a distinct line signature in the spectroscopic observations made by JWST. Using the latest NIRSpec IFU spectroscopic observations from JWST, we put the strongest bound on the photon coupling for QCD axion/ ALP DM in the mass range between 0.47 and 2.55 eV. In particular, we are able to probe a new mass range for ALP DM between $\sim$ 0.47 eV to 0.78 eV beyond what can be probed by globular cluster observations. We constrain well-motivated and UV complete models of QCD axion and ALP DM, including predictions from some models derived from string theory and/ or various Grand Unification scenarios. Future JWST observations of DM-rich systems with a better understanding of the astrophysical and instrumental backgrounds can thus enable us to potentially discover QCD axion and ALP DM. The datasets used in this work are available at: https://dx.doi.org/10.17909/3e5f-nv69

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arXiv2025

$ν$ limits from Super-Kamiokande on dark matter-electron scattering in the Sun

Particle dark matter scattering on electrons in the Sun may gravitationally capture and self-annihilate inside it to neutrinos and anti-neutrinos, or other final states that in turn decay to them. Using up-to-date measurements by Super-Kamiokande of the fluxes of atmospheric electron-type and muon-type neutrinos, we set the most stringent limits on the electron scattering cross sections of dark matter down to about $10^{-40}-10^{-39}$ cm$^2$ over a mass range of 4$-$200 GeV. These outdo direct searches for dark matter-electron scattering and previously set limits at IceCube. We also derive corresponding reaches at Hyper-K, and show that atmospheric neutrino observations restricted to the direction of the Sun can improve sensitivities.

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arXiv2024

Bounds on ultralight bosons from the Event Horizon Telescope observation of Sgr A$^*$

Recent observation of Sagittarius A$^*$ (Sgr A$^*$) by the Event Horizon Telescope (EHT) collaboration has uncovered various unanswered questions in black hole (BH) physics. Besides, it may also probe various beyond the Standard Model (BSM) scenarios. One of the most profound possibilities is the search for ultralight bosons (ULBs) using BH superradiance (SR). EHT observations imply that Sgr A$^*$ has a non-zero spin. Using this observation, we derive bounds on the mass of ULBs with purely gravitational interactions. Considering self-interacting ultralight axions, we constrain new regions in the parameter space of decay constant, for a certain spin of Sgr A$^*$. Future observations of various spinning BHs can improve the present constraints on ULBs.

astro-ph.HE↗

arXiv2024

Cosmic-ray boosted dark matter in Xe-based direct detection experiments

LUX-ZEPLIN (LZ) collaboration has achieved the strongest constraint on weak-scale dark matter (DM)-nucleon spin-independent (SI) scattering cross section in a large region of parameter space. In this paper, we take a complementary approach and study the prospect of detecting cosmic-ray boosted sub-GeV DM in LZ. In the absence of a signal for DM, we improve upon the previous constraints by a factor of $\sim 2$ using the LZ result for some regions of the parameter space. We also show that upcoming XENONnT and future Darwin experiments will be sensitive to cross sections smaller by factors of $\sim 3$ and $\sim 10$ compared to the current LZ limit, respectively.

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arXiv2023

Primordial power spectrum in light of JWST observations of high redshift galaxies

Early data releases of JWST have revealed several high redshift massive galaxy candidates by photometry, and some of them have been confirmed spectroscopically. We study their implications on the primordial power spectrum. In the first part, we use the CEERS photometric survey data, along with respective spectroscopic updates, to compute the cumulative comoving stellar mass density. We find that a very high star formation efficiency (unlikely in various theoretical scenarios) is required to explain these observations within Lambda cold dark matter ($Λ$CDM) cosmology. We show that the tension can be eased if the primordial power spectrum has a blue tilt. In the second part, we study spectroscopically confirmed galaxies reported in the JADES survey to investigate their implications on a red-tilted primordial power spectrum. We estimate the star formation efficiency from an earlier observation at similar redshift by {\it Spitzer}, and find that the star formation efficiency is an order of magnitude smaller than required to explain the CEERS photometric observations mentioned earlier. Using the estimated star formation efficiency, we find the strongest constraints on the red tilt of the power spectrum over some scales. Our study shows that JWST will be an excellent probe of the power spectrum and can lead to novel discoveries.

astro-ph.CO↗

arXiv2023

Can LIGO Detect Non-Annihilating Dark Matter?

Dark matter from the galactic halo can accumulate in neutron stars and transmute them into sub-2.5 $M_{\odot}$ black holes if the dark matter particles are heavy, stable, and have interactions with nucleons. We show that non-detection of gravitational waves from mergers of such low-mass black holes can constrain the interactions of non-annihilating dark matter particles with nucleons. We find benchmark constraints with LIGO O3 data, viz., $σ_{χn} \geq {\cal O}(10^{-47})$ cm$^2$ for bosonic DM with $m_χ\sim$ PeV (or $m_χ\sim$ GeV, if they can Bose-condense) and $\geq {\cal O}(10^{-46})$ cm$^2$ for fermionic DM with $m_χ\sim 10^3$ PeV. These bounds depend on the priors on DM parameters and on the currently uncertain binary neutron star merger rate density. However, with increased exposure by the end of this decade, LIGO will probe cross-sections that are many orders of magnitude below the neutrino floor and completely test the dark matter solution to missing pulsars in the Galactic center, demonstrating a windfall science-case for gravitational wave detectors as probes of particle dark matter.

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