arXiv subjects

Anupam Ray

Publications and source records attributed to Anupam Ray.

29 records · Page 2Linked to original sources

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.

hep-ph↗

arXiv2023

Dark Matter Annihilation inside Large Volume Neutrino Detectors

New particles in theories beyond the standard model can manifest as stable relics that interact strongly with visible matter and make up a small fraction of the total dark matter abundance. Such particles represent an interesting physics target since they can evade existing bounds from direct detection due to their rapid thermalization in high-density environments. In this work we point out that their annihilation to visible matter inside large-volume neutrino telescopes can provide a new way to constrain or discover such particles. The signal is the most pronounced for relic masses in the GeV range, and can be efficiently constrained by existing Super-Kamiokande searches for di-nucleon annihilation. We also provide an explicit realization of this scenario in the form of secluded dark matter coupled to a dark photon, and we show that the present method implies novel and stringent bounds on the model that are complementary to direct constraints from beam dumps, colliders, and direct detection experiments.

hep-ph↗

arXiv2023

Mergers as a Probe of Particle Dark Matter

Black holes below Chandrasekhar mass limit (1.4 $M_{\odot}$) can not be produced via any standard stellar evolution. Recently, gravitational wave experiments have also discovered unusually low mass black holes whose origin is yet to be known. We propose a simple yet novel formation mechanism of such low mass black holes. Non-annihilating particle dark matter, owing to their interaction with stellar nuclei, can gradually accumulate inside compact stars, and eventually swallows them to low mass black holes, ordinarily impermissible by the Chandrasekhar limit. We point out several avenues to test this proposal, concentrating on the cosmic evolution of the binary merger rates.

hep-ph↗

arXiv2023

Celestial Objects as Strongly-Interacting Non-Annihilating Dark Matter Detectors

Non-annihilating dark matter particles, owing to their interactions with ordinary baryonic matter, can efficiently accumulate inside celestial objects. For heavy mass, they gravitate toward the core of the celestial objects, thermalize in a small core region, and eventually form tiny black holes via core collapse, resulting destruction of the host objects. We demonstrate that the existence of a variety of celestial objects provides stringent constraints on strongly-interacting heavy dark matter, a blind-spot for the terrestrial dark matter detectors as well as for the cosmological probes. Celestial objects with larger sizes and lower core temperatures, such as Jupiter, are the most optimal detectors to probe the strongly-interacting heavy non-annihilating dark matter.

hep-ph↗

arXiv2022

Probing Ultra-light Primordial Black Holes as a Dark Matter Candidate

Dark Matter (DM) is omnipresent in our universe. Despite its abundance, the microscopic identity of DM still remains a mystery. Primordial black holes (PBHs), possibly formed via gravitational collapse of large density perturbations in the early universe, are one of the earliest proposed and viable DM candidates. Recent studies indicate that PBHs can make up a large or even entire fraction of the DM density for a wide range of masses. Here, we briefly review the observational constraints on PBHs as DM, concentrating on the ultra-light mass window. Ultra-light PBHs emit particles via Hawking radiation and can be probed by observing such Hawking evaporated particles in various space as well as ground based detectors. We also outline how next-generation gamma ray telescopes can set a stringent exclusion limit on ultra-light PBH DM by probing low energy photons.

hep-ph↗

arXiv2022

Constraining primordial black holes as dark matter using the global 21-cm signal with X-ray heating and excess radio background

Using the global 21-cm signal measurement by the EDGES collaboration, we derive constraints on the fraction of the dark matter that is in the form of primordial black holes (PBHs) with masses in the range $10^{15}$-$10^{17}\,$g. Improving upon previous analyses, we consider the effect of the X-ray heating of the intergalactic medium on these constraints, and also use the full shape of the 21-cm absorption feature in our inference. In order to account for the anomalously deep absorption amplitude, we also consider an excess radio background motivated by LWA1 and ARCADE2 observations. Because the heating rate induced by PBH evaporation evolves slowly, the data favour a scenario in which PBH-induced heating is accompanied by X-ray heating. Also, for the same reason, using the full measurement across the EDGES observation band yields much stronger constraints on PBHs than just the redshift of absorption. We find that 21-cm observations exclude $f_{\mathrm{PBH}} \gtrsim 10^{-9.7}$ at 95% CL for $M_{\mathrm{PBH}}=10^{15}\,$g. This limit weakens approximately as $M_{\mathrm{PBH}}^4$ towards higher masses, thus providing the strongest constraints on ultralight evaporating PBHs as dark matter over the entire mass range $10^{15}$-$10^{17}\,$g. Under the assumption of a simple spherical gravitational collapse based on the Press-Schechter formalism, we also derive bounds on the curvature power spectrum at extremely small scales ($k\sim 10^{15}\,$Mpc$^{-1}$). This highlights the usefulness of global 21-cm measurements, including non-detections, across wide frequency bands for probing exotic physical processes.

astro-ph.CO↗

arXiv2021

Near future MeV telescopes can discover asteroid-mass primordial black hole dark matter

Primordial black holes (PBHs), formed out of large overdensities in the early Universe, are a viable dark matter (DM) candidate over a broad range of masses. Ultra-light, asteroid-mass PBHs with masses around $10^{17}$ g are particularly interesting as current observations allow them to constitute the entire DM density. PBHs in this mass range emit $\sim$ MeV photons via Hawking radiation which can directly be detected by the gamma ray telescopes, such as the upcoming AMEGO. In this work we forecast how well an instrument with the sensitivity of AMEGO will be able to detect, or rule out, PBHs as a DM candidate, by searching for their evaporating signature when marginalizing over the Galactic and extra-Galactic gamma-ray backgrounds. We find that an instrument with the sensitivity of AMEGO could exclude non-rotating PBHs as the only DM component for masses up to $7 \times 10^{17}$ g at 95% confidence level (C.L.) for a monochromatic mass distribution, improving upon current bounds by nearly an order of magnitude. The forecasted constraints are more stringent for PBHs that have rotation, or which follow extended mass distributions.

astro-ph.CO↗

arXiv2021

Low Mass Black Holes from Dark Core Collapse

Unusual masses of black holes being discovered by gravitational wave experiments pose fundamental questions about the origin of these black holes. Black holes with masses smaller than the Chandrasekhar limit $\approx1.4\,M_\odot$ are essentially impossible to produce through stellar evolution. We propose a new channel for production of low mass black holes: stellar objects catastrophically accrete non-annihilating dark matter, and the small dark core subsequently collapses, eating up the host star and transmuting it into a black hole. The wide range of allowed dark matter masses allows a smaller effective Chandrasekhar limit, and thus smaller mass black holes. We point out several avenues to test our proposal, focusing on the redshift dependence of the merger rate. We show that redshift dependence of the merger rate can be used as a probe of the transmuted origin of low mass black holes.

astro-ph.HE↗

arXiv2020

Dark matter capture in celestial objects: light mediators, self-interactions, and complementarity with direct detection

We generalize the formalism for DM capture in celestial bodies to account for arbitrary mediator mass, and update the existing and projected astrophysical constraints on DM-nucleon scattering cross section from observations of neutron stars. We show that the astrophysical constraints on the DM-nucleon interaction strength, that were thought to be the most stringent, drastically weaken for light mediators and can be completely voided. For asymmetric DM, existing astrophysical constraints are completely washed out for mediators lighter than 5 MeV, and for annihilating DM the projected constraints are washed out for mediators lighter than 0.25 MeV. Related terrestrial direct detection bounds also weaken, but in a complementary fashion; they supersede the astrophysical capture bounds for small or large DM mass, respectively for asymmetric or annihilating DM. Repulsive self-interactions of DM have an insignificant impact on the total capture rate, but a significant impact on the black hole formation criterion. This further weakens the constraints on DM-nucleon interaction strength for asymmetric self-repelling DM, whereas constraints remain unaltered for annihilating self-repelling DM. We use the correct Hawking evaporation rate of the newly formed black hole, that was approximated as a blackbody in previous studies, and show that, despite a more extensive alleviation of collapse as a result, the observation of a neutron star collapse can probe a wide range of DM self-interaction strengths.

hep-ph↗

arXiv2020

Neutrino and Positron Constraints on Spinning Primordial Black Hole Dark Matter

Primordial black holes can have substantial spin -- a fundamental property that has a strong effect on its evaporation rate. We conduct a comprehensive study of the detectability of primordial black holes with non-negligible spin, via the searches for the neutrinos and positrons in the MeV energy range. Diffuse supernova neutrino background searches and observation of the 511 keV gamma-ray line from positrons in the Galactic center set competitive constraints. Spinning primordial black holes are probed up to a slightly higher mass range compared to non-spinning ones. Our constraint using neutrinos is slightly weaker than that due to the diffuse gamma-ray background, but complementary and robust. Our positron constraints are typically weaker in the lower mass range and stronger in the higher mass range for the spinning primordial black holes compared to the non-spinning ones. They are generally stronger than those derived from the diffuse gamma-ray measurements for primordial black holes having masses greater than a few $\times \, 10^{16}$g.

hep-ph↗

arXiv2020

Galactic Positron Excess from Selectively Enhanced Dark Matter Annihilation

Precision measurements of the positron flux in cosmic ray have revealed an unexplained bump in the spectrum around $E\simeq 300\,\mathrm{GeV}$, not clearly attributable to known astrophysical processes. We propose annihilation of dark matter of mass $m_χ= 780\,\mathrm{GeV}$ with a late-time cross section $σv = 4.63\times 10^{-24}\,\mathrm{cm^3\,s^{-1}}$ as a possible source. The nonmonotonic dependence of the annihilation rate on dark matter velocity, owing to a selective $p$-wave Sommerfeld enhancement, allows such a large signal from the Milky Way without violating corresponding constraints from CMB and dwarf galaxy observations. We briefly explore other signatures of this scenario, and outline avenues to test it in future experiments.

hep-ph↗