arXiv subjects

Ranjan Laha

Publications and source records attributed to Ranjan Laha.

At least 55 records · Page 3Linked to original sources

arXiv2019

Dark Matter Bound States from Three-Body Recombination

The small-scale structure problems of the universe can be solved by self-interacting dark matter that becomes strongly interacting at low energies. A particularly predictive model is resonant short-range self-interactions, with a dark-matter mass of about 19 GeV and a large S-wave scattering length of about 17 fm. Such a model makes definite predictions for the few-body physics of weakly bound clusters of the dark-matter particles. We calculate the production of two-body bound clusters by three-body recombination in the early universe under the assumption that the dark matter particles are identical bosons, which is the most favorable case for forming larger clusters. The fraction of dark matter in the form of two-body bound clusters can increase by as much as 4 orders of magnitude when the dark-matter temperature falls below the binding energy, but its present value remains less than 10^(-6).

hep-ph↗

arXiv2018

Production of dark-matter bound states in the early universe by three-body recombination

The small-scale structure problems of the universe can be solved by self-interacting dark matter that becomes strongly interacting at low energy. A particularly predictive model for the self-interactions is resonant short-range interactions with an S-wave scattering length that is much larger than the range. The velocity dependence of the cross section in such a model provides an excellent fit to self-interaction cross sections inferred from dark-matter halos of galaxies and clusters of galaxies if the dark-matter mass is about 19 GeV and the scattering length is about 17 fm. Such a model makes definite predictions for the few-body physics of weakly bound clusters of the dark-matter particles. The formation of the two-body bound cluster is a bottleneck for the formation of larger bound clusters. We calculate the production of two-body bound clusters by three-body recombination in the early universe under the assumption that the dark matter particles are identical bosons, which is the most favorable case. If the dark-matter mass is 19 GeV and the scattering length is 17 fm, the fraction of dark matter in the form of two-body bound clusters can increase by as much as 4 orders of magnitude when the dark-matter temperature falls below the binding energy, but its present value remains less than 10^(-6). The present fraction can be increased to as large as 10^(-3) by relaxing the constraints from small-scale structure and decreasing the mass of the dark matter particle.

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arXiv2018

Cuckoo's Eggs in Neutron Stars: Can LIGO Hear Chirps from the Dark Sector?

We explore in detail the possibility that gravitational wave signals from binary inspirals are affected by a new force that couples only to dark matter particles. We discuss the impact of both the new force acting between the binary partners as well as radiation of the force carrier. We identify numerous constraints on any such scenario, ultimately concluding that observable effects on the dynamics of binary inspirals due to such a force are not possible if the dark matter is accrued during ordinary stellar evolution. Constraints arise from the requirement that the astronomical body be able to collect and bind at small enough radius an adequate number of dark matter particles, from the requirement that the particles thus collected remain bound to neutron stars in the presence of another neutron star, and from the requirement that the theory allows old neutron stars to exist and retain their charge. Thus, we show that any deviation from the predictions of general relativity observed in binary inspirals must be due either to the material properties of the inspiraling objects themselves, such as a tidal deformability, to a true fifth force coupled to baryons, or to a non-standard production mechanism for the dark matter cores of neutron stars. Viable scenarios of the latter type include production of dark matter in exotic neutron decays, or the formation of compact dark matter objects in the early Universe that later seed star formation or are captured by stars.

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arXiv2018

Multi-PeV Signals from a New Astrophysical Neutrino Flux Beyond the Glashow Resonance

The IceCube neutrino discovery was punctuated by three showers with $E_ν$ ~ 1-2 PeV. Interest is intense in possible fluxes at higher energies, though a marked deficit of $E_ν$ ~ 6 PeV Glashow resonance events implies a spectrum that is soft and/or cutoff below ~few PeV. However, IceCube recently reported a through-going track event depositing 2.6 $\pm$ 0.3 PeV. A muon depositing so much energy can imply $E_{ν_μ} \gtrsim$ 10 PeV. We show that extending the soft $E_ν^{-2.6}$ spectral fit from TeV-PeV data is unlikely to yield such an event. Alternatively, a tau can deposit this much energy, though requiring $E_{ν_τ}$ ~10x higher. We find that either scenario hints at a new flux, with the hierarchy of $ν_μ$ and $ν_τ$ energies suggesting a window into astrophysical neutrinos at $E_ν$ ~ 100 PeV if a tau. We address implications, including for ultrahigh-energy cosmic-ray and neutrino origins.

astro-ph.HE↗

arXiv2018

Constraints on dark matter annihilation to fermions and a photon

We consider Majorana dark matter annihilation to fermion - anti-fermion pair and a photon in the effective field theory paradigm, by introducing dimension 6 and dimension 8 operators in the Lagrangian. For a given value of the cut-off scale, the latter dominates the annihilation process for heavier dark matter masses. We find a cancellation in the dark matter annihilation to a fermion - anti-fermion pair when considering the interference of the dimension 6 and the dimension 8 operators. Constraints on the effective scale cut-off is derived while considering indirect detection experiments and the relic density requirements and they are compared to the bound coming from collider experiments.

hep-ph↗

arXiv2018

Looking for Galactic Diffuse Dark Matter in INO-MagICAL Detector

The Weakly Interacting Massive Particle (WIMP) is a popular particle physics candidate for the dark matter (DM). It can annihilate and/or decay to neutrino and antineutrino pair. The proposed 50 kt Magnetized Iron CALorimeter (MagICAL) detector at the India-based Neutrino Observatory (INO) can observe these pairs over the conventional atmospheric neutrino and antineutrino fluxes. If we do not see any excess of events in ten years, then INO-Magical can place competitive limits on self-annihilation cross-section ($\langleσv\rangle$) and decay lifetime ($τ$) of dark matter at 90\% C.L.: $\langleσv\rangle\leq 1.87\,\times\,10^{-24}$ cm$^3$ s$^{-1}$ and $τ\geq 4.8\,\times\,10^{24}$ s for $m_χ$ = 10 GeV assuming the NFW as DM density profile.

hep-ph↗

arXiv2018

The effect of hydrodynamical simulation inspired dark matter velocity profile on directional detection of dark matter

Directional detection is an important way to detect dark matter. An input to these experiments is the dark matter velocity distribution. Recent hydrodynamical simulations have shown that the dark matter velocity distribution differs substantially from the Standard Halo Model. We study the impact of some of these updated velocity distribution in dark matter directional detection experiments. We calculate the ratio of events required to confirm the forward-backward asymmetry and the existence of the ring of maximum recoil rate using different dark matter velocity distributions for $^{19}$F and Xe targets. We show that with the use of updated dark matter velocity profiles, the forward-backward asymmetry and the ring of maximum recoil rate can be confirmed using a factor of $\sim$2 - 3 less events when compared to that using the Standard Halo Model.

astro-ph.CO↗

arXiv2018

Robust measurement of supernova $ν_e$ spectra with future neutrino detectors

Measuring precise all-flavor neutrino information from a supernova is crucial for understanding the core-collapse process as well as neutrino properties. We apply a chi-squared analysis for different detector setups to explore determination of $ν_{e}$ spectral parameters. Using a long-term two-dimensional core-collapse simulation with three time varying spectral parameters, we generate mock data to examine the capabilities of the current Super-Kamiokande detector and compare the relative improvements that gadolinium, Hyper-Kamiokande, and DUNE would have. We show that in a realistic three spectral parameter framework, the addition of gadolinium to Super-Kamiokande allows for a qualitative improvement in $ν_e$ determination. Significant improvements will be made by Hyper-Kamiokande and DUNE, allowing for much more precise determination of $ν_e$ spectral parameters.

astro-ph.HE↗

arXiv2017

IC at IC: IceCube can constrain the intrinsic charm of the proton

The discovery of extraterrestrial neutrinos in the $\sim$ 30 TeV -- PeV energy range by IceCube provides new constraints on high energy astrophysics. An important background to the signal are the prompt neutrinos which originate from the decay of charm hadrons produced by high energy cosmic-ray particles interacting in the Earth's atmosphere. It is conventional to use the calculations of charm hadroproduction using gluon splitting $g \to c \bar c$ alone. However, QCD predicts an additional "intrinsic" component of the heavy quark distribution which arises from diagrams where heavy quarks are multiply connected to the proton's valence quarks. We estimate the prompt neutrino spectrum due to intrinsic charm. We find that the atmospheric prompt neutrino flux from intrinsic charm is comparable to those calculated using QCD computations not including intrinsic charm, once we normalize the intrinsic charm differential cross sections to the ISR and the LEBC-MPS collaboration data. In future, IceCube will constrain the intrinsic charm content of the proton and will contribute to one of the major questions in high energy physics phenomenology.

hep-ph↗

arXiv2017

Diffuse axion-like particle searches

We propose a new method to search for axion-like particles (ALPs) based on the gamma-rays produced concomitant with high-energy astrophysical neutrinos. The existence of high-energy neutrinos implies production of gamma-rays in the same sources. Photons can convert into ALPs in the sources' magnetic fields, and will travel as ALPs through extragalactic space. Back-conversion in the Milky Way's magnetic field leads to a diffuse anisotropic high-energy photon flux that existing and upcoming gamma-ray detectors, like HAWC, CTA, and LHAASO can detect. This method probes unexplored ALP parameter space, with LHAASO being realistically sensitive to couplings above $10^{-11}\, \rm{GeV^{-1}}$ and masses up to $3\times 10^{-6} \, \rm{eV}$ in ten years. Our technique also explores viable ALP dark matter parameter space.

hep-ph↗

arXiv2017

The Doppler effect on indirect detection of dark matter using dark matter only simulations

Indirect detection of dark matter is a major avenue for discovery. However, baryonic backgrounds are diverse enough to mimic many possible signatures of dark matter. In this work, we study the newly proposed technique of dark matter velocity spectroscopy\,\cite{speckhard2016}. The non-rotating dark matter halo and the Solar motion produce a distinct longitudinal dependence of the signal which is opposite in direction to that produced by baryons. Using collisionless dark matter only simulations of Milky Way like halos, we show that this new signature is robust and holds great promise. We develop mock observations by high energy resolution X-ray spectrometer on a sounding rocket, the Micro-X experiment, to our test case, the 3.5 keV line. We show that by using six different pointings, Micro-X can exclude a constant line energy over various longitudes at $\geq$ 3$σ$. The halo triaxiality is an important effect and it will typically reduce the significance of this signal. We emphasize that this new {\it smoking gun in motion} signature of dark matter is general, and is applicable to any dark matter candidate which produces a sharp photon feature in annihilation or decay.

astro-ph.CO↗

arXiv2017

Indirect searches of Galactic diffuse dark matter in INO-MagICAL detector

The signatures for the existence of dark matter are revealed only through its gravitational interaction. Theoretical arguments support that the Weakly Interacting Massive Particle (WIMP) can be a class of dark matter and it can annihilate and/or decay to Standard Model particles, among which neutrino is a favorable candidate. We show that the proposed 50 kt Magnetized Iron CALorimeter (MagICAL) detector under the India-based Neutrino Observatory (INO) project can play an important role in the indirect searches of Galactic diffuse dark matter in the neutrino and antineutrino mode separately. We present the sensitivity of 500 kt$\cdot$yr MagICAL detector to set limits on the velocity-averaged self-annihilation cross-section ($\langleσv\rangle$) and decay lifetime ($τ$) of dark matter having mass in the range of 2 GeV $\leq m_χ\leq $ 90 GeV and 4 GeV $\leq m_χ\leq $ 180 GeV respectively, assuming no excess over the conventional atmospheric neutrino and antineutrino fluxes at the INO site. Our limits for low mass dark matter constrain the parameter space which has not been explored before. We show that MagICAL will be able to set competitive constraints, $\langleσv\rangle\leq 1.87\,\times\,10^{-24}$ cm$^3$ s$^{-1}$ for $χχ\rightarrowν\barν$ and $τ\geq 4.8\,\times\,10^{24}$ s for $χ\rightarrowν\barν$ at 90$\%$ C.L. (1 d.o.f.) for $m_χ$ = 10 GeV assuming the NFW as dark matter density profile.

hep-ph↗

arXiv2016

Supernova Physics at DUNE

The DUNE/LBNF program aims to address key questions in neutrino physics and astroparticle physics. Realizing DUNE's potential to reconstruct low-energy particles in the 10-100 MeV energy range will bring significant benefits for all DUNE's science goals. In neutrino physics, low-energy sensitivity will improve neutrino energy reconstruction in the GeV range relevant for the kinematics of DUNE's long-baseline oscillation program. In astroparticle physics, low-energy capabilities will make DUNE's far detectors the world's best apparatus for studying the electron-neutrino flux from a supernova. This will open a new window to unrivaled studies of the dynamics and neutronization of a star's central core in real time, the potential discovery of the neutrino mass hierarchy, provide new sensitivity to physics beyond the Standard Model, and evidence of neutrino quantum-coherence effects. The same capabilities will also provide new sensitivity to `boosted dark matter' models that are not observable in traditional direct dark matter detectors.

hep-ex↗

arXiv2015

Directional detection of dark matter in universal bound states

It has been suggested that several small-scale structure anomalies in $Λ$CDM cosmology can be solved by strong self-interaction between dark matter particles. It was shown by Braaten and Hammer that the presence of a near threshold S-wave resonance can make the scattering cross section at nonrelativistic speeds come close to saturating the unitarity bound. This can result in the formation of a stable bound state of two asymmetric dark matter particles (we call the bound state as darkonium). Laha and Braaten studied the nuclear recoil energy spectrum in dark matter direct detection experiments due to this incident bound state. Here we study the angular recoil spectrum, and show that it is uniquely determined up to normalization by the S-wave scattering length. Observing this angular recoil spectrum in a dark matter directional detection experiment will uniquely determine many of the low-energy properties of dark matter independent of the underlying dark matter microphysics.

hep-ph↗

arXiv2015

Testing the Dark Matter Scenario for PeV Neutrinos Observed in IceCube

Late time decay of very heavy dark matter is considered as one of the possible explanations for diffuse PeV neutrinos observed in IceCube. We consider implications of multimessenger constraints, and show that proposed models are marginally consistent with the diffuse gamma-ray background data. Critical tests are possible by a detailed analysis and identification of the sub-TeV isotropic diffuse gamma-ray data observed by Fermi and future observations of sub-PeV gamma rays by observatories like HAWC or Tibet AS+MD. In addition, with several-year observations by next-generation telescopes such as IceCube-Gen2, muon neutrino searches for nearby dark matter halos such as the Virgo cluster should allow us to rule out or support the dark matter models, independently of gamma-ray and anisotropy tests.

hep-ph↗

arXiv2015

Dark Matter Velocity Spectroscopy

Dark matter decays or annihilations that produce line-like spectra may be smoking-gun signals. However, even such distinctive signatures can be mimicked by astrophysical or instrumental causes. We show that velocity spectroscopy-the measurement of energy shifts induced by relative motion of source and observer-can separate these three causes with minimal theoretical uncertainties. The principal obstacle has been energy resolution, but upcoming experiments will reach the required 0.1% level. As an example, we show that the imminent Astro-H mission can use Milky Way observations to separate possible causes of the 3.5-keV line. We discuss other applications.

astro-ph.CO↗

arXiv2014

New Power to Measure Supernova $ν_e$ with Large Liquid Scintillator Detectors

We examine the prospects for detecting supernova $ν_e$ in JUNO, RENO-50, LENA, or other approved or proposed large liquid scintillator detectors. The main detection channels for supernova $ν_e$ in a liquid scintillator are its elastic scattering with electrons and its charged-current interaction with the $^{12}$C nucleus. In existing scintillator detectors, the numbers of events from these interactions are too small to be very useful. However, at the 20-kton scale planned for the new detectors, these channels become powerful tools for probing the $ν_e$ emission. We find that the $ν_e$ spectrum can be well measured, to better than $\sim 40\%$ precision for the total energy and better than $\sim 25\%$ precision for the average energy. This is adequate to distinguish even close average energies, e.g., 11 MeV and 14 MeV, which will test the predictions of supernova models. In addition, it will help set constraints on neutrino mixing effects in supernovae by testing non-thermal spectra. Without such large liquid scintillator detectors (or Super-Kamiokande with added gadolinium, which has similar capabilities), supernova $ν_e$ will be measured poorly, holding back progress on understanding supernovae, neutrinos, and possible new physics.

hep-ph↗

arXiv2014

Constraints on New Neutrino Interactions via Light Abelian Vector Bosons

We calculate new constraints on extra neutrino interactions via light Abelian vector bosons, where the boson mass arises from Stuckelberg mechanism. We use the requirement that $Z$, $W$, and kaon decays, as well as electron-neutrino scattering, are not altered by the new interactions beyond what is allowed by experimental uncertainties. These constraints are strong and apply to neutrinophilic dark matter, where interactions of neutrinos and dark matter via a new gauge boson are important. In particular, we show that models where neutrino interactions are needed to solve the small-scale structure problems in the $Λ$CDM cosmology are constrained.

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