Dark Matter Density Research Articles

Evolution of the DM distribution function in the density spikes around PBHs

At the cosmological stage of radiation dominance, dark matter density spikes should form around primordial black holes. In the case when dark matter particles are able to annihilate, the density in the central regions of the spikes decreases due to the elimination of particles, which gives an upper bound on the central density. In this paper, the modification of the central density profile is investigated, taking into account the distribution of the particle orbits. The orbits in spike around a primordial black hole are very elongated, almost radial, and the angular momentum distribution has an exponential form. For such an initial distribution function, it is obtained that a cusp with the exponent ≈-0.7 is formed in the central region, instead of an annihilation plateau. The presence of the cusp provides some correction to the rate of dark matter annihilation around primordial black holes.

Explaining the cosmological dark matter coincidence in asymmetric dark QCD

To properly solve the coincidence problem (ΩDM≃5ΩVM) in a model of asymmetric dark matter, one cannot simply relate the number densities of visible and dark matter without also relating their particle masses. Following previous work, we consider a framework where the dark matter is a confined state of a dark QCD gauge group whose confinement scale is dynamically related to the QCD confinement scale by a mechanism utilizing infrared fixed points of the two gauge couplings. In this work we present a new, “zero-coupling infrared fixed point” approach, which allows a larger proportion of models in this framework to generically relate the masses of the visible and dark matter particles. Due to the heavy mass scale required for the new field content, we introduce supersymmetry to the theory. We consider how these models may be incorporated in a full theory of asymmetric dark matter, presenting some example leptogenesis-like models. We also discuss the phenomenology of these models; in particular, there are gravitational wave signals which, while weak, may be measurable at future mHz and μHz detectors. Published by the American Physical Society 2024

Improved constraints on dark matter annihilations around primordial black holes

Cosmology may give rise to appreciable populations of both particle dark matter and primordial black holes (PBH) with the combined mass density providing the observationally inferred value ΩDM ≈ 0.26. Early studies highlighted that scenarios with both particle dark matter and PBH are strongly excluded by γ-ray limits for particle dark matter with a velocity independent thermal cross section 〈σν〉 ~ 3 × 10−26cm3/s, as is the case for classic WIMP dark matter. Here we examine the limits from di use γ-rays on velocity-dependent, including annihilations which are p-wave with 〈σν〉 ∝ v2 or d-wave 〈σν〉 ∝ v4, which we find to be considerably less constraining. This work also utilizes a refined treatment of the PBH dark matter density profile. Importantly, we highlight that even if the freeze-out process is p-wave it is typical for (loop/phase-space) suppressed s-wave processes to actually provide the leading contributions to the experimentally constrained γ-ray flux from the PBH halo.

Debiasing with Diffusion: Probabilistic Reconstruction of Dark Matter Fields from Galaxies with CAMELS

Galaxies are biased tracers of the underlying cosmic web, which is dominated by dark matter (DM) components that cannot be directly observed. Galaxy formation simulations can be used to study the relationship between DM density fields and galaxy distributions. However, this relationship can be sensitive to assumptions in cosmology and astrophysical processes embedded in galaxy formation models, which remain uncertain in many aspects. In this work, we develop a diffusion generative model to reconstruct DM fields from galaxies. The diffusion model is trained on the CAMELS simulation suite that contains thousands of state-of-the-art galaxy formation simulations with varying cosmological parameters and subgrid astrophysics. We demonstrate that the diffusion model can predict the unbiased posterior distribution of the underlying DM fields from the given stellar density fields while being able to marginalize over uncertainties in cosmological and astrophysical models. Interestingly, the model generalizes to simulation volumes ≈500 times larger than those it was trained on and across different galaxy formation models. The code for reproducing these results can be found at https://github.com/victoriaono/variational-diffusion-cdm ✎.

Determination of dark matter distribution in Ursa Major III and constraints on dark matter annihilation* *Supported by the National Natural Science Foundation of China (11947005, 12175248, 12205388, 12227804), the Science & Technology Development Fund of Tianjin Education Commission for Higher Education (2020KJ003), and the PhD Research Startup Foundation of Tianjin Normal University (52XB1912)

The recently discovered satellite dwarf galaxy Ursa Major III provides a promising opportunity to explore the signatures resulting from dark matter (DM) annihilation owing to its proximity and large J-factor. Given the absence of an excess of γ-ray signatures originating from Ursa Major III, observations of γ-rays, such as those from Fermi-LAT, can be utilized to set constraints on the DM annihilation cross-section. In this study, we determined the DM density profile and considered the relationship between DM density and velocity dispersion at different locations within Ursa Major III through Jeans analysis. We calculated the J-factor of Ursa Major III for s-wave annihilation along with the effective J-factors for p-wave and Sommerfeld enhanced annihilation scenarios. Employing these derived J-factors, we set stringent constraints on DM annihilation cross-sections in three scenarios. Given the substantial impact of member star identification on the J-factor of Ursa Major III, we further calculated J-factors under the exclusion of the largest velocity outlier. Our analysis reveals a notable reduction in the median value and an increase in the deviation of J-factors, thereby leading to considerably weaker constraints.

Probing black holes in a dark matter spike of M87 using quasinormal modes

Dark matter density can be significantly enhanced by the supermassive black hole at the galactic center, leading to a structure called dark matter spike. Dark matter spike may change the spacetime properties of black holes that constitute deviations from GR black holes. Based on these interesting background, we construct a set of solutions of black holes in a dark matter spike under the Newtonian approximation and full relativity. Combining the mass model of M87, we study the quasinormal modes of black holes in the scalar field and axial gravitational perturbation, then compared them with Schwarzschild black hole. Besides, the impacts of dark matter on the quasinormal mode of black holes have been studied in depth. In particular, in the axial gravitational perturbation, our results show that the impacts of dark matter spike on the quasinormal mode of black holes can reach up to 10-4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^{-4}$$\\end{document}. These new features from quasinormal mode of black holes under the Newtonian approximation and full relativity may provide some help for the establishment of the final dark matter model, and provide a new thought for the indirect detection of dark matter.

Constraining dark photon parameters based on the very high energy observations of blazars

Dark photon is a new gauge boson beyond the Standard Model as a kind of dark matter (DM) candidate. Dark photon dark matter (DPDM) interacts with electromagnetic fields via kinetic mixing, implicating an approach to give a constraint with extragalactic very high energy (VHE) sources. In this work, we attempt to constrain the kinetic mixing from the photon-dark photon scattering process in the host galaxy of blazar, the intergalactic medium and the Milky Way. The VHE photons from a blazar would pass through a dense DM spike around the supermassive black hole where the absorption from DPDM is dramatically enhanced. The kinetic mixing is constrained to be ϵ∼10-7\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\epsilon \\sim 10^{-7}$$\\end{document} at a 95%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\%$$\\end{document} confidence level with mD∼0.03-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$m_\ extrm{D}\\sim 0.03 {-} 1$$\\end{document} eV mass range from the observations of Markarian (Mrk) 421 and Mrk 501.

TensorFlow Hydrodynamics Analysis for Ly-[formula omitted] Simulations

We introduce the Python program THALAS (TensorFlow Hydrodynamics Analysis for Lyman-Alpha Simulations), which maps baryon fields (baryon density, temperature, and velocity) to Lyα optical depth fields in both real space and redshift space. Unlike previous Lyα codes, THALAS is fully differentiable, enabling a wide variety of potential applications for general analysis of hydrodynamical simulations and cosmological inference. To demonstrate THALAS’s capabilities, we apply it to the Lyα forest inversion problem: given a Lyα optical depth field, we reconstruct the corresponding real-space dark matter density field. Such applications are relevant to both cosmological and three-dimensional tomographic analyses of Lyman Alpha forest data.

Wormholes in dwarf and spiral galactic halo regions

In this article, we study solutions which describe wormholes in the halos of dwarf and massive spiral galaxies with different morphologies, masses, sizes and gas fractions by taking observed flat rotation curves as input. We assume Singular Isothermal Sphere (SIS) dark matter density profile. This result confirms the possible existence of wormholes in both dwarf and massive spiral galaxies.

Constraining neutrino-DM interactions with Milky Way dwarf spheroidals and supernova neutrinos

We constrain the neutrino-dark matter cross section using properties of the dark matter density profiles of Milky Way dwarf spheroidal galaxies. The constraint arises from core-collapse supernova neutrinos scattering on dark matter as a form of energy injection, allowing the transformation of the dark matter density profile from a cusped profile to a flatter profile. We assume a standard cosmology of dark energy and cold, collisionless, and non-self-interacting dark matter. By requiring that the dark matter cores do not lose too much mass or overshoot constraints from stellar kinematics, we place an upper limit on the cross section of σν−DM(Eν=15 MeV,mχ≲130 GeV)≈3.4×10−23 cm2 and σν−DM(Eν=15 MeV,mχ≳130 GeV)≈3.2×10−27(mχ1 GeV)2 cm2, which is stronger than previous bounds for these energies. Consideration of baryonic feedback or host galaxy effects on the dark matter profile can strengthen this constraint. Published by the American Physical Society 2024

A study on vector mediator top-philic dark matter

We conducted a study on a simplified dark matter model that introduces a vector-like intermediate particle, facilitating exclusive interactions between dark matter and the top quark in the Standard Model. The analysis focused on the relic density of Dirac-type fermion dark matter and highlighted the complementary role of direct detection in constraining the dark matter model. Notably, in instances when dark matter mass is small, the tree-level two-body annihilation process experiences suppression. In such scenarios, the contributions of the three-body process ( χχ¯→tb¯W− ) and the one-loop process ( χχ¯→gg ) dominate the relic abundance. With regard to direct detection, calculations were performed for the two-loop contribution to the dark-matter–gluon interaction, yielding the corresponding spin-independent scattering cross section.

Asymmetric dark matter and Sommerfeld enhancement

We study the relic density of asymmetric dark matter with long-range interactions by considering the Sommerfeld effect. We find that the annihilation cross section of asymmetric dark matter is enhanced by the Sommerfeld effect and thus the relic density is decreased. Then we use the Planck data to constrain the asymmetry factor, coupling, and to derive the upper bounds on the dark matter mass in s-wave and p-wave annihilation cases.

Dark matter in the Milky Way: Measurements up to 3 kpc from the Galactic plane above the Sun

We probe the gravitational force perpendicular to the Galactic plane at the position of the Sun based on a sample of red giants, with measurements taken from the DR3 Gaia catalogue. Measurements far out of the Galactic plane up to 3.5 kpc allow us to determine directly the total mass density, where dark matter is dominant and the stellar and gas densities are very low. In a complementary way, we have also used a new determination of the local baryonic mass density to help determine the density of dark matter in the Galactic plane at the solar position. For the local mass density of dark matter, we obtained $ dm $0.0008\,M$_ $ = 0.486 pm 0.030 Gev\ $. For the flattening of the gravitational potential of the dark halo, it is $q_ phi,h For its density, $q_ rho,h $=0.781pm 0.055.

Dark Matter halo parameters from overheated exoplanets via Bayesian hierarchical inference

Dark Matter (DM) can become captured, deposit annihilation energy, and hence increase the heat flow in exoplanets and brown dwarfs. Detecting such a DM-induced heating in a population of exoplanets in the inner kpc of the Milky Way thus provides potential sensitivity to the galactic DM halo parameters. We develop a Bayesian Hierarchical Model to investigate the feasibility of DM discovery with exoplanets and examine future prospects to recover the spatial distribution of DM in the Milky Way. We reconstruct from mock exoplanet datasets observable parameters such as exoplanet age, temperature, mass, and location, together with DM halo parameters, for representative choices of measurement uncertainty and the number of exoplanets detected. We find that detection of ℴ(100) exoplanets in the inner Galaxy can yield quantitative information on the galactic DM density profile, under the assumption of 10% measurement uncertainty. Even as few as ℴ(10) exoplanets can deliver meaningful sensitivities if the DM density and inner slope are sufficiently large.https://github.com/mariabenitocst/exoplanets

HSTPROMO Internal Proper-motion Kinematics of Dwarf Spheroidal Galaxies. I. Velocity Anisotropy and Dark Matter Cusp Slope of Draco

We analyze four epochs of Hubble Space Telescope imaging over 18 yr for the Draco dwarf spheroidal galaxy. We measure precise proper motions for hundreds of stars and combine these with existing line-of-sight (LOS) velocities. This provides the first radially resolved 3D velocity dispersion profiles for any dwarf galaxy. These constrain the intrinsic velocity anisotropy and resolve the mass–anisotropy degeneracy. We solve the Jeans equations in oblate axisymmetric geometry to infer the mass profile. We find the velocity dispersion to be radially anisotropic along the symmetry axis and tangentially anisotropic in the equatorial plane, with a globally averaged value βB¯=−0.20−0.53+0.28 , (where 1 – βB≡〈vtan2〉/〈vrad2〉 in 3D). The logarithmic dark matter (DM) density slope over the observed radial range, Γdark, is −0.83−0.37+0.32 , consistent with the inner cusp predicted in ΛCDM cosmology. As expected given Draco’s low mass and ancient star formation history, it does not appear to have been dissolved by baryonic processes. We rule out cores larger than 487, 717, and 942 pc at 1σ, 2σ, and 3σ confidence, respectively, thus imposing important constraints on the self-interacting DM cross section. Spherical models yield biased estimates for both the velocity anisotropy and the inferred slope. The circular velocity at our outermost data point (900 pc) is 24.19−2.97+6.31kms−1 . We infer a dynamical distance of 75.37−4.00+4.73 kpc and show that Draco has a modest LOS rotation, with v/σ=0.22±0.09 . Our results provide a new stringent test of the so-called “cusp–core” problem that can be readily extended to other dwarfs.

Dark matter line searches with the Cherenkov Telescope Array

Monochromatic gamma-ray signals constitute a potential smoking gun signature for annihilating or decaying dark matter particles that could relatively easily be distinguished from astrophysical or instrumental backgrounds. We provide an updated assessment of the sensitivity of the Cherenkov Telescope Array (CTA) to such signals, based on observations of the Galactic centre region as well as of selected dwarf spheroidal galaxies. We find that current limits and detection prospects for dark matter masses above 300 GeV will be significantly improved, by up to an order of magnitude in the multi-TeV range. This demonstrates that CTA will set a new standard for gamma-ray astronomy also in this respect, as the world's largest and most sensitive high-energy gamma-ray observatory, in particular due to its exquisite energy resolution at TeV energies and the adopted observational strategy focussing on regions with large dark matter densities. Throughout our analysis, we use up-to-date instrument response functions, and we thoroughly model the effect of instrumental systematic uncertainties in our statistical treatment. We further present results for other potential signatures with sharp spectral features, e.g. box-shaped spectra, that would likewise very clearly point to a particle dark matter origin.

Feedback in the dark: a critical examination of CMB bounds on primordial black holes

If present in the early universe, primordial black holes (PBHs) would have accreted matter and emitted high-energy photons, altering the statistical properties of the Cosmic Microwave Background (CMB). This mechanism has been used to constrain the fraction of dark matter that is in the form of PBHs to be much smaller than unity for PBH masses well above one solar mass. Moreover, the presence of dense dark matter mini-halos around the PBHs has been used to set even more stringent constraints, as these would boost the accretion rates.In this work, we critically revisit CMB constraints on PBHs taking into account the role of the local ionization of the gas around them. We discuss how the local increase in temperature around PBHs can prevent the dark matter mini-halos from strongly enhancing the accretion process, in some cases significantly weakening previously derived CMB constraints. We explore in detail the key ingredients of the CMB bound and derive a conservative limit on the cosmological abundance of massive PBHs.

Bursting with Feedback: The Relationship between Feedback Model and Bursty Star Formation Histories in Dwarf Galaxies

Due to their inability to self-regulate, ultrafaint dwarfs are sensitive to prescriptions in subgrid physics models that converge and regulate at higher masses. We use high-resolution cosmological simulations to compare the effect of bursty star formation histories (SFHs) on dwarf galaxy structure for two different subgrid supernova (SN) feedback models, superbubble and blastwave, in dwarf galaxies with stellar masses from 5000 < M */M ⊙ < 109. We find that in the “MARVEL-ous Dwarfs” suite both feedback models produce cored galaxies and reproduce observed scaling relations for luminosity, mass, and size. Our sample accurately predicts the average stellar metallicity at higher masses, however low-mass dwarfs are metal poor relative to observed galaxies in the Local Group. We show that continuous bursty star formation and the resulting stellar feedback are able to create dark matter (DM) cores in the higher dwarf galaxy mass regime, while the majority of ultrafaint and classical dwarfs retain cuspy central DM density profiles. We find that the effective core formation peaks at M */M halo ≃ 5 × 10−3 for both feedback models. Both subgrid SN models yield bursty SFHs at higher masses; however, galaxies simulated with superbubble feedback reach maximum mean burstiness values at lower stellar mass fractions relative to blastwave feedback. As a result, core formation may be better predicted by stellar mass fraction than the burstiness of SFHs.

Effect of Einasto spike and isothermal dark matter density profile on the geometry of wormhole in [formula omitted] gravity

In the present article, we uncover striking properties of traversable wormhole solutions generated under a newly developed f(ℜ,Lm) gravitational theory. Two distinct dark matter density profiles—the Einasto spike and the Pseudo-isothermal model—are employed to demonstrate the existence of stable wormhole geometries with throat radii of 1.18 km and 1.41 km, respectively. Through a rigorous analytical and plot-based survey, we delve deeper into the exotic matter characteristics of these wormhole structures and analyze their matter content in the context of energy conditions. Impressively, both wormhole models exhibit an adiabatic index greater than 1.34 (Γ>43), indicating their inherent stability. What is more, our study of the anisotropy parameter reveals the attractive nature of these wormhole solutions, a crucial property for their potential traversability. This novel work not only broadens our understanding of modified gravity theories but also highlights the remarkable possibilities of traversable wormholes, opening up new avenues in theoretical physics and in the exploration of exotic spacetime geometries.

Dark matter scattering constraints from observations of stars surrounding Sgr A*

High-resolution infrared data have revealed several young stars in close proximity to Sgr A*. These stars may encounter extremely high dark matter densities. We examine scenarios where dark matter scatters on stellar gas, accumulates in stellar cores, and then annihilates. We study the stars S2, S62, S4711, and S4714 and find three observable effects. First, dark matter interactions can inhibit star formation close to Sgr A*, favoring scenarios where these stars migrate into the Galactic Center. Second, dark matter interactions can delay main sequence evolution, making stars older than they appear. Third, very high dark matter densities can inject enough energy to disrupt main sequence stars, allowing S-star observations to constrain the dark matter density near Sgr A*. Published by the American Physical Society 2024