Dark Matter Component Research Articles

Sun heated MeV-scale dark matter and the XENON1T electron recoil excess

The XENON1T collaboration reported an excess of the low-energy electron recoil events between 1 and 7 keV. We explore the possibility to explain such an anomaly by the MeV-scale dark matter (DM) heated by the interior of the Sun due to the same DM-electron interaction as in the detector. The kinetic energies of heated DM particles can reach a few keV, and can potentially account for the excess signals detected by XENON1T. We study different form factors of the DM-electron interactions, F(q) ∝ qi with q being the momentum exchange and i = 0, 1, 2, and find that for all these cases the inclusion of the Sun-heated DM component improves the fit to the XENON1T data. The inferred DM-electron scattering cross section (at q = αme where α is the fine structure constant and me is electron mass) is from ∼ 10−38 cm2 (for i = 0) to ∼ 10−42 cm2 (for i = 2). We also derive constraints on the DM-electron cross sections for these form factors, which are stronger than previous results with similar assumptions. We emphasize that the Sun-heated DM scenario relies on the minimum assumption on DM models, which serves as a general explanation of the XENON1T anomaly via DM-electron interaction. The spectrum of the Sun-heated DM is typically soft comparing to other boosted DM, so the small recoil events are expected to be abundant in this scenario. More sensitive direct detection experiments with lower thresholds can possibly distinguish this scenario with other boosted DM models or solar axion models.

КОМПОНЕНТ ТЕМНОЇ МАТЕРІЇ І СОНЦЕ

Some consequences from the hypothesis of the origin of particles of one of the components of dark matter are presented. The reason for the hypothesis was the observational data of stellar radiation, considered through the prism of the relationship of all phenomena in Nature and the law of conservation of energy. It is argued that a part of the stellar electromagnetic radiation, which does not participate in the interaction with baryonic matter, will not wander forever in space. This radiation will interact with a subtle level of matter, continuously giving it its energy, shifting to the microwave region. In this frequency region, two quanta of close energies can form a neutral boson of spin 0, or spin 2, on opposite “courses”. Based on the observed spectrum of cosmic microwave radiation, it is assumed that these Bose particles have a continuous mass spectrum. These light nonrelativistic bosons are precisely the component of the thin medium that interacts with stellar radiation, taking energy from it. Bose particles participate in gravitational interactions. This means that in addition to the distribution of dark matter around galaxies, an increased concentration of particles in the form of large clouds can be observed in it. If an internal shock wave appears in such a cloud, located far from galactic streams of baryon particles, it will destroy the particles of the cloud, creating “strange radio circles” visible exclusively in the radio range. The gravitational interaction causes dark particles to drift towards large clusters of visible matter. The process of their drift to massive objects will be accompanied by resistance from the outgoing stellar radiation. Therefore, near the surface of a burning star, these particles themselves will resist the outgoing radiation, shifting it towards longer wavelengths. The plasma ejected by the star, with sufficient energy of its particles, is capable of destroying the particles of the dark component, creating pairs of photons and providing itself with "seed" quanta for bremsstrahlung. Free quanta remaining from the decay of dark particles will give microwave radiation. Therefore, burning stars should exhibit a redshift in the emission spectra and microwave radiation. Taking a certain model in the distribution of the dark component of matter near the Sun, it is possible to predict the nature of the redshift in the spectra of its radiation as the observation point moves along the solar disk from its center to the limb. A similar conclusion is made regarding the intensity of microwave radiation near the surface of the star. The galactic movement of the Sun should lead to some temperature effects associated with a denser counter flow of dark particles to the corresponding area of the solar surface. Knowing the direction of motion of the Sun in the Galaxy, based on the results of the temperature deviation on the surface of the star, one can determine the local speed and direction of movement of the cloud of the dark component of matter.

An analytical model for the Maxwell radiation field in an axially symmetric galaxy

Abstract The Maxwell radiation field is an essential physical characteristic of a galaxy. Here, an analytical model is built to simulate that field in an axisymmetric galaxy. This analytical model is based on an explicit representation for axisymmetric source-free Maxwell fields. In a previous work, the general applicability of this representation has been proved. The model is adjusted by fitting to it the sum of spherical radiations emitted by the composing “stars.” The huge ratio distance/wavelength needs to implement a numerical precision better than the quadruple precision. The model passes a validation test based on a spherically symmetric solution. The results for a set of “stars” representative of a disk galaxy indicate that the field is highest near the disk axis, and there the axial component of E {\bf{E}} dominates over the radial one. This work will allow us in the future to check if the interaction energy predicted by an alternative theory of gravitation might be a component of dark matter.

Non-vacuum relativistic extensions of MOND using metric theories of gravity with curvature–matter couplings and their applications to the accelerated expansion of the universe without dark components

We discuss the advantages of using metric theories of gravity with curvature–matter couplings in order to construct a relativistic generalization of the simplest version of Modified Newtonian Dynamics (MOND), where Tully–Fisher scalings are valid for a wide variety of astrophysical objects. We show that these proposals are valid at the weakest perturbation order for trajectories of massive and massless particles (photons). These constructions can be divided into local and non-local metric theories of gravity with curvature–matter couplings. Using the simplest two local constructions in an FLRW universe for dust, we show that there is no need for the introduction of dark matter and dark energy components into the Friedmann equation in order to account for type Ia supernovae observations of an accelerated universe at the present epoch.

The stellar halos of ETGs in the IllustrisTNG simulations

Stellar halos in early-type galaxies (ETGs) are shaped by their accretion and merger histories. We use a sample of 1114 ETGs in the TNG100 simulation of the IllustrisTNG suite with stellar masses 1010.3 ≤ M*/M⊙ ≤ 1012, selected at z = 0 within the range of the g − r colour and λ-ellipticity diagram populated by observed ETGs. We study how the rotational support and intrinsic shapes of the stellar halos depend on the fraction of stars accreted, both overall and separately, by major, minor, and mini mergers. Accretion histories in TNG100 ETGs as well as the final radial distributions of ex-situ stars fexsitu(R) relative to in-situ (“accretion classes”) strongly correlate with stellar mass. Low-mass galaxies have characteristic peaked rotation profiles and near-oblate shapes with rounder halos that are completely driven by the in-situ stars. At high fexsitu, major mergers decrease the in-situ peak in rotation velocity, flatten the V*/σ*(R) profiles, and increase the triaxiality of the stellar halos. Kinematic transition radii do not trace the transition between in-situ- and ex-situ-dominated regions, but for systems with M* > 1010.6 M⊙ the local rotational support of the stellar halos decreases with the local ex-situ fraction fexsitu(R) at fixed M*, and their triaxiality increases with fexsitu(R). These correlations between rotational support, intrinsic shapes, and local fexsitu are followed by fast and slow rotators alike with a continuous and overlapping sequence of properties, but slow rotators are concentrated at the high-fexsitu end dominated by dry major mergers. We find that in ∼20% of high-mass ETGs, the central regions are dominated by stars from a high-redshift compact progenitor. Merger events dynamically couple stars and dark matter: in high-mass galaxies and at large radii where fexsitu ≳ 0.5, both components tend to have similar intrinsic shapes and rotational support, and nearly aligned principal axes and spin directions. Based on these results we suggest that extended photometry and kinematics of massive ETGs (M* > 1010.6 M⊙) can be used to estimate the local fraction of ex-situ stars, and to approximate the intrinsic shapes and rotational support of the co-spatial dark matter component.

Unifying inflation with early and late dark energy epochs in axion F(R) gravity

We provide a theoretical model of $F(R)$ gravity in which it is possible to describe in a unified way inflation, an early and a late dark energy era, in the presence of a light axion particle which plays the role of the dark matter component of the Universe. Particularly, the early-time phenomenology is dominated by an $R^2$ term, while the presence of the other terms $f(R)$ ensure the occurrence of the early and late-time dark energy eras. The inflationary phenomenology is compatible with the Planck 2018 data for inflation, while the late-time dark energy era is compatible with the Planck 2018 constraints on the cosmological parameters. Also, the model exhibits an early dark energy era, at $z\sim 2.5$ approximately, followed by a deceleration era, which starts at approximately $z\sim 1.5$, which in turn is followed by a late-time dark energy era for redshifts $z\sim 0.5$, which lasts for approximately 5 billion years up to present time. A notable feature of our model is that the dark energy era is free from dark energy oscillations, at least in the redshift interval $z=[0,10]$. In addition, we also discuss several features related to observational data at $z\sim 2.34$, at which redshift intricate observational data exist in the literature. Moreover, the numerical code for the dark energy phenomenology, written in Python 3, is presented in the end of the article. Finally, the model has another interesting characteristic, a sudden jump of the value of the Hubble rate in the redshift interval $z\sim [2,2.6]$ where its value suddenly increases and then decreases until $z\sim 0$.

Observing primordial magnetic fields through Dark Matter

Primordial magnetic fields are often thought to be the early Universe seeds that have bloomed into what we observe today as galactic and extra-galactic magnetic fields. Owing to their minuscule strength, primordial magnetic fields are very hard to detect in cosmological and astrophysical observations. We show how this changes if a part of neutral Dark Matter has a magnetic susceptibility. In this way, by studying Dark Matter one can obtain information about the properties of primordial magnetic fields, even if the latter have a comoving amplitude B0 ≲ 0.01 nG. In our model Dark Matter is a stable singlet scalar χ, which interacts with electromagnetism through the Rayleigh operator as χ2FμνFμν/Λ2. For primordial magnetic fields present in the early Universe this operator forces the Z2-symmetry of the model to be spontaneously broken. Later, when the primordial magnetic field redshifts below a critical value, the symmetry is restored through an “inverse phase transition”. At that point the field χ begins to oscillate and acts as a “magnetomorphic” Dark Matter component, inheriting the properties of the primordial magnetic field space distribution. In particular, for a nearly flat spectrum of magnetic field fluctuations, the scalar χ carries a statistically anisotropic isocurvature mode. We discuss the parameter space of the model and consider the possibility that the bulk of the Dark Matter is composed of the same particles χ produced via the freeze-in mechanism.

An EAGLE view of the missing baryons

Context. A significant fraction of the predicted baryons remain undetected in the local Universe. We adopted the common assumption that a large fraction of the missing baryons correspond to the hot (log T(K) = 5.5–7) phase of the warm-hot intergalactic medium (WHIM). We base our missing baryons search on the scenario whereby the WHIM has been heated up via accretion shocks and galactic outflows, and it is concentrated towards the filaments of the cosmic web. Aims. Our aim is to improve the observational search for the poorly detected hot WHIM. Methods. We detected the filamentary structure within the EAGLE hydrodynamical simulation by applying the Bisous formalism to the galaxy distribution. To test the reliability of our results, we used the MMF/NEXUS+ classification of the large-scale environment of the dark matter component in EAGLE. We then studied the spatio-thermal distribution of the hot baryons within the extracted filaments. Results. While the filaments occupy only ≈5% of the full simulation volume, the diffuse hot intergalactic medium in filaments amounts to ≈23%−25% of the total baryon budget, or ≈79%−87% of all the hot WHIM. The optimal filament sample, with a missing baryon mass fraction of ≈82%, is obtained by selecting Bisous filaments with a high galaxy luminosity density. For these filaments, we derived analytic formulae for the radial gas density and temperature profiles, consistent with recent Planck Sunyaev-Zeldovich and cosmic microwave background lensing observations within the central r ≈ 1 Mpc. Conclusions. Results from the EAGLE simulation suggest that the missing baryons are strongly concentrated towards the filament axes. Since the filament finding methods used here are applicable to galaxy surveys, a large fraction of the missing baryons can be localised by focusing the observational efforts on the central ∼1 Mpc regions of the filaments. To optimise the observational signal, it is beneficial to focus on the filaments with the highest galaxy luminosity densities detected in the optical data.

Impact of loop-induced processes on the boosted dark matter interpretation of the XENON1T excess

We consider the boosted dark matter solution of the XENON1T excess to constrain the framework through loop-generated processes. The interaction of the boosted dark matter component, which sources the signal, effectively couples the cold dark matter background to the electrons, making it potentially visible in the electron recoil searches. Similarly, once the radiative corrections due to the Standard Model are taken into account, dark matter also scatters on quarks and becomes observable in nuclear recoil measurements. By analysing these processes in a class of effective models built on vector and scalar couplings, we find that the current direct detection constraints exclude the upper mass range selected by the anomaly, especially if the boosted component is generated through dark matter annihilation.

Galactic rotation curve and dark matter according to gravitomagnetism

Historically, the existence of dark matter has been postulated to resolve discrepancies between astrophysical observations and accepted theories of gravity. In particular, the measured rotation curve of galaxies provided much experimental support to the dark matter concept. However, most theories used to explain the rotation curve have been restricted to the Newtonian potential framework, disregarding the general relativistic corrections associated with mass currents. In this paper it is shown that the gravitomagnetic field produced by the currents modifies the galactic rotation curve, notably at large distances. The coupling between the Newtonian potential and the gravitomagnetic flux function results in a nonlinear differential equation that relates the rotation velocity to the mass density. The solution of this equation reproduces the galactic rotation curve without recourse to obscure dark matter components, as exemplified by three characteristic cases. A bi-dimensional model is developed that allows to estimate the total mass, the central mass density, and the overall shape of the galaxies, while fitting the measured luminosity and rotation curves. The effects attributed to dark matter can be simply explained by the gravitomagnetic field produced by the mass currents.

Weighing the Galactic disk in sub-regions of the solar neighbourhood using Gaia DR2

Aims. We infer the gravitational potential of the Galactic disk by analysing the phase-space densities of 120 stellar samples in 40 spatially separate sub-regions of the solar neighbourhood, using Gaia’s second data release (DR2), in order to quantify spatially dependent systematic effects that bias this type of measurement. Methods. The gravitational potential was inferred under the assumption of a steady state in the framework of a Bayesian hierarchical model. We performed a joint fit of our stellar tracers’ three-dimensional velocity distribution, while fully accounting for the astrometric uncertainties of all stars as well as dust extinction, and we also masked angular areas of known open clusters. The inferred gravitational potential is compared, post-inference, to a model for the baryonic matter and halo dark matter components. Results. We see an unexpected but clear trend for all 40 spatially separate sub-regions: Compared to the potential derived from the baryonic model, the inferred gravitational potential is significantly steeper close to the Galactic mid-plane (≲60 pc), but flattens such that the two agree well at greater distances (∼400 pc). The inferred potential implies a total matter density distribution that is highly concentrated to the Galactic mid-plane and decays quickly with height. We see a dependence on the Galactic radius that is consistent with a disk scale length of a few kiloparsecs. Apart from this, there are discrepancies between stellar samples, implying spatially dependent systematic effects which are, at least in part, explained by substructures in the phase-space distributions. Conclusions. In terms of the inferred matter density distribution, the very low matter density that is inferred at greater heights (≳300 pc) is inconsistent with the observed scale height and matter distribution of the stellar disk, which cannot be explained by a misunderstood density of cold gas or other hidden mass. Our interpretation is that these results must be biased by a time-varying phase-space structure, possibly a breathing mode, that is large enough to affect all stellar samples in the same manner.

Dark matter models for the 511 keV galactic line predict keV electron recoils on Earth

We propose models of Dark Matter that account for the 511 keV photon emission from the Galactic Centre, compatibly with experimental constraints and theoretical consistency, and where the relic abundance is achieved via p-wave annihilations or, in inelastic models, via co-annihilations. Due to the Dark Matter component that is inevitably upscattered by the Sun, these models generically predict keV electron recoils at detectors on Earth, and could naturally explain the excess recently reported by the XENON1T collaboration. The very small number of free parameters make these ideas testable by detectors like XENONnT and Panda-X, by accelerators like NA64 and LDMX, and by cosmological surveys like the Simons observatory and CMB-S4. As a byproduct of our study, we recast NA64 limits on invisibly decaying dark photons to other particles.

On the origin of the gamma-ray emission from Omega Centauri: millisecond pulsars and dark matter annihilation

We explore two possible scenarios to explain the observed γ-ray emission associated with the atypical globular cluster ω-Centauri: emission from millisecond pulsars (MSP) and dark matter (DM) annihilation. In the first case we predict the total number of MSPs in the globular cluster (n=45+22−16) using a new Bayesian method that combines the observational uncertainty in γ-ray counts with the intrinsic variation in individual pulsar luminosities. A DM interpretation is motivated by the possibility of ω-Centauri being the remnant core of an ancient dwarf galaxy hosting a surviving DM component. At least two annihilation channels, light quarks and muons, can plausibly produce the observed γ-ray spectrum. We are able to constrain the DM particle mass despite substantial uncertainties in the shape of the density profile (10 GeV ≲ mχ ≲ 30 GeV for annihilation into light quarks and 5 GeV ≲ mχ ≲ 9 GeV for annihilation into muons). We translate upper limits on ω-Centauri's remnant dark matter content into lower limits on the annihilation cross section (⟨ σ v⟩ ≳ 10−29 cm3 s −1 and ⟨ σ v⟩ ≳ 10−28 cm3 s −1 for quarks and muons respectively), taking into account the spatial extension of the DM halo. Moreover, there is a relatively small range of DM density profiles which are consistent with ω-Centauri's kinematics and stellar mass and can explain its γ-ray spectrum while simultaneously evading CMB constraints on dark matter annihilation. Further analysis of ω-Centauri's internal kinematics, and/or additional information on the resident MSP population will yield much stronger constraints and shed light about the origin of this otherwise mysterious γ-ray source.

Current bounds and future prospects of light neutralino dark matter in the NMSSM

Unlike its minimal counterpart, the Next to Minimal supersymmetric Standard Model (NMSSM) allows the possibility that the lightest neutralino could have a mass as small as $\sim 1 {\rm GeV}$ while still providing a significant component of relic dark matter (DM). Such a neutralino can provide an invisible decay mode to the Higgs as well. Further, the observed SM-like Higgs boson ($H_{125}$) could also have an invisible branching fraction as high as $\sim 19\%$. Led by these facts, we first delineate the region of parameter space of the NMSSM with a light neutralino ($M_{{\tilde{\chi}}_{1}^{0}} < 62.5 {\rm GeV}$) that yields a thermal neutralino relic density smaller than the measured relic density of cold dark matter, and is also compatible with constraints from collider searches, searches for dark matter, and from flavor physics. We then examine the prospects for probing the NMSSM with a light neutralino via direct DM detection searches, via invisible Higgs boson width experiments at future $e^+e^-$ colliders, via searches for a light singlet Higgs boson in $2b2\mu$, $2b2\tau$ and $2\mu2\tau$ channels and via pair production of winos or doublet higgsinos at the high luminosity LHC and its proposed energy upgrade. For this last-mentioned electroweakino search, we perform a detailed analysis to map out the projected reach in the $3l+{\rm E{\!\!\!/}_T}$ channel, assuming that chargino decays to $W {\tilde{\chi}}_{1}^{0}$ and the neutralino(s) decay to $Z$ or $H_{125}$ + ${\tilde{\chi}}_{1}^{0}$. We find that the HL-LHC can discover SUSY in just part of the parameter space in each of these channels, which together can probe almost the entire parameter space. The HE-LHC probes essentially the entire region with higgsinos (winos) lighter than 1 TeV (2 TeV) independently of how the neutralinos decay, and leads to significantly larger signal rates.

Extending Friedmann Equations Using Fractional Derivatives Using a Last Step Modification Technique: The Case of a Matter Dominated Accelerated Expanding Universe

We present a toy model for extending the Friedmann equations of relativistic cosmology using fractional derivatives. We do this by replacing the integer derivatives, in a few well-known cosmological results with fractional derivatives leaving their order as a free parameter. All this with the intention to explain the current observed acceleration of the Universe. We apply the Last Step Modification technique of fractional calculus to construct some useful fractional equations of cosmology. The fits of the unknown fractional derivative order and the fractional cosmographic parameters to SN Ia data shows that this simple construction can explain the current accelerated expansion of the Universe without the use of a dark energy component with a MOND-like behaviour using Milgrom’s acceleration constant which sheds light into to the non-necessity of a dark matter component as well.

Scalar field propagation in braneworld black hole scenario obtained from Nash theorem

We determine the scalar field evolution of a braneworld localized black hole with both dark matter and dark energy components, obtained within a dynamical and continuous embedding formalism by use of Nash’s theorem. We further extract the associated quasinormal modes for both de Sitter–Schwarzschild-Dark matter and anti-de Sitter–Schwarzschild-Dark matter solutions, for the different causal structures (one, two or three horizon spacetimes) given by the space of parameters. By comparison with standard solutions within stand alone general relativity, we conclude with comments on possible observable astrophysical differences via quasinormal spectra, and remark on the interpretations of previous AdS/CFT correspondence scenarios.

Analysis of Bianchi Type V Holographic Dark Energy Models in General Relativity and Lyra’s Geometry

In this paper, we analyze anisotropic and homogeneous Bianchi type V spacetime in the presence of dark matter and holographic dark energy model components in the framework of general relativity and Lyra’s geometry. The solutions of differential equation fields have been obtained by considering two specific cases, namely, the expansion scalar θ in the model is proportional to the shear scalar σ and the average scale factor taken as hybrid expansion form. The solutions for field equations are obtained in general relativity and Lyra’s geometry. The energy density of dark matter in both natures was obtained and compared so that the energy density of dark matter in general relativity is slightly different from the energy density of dark matter in Lyra’s geometry. A similar behavior occurred in case of pressure and EoS parameter of holographic dark energy model in respective frameworks. Also, it is concluded that the physical parameters such as the average Hubble parameter, spatial volume, anisotropy parameter, expansion scalar, and shear scalar are the same in both frameworks. Moreover, it is observed that the gauge function β t is a decreasing function of cosmic time in Lyra’s geometry, and for late times, the gauge function β t converges to zero and Lyra’s geometry reduces to general relativity in all respects. Finally, we conclude that our models are a close resemblance to the Λ CDM cosmological model in late times and consistent with the recent observations of cosmological data.

Searching for light in the darkness: Bounds on ALP dark matter with the optical MUSE-faint survey

We use MUSE spectroscopic observations of the dwarf spheroidal galaxy Leo T between 470 and 935 nm to search for radiative decays of axion like particles (ALPs). Under the assumption that ALPs constitute the dark matter component of the Leo T halo, we derive bounds on the effective ALP-two-photon coupling. We improve existing limits by more than one order of magnitude in the ALP mass range 2.7-5.3 eV.

Search for Gravitational Waves from High-Mass-Ratio Compact-Binary Mergers of Stellar Mass and Subsolar Mass Black Holes.

We present the first search for gravitational waves from the coalescence of stellar mass and subsolar mass black holes with masses between 20-100 M_{⊙} and 0.01-1 M_{⊙}(10-10^{3} M_{J}), respectively. The observation of a single subsolar mass black hole would establish the existence of primordial black holes and a possible component of dark matter. We search the ∼164 day of public LIGO data from 2015-2017 when LIGO-Hanford and LIGO-Livingston were simultaneously observing. We find no significant candidate gravitational-wave signals. Using this nondetection, we place a 90% upper limit on the rate of 30-0.01 M_{⊙} and 30-0.1 M_{⊙} mergers at <1.2×10^{6} and <1.6×10^{4} Gpc^{-3} yr^{-1}, respectively. If we consider binary formation through direct gravitational-wave braking, this kind of merger would be exceedingly rare if only the lighter black hole were primordial in origin (<10^{-4} Gpc^{-3} yr^{-1}). If both black holes are primordial in origin, we constrain the contribution of 1(0.1)M_{⊙} black holes to dark matter to <0.3(3)%.

Cosmological Advection Flows in the Presence of Primordial Black Holes as Dark Matter and Formation of First Sources.

In the inflation-based cosmology the dark matter (DM) density component starts moving with respect to the universal expansion at z_{eq}∼3200 while baryons remain frozen until z_{rec}∼1100. It has been suggested that in this case postlinear corrections to the evolution of small fluctuations would result, for the standard Λ-dominated cold DM (CDM) model, in delayed formation of early objects as supersonic advection flows develop after recombination, so baryons are not immediately captured by the DM gravity on small scales. We develop the hydrodynamical description of such two-component advection and show that, in the supersonic regime, the advection within irrotational fluids is governed by the gradient of the difference of the kinetic energies of the two (DM and baryonic here) components. We then apply this formalism to the case where DM is made up of LIGO-type black holes (BHs) and show that there the advection process on scales relevant for early structure collapse will differ significantly from the earlier discussed (CDM) case because of the additional granulation component to the density field produced during inflation. The advection here will lead efficiently to the common motion of the DM and baryon components on scales relevant for collapse and formation of first luminous sources. This leads to early collapse, making it easier to explain the existence of supermassive BHs observed in quasars at high z>7. The resultant net advection rate reaches minimum around ≲10^{9} M_{⊙} and subsequently rises to a secondary maximum near the typical mass of ∼10^{12} M_{⊙}, which may be an important consideration for formation of galaxies at z≲(a few).