arXiv subjects

A. V. Ivanchik

Publications and source records attributed to A. V. Ivanchik.

At least 19 recordsLinked to original sources

arXiv2026

Hyperfine transitions in atoms and rotational transitions in molecules of the early Universe as a possible source of CMB distortions

In the near future, measurements are expected to detect the influence of the hyperfine transition in the ground state of the hydrogen atom on the cosmic microwave background (CMB) spectrum. This raises the question of what other substances could produce similar distortions and to what extent. This work presents a systematic analysis of the potential for the most abundant atoms, molecules, and their ions to distort the CMB spectrum. In addition, the wavelength ranges for all the transitions considered in which such distortions might be observed have been calculated. As a result, we conclude that the distortions caused by the most abundant elements are orders of magnitude smaller than those produced by hydrogen.

physics.gen-ph↗

arXiv2026

SRG/eROSITA-SDSS view on the relation between X-ray and UV emission for quasars

Motivated by the idea of using quasars as standardizable candles for cosmology, we examine the relation between X-ray (at 2 keV, $L_{\rm 2keV}$) and ultraviolet (at 2500 Angstrom, $L_{\rm 2500}$) monochromatic luminosities of quasars using a sample of 2414 X-ray sources from the SRG/eROSITA all-sky survey cross-matched with the Sloan Digital Sky Survey data release 16 quasar catalogue (SDSS DR16Q), at redshifts between 0.5 and 2.5. These objects are bright both in X-rays and in the optical, so that the sample is characterized by nearly 100% statistical completeness. We have developed a new method for determining the $L_{\rm 2keV}-L_{\rm 2500}$ relation, which consistently takes into account (i) X-ray and UV flux limited object selection, (ii) X-ray and UV variability of quasars, and (iii) the decreasing space density of quasars with increasing luminosity. Assuming a linear relation between $l_{\rm X}\equiv\log(L_{\rm 2keV}/[{\rm erg\,s^{-1}\,Hz^{-1}}])$ and $l_{\rm UV}\equiv\log(L_{\rm 2500}/[{\rm erg\,s^{-1}\,Hz^{-1}}])$, we find the slope, $γ=0.69\pm0.02$ (hereafter all uncertainties are quoted at the 68% confidence level), and normalization, $l_{\rm X}=26.47\pm0.02$ at $l_{\rm UV}=30.5$, of the $L_{\rm 2keV}$ ($L_{\rm 2500}$) dependence. These values are not substantially different from the results of previous studies. A key novel aspect of our work is allowance for intrinsic scatter (which adds to the dispersion induced by quasar variability and flux measurement uncertainties) of the $L_{\rm 2keV}-L_{\rm 2500}$ relation in both variables, i.e. in X-ray and UV luminosity. The intrinsic X-ray scatter ($σ^2_{\rm intX}=0.063\pm0.005$) strongly dominates over the UV one ($σ^2_{\rm intUV}=0.002^{+0.003}_{-0.002}$). Further studies should seek to explain this behaviour in terms of accretion onto supermassive black holes and orientation of quasars with respect to the observer.

astro-ph.HE↗

arXiv2025

Low-Energy Neutrinos from Primordial Black Holes: A New Possibility for Observing Hawking Radiation

The study of primordial black holes (PBHs) and the Hawking radiation they produce represents a significant step toward understanding the role of these phenomena in the cosmological evolution of the Universe. PBHs could be a component of dark matter, the seeds of supermassive black holes, and sources of Hawking radiation, which, unlike the radiation from other black holes, might be observable. Over the course of the evolution of the Universe from the Big Bang to the present day, PBHs have lost a substantial portion of their mass through neutrino radiation. This occurs because, for black holes with masses $M\lesssim10^{23}\,$g, the radiation of the lightest massive particles - neutrinos - becomes significant alongside the emission of photons. This neutrino radiation eventually dominates the emission process. By the present time ($t_0=13.8$ Gyr), only black holes with masses $\lesssim 10^{15}\,$g have largely evaporated, meaning that the total emission spectrum of PBHs is now dominated by the neutrino component. In this paper, we present new estimates of the neutrino spectra emitted by PBHs of various masses, with a particular focus on low-energy radiation ($E_{kin} \in [0.01 ÷1]\, $eV) for the first time. Our calculations demonstrate that black holes in the mass range $[10^{9}\div10^{11}]\,$g emit neutrinos with intensities that exceed the background fluxes from known astrophysical sources in the low-energy range. In contrast, in the high-energy range, the emission remains below the background level, consistent with observational constraints. These findings open new avenues for the potential detection of PBH radiation and could stimulate advancements in neutrino detection technologies, particularly in the low-energy regime. The observation of neutrinos in this energy range represents one of the few opportunities to confirm the existence of Hawking radiation.

astro-ph.CO↗

arXiv2024

Neutrino at different epochs of the Friedmann Universe

Nowadays, at least two relics of the Big Bang have survived - the cosmological microwave background (CMB) and the cosmological neutrino background (C$ν$B). Being the second most abundant particle in the Universe, the neutrino has a significant impact on its evolution from the Big Bang to the present day. Neutrinos affect the following cosmological processes: the expansion rate of the Universe, its chemical and isotopic composition, the CMB anisotropy and the formation of the large-scale structure of the Universe. Another relic neutrino background is theoretically predicted, it consists of non-equilibrium antineutrinos of Primordial Nucleosynthesis arising as a result of the decays of neutrons and tritium nuclei. Such antineutrinos are an indicator of the baryon asymmetry of the Universe. In addition to experimentally detectable active neutrinos, the existence of sterile neutrinos is theoretically predicted to generate neutrino masses and explain their oscillations. Sterile neutrinos can also solve such cosmological problems as the baryonic asymmetry of the Universe and the nature of dark matter. The recent results of several independent experiments point to the possibility of the existence of a light sterile neutrino. However, the existence of such a neutrino is inconsistent with the predictions of the Standard Cosmological Model. The inclusion of a non-zero lepton asymmetry of the Universe and/or increasing the energy density of active neutrinos can eliminate these contradictions and reconcile the possible existence of sterile neutrinos with Primordial Nucleosynthesis, the CMB anisotropy, and also reduce the H$_0$-tension. In this brief review, we discuss the influence of the physical properties of active and sterile neutrinos on the evolution of the Universe from the Big Bang to the present day.

astro-ph.CO↗

arXiv2024

X-Ray Variability of SDSS Quasars Based on the SRG/eROSITA All-Sky Survey

We examine the long-term (rest-frame time scales from a few months to $\sim 20$ years) X-ray variability of a sample of 2344 X-ray bright quasars from the SDSS DR14Q Catalogue, based on the data of the SRG/eROSITA All-Sky Survey complemented for $\sim 7$% of the sample by archival data from the XMM-Newton Serendipitous Source Catalogue. We characterise variability by a structure function, $SF^2(Δt)$. We confirm the previously known anti-correlation of the X-ray variability amplitude with luminosity. We also study the dependence of X-ray variability on black hole mass, $M_{\rm BH}$, and on an X-ray based proxy of the Eddington ratio, $λ_{\rm X}$. Less massive black holes prove to be more variable for given Eddington ratio and time scale. X-ray variability also grows with decreasing Eddington ratio and becomes particularly strong at $λ_{\rm X}$ of less than a few per cent. We confirm that the X-ray variability amplitude increases with increasing time scale. The $SF^2(Δt)$ dependence can be satisfactorily described by a power law, with the slope ranging from $\sim 0$ to $\sim 0.4$ for different ($M_{\rm BH}$, $λ_{\rm X}$) subsamples (except for the subsample with the lowest black hole mass and lowest Eddington ratio, where it is equal to $1.1\pm 0.4$)

astro-ph.HE↗

arXiv2024

A New Precise Determination of the Primordial Abundance of Deuterium: Measurement in the metal-poor sub-DLA system at z=3.42 towards quasar J1332+0052

The theory of Big Bang nucleosynthesis, coupled with an estimate of the primordial deuterium abundance (D/H)_pr, offers insights into the baryon density of the Universe. Independently, the baryon density can be constrained during a different cosmological era through the analysis of cosmic microwave background (CMB) anisotropy. The comparison of these estimates serves as a rigorous test for the self-consistency of the Standard Cosmological Model and stands as a potent tool in the quest for new physics beyond the Standard Model of Particle Physics. For a meaningful comparison, a clear understanding of the various systematic errors affecting deuterium measurements is crucial. Given the limited number of D/H measurements, each new estimate carries significant weight. This study presents the detection of DI absorption lines in a metal-poor sub-Damped Lyman-alpha system ([O/H]=-1.71+-0.02, logN(HI)=19.304+-0.004) at z_abs=3.42 towards the quasar J1332+0052. Through simultaneous fitting of HI and DI Lyman-series lines, as well as low-ionization metal lines, observed at high spectral resolution and high signal-to-noise using VLT/UVES and Keck/HIRES, we derive log(DI/HI)=-4.622+-0.014, accounting for statistical and systematic uncertainties of 0.008dex and 0.012dex, respectively. Thanks to negligible ionization corrections and minimal deuterium astration at low metallicity, this D/H ratio provides a robust measurement of the primordial deuterium abundance, consistent and competitive with previous works. Incorporating all prior measurements, the best estimate of the primordial deuterium abundance is constrained as: (D/H)_pr=(2.533+-0.024)*10^-5. This represents a 5% improvement in precision over previous studies and reveals a moderate tension with the expectation from the Standard Model (~2.2sig). This discrepancy underscores the importance of further measurements in the pursuit of new physics.

astro-ph.CO↗

arXiv2023

Binomial Line Cox Processes: Statistical Characterization and Applications in Wireless Network Analysis

The current analysis of wireless networks whose transceivers are confined to streets is largely based on Poissonian models, such as Poisson line processes and Poisson line Cox processes. We demonstrate important scenarios where a model with a finite and deterministic number of streets, termed binomial line process, is more accurate. We characterize the statistical properties of the BLP and the corresponding binomial line Cox process and apply them to analyze the performance of a network whose access points are deployed along the streets of a city. Such a deployment scenario will be typical for 5G and future wireless networks. In order to obtain a fine-grained insight into the network performance, we derive the meta distribution of the signal-to-interference and noise ratio. Accordingly, we investigate the mean local delay in transmission and the density of successful transmission. These metrics, respectively, characterize the latency and coverage performance of the network and are key performance indicators of next-generation wireless systems.

cs.IT↗

arXiv2022

Determination of HII region metallicity in the context of estimating the primordial helium abundance

The primordial $^4$He abundance (Y$_p$) is one of the key characteristics of Primordial Nucleosynthesis processes that occurred in the first minutes after the Big Bang. Its value depends on the baryon/photon ratio $η\equiv n_b/n_γ$, and is also sensitive to the relativistic degrees of freedom which affect the expansion rate of the Universe at the radiation-dominated era. The most used method of the determination of Y$_p$ is the study of the metal deficient HII regions located in blue compact dwarf galaxies (BCDs). In this paper, we discuss in detail various methods of the determination of HII region metallicity in the context of Y$_p$ analyses. We show that some procedures used in the methods lead to biases in the metallicity estimates and underestimation of their uncertainties. We propose a modified method for the metallicity determination, as well as an additional criterion for selecting objects. We have selected 69 objects (26 objects with high quality spectra from the HeBCD+NIR database and 43 objects from the SDSS catalog), for which we estimate Y and O/H using the proposed method. We have estimated Y$_p=0.2470\pm0.0020$ which is one of the most accurate estimates obtained up to date. Its comparison with the value Y$_p=0.2470\pm0.0002$ obtained as a result of numerical modelling of Primordial Nucleosynthesis with the value of $Ω_b$ taken from the analysis of the CMB anisotropy (Planck mission), is an important tool for studying the self-consistency of the Standard cosmological model (a possible discrepancy between these estimates could be an indicator of a new physics). The application of the proposed method allows one to more correctly estimate Y$_p$ and the slope $d$Y/$d$(O/H). Further analysis of the data from the SDSS catalog can significantly increase the statistics of objects for the regression analysis, which in turn can refine the Y$_p$ estimate.

astro-ph.CO↗

arXiv2021

Estimation of the CMB temperature from atomic C\,{\sc i} and molecular CO lines in the interstellar medium of early galaxies

The linear increase of the cosmic microwave background (CMB) temperature with cosmological redshift, $T_{\rm CMB} = T_0(1 + z)$, is a prediction of the standard cosmological $Λ$CDM model. There are currently two methods to measure this dependence at redshift $z>0$, and that is equally important to estimate the CMB temperature $T_0$ at the present epoch $z=0$. The first method is based on the Sunyaev-Zeldovich (SZ) effect for a galaxy cluster. aThe second method is based on the analysis of the populations of atomic and molecular energy levels observed in the absorption spectra of quasars. This method allows $T_{\rm CMB}(z)$ to be measured directly. We present new estimates of $T_{\rm CMB}(z_i)$ in the redshift range $1.7\le z_i \le3.3$ based on the analysis of excitation of the CO rotational levels and C\,{\sc i} fine-structure levels in 15 absorption systems. We take into account collisional excitation of CO and C\,{\sc i} with hydrogen atoms and H$_2$ and radiative pumping of C\,{\sc i} by the interstellar ultraviolet radiation. Applying this corrections leads to a systematic decrease in the previously obtained estimates of $T_{\rm CMB}(z_i)$ (for some systems the magnitude of the effect is $\sim$10\%). Combining our measurements with the measurements of $T_{\rm CMB}(z)$ in galaxy clusters we have obtained a constraint on the parameter $β=+0.010\pm0.013$, which characterizes the deviation of the CMB temperature from the standard relation, $T_{\rm CMB} = T_0(1 + z)^{1-β}$, and an independent estimate of the CMB temperature at the present epoch, $T_0 = 2.719\pm0.009$\,K, which agrees well with the estimate from orbital measurements, $T_0 = 2.7255\pm0.0006$\,K. This independent estimate is very important because it was obtained using cosmological data, in contrast to satellite measurements, which are obtained "here" and "now".

astro-ph.CO↗

arXiv2021

A new determination of the primordial helium abundance using the analyses of HII region spectra from SDSS

The precision measurement of the primordial helium abundance $Y_p$ is a powerful probe of the early Universe. The most common way to determine $Y_p$ is analyses of observations of metal-poor \HII regions found in blue compact dwarf galaxies. We present the spectroscopic sample of 100 \HII regions collected from the Sloan Digital Sky Survey. The final analysed sample consists of our sample and HeBCD database from Izotov et al. 2007. We use a self-consistent procedure to determine physical conditions, current helium abundances, and metallicities of the \HII regions. From a regression to zero metallicity, we have obtained $Y_p = 0.2462 \pm 0.0022$ which is one of the most stringent constraints obtained with such methods up to date and is in a good agreement with the Planck result $Y_{\rm p}^{\it {Planck}} = 0.2471 \pm 0.0003$. Using the determined value of $Y_p$ and the primordial deuterium abundance taken from Particle Data Group (Zyla et al. 2020) we put a constraint on the effective number of neutrino species $N_{\rm eff} = 2.95 \pm 0.16$ which is consistent with the Planck one $N_{\rm eff} = 2.99 \pm 0.17$. Further increase of statistics potentially allows us to achieve Planck accuracy, which in turn will become a powerful tool for studying the self-consistency of the Standard Cosmological Model and/or physics beyond.

astro-ph.CO↗

arXiv2021

Influence of radiative pumping on the HD rotational level populations in diffuse molecular clouds of the interstellar medium

We present a theoretical calculation of the influence of ultraviolet radiative pumping on the excitation of the rotational levels of the ground vibrational state for HD molecules under conditions of the cold diffuse interstellar medium (ISM). Two main excitation mechanisms have been taken into account in our analysis: (i) collisions with atoms and molecules and (ii) radiative pumping by the interstellar ultraviolet (UV) radiation field. The calculation of the radiative pumping rate coefficients $Γ_{\rm ij}$ corresponding to Drane's model of the field of interstellar UV radiation, taking into account the self-shielding of HD molecules, is performed. We found that the population of the first HD rotational level ($J = 1$) is determined mainly by radiative pumping rather than by collisions if the thermal gas pressure $p_{\rm th}\le10^4\left(\frac{I_{\rm{UV}}}{1}\right)\,\mbox{K\,cm}^{-3}$ and the column density of HD is lower than $\log N({\rm{HD}})<15$. Under this constraint the populations of rotational levels of HD turns out to be as well a more sensitive indicator of the UV radiation intensity than the fine-structure levels of atomic carbon. We suggest that taking into account radiative pumping of HD rotational levels may be important for the problem of the cooling of primordial gas at high redshift: ultraviolet radiation from first stars can increase the rate of HD cooling of the primordial gas in the early Universe.

astro-ph.GA↗

arXiv2019

X-shooter observations of strong H$_2$-bearing DLAs at high redshift

We present results from spectroscopic observations with X-shooter at the Very Large Telescope of seven H2-bearing DLAs at high redshifts (z$_{\rm abs}\sim 2.5-3$). These DLAs were originally selected from the presence of strong H$_2$ lines directly seen at the DLA redshift in low-resolution, low S/N SDSS spectra. We confirm the detection of molecular hydrogen in all of them. We measure the column densities of HI, H$_2$ in various rotational levels, and metal species, and associated dust extinction. The metallicities, obtained from undepleted species, are in the range logZ=-0.8 to -0.2. We discuss the chemical enrichment in these clouds and compare their properties with that of other molecular-rich systems selected by other means. In particular, we show that three different methods of pre-selection of H$_2$-bearing DLAs in the SDSS have their own biases but complement each other mostly in terms of chemical enrichment. We use the rotational excitation of H$_2$ molecules together with the fine-structure energy levels of neutral carbon to constrain the physical conditions in the gas with the help of numerical modeling as well as analytical expressions for the surface density at which atomic to molecular conversion happens. We find that the H$_2$-bearing medium revealed by the studied DLAs has typical values for the kinetic temperature, hydrogen density, and UV radiation field of, respectively, T$\sim$100K, $n_{\rm H}\sim 100$ cm$^{-3}$, and I$_{\rm UV}$ about twice the intensity of the Draine field. Detailed studies combining different selections should, therefore, bring important clues to understand the HI-H$_2$ transition at high redshift.

astro-ph.GA↗

arXiv2018

Absorption of Photons from Distant Gamma-Ray Sources

Being the largest gravitationally bound structures in the Universe, galaxy clusters are huge reservoirs of photons generated by the bremsstrahlung of a hot cluster gas. We consider the absorption of high-energy photons from distant cosmological gamma-ray sources by the bremsstrahlung of galaxy clusters. The magnitude of this effect is the third in order of smallness after the effects of absorption by the cosmic microwave background and absorption by the extragalactic background light. Our calculations of the effect of absorption by the bremsstrahlung of galaxy clusters have shown that this effect manifests itself in the energy range 1--100 GeV and can be $τ\sim 10^{-5}$.

astro-ph.HE↗

arXiv2017

CO-dark molecular gas at high redshift: very large H$_2$ content and high pressure in a low metallicity damped Lyman-alpha system

We present a detailed analysis of a H$_2$-rich, extremely strong intervening Damped Ly-$α$ Absorption system (DLA) at $z_{\rm abs}=2.786$ towards the quasar J$\,$0843+0221, observed with the Ultraviolet and Visual Echelle Spectrograph on the Very Large Telescope. The total column density of molecular (resp. atomic) hydrogen is $\log N$(H$_2$)=$21.21\pm0.02$ (resp. $\log N$(H$\,$I)=$21.82\pm0.11$), making it to be the first case in quasar absorption lines studies with H$_2$ column density as high as what is seen in $^{13}$CO-selected clouds in the Milky-Way. We find that this system has one of the lowest metallicity detected among H$_2$-bearing DLAs, with $\rm [Zn/H]=-1.52^{+0.08}_{-0.10}$. This can be the reason for the marked differences compared to systems with similar H$_2$ column densities in the local Universe: $(i)$ the kinetic temperature, $T\sim$120~K, derived from the $J=0,1$ H$_2$ rotational levels is at least twice higher than expected; $(ii)$ there is little dust extinction with A$_V < 0.1$; $(iii)$ no CO molecules are detected, putting a constraint on the $X_{\rm CO}$ factor $X_{\rm CO}> 2\times 10^{23} $ cm$^{-2}$/(km/s\,K), in the very low metallicity gas. Low CO and high H$_2$ contents indicate that this system represents "CO-dark/faint" gas. We investigate the physical conditions in the H$_2$-bearing gas using the fine-structure levels of C$\,$I, C$\,$II, Si$\,$II and the rotational levels of HD and H$_2$. We find the number density to be about $n \sim 260-380\,$cm$^{-3}$, implying a high thermal pressure of $(3-5) \times 10^4\,$cm$^{-3}\,$K. We further identify a trend of increasing pressure with increasing total hydrogen column density. This independently supports the suggestion that extremely strong DLAs (with $\log\,$N(H) $\sim 22$) probe high-z galaxies at low impact parameters.

astro-ph.GA↗

arXiv2016

Estimation of physical conditions in the cold phase of the ISM in the sub-DLA system at z = 2.06 in the spectrum of the quasar J2123-0050

An independent analysis of the molecular hydrogen absorption system at z = 2.059 in the spectrum of the quasar J2123-0050 is presented. The H_2 system consists of two components (A and B) with column densities log N^A(H_2) = 17.94+/-0.01 and log N^B(H_2) = 15.16+/-0.02. The spectrum exhibits the lines of HD molecules (log N^A(HD) = 13.87+/-0.06) and the neutral species C I and Cl I associated with the H_2 absorption system. For the molecular hydrogen lines near the quasar's Ly_beta and O VI emission lines, we detect a nonzero residual flux, ~3% of the total flux, caused by the effect of partial coverage of the quasar's broad-line region by an H_2 cloud. The uniqueness of the system being investigated is manifested in a high abundance of the neutral species H_2 and C I at the lowest H I column density, log N(H I) = 19.18+/-0.15, among the high redshift systems. The N(HD)/2N(H_2) ratio for component A has turned out to be also unusually high, (4.26+/-0.60)x10^{-5}. We have investigated the physical conditions in components A and B. Component A represents the optically thick case; the gas has a low number density (n~30 cm^{-3}) and a temperature T~140 K. In component B, the medium is optically thin with n<100 cm^{-3} and T<100 K. The ultraviolet (UV) background intensity in the clouds exceeds the mean intensity in our Galaxy by almost an order of magnitude. A high gas ionization fraction, n(H+)/n(H)~10^{-2}, which can be the result of partial shielding of the system from hard UV radiation, is needed to describe the high HD and C I column densities. Using our simulations with the PDR Meudon code, we can reconstruct the observed column densities of the species within the model with a constant density n(H)=40 cm^{-3}. A high H_2 formation rate (higher than the mean Galactic value by a factor of 10-40) and high gas ionization fraction and UV background intensity are needed in this case.

astro-ph.GA↗

arXiv2015

The primordial deuterium abundance: subDLA system at $z_{\rm abs}=2.437$ towards the QSO J1444+2919

We report a new detection of neutral deuterium in the sub Damped Lyman Alpha system with low metallicity [O/H]\,=\,$-2.042 \pm 0.005$ at $z_{\rm abs}=2.437$ towards QSO~J\,1444$+$2919. The hydrogen column density in this system is log$N$(H\,{\sc i})~$=19.983\pm0.010$ and the measured value of deuterium abundance is log(D/H)~$=-4.706\pm0.007_{\rm stat}\pm0.067_{\rm syst}$. This system meets the set of strict selection criteria stated recently by Cooke et al. and, therefore, widens the {\it Precision Sample} of D/H. However, possible underestimation of systematic errors can bring bias into the mean D/H value (especially if use a weighted mean). Hence, it might be reasonable to relax these selection criteria and, thus, increase the number of acceptable absorption systems with measured D/H values. In addition, an unweighted mean value might be more appropriate to describe the primordial deuterium abundance. The unweighted mean value of the whole D/H data sample available to date (15 measurements) gives a conservative value of the primordial deuterium abundance (D/H)$_{\rm p}=(2.55\pm 0.19)\times10^{-5}$ which is in good agreement with the prediction of analysis of the cosmic microwave background radiation for the standard Big Bang nucleosynthesis. By means of the derived (D/H)$_{\rm p}$ value the baryon density of the Universe $Ω_{\rm b}h^2=0.0222\pm0.0013$ and the baryon-to-photon ratio $η_{10} = 6.09\pm 0.36$ have been deduced. These values have confident intervals which are less stringent than that obtained for the {\it Precision Sample} and, thus, leave a broader window for new physics. The latter is particularly important in the light of the lithium problem.

astro-ph.GA↗

arXiv2015

Spectral distortions of the CMB dipole

We consider the distortions of the cosmic microwave background (CMB) dipole anisotropy related to the primordial recombination radiation (PRR) and primordial $y$- and $μ$-distortions. The signals arise due to our motion relative to the CMB restframe and appear as a frequency-dependent distortion of the CMB temperature dipole. To leading order, the expected relative distortion of the CMB dipole does not depend on the particular observation directions and reaches the level of $10^{-6}$ for the PRR- and $μ$-distortions and $10^{-5}$ for the $y$-distortion in the frequency range 1 -- 700 GHz. The temperature differences arising from the dipole anisotropy of the relic CMB distortions depend on the observation directions. For mutually opposite directions, collinear to the CMB dipole axis, the temperature differences because of the PRR- and $μ$-dipole anisotropy attain values $ΔT\simeq 10\,$nK in the considered range. The temperature difference arising from the $y$-dipole anisotropy may reach values of up to $1\,μ$K. The key features of the considered effect are as follow: (i) an observation of the effect does not require absolute calibration; (ii) patches of sky with minimal foreground contamination can be chosen. Future measurements of the CMB dipole distortion thus will provide an alternative method for direct detection of the PRR-, $y$-, and $μ$-distortions. The $y$-distortion dipole may be detectable with PIXIE at a few standard deviations.

astro-ph.CO↗

arXiv2015

Variation of the baryon-to-photon ratio due to decay of dark matter particles

The influence of dark matter particle decay on the baryon-to-photon ratio has been studied for different cosmological epochs. We consider different parameter values of dark matter particles such as mass, lifetime, the relative fraction of dark matter particles. It is shown that the modern value of the dark matter density $Ω_{\rm CDM}=0.26$ is enough to lead to variation of the baryon-to-photon ratio up to $Δη/ η\sim 0.01 ÷1$ for decays of the particles with masses 10 GeV $÷$ 1 TeV. However, such processes can also be accompanied by emergence of an excessive gamma ray flux. The observational data on the diffuse gamma ray background are used to making constraints on the dark matter decay models and on the maximum possible variation of the baryon-to-photon ratio $Δη/η\lesssim10^{-5}$. Detection of such variation of the baryon density in future cosmological experiments can serve as a powerful means of studying properties of dark matter particles.

astro-ph.CO↗