arXiv subjects

V. Dubrovich

Publications and source records attributed to V. Dubrovich.

8 recordsLinked to original sources

arXiv2022

Finite time effects in single and double Compton scattering

The process of Compton scattering by a free electron with subsequent reemission of one or two photons is considered in the assumption of finite interaction time. The corresponding cross sections are obtained in the framework of relativistic quantum electrodynamics using a modified form of fermion propagator with complex transmitted momentum. It is shown that finite time effects can be observable at sufficiently low energies of scattered photons. The proposed method also regularizes arising infrared divergence in the cross section of the double Compton effect. Possible experimental verification of considered theoretical approach is discussed.

physics.atom-ph↗

arXiv2021

Some features of the direct and inverse double Compton effect as applied to astrophysics

In the present paper, we consider the process of inverse double Compton (IDC) scattering in the context of astrophysical applications. It is assumed that the two hard X-ray photons emitted from an astrophysical source are scattered on a free electron and converted into a single soft photon of optical range. Using QED S-matrix formalism for the derivation of a cross-section of direct double Compton (DDC) and assuming detailed balance conditions we give an analytical expression for the cross-section of the IDC process. It is shown that at fixed energies of incident photons the inverse cross-section has no infra-red divergences and its behavior is completely defined by the spectral characteristics of the photon source itself, in particular, by the finite interaction time of radiation with an electron. Thus, even for the direct process, the problem of resolving infrared divergence actually refers to a real physical source of radiation in which photons are never actually plane waves. As a result the physical frequency profile of the scattered radiation for direct as well as inverse double Compton processes is a function of both the intensity and line shape of the incident photon field.

hep-ph↗

arXiv2019

On the possibility of observable signatures of $ μp $ and $ (μ^4\mathrm{He})^{+} $ lines on the spectra of astrophysical sources

We examine the processes of the luminescence in subordinate lines of muonic hydrogen $ μp $ and muonic helium ion $ (μ^4\mathrm{He})^{+} $ in the presence of background source of X-ray emission. It is supposed that a certain amount of muonic atoms existing in the vicinity of astrophysical source reemits absorbed radiation in the subordinate lines. The intensity of luminescence of such a process is proportional to the quantum yield which was calculated for different pumping channels and different models of spectra. It is shown that the luminescent lines of muonic hydrogen and muonic helium ion can be very noticeable in the spectrum of background source.

physics.atom-ph↗

arXiv2018

Local burst model of CMB temperature fluctuations: luminescence in lines of primary para- and orthohelium

We have considered the formation of the luminescent subordinate HeI lines by the absorption of continuum radiation from a source in the lines of the main HeI series in the expanding Universe. It is suggested that at some moment of time, corresponding to the redshift $z_{0}$, a burst of superequilibrium blackbody radiation with a temperature $ T+ΔT $ occurs. This radiation is partially absorbed at different $z <z_{0}$ in the lines of the main HeI series and then converted into the radiation of subordinate lines. If $ ν_{ij} $ is the laboratory frequency of the transition of some subordinate line originating at some $z$, then in the present time its frequency will be $ ν=ν_{ij}/(1+z) $. For different $z$ (and, consequently, for different $ ν$), the quantum yield for the subordinate lines of para- and orthohelium - the number of photons emitted in the subordinate line, per one initial excited atom and line profiles are calculated. Different pumping channels were considered. Spatial and angular distributions of radiation intensity of luminescent lines for the spherically symmetric radiation sources are presented. It is shown that for sufficiently large $ ΔT/T $, the luminescent lines can be very noticeable in the spectrum of blackbody background radiation.

physics.atom-ph↗

arXiv2011

A search for HeH+ and CH in a high-redshift QSO

We performed a search for the HeH+ J=1-0 line (ν_{rest} = 2010.183873 GHz) and simultaneously for the CH ^2Π_{3/2}(F_2)J=3/2 - ^2Π_{1/2}(F_2)J=1/2 lines (ν_{rest}\approx 2006.8 and 2010.8 GHz) toward one of the highest-redshift quasars known, SDSS J114816.64+525150.3 (z= 6.4189). No clearly visible line was detected after obtaining an rms noise level of ~ 0.4 mK (~ 3 mJy) in 16 MHz (18 km s^{-1}) channels. At a level of 2.9sigma, however, there is a tentative emission feature shifted by about 100 km s^{-1} from the expected frequency of the HeH+ line. This shift is well within the width of the line profiles for CO and C+. The putative feature is about four times narrower than the previously detected CO and C+ lines. The difference in velocities as well as in the line widths could be explained by quite different conditions required for formation and excitation of HeH+ with respect to CO and C+. The HeH+ emission, if real, could probably arise in the dense ionized gas of this QSO. The velocity integrated flux in this tentative feature is 0.62 +/- 0.21 Jy km s^{-1} which corresponds to a total luminosity of L(HeH+)\approx 7.1 x 10^8 L_{sun}. As long as there is no independent confirmation, these values should be considered rather as upper limits.

astro-ph.CO↗

arXiv2010

Two-photon decays of highly excited states in hydrogen

The relativistic and nonrelativistic approaches for the calculations of the two-photon decay rates of highly excited states in hydrogen are compared. The dependence on the principal quantum number (n) of the ns, nd, and np initial states is investigated up to n = 100 for the nonresonant emissions. For the ns states together with the main E1E1 channel the contributions of higher multipoles (M1M1, E2E2, E1M2) are considered. For the np states the E1M1 and E1E2 channels are evaluated. Moreover, the simple analytical formula for the E1M1 decay is derived in the nonrelativistic limit.

physics.atom-ph↗

arXiv2009

Chemistry of heavy elements in the Dark Ages

Primordial molecules were formed during the Dark Ages, i.e. the time between recombination and reionization in the early Universe. The purpose of this article is to analyze the formation of primordial molecules based on heavy elements during the Dark Ages, with elemental abundances taken from different nucleosynthesis models. We present calculations of the full non-linear equation set governing the primordial chemistry. We consider the evolution of 45 chemical species and use an implicit multistep method of variable order of precision with an adaptive stepsize control. We find that the most abundant Dark Ages molecules based on heavy elements are CH and OH. Non-standard nucleosynthesis can lead to higher heavy element abundances while still satisfying the observed primordial light abundances. In that case, we show that the abundances of molecular species based on C, N, O and F can be enhanced by two orders of magnitude compared to the standard case, leading to a CH relative abundance higher than that of HD+ or H2D+.

astro-ph.CO↗

arXiv2001

Negative intensity patches in angular variations of CMB as a probe of the period of reionization

The observational tests for the period of reionization of the universe are discussed. We show that this period can be observed as {\it negative} intensity patches of the CMB radiation with the amplitude $δT/T\sim 10^{-5}$ and the angular sizes $θ_T\sim$10 angular seconds in range of the wavelength 0.1 cm$\leqλ\leq$1 cm. The expected number density and frequency dependence of the amplitude permit to recognize this effect and to discriminate it from the noise. This method applied to the small scale variations of CMB temperature complements well the traditional spectral approach. The number density and the amplitude of observed 'negative' intensity patches depend upon the redshift of reionization that allow to estimate roughly this redshift. The ionized bubbles formed just before the period of reionization could also be seen as the highest peaks. The expected results are sensitive to the Jeans scale at the period of reionization, to the small scale shape of the primordial power spectrum and to the mass of dark matter particles.

astro-ph↗