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We present a model for the transport of anisotropic turbulence in an accretion disc. The model uses the Reynolds stress tensor approach in the mean field approximation. To study the role of convection in a protoplanetary disc, we combine the turbulence model with a radiative transfer calculation, and also include convection using the mixing length approximation. We find that the turbulence generated by convection causes the angular momentum of the accretion disc to be directed outwards. We also confirm the conclusions of other authors that turbulent convection is unable to provide the observed disc accretion rates as well as a heat source sufficient for the convection to be self-sustaining. The reasons for the latter are the strong anisotropy of the turbulence together with the low efficiency of the energy transfer from the background velocity shear to the turbulent stress tensor., Comment: MNRAS accepted | 15 pages, 8 figures

Dark photons are hypothetical massive vector particles that could mix with ordinary photons. The simplest theoretical model is fully characterised by only two parameters: the mass of the dark photon m$_{\gamma^{\mathrm{D}}}$ and its mixing parameter with the photon, $\varepsilon$. The sensitivity of the SHiP detector is reviewed for dark photons in the mass range between 0.002 and 10 GeV. Different production mechanisms are simulated, with the dark photons decaying to pairs of visible fermions, including both leptons and quarks. Exclusion contours are presented and compared with those of past experiments. The SHiP detector is expected to have a unique sensitivity for m$_{\gamma^{\mathrm{D}}}$ ranging between 0.8 and 3.3$^{+0.2}_{-0.5}$ GeV, and $\varepsilon^2$ ranging between $10^{-11}$ and $10^{-17}$.

We propose to build and operate a detector that, for the first time, will measure the process $pp\to\nu X$ at the LHC and search for feebly interacting particles (FIPs) in an unexplored domain. The TI18 tunnel has been identified as a suitable site to perform these measurements due to very low machine-induced background. The detector will be off-axis with respect to the ATLAS interaction point (IP1) and, given the pseudo-rapidity range accessible, the corresponding neutrinos will mostly come from charm decays: the proposed experiment will thus make the first test of the heavy flavour production in a pseudo-rapidity range that is not accessible by the current LHC detectors. In order to efficiently reconstruct neutrino interactions and identify their flavour, the detector will combine in the target region nuclear emulsion technology with scintillating fibre tracking layers and it will adopt a muon identification system based on scintillating bars that will also play the role of a hadronic calorimeter. The time of flight measurement will be achieved thanks to a dedicated timing detector. The detector will be a small-scale prototype of the scattering and neutrino detector (SND) of the SHiP experiment: the operation of this detector will provide an important test of the neutrino reconstruction in a high occupancy environment., Comment: Letter of Intent

We consider scenario of merger of two stellar mass black holes surrounded by an accretion disk. Due to emission of gravitational waves, the mass of the central object decreases and accretion disk experiences perturbation. Calculations show that the main consequence of this disturbance is formation of a shock wave propagating from the center of the disk to its periphery. Light curve is computed and duration of the flash is estimated under assumption that the flash terminates when the luminosity returns to the initial value. It is shown that, if the total mass of the merging binary is 55 M_sol (like in the event GW170814), the flash produced by the shock will increase bolometric luminosity of the disk by 4--6 orders of magnitude, up to 10^{45} erg/s (absolute stellar magnitude -23.8^m). With account of the distance to the source (540 Mpc) and for reasonable assumptions on the parameters of the accretion disk, it turns out that the apparent magnitude of the flash at the maximum of the spectral flux density should be 12.8^m -- 14.2^m, while duration of the flash --- few minutes. The main part of the shock radiation flux is emitted in the X-ray and gamma-ray ranges. In the spectral band of the EPIC instrument of the XMM-Newton observatory or the telescope eROSITA of the Spectrum-RG observatory (0.3--10 keV), luminosity will increase by 3--4 orders of magnitude, up to 10^{44} erg/s, corresponding to the apparent stellar magnitude about 17^m. Luminosity is at maximum in the observational band of the IBIS instrument of the INTEGRAL observatory (20 keV -- 10 MeV) and will be 10^{44} -- 10^{45} erg/s, corresponding to the apparent flux 10^{-4} photons per cm^2/s/keV at the wavelength ~100 keV. From the far UV to the longer wavelengths, the brightening is virtually absent., Comment: Accepted in Astronomy Reports

We suggest a mechanism for generation of radio emission from polars. It is based on the cyclotron radiation of thermal electrons at the background of fluctuating magnetic field. The source of fluctuations is Alfv\'{e}n wave turbulence. Expressions for the radiation spectrum and degree of polarization are obtained. By the example of the polar AM~Her, the fluxes of radio emission from the accretion stream are calculated. Within the framework of proposed emission model, with realistic plasma characteristics, it is possible to reproduce observed radiation fluxes in the VLA bands., Comment: Accepted in Astronomy Reports

Accretion disks in binary systems can experience hydrodynamic impact at inner as well as outer edges. The first case is typical for protoplanetary disks around young T Tau stars. The second one is typical for circumstellar disks in close binaries. As a result of such an impact, perturbations with different scales and amplitudes are excited in the disk. We investigated the nonlinear evolution of perturbations of a finite, but small amplitude, at the background of sub-Keplerian flow. Nonlinear effects at the front of perturbations lead to the formation of a shock wave, namely the discontinuity of the density and radial velocity. At this, the tangential flow in the neighborhood of the shock becomes equivalent to the flow in in the boundary layer. Instability of the tangential flow further leads to turbulization of the disk. Characteristics of the turbulence depend on perturbation parameters, but alpha-parameter of Shakura-Sunyaev does not exceed ~0.1., Comment: Accepted in Astronomy Reports

We present a method that can be used to recover the spectrum of turbulence from observations of optically thin emission lines formed in astrophysical disks. Within this method we analyze how line intensity fluctuations depend on the angular resolution of the instrument, used for the observations. The method allows us to restore the slope of the power spectrum of velocity turbulent pulsations and estimate the upper boundary of the turbulence scale., Comment: Accepted for publication in MNRAS. 14 pages, 7 figures

$\Lambda$CDM-model predicts an excess of dark halos compared to the observations. The excess is seen from the estimates of the virialized mass inside the Local Supercluster and its surroundings. It is shown that account for cosmological velocity fluctuations in the process of formation of the population of dark halos it is possible to eliminate this contradiction remaining within the framework of the $\Lambda$CDM cosmology. Based on the formalism of Press and Schechter, we suggest a model of formation of dark halo population which takes into account the kinematic effects in the dark matter. The model allows a quantitative explanation for the observable deficit of the virialized mass in the local Universe., Comment: 7 figures; to appear in Astronomy Reports (Apr. 2015)

The arising of turbulence in gas-dynamic (non-magnetic) accretion disks is a major issue of modern astrophysics. Such accretion disks should be stable against the turbulence generation, in contradiction to observations. Searching for possible instabilities leading to the turbulization of gas-dynamic disks is one of the challenging astrophysical problems. In 2004, we showed that in accretion disks in binary stars the so-called precessional density wave forms and induces additional density and velocity gradients in the disk. Linear analysis of the fluid instability of an accretion disk in a binary system revealed that the presence of the precessional wave in the disk due to tidal interaction with the binary companion gives rise to instability of radial modes with the characteristic growth time of tenths and hundredths of the binary orbital period. The radial velocity gradient in the precessional wave is shown to be responsible for the instability. A perturbation becomes unstable if the velocity variation the perturbation wavelength scale is about or higher than the sound speed. Unstable perturbations arise in the inner part of the disk and, by propagating towards its outer edge, lead to the disk turbulence with parameters corresponding to observations (the Shakura-Sunyaev parameter $\alpha \lesssim 0.01$)., Comment: Appeared in Phys. Usp

A modification of the Press-Schechter theory allowing for presence of a background large-scale structure (LSS) - a supercluster or a void, is proposed. The LSS is accounted as the statistical constraints in form of linear functionals of the random overdensity field. The deviation of the background density within the LSS is interpreted in a pseudo-cosmological sense. Using the constraints formalism may help us to probe non-trivial spatial statistics of haloes, e.g. edge and shape effects on boundaries of the superclusters and voids. Parameters of the constraints are connected to features of the LSS: its mean overdensity, a spatial scale and a shape, and spatial momenta of higher orders. It is shown that presence of a non-virialized LSS can lead to an observable deviation of the mass function. This effect is exploited to build a procedure to recover parameters of the background perturbation from the observationally estimated mass function., Comment: 23 pages, 6 figures; to be appeared in Astronomy Reports, 2014, Vol. 58, No. 6, pp. 386-398

It is commonly believed that most of the stars born in associations decaying with characteristic velocities of stars ~10 km/s. For dwarf galaxies the decay can lead to ejection of stars from the galaxy. The effect is studied for spheroidal and disk dwarf galaxies, and is shown to have substantional observational consequences for disk galaxies with escape velocities up to 20 km/s, or dynamical masses up to 10^8 M_sol. The ejection of stars can (i) reduce the abundances of the products of Type Ia supernovae and, to a lesser degree, Type II supernovae, in disk stars, (ii) chemically enrich the galactic halo and intergalactic medium, (iii) lead to the loss of 50% of the stellar mass in galaxies with masses ~10^7 M_sol and the loss of all stars in system with masses 10^5 M_sol, (iv) increase the mass-to-luminosity ratio of the galaxies., Comment: 15 pages, 3 figures

We suggest a model for star formation function and a model for dissipation of the turbulent energy of interstellar medium. Star formation function takes into account the effect of turbulization of the ISM. It is shown that application of mentioned relations to the hierarchical scenario of formation of galaxies allows to explain the observed delay of star formation in the Galaxy that corresponds to the range of stellar ages from 8--9 to 10--12 Gyr., Comment: 12 pages, 4 figures; revtex 4

The models of star formation function and of dissipation of turbulent energy of interstellar medium are proposed. In star formation model the feedback of supernovae is taken into account. It is shown that hierarchical scenario of galaxy formation with proposed models is able to explain the observable star formation pause in the Galaxy., Comment: Published in Proceedings of the 14th Young Scientists Conference on Astronomy and Space Physics, Kyiv, Ukraine, April 23-28, 2007

A new method for computation of gas cooling for Lagrange approach is suggested. The method is based on precalculation of cooling law for known cooling function. Unlike implicit methods, this method is very efficient, it is an one-step method which is even more accurate than implicit methods of the same order., Comment: submitted to JCompPhys, 5 pages, 1 figure

We study the evolution of the [O/Fe]-[Fe/H] relation and the dependence of the iron abundance on distance from the galactic plane z in a one-zone model for a disk galaxy, starting from the beginning of star formation (Wiebe98). We obtain good agreement with the observational data, including, for the first time, agreement for the [Fe/H]-z relation out to heights of 16 kpc. We also study the influence of the presence of dark matter in the galaxies on the star-formation rate. Comparison of the observed luminosity of the Galaxy with the model prediction places constraints on the fractional mass of dark matter, which cannot be much larger than the fractional mass of visible matter, at least within the assumed radius of the Galaxy, 20 kpc. We studied the evolution of disk galaxies with various masses, which should obey the Tully-Fisher relation, M \propto R^2. The Tully-Fisher relation can be explained as a combination of a selection effect related to the observed surface brightnesses of galaxies with large radii and the conditions for the formation for elliptical galaxies., Comment: 14 pages, more than ten misprints are corrected