arXiv subjects

Igor Novikov

Publications and source records attributed to Igor Novikov.

At least 19 recordsLinked to original sources

arXiv2025

Quantum algorithm for Ewald summation based computation of long-range electrostatics

In computational molecular science, calculation of electrostatic interactions involving charged atoms - the strongest interactions in condensed phases, is a major bottleneck. We propose a quantum-classical algorithm for fast, yet, accurate computation of the Coulomb electrostatic energy for a system of point charges. The algorithm employs the Ewald method based decomposition of electrostatic energy into several energy terms, of which the "Fourier component" (long-range electrostatics) computed on a quantum device, utilizing the power of Quantum Fourier Transform (QFT). We demonstrate that the algorithm complexity is $N \log M$ and that the quantum advantage for a system of point charges in the three-dimensional space is achieved when the number of grid points $M^3$ exceeds the number of charges $N$. The numerical error is small $<10^{-3}$. The algorithm can be implemented to run the all-atom Molecular Dynamics simulations on a quantum device requiring 15 qubits, thereby expanding the scope of applications of QFT-based methods to computational chemistry and biophysics.

quant-ph↗

arXiv2024

Observing of background electromagnetic radiation of the real sky through the throat of a wormhole

The numerical investigation conducted in this paper addresses the problem of CMB radiation imaging as seen through the throat of the Ellis-Bronnikov-Morris-Thorne wormhole. It is assumed that both throats of the wormhole are relatively close to our stellar neighborhood, so close that the view of the ambient background radiation by an observer at the other throat of the wormhole is virtually identical to that seen from the Solar System neighborhood. A map of the temperature distribution of the cosmic microwave background radiation observed through the mouth of the wormhole has been constructed as well as a view of the Milky Way through the mouth of the wormhole. The resultant image contains characteristic details that enable it to be distinguished from an image produced by a black hole.

gr-qc↗

arXiv2019

Numerical simulations of wind-driven protoplanetary nebulae. I. near-infrared emission

To understand how the circumstellar environments of post-AGB stars develop into planetary nebulae, we initiate a systematic study of 2D axisymmetric hydrodynamic simulations of protoplanetary nebula (pPN) with a modified ZEUS code. The aim of this first work is to compare the structure of prolate ellipsoidal winds into a stationary ambient medium where both media can be either atomic or molecular. We specifically model the early twin-shock phase which generates a decelerating shell. A thick deformed and turbulent shell grows when an atomic wind expands into an atomic medium. In all other cases, the interaction shell region fragments into radial protrusions due to molecular cooling and chemistry. The resulting fingers eliminate any global slip parallel to the shell surface. This rough surface implies that weak shocks are prominent in the excitation of the gas despite the fast speed of advance. This may explain why low excitation molecular hydrogen is found towards the front of elliptical pPN. We constrain molecular dissociative fractions and timescales of fast $\mathrm H_2$ winds and the pPN lifetime with wind densities $\mathrm{\sim10^{5}cm^{-3}}$ and shock speeds of $\mathrm{80\sim200\,km\,s^{-1}}$. We identify a variety of stages associated with thermal excitation of H$_2$ near-infrared emission. Generated line emission maps and position-velocity diagrams enable a comparison and distinction with post-AGB survey results. The $\mathrm{1\to0 \, S(1)}$ $\&$ $\mathrm{2\to1 \, S(1)}$ lines are lobe-dominated bows rather than bipolar shells.

astro-ph.SR↗

arXiv2019

Numerical simulations of wind-driven protoplanetary nebulae. II. signatures of atomic emission

We follow up on our systematic study of axisymmetric hydrodynamic simulations of protoplanetary nebula. The aim of this work is to generate the atomic analogues of the $\mathrm H_2$ near-infrared models of Paper I with the ZEUS code modified to include molecular and atomic cooling routines. We investigate stages associated with strong $\mathrm {[Fe II]}$ 1.64 $\mathrm {μm}$ and $\mathrm {[S II]}$ 6716 Å forbidden lines, the $\mathrm {[O I]}$ 6300 Å airglow line, and H$\mathrm α\, 6563$ Å emission. We simulate ($\mathrm{80\sim200\,km\,s^{-1}}$) dense ($\mathrm{\sim10^{5}\,cm^{-3}}$) outflows expanding into a stationary ambient medium. In the case of an atomic wind interacting with an atomic medium, a decelerating advancing turbulent shell thickens with time. This contrasts with all other cases where a shell fragments into a multitude of cometary-shaped protrusions with weak oblique shocks as the main source of gas excitation. We find that the atomic wind-ambient simulation leads to considerably higher excitation, stronger peak and integrated atomic emission as the nebula expands. The weaker emission when one component is molecular is due to the shell fragmentation into fingers so that the shock surface area is increased and oblique shocks are prevalent. Position-velocity diagrams indicate that the atomic-wind model may be most easy to distinguish with more emission at higher radial velocities. With post-AGB winds and shells often highly obscured and the multitude of configurations that are observed, this study suggests and motivates selection criteria for new surveys.

astro-ph.SR↗

arXiv2013

Special features in the asymptotic expression of the electromagnetic spectrum from dipole which free fall into a Schwarzschild black hole

The characteristic features were found in the electromagnetic spectrum of radiation from free falling dipole, when it is fall radially into a Schwarzschild black hole. These features can be used as another method for the black hole mass determinating. Also, these features can be used for the determination some characteristics of the magnetosphere or the accretion disk around the black hole.

gr-qc↗

arXiv2012

On stability of a new model of wormhole

We investigate the stability of the wormhole of the Mors-Thorne-Ellis-Bronnikov type. In our model the matter inside it consists of a radial magnetic field and an ideal phantom-fluid. Properties of the matter are described in section 1, 2 and 3 of this paper. We consider spherical perturbations only and find examples of the stable wormholes against these perturbations.

gr-qc↗

arXiv2012

Non-singular Brans-Dicke cosmology with cosmological constant

We consider Brans-Dicke cosmology with cosmological constant with negative w parameter and an arbitrary (in general non-vanishing) scale factor at the Big Bang. The field equations describe the flat universe, current observational values for Hubble constant H and deceleration parameter q play a role of initial conditions. In order to solve field equations we adopt the approach of Uehara and Kim (1982). They considered only positive values of w, hence our solution is a new one and has not been described in their paper. Our main result is that unlike the standard cosmology the scale factor may not vanish in it's evolution back in time. In other words our model displays a cosmological bounce and avoids the initial singularity. The formula for the scale factor, leading to the bounce, is only valid for the dust-filled universe and hence cannot be adequate for the hot stage in the early universe when the bounce happens. So, the results of this paper are only qualitative in nature and must be used to obtain initial values for the hot stage of the unverse when one considers the evolution back in time.

gr-qc↗

arXiv2011

A new method for reconstructing the density distribution of matter in the disks of spiral galaxies from the rotation velocity curve in it

In this paper we propose a new method for reconstructing the surface density of matter in flat disks of spiral galaxies. The surface density is expressed through observational rotation velocity curves of visible matter in the disks of spiral galaxies. The new method is not based on quadrature of special functions. The found solution is used for processing and analysis of observational data from several spiral galaxies. The new method can be used to more accurately estimate the amount of dark matter in spiral galaxies.

astro-ph.GA↗

arXiv2010

Physics of the interior of a black hole with an exotic scalar matter

We use a numerical code to consider the nonlinear processes arising when a Reissner-Nordstrom black hole is irradiated by an exotic scalar field (modelled as a free massless scalar field with an opposite sign for its energy-momentum tensor). These processes are quite different from the processes arising in the case of the same black hole being irradiated by a pulse of a normal scalar field. In our case, we did not observe the creation of a spacelike strong singularity in the T-region of the space-time. We investigate the antifocusing effects in the gravity field of the exotic scalar field with the negative energy density and the evolution of the mass function. We demonstrate the process of vanishing of the black hole when it is irradiated by a strong pulse of an exotic scalar field.

gr-qc↗

arXiv2009

Passage of radiation through wormholes

We investigate numerically the process of the passage of a radiation pulse through a wormhole and the subsequent evolution of the wormhole that is caused by the gravitational action of this pulse. The initial static wormhole is modeled by the spherically symmetrical Armendariz-Picon solution with zero mass. The radiation pulses are modeled by spherically symmetrical shells of self-gravitating massless scalar fields. We demonstrate that the compact signal propagates through the wormhole and investigate the dynamics of the fields in this process for both cases: collapse of the wormhole into the black hole and for the expanding wormhole.

gr-qc↗

arXiv2008

Passage of radiation through wormholes and formation of black holes

This paper has been withdrawn by the authors due to overlap with other papers.

gr-qc↗

arXiv2005

Statistics of phase correlations as a test for non-Gaussianity of the CMB maps

Gaussianity is the very base for derivation of the cosmological parameters from the CMB angular power spectrum. Non-Gaussian signal, whether originated from experimental error or primordial source, could mimic extra power in the power spectrum, thereby leading to a wrong set of parameters. In this paper we present a new Gaussianity analysis of the derived CMB singals. It is based on the trigonometric moments of phases, which can be concluded with a ``mean angle'', allowing us to see the global trend of non-Gaussianity of the signals. These moments are also closely related to the Pearson's random walks. We apply these analyses on the derived CMB maps and their different morphologies manifest themselves through these functions. We also comment on rotational invariance of the trigonometric moments of phases as a non-Gaussianity test.

astro-ph↗

arXiv2005

Properties of four numerical schemes applied to a scalar nonlinear scalar wave equation with a GR-type nonlinearity

We study stability, dispersion and dissipation properties of four numerical schemes (Iterative Crank-Nicolson, 3'rd and 4'th order Runge-Kutta and Courant-Fredrichs-Levy Non-linear). By use of a Von Neumann analysis we study the schemes applied to a scalar linear wave equation as well as a scalar non-linear wave equation with a type of non-linearity present in GR-equations. Numerical testing is done to verify analytic results. We find that the method of lines (MOL) schemes are the most dispersive and dissipative schemes. The Courant-Fredrichs-Levy Non-linear (CFLN) scheme is most accurate and least dispersive and dissipative, but the absence of dissipation at Nyquist frequency, if fact, puts it at a disadvantage in numerical simulation. Overall, the 4'th order Runge-Kutta scheme, which has the least amount of dissipation among the MOL schemes, seems to be the most suitable compromise between the overall accuracy and damping at short wavelengths.

gr-qc↗

arXiv2005

Physics of the interior of a spherical, charged black hole with a scalar field

We analyse the physics of nonlinear gravitational processes inside a spherical charged black hole perturbed by a self-gravitating massless scalar field. For this purpose we created an appropriate numerical code. Throughout the paper, in addition to investigation of the properties of the mathematical singularities where some curvature scalars are equal to infinity, we analyse the properties of the physical singularities where the Kretschmann curvature scalar is equal to the planckian value. Using a homogeneous approximation we analyse the properties of the spacetime near a spacelike singularity in spacetimes influenced by different matter contents namely a scalar field, pressureless dust and matter with ultrarelativistic isotropic pressure. We also carry out full nonlinear analyses of the scalar field and geometry of spacetime inside black holes by means of an appropriate numerical code with adaptive mesh refinement capabilities. We use this code to investigate the nonlinear effects of gravitational focusing, mass inflation, matter squeeze, and these effects dependence on the initial boundary conditions. It is demonstrated that the position of the physical singularity inside a black hole is quite different from the positions of the mathematical singularities. In the case of the existence of a strong outgoing flux of the scalar field inside a black hole it is possible to have the existence of two null singularities and one central $r=0$ singularity simultaneously.

gr-qc↗

arXiv2003

Inhomogenous Primordial Baryon Distributions on Sub-Galactic Scales: High-z Galaxy Formation with WDM

For the Warm Dark Matter (WDM) cosmological model the implications of strongly inhomogenous, primordial baryon distribution on sub-galactic scales for Big Bang Nucleosynthesis, Cosmic Microwave Background anisotropies and Galaxy Formation (including fully non-linear evolution to z=0) are discussed, and the inflationary theory leading to such distributions is briefly reviewed. It is found that Big Bang Nucleosynthesis is essentially unaffected relative to SBBN and that the change in recombination history at z~1500-700 relative to ``standard'' theory leads to differences in the anisotropy and polarization power spectra, which should be detectable by the Planck satellite provided systematic effects can be accounted for. Moreover, it is shown by fully cosmological, hydro/gravity simulations that the formation of galactic discs is only weakly affected by going from smooth to highly non-homogenous, initial baryon distributions. In particular, the final disc angular momenta at z=0 are as large as for the standard case and the ``disc angular momentum problem'' is solved to within a factor of two or better without invoking (hypothetical) energetic feedback events. A very desirable difference relative to the the standard WDM model, however, is that the on-set of star (and AGN) formation happens earlier. For the ``optimal'' free-streaming mass scale of M_f~1.5x10^11 h^-1 Msun the redshift of formation of the first stars increases from z_*=4-5 to >6.5, in much better agreement with observational data on high-redshift galaxies and QSOs. It will, however, not be possible to push z_* above ~10, because at higher redshifts the gas velocity field is nowhere compressive. Probing the ``dark ages'' will hence enable a direct test of this theory.

astro-ph↗

arXiv2002

The Interior of Black Holes and their Astrophysics

Gravity warps space and time into a funnel and generates a black hole when a cosmic body undergoes a catastrophic collapse. What can one say about the interior of a black hole? The important point is that inside a black hole the space radial direction becomes time, and time becomes a space direction. The path into the gravitational abyss of the interior of a black hole is a progression in time. There is a peculiar region inside a black hole where some characteristics of the space-time curvature become singular. We call this region singularity. The colossal tidal gravitational forces near singularity modify physical laws. Space and time are not only strongly curved near the singularity, but they split into quanta. The fall into the singularity is unstoppable for a body inside a black hole. This paper also addresses the following questions: Can one see what happens inside a black hole? Can a falling observer cross the singularity without being crushed? Can new baby universes arise inside a black hole? An answer to all these questions is probably ``yes''. We give also a brief review of the modern black hole astrophysics.

astro-ph↗

arXiv2001

Local and global properties of conformally flat initial data for black hole collisions

We study physical properties of conformal initial value data for single and binary black hole configurations obtained using conformal-imaging and conformal-puncture methods. We investigate how the total mass M_tot of a dataset with two black holes depends on the configuration of linear or angular momentum and separation of the holes. The asymptotic behavior of M_tot with increasing separation allows us to make conclusions about an unphysical ``junk'' gravitation field introduced in the solutions by the conformal approaches. We also calculate the spatial distribution of scalar invariants of the Riemann tensor which determine the gravitational tidal forces. For single black hole configurations, these are compared to known analytical solutions. Spatial distribution of the invariants allows us to make certain conclusions about the local distribution of the additional field in the numerical datasets.

gr-qc↗

arXiv1999

Adaptive mesh refinement approach to construction of initial data for black hole collisions

The initial data for black hole collisions is constructed using a conformal-imaging approach and a new adaptive mesh refinement technique, a fully threaded tree (FTT). We developed a second-order accurate approach to the solution of the constraint equations on a non-uniformly refined high resolution Cartesian mesh including second-order accurate treatment of boundary conditions at the black hole throats. Results of test computations show convergence of the solution as the numerical resolution is increased. FTT-based mesh refinement reduces the required memory and computer time by several orders of magnitude compared to a uniform grid. This opens up the possibility of using Cartesian meshes for very high resolution simulations of black hole collisions.

gr-qc↗