arXiv subjects

Yu. V. Dumin

Publications and source records attributed to Yu. V. Dumin.

10 recordsLinked to original sources

arXiv2023

On the Probable Interpretation of Anticorrelation between the Proton Temperature and Density in the Solar Wind

The anticorrelated distributions of temperature and density of protons are a well-known property of the solar wind. Nevertheless, it is unclear till now if they are formed by some kind of the universal physical mechanism? Unfortunately, a straightforward comparison of the characteristic relaxation times for the temperature and density, on the one hand, and pressure, on the other hand, encounters the problem of inapplicability of the hydrodynamical approach in the situation when the free-path length of the protons is considerably greater than the spatial scale of the structures under consideration. To resolve this problem, some kinds of the MHD turbulence - reducing the effective free paths - are usually assumed. In the present paper, we use an alternative approach based on the electrostatic (Langmuir) turbulence, described by the mathematical formalism of the spin-type Hamiltonians, which was actively discussed in the recent time in the literature on statistical physics. As follows from the corresponding calculations, formation of the anticorrelated distributions of temperature and density is a universal property of the strongly-nonequilibrium plasmas governed by the spin-type Hamiltonians when they gradually approach the thermodynamic equilibrium. So, just this phenomenon could be responsible for the anticorrelations observed in the solar wind.

astro-ph.SR↗

arXiv2019

Topological model of the anemone microflares in the solar chromosphere

Context: The chromospheric anemone microflares, which were discovered by Hinode satellite about a decade ago, are specific transient phenomena starting from a few luminous ribbons on the chromospheric surface and followed by an eruption upward. While the eruptive stage was studied in sufficient detail, a quantitative theory of formation of the initial multi-ribbon structure remains undeveloped until now. Aims: We construct a sufficiently simple but general model of the magnetic field sources that is able to reproduce all the observed types of luminous ribbons by varying only a single parameter. Methods: As a working tool, we employed the Gorbachev-Kel'ner-Somov-Shvarts (GKSS) model of the magnetic field, which was originally suggested about three decades ago to explain fast ignition of the magnetic reconnection over considerable spatial scales by tiny displacements of the magnetic sources. Quite unexpectedly, this model turns out to be efficient for the description of generic multi-ribbon structures in the anemone flares as well. Results: As follows from our numerical simulation, displacement of a single magnetic source (sunspot) with respect to three other sources results in a complex transformation from three to four ribbons and then again to three ribbons, but with an absolutely different arrangement. Such structures closely resemble the observed patterns of emission in the anemone microflares.

astro-ph.SR↗

arXiv2011

On the Specific Features of Temperature Evolution in Ultracold Plasmas

A theoretical interpretation of the recent experimental studies of temperature evolution in the course of time in the freely-expanding ultracold plasma bunches, released from a magneto-optical trap, is discussed. The most interesting result is finding the asymptotics of the form T_e ~ t^{-(1.2 +/- 0.1)} instead of t^{-2}, which was expected for the rarefied monatomic gas during inertial expansion. As follows from our consideration, the substantially decelerated decay of the temperature can be well explained by the specific features of the equation of state for the ultracold plasmas with strong Coulomb's coupling, whereas a heat release due to inelastic processes (in particular, three-body recombination) does not play an appreciable role in the first approximation. This conclusion is confirmed both by approximate analytical estimates, based on the model of "virialization" of the charged-particle energies, and by the results of "ab initio" numerical simulation. Moreover, the simulation shows that the above-mentioned law of temperature evolution is approached very quickly--when the virial criterion is satisfied only within a factor on the order of unity.

physics.plasm-ph↗

arXiv2006

Testing the "Dark-Energy"-Dominated Cosmology via the Solar-System Experiments

The effect of "dark energy" (i.e. the Lambda-term in Einstein equations) is sought for at the interplanetary scales by comparing the rates of secular increase in the lunar orbit obtained by two different ways: (1) measured immediately by the laser ranging and (2) estimated independently from the deceleration of the Earth's proper rotation. The first quantity involves both the well-known effect of geophysical tides and the Kottler effect of Lambda-term (i.e. a kind of the "local" Hubble expansion), while the second quantity is associated only with the tidal influence. The difference between them, 2.2 +/- 0.3 cm/yr, can be attributed just to the local Hubble expansion with rate H_0^(loc) = 56 +/- 8 km/s/Mpc. Assuming that Hubble expansion is formed locally only by the uniformly distributed dark energy (Lambda-term), while globally also by a clumped substance (for the most part, the cold dark matter), the total (large-scale) Hubble constant should be H_0 = 65 +/- 9 km/s/Mpc. This is in reasonable agreement both with the commonly-accepted WMAP result, H_0 = 71 +/- 3.5 km/s/Mpc, and with the data on supernovae Ia distribution. The above coincidence can serve as one more argument in favor of the dark energy.

astro-ph↗

arXiv2005

On the Efficiency of Topological Defect Formation in the Systems of Various Size and (Quasi-) Dimensionality

The experiments on verification of the Kibble-Zurek mechanism showed that topological defects are formed most efficiently in the systems of small size or low (quasi-)dimensionality, whereas in the macroscopic two- and three-dimensional samples a concentration of the defects, as a rule, is strongly suppressed. A reason for universality of such behavior can be revealed by considering a strongly-nonequilibrium symmetry-breaking phase transition in the simplest phi-4 field model. It is shown that the resulting distribution of the defects (domain walls) is formally reduced to the well-known Ising model, whose behavior changes dramatically in passing from a finite to infinite size of the system and from the low (D=1) to higher (D>=2) dimensionality.

hep-ph↗

arXiv2003

A New Application of the Lunar Laser Retroreflectors: Searching for the "Local" Hubble Expansion

Precise measurements of the Earth-Moon distance by the lunar laser ranging (LLR), which begun in the early 1970's, contributed significantly to geodesy, geophysics, and lunar planetology, as well as enabled astrophysicists to perform several fine tests of the relativistic gravitational field theory (General Relativity). Yet another promising application of LLR arises just now in the context of recent cosmological models, whose dynamics is substantially affected by some kinds of the dark matter (or the so-called "dark energy") uniformly distributed in space, and therefore should be accompanied by some residual Hubble expansion at any spatial scales, particularly, in the Earth-Moon system. The "local" Hubble expansion can be revealed by comparing the rate of increase in the lunar semi-major axis measured by LLR (which should be produced both by the well-known tidal exchange of angular momentum between the Earth and Moon and the local Hubble expansion) with the same quantity derived indirectly from astrometric data on the Earth's rotation deceleration (which is produced only by the tidal interaction). Such analysis really points to the discrepancy 1.3 cm/yr, which corresponds to the local Hubble constant H_0^(loc) = 33 +/- 5 (km/s)/Mpc. This value is about two times less than at intergalactic scales but many orders of magnitude greater than was predicted in earlier theoretical works.

astro-ph↗

arXiv2002

On the Influence of Einstein-Podolsky-Rosen Effect on the Domain Wall Formation during the Cosmological Phase Transitions

Search for the mechanisms suppressing formation of Higgs field defects (e.g. domain walls) during the cosmological phase transitions is one of key problems in explanation of the observed large-scale uniformity of the space-time. One of the possible solutions can be based on accounting for Einstein-Podolsky-Rosen (EPR) correlations. Namely, if a coherent quantum state of the Higgs field was formed in the course of its previous evolution, then reduction to the state with broken symmetry during the phase transition should be correlated even at the scales exceeding the local cosmological horizons. Detailed consideration of the simplest one-dimensional cosmological model with Z2 Higgs field demonstrates that, at certain parameters of the Lagrangian, EPR-correlations really result in a substantial suppression of spontaneous formation of the domain walls.

hep-ph↗

arXiv2002

On a probable manifestation of Hubble expansion at the local scales, as inferred from LLR data

Processing the data of lunar laser ranging (LLR), whose accuracy now reaches a few millimeters, points to the effect of anomalous increase in the lunar semimajor axis (with an excessive rate 1.3 cm/yr), which cannot be attributed to the well-known tidal exchange of angular momentum between the Earth and Moon. One of the possible interpretations of the above-mentioned anomaly may be the "local" Hubble expansion with H = 33 +/- 5 (km/s)/Mpc. This small value of the local Hubble constant (about two times less than at intergalactic scales) can be reasonably explained if it is formed only by some kind of an unclumped "dark matter" or "dark energy", while the other kinds of matter experienced a gravitational instability, formed compact objects, and no longer contribute to the formation of Hubble expansion at the local scales.

astro-ph↗

arXiv2000

On the Physical Nature of the Magnetic-Field Freezing-in Effect in Collisionless Cosmic Plasmas

Attention is drawn to a fundamental difference between the physical mechanisms responsible for the magnetic field freezing-in effect in spatially isotropic (collisional) and strongly anisotropic (collisionless) plasmas. (The first case is characteristic of internal regions of the Sun and other stars; the second, for the solar corona, interplanetary and interstellar medium, planetary ionospheres and magnetospheres, cometary tails.) It is shown that particles of a collisionless plasma remain in the same field line during their motion because of the properties of electrodynamic drift which stem from the divergence-free character of the magnetic field and the equipotentiality of the field lines (but not as a result of the appearance of induction currents, compensating variations of the external magnetic flux through a closed contour, as in the case of isotropic conductivity of the plasma).

astro-ph↗

arXiv2000

On a Probable Contribution of the Einstein-Podolsky-Rosen Effect to Solving the Problem of Homogeneity of the Universe

Evading formation of the domain walls in cosmological phase transitions is one of key problems to be solved for explanation of the observed large-scale homogeneity of the Universe. The previous attempts to get around this obstacle led to imposing severe observational constraints on the parameters of the fields involved. Aim of the present report is to show that yet another way to overcome the above problem is accounting for Einstein-Podolsky-Rosen (EPR) effect. Namely, if the scalar (Higgs) field was presented by a single coherent quantum state at the initial instant of time, then its reduction during a phase transition at some later instant should be correlated even at distances exceeding the local cosmological horizon. Consideration of a simplest one-dimensional cosmological model with Z_2 Higgs field demonstrates that EPR correlations can substantially reduce the probability of spontaneous creation of the domain walls, and such effect seems to be even more promising in the cases of two- and three-dimensional geometry.

astro-ph↗