arXiv subjects

A. Gusev

Publications and source records attributed to A. Gusev.

16 recordsLinked to original sources

arXiv2025

A Comprehensive Analysis on the Nature of the Spiral Arms in NGC 3686, NGC 4321, and NGC 2403

In theoretical investigations, various mechanisms have been put forward to explain the emergence of spiral patterns in galaxies. One of the few ways to find out the nature of spirals in a particular galaxy is to consider the so-called corotation radius, or corotation resonance. A distinctly defined corotation resonance is likely to indicate the existence of a spiral density wave, while the chaotic distribution of their positions may suggest a dynamic nature to the spiral structure. In this study, we analyzed measurements of the corotation radius obtained using several methods for three galaxies (NGC 3686, NGC 4321, and NGC 2403) that exhibit different morphologies of spiral structures. We also performed independent measurements to estimate the location of the resonance, which allowed us to determine whether each galaxy has a clear corotation radius position. This examination, along with other tests such as stellar age gradient, interlocking resonances, and the radial distribution of metallicity, enables us to understand the mechanism that may be responsible for the formation of spiral arms in the studied galaxies.

astro-ph.GA↗

arXiv2019

Fast high-power thyristors triggered in impact-ionization wave mode

GTO-like thyristors 5STH-2045H0002 (4.5 kV, 18 kA/us) developed by ABB semiconductors are currently used at CERN in LHC Beam Dumping System (LBDS): high-power switches with high dI/dt capability and low turn-on delay time are required. Implementation of the impact-ionization triggering in GTO-like thyristor enhances its switching performance and gives new information about semiconductor physics. In this work thyristors of 5STH-2045H0002 type triggered in impact-ionization wave mode are investigated. An SOS generator providing a dV/dt of several kV/ns was used as a source of triggering pulses. A thyristor switching time of approximately 200-300 ps was observed. Maximum discharge parameters were obtained for two series connected thyristors at a charging voltage of 10 kV, and a capacitor stored energy of ~300 J: peak current of 43 kA, dI/dt of 120 kA/us (limited by the discharge circuit), FWHM of 1.5 us. A single thyristor was tested in the repetitive mode at the charging voltage of 4.2 kV, and the stored energy of 18 J: peak current of 5.5 kA, dI/dt of 40 kA/us, FWHM of 1.5 us were obtained. No thyristor degradation was observed after more than one million pulses at a PRF up to 1 kHz in burst mode. Thyristor recovery time was ~250 us. The switching efficiency was up to 98% depending on dV/dt and stored energy.

physics.ins-det↗

arXiv2018

On generation of the Bargmann-Moshinsky basis of SU(3) group

An efficient procedure of orthonormalisation of the Bargmann-Moshinsky (BM) basis is examined using analytical formulas of the overlap integrals of the BM basis. Calculations of components of the quadrupole operator between the both BM and the orthonormalised bases needed for construction of the nuclear models are tested. The proposed procedure is also implemented as the Fortran program.

nucl-th↗

arXiv2016

Phase separation in iron chalcogenide superconductor Rb0.8+xFe1.6+ySe2 as seen by Raman light scattering and band structure calculations

We report Raman light scattering in the phase separated superconducting single crystal Rb0.77Fe1.61Se2 with Tc = 32 K. The spectra have been measured in a wide temperature range 3K -500K. The observed phonon lines from the majority vacancy ordered Rb2Fe4Se5 (245) antiferromagnetic phase with TN= 525 K demonstrate modest anomalies in frequency, intensity and halfwidth at the superconductive phase transition. We identify phonon lines from the minority compressed Rb{\delta}Fe2Se2 (122) conductive phase. The superconducting gap with dx2-y2 symmetry is also detected in our spectra. In the range 0-600 cm-1 we observed the low intensive but highly polarized B1g-type background which becomes well structured under cooling. The possible magnetic or multiorbital origin of this background has been discussed. We argue that phase separation in M0.8+xFe1.6+ySe2 has pure magnetic origin. It occurs below Neel temperature when iron magnetic moment achieves some critical magnitude. We state that there is a spacer between the majority 245 and minority 122 phases. Using ab-initio spin polarized band structure calculations we demonstrate that compressed vacancy ordered Rb2Fe4Se5 phase can be conductive and therefore may serve as a protective interface spacer between the pure metallic Rb{\delta}Fe2Se2 phase and the insulating Rb2Fe4Se5 phase providing the percolative Josephson-junction like superconductivity in the whole sample of Rb0.8+xFe1.6+ySe2 Our lattice dynamics calculations show significant difference in the phonon spectra of the conductive and insulating Rb2Fe4.Se5 phases.

cond-mat.supr-con↗

arXiv2015

Muon-spin-rotation study of the magnetic structure in the tetragonal antiferromagnetic state of weakly underdoped Ba$ _{1-x} $K$ _{x} $Fe$ _{2} $As$ _{2} $

With muon spin rotation ($ μ$SR) we studied the transition between the orthorhombic antiferromagnetic (o-AF) and the tetragonal antiferromagnetic (t-AF) states of a weakly underdoped Ba$ _{1-x} $K$ _{x} $Fe$ _{2} $As$ _{2} $ single crystal. We observed some characteristic changes of the magnitude and the orientation of the magnetic field at the muon site which, due to the fairly high point symmetry of the latter, allow us to identify the magnetic structure of the t-AF state. It is the so-called, inhomogeneous double-$\mathbf{Q}$ magnetic structure with $ c $-axis oriented moments which has a vanishing magnetic moment on half of the Fe sites.

cond-mat.supr-con↗

arXiv2015

Gravitational Redshift Experiment with the Space Radio Telescope RadioAstron

A unique test of general relativity is possible with the space radio telescope RadioAstron. The ultra-stable on-board hydrogen maser frequency standard and the highly eccentric orbit make RadioAstron an ideal instrument for probing the gravitational redshift effect. Large gravitational potential variation, occurring on the time scale of $\sim$24 hr, causes large variation of the on-board H-maser clock rate, which can be detected via comparison with frequency standards installed at various ground radio astronomical observatories. The experiment requires specific on-board hardware operating modes and support from ground radio telescopes capable of tracking the spacecraft continuously and equipped with 8.4 or 15 GHz receivers. Our preliminary estimates show that $\sim$30 hr of the space radio telescope's observational time are required to reach $\sim 2\times10^{-5}$ accuracy in the test, which would constitute a factor of 10 improvement over the currently achieved best result.

gr-qc↗

arXiv2011

Coexistence of Superconductivity and Magnetism in FeSe_1-x under Pressure

An extended investigation of the electronic phase diagram of FeSe$_{1-x}$ up to pressures of $p\simeq2.4$\,GPa by means of ac and dc magnetization, zero field muon spin rotation (ZF $μ$SR), and neutron diffraction is presented. ZF $μ$SR indicates that at pressures $p\geq0.8$\,GPa static magnetic order occurs in FeSe$_{1-x}$ and occupies the full sample volume for $p\gtrsim 1.2$\,GPa. ac magnetization measurements reveal that the superconducting volume fraction stays close to 100% up to the highest pressure investigated. In addition, above $p\geq1.2$\,GPa both the superconducting transition temperature $T_{\rm c}$ and the magnetic ordering temperature $T_{\rm N}$ increase simultaneously, and both superconductivity and magnetism are stabilized with increasing pressure. Calculations indicate only one possible muon stopping site in FeSe$_{1-x}$, located on the line connecting the Se atoms along the $c$-direction. Different magnetic structures are proposed and checked by combining the muon stopping calculations with a symmetry analysis, leading to a similar structure as in the LaFeAsO family of Fe-based superconductors. Furthermore, it is shown that the magnetic moment is pressure dependent and with a rather small value of $μ\approx 0.2\,μ_B$ at $p\simeq2.4$\,GPa.

cond-mat.supr-con↗

arXiv2011

Anomalous optical phonons in FeTe pnictides: spin state, magnetic order, and lattice anharmonicity

Polarized Raman-scattering spectra of non-superconducting, single-crystalline FeTe are investigated as function of temperature. We have found a relation between the magnitude of ordered magnetic moments and the linewidth of A1g phonons at low temperatures. This relation is attributed to the intermediate spin state (S=1) and the orbital degeneracy of the Fe ions. Spin-phonon coupling constants have been estimated based on microscopic modeling using density-functional theory and analysis of the local spin density. Our observations show the importance of orbital degrees of freedom for the Fe-based superconductors with large ordered magnetic moments, while small magnetic moment of Fe ions in some iron pnictides reflects the low spin state of Fe ions in those systems.

cond-mat.str-el↗

arXiv2008

LCG MCDB -- a Knowledgebase of Monte Carlo Simulated Events

In this paper we report on LCG Monte Carlo Data Base (MCDB) and software which has been developed to operate MCDB. The main purpose of the LCG MCDB project is to provide a storage and documentation system for sophisticated event samples simulated for the LHC collaborations by experts. In many cases, the modern Monte Carlo simulation of physical processes requires expert knowledge in Monte Carlo generators or significant amount of CPU time to produce the events. MCDB is a knowledgebase mainly dedicated to accumulate simulated events of this type. The main motivation behind LCG MCDB is to make the sophisticated MC event samples available for various physical groups. All the data from MCDB is accessible in several convenient ways. LCG MCDB is being developed within the CERN LCG Application Area Simulation project.

hep-ph↗

arXiv2007

Prospects in the orbital and rotational dynamics of the Moon with the advent of sub-centimeter lunar laser ranging

Lunar Laser Ranging (LLR) measurements are crucial for advanced exploration of the laws of fundamental gravitational physics and geophysics. Current LLR technology allows us to measure distances to the Moon with a precision approaching 1 millimeter. As NASA pursues the vision of taking humans back to the Moon, new, more precise laser ranging applications will be demanded, including continuous tracking from more sites on Earth, placing new CCR arrays on the Moon, and possibly installing other devices such as transponders, etc. Successful achievement of this goal strongly demands further significant improvement of the theoretical model of the orbital and rotational dynamics of the Earth-Moon system. This model should inevitably be based on the theory of general relativity, fully incorporate the relevant geophysical processes, lunar librations, tides, and should rely upon the most recent standards and recommendations of the IAU for data analysis. This paper discusses methods and problems in developing such a mathematical model. The model will take into account all the classical and relativistic effects in the orbital and rotational motion of the Moon and Earth at the sub-centimeter level. The new model will allow us to navigate a spacecraft precisely to a location on the Moon. It will also greatly improve our understanding of the structure of the lunar interior and the nature of the physical interaction at the core-mantle interface layer. The new theory and upcoming millimeter LLR will give us the means to perform one of the most precise fundamental tests of general relativity in the solar system.

gr-qc↗

arXiv2006

A standard format for Les Houches Event Files

A standard file format is proposed to store process and event information, primarily output from parton-level event generators for further use by general-purpose ones. The information content is identical with what was already defined by the Les Houches Accord five years ago, but then in terms of Fortran commonblocks. This information is embedded in a minimal XML-style structure, for clarity and to simplify parsing.

hep-ph↗

arXiv2006

Les Houches Physics at TeV Colliders 2005, Standard Model and Higgs working group: Summary report

This Report summarises the activities of the "SM and Higgs" working group for the Workshop "Physics at TeV Colliders", Les Houches, France, 2-20 May, 2005. On the one hand, we performed a variety of experimental and theoretical studies on standard candles (such as W, Z, and ttbar production), treating them either as proper signals of known physics, or as backgrounds to unknown physics; we also addressed issues relevant to those non-perturbative or semi-perturbative ingredients, such as Parton Density Functions and Underlying Events, whose understanding will be crucial for a proper simulation of the actual events taking place in the detectors. On the other hand, several channels for the production of the Higgs, or involving the Higgs, have been considered in some detail. The report is structured into four main parts. The first one deals with Standard Model physics, except the Higgs. A variety of arguments are treated here, from full simulation of processes constituting a background to Higgs production, to studies of uncertainties due to PDFs and to extrapolations of models for underlying events, from small-$x$ issues to electroweak corrections which may play a role in vector boson physics. The second part of the report treats Higgs physics from the point of view of the signal. In the third part, reviews are presented on the current status of multi-leg, next-to-leading order and of next-to-next-to-leading order QCD computations. Finally, the fourth part deals with the use of Monte Carlos for simulation of LHC physics.

hep-ph↗

arXiv2003

The universe evolution as a possible mechanism of formation of galaxies and their clusters

The Kepler problem is considered in a space with the Friedmann--Lemaitre--Robertson--Walker metrics of the expanding universe. The covariant differential of the Friedmann coordinates (X=a(t)x) is considered as a possible mechanism of the formation of galaxies and clusters of galaxies. The cosmic evolution leads to decreasing energy of particles, causing free particles to be captured in bound states. In this approach the evolution of the universe plays the role usually inscribed to Cold Dark Matter.

astro-ph↗

arXiv2002

Origin of Matter from Vacuum in Conformal Cosmology

We introduce the hypothesis that the matter content of the universe can be a product of the decay of primordial vector bosons. The effect of the intensive cosmological creation of these primordial vector $W, ~Z $ bosons from the vacuum is studied in the framework of General Relativity and the Standard Model where the relative standard of measurement identifying conformal quantities with the measurable ones is accepted. The relative standard leads to the conformal cosmology with the z-history of masses with the constant temperature, instead of the conventional z-history of the temperature with constant masses in inflationary cosmology. In conformal cosmology both the latest supernova data and primordial nucleosynthesis are compatible with a stiff equation of state associated with one of the possible states of the infrared gravitation field. The distribution function of the created bosons in the lowest order of perturbation theory exposes a cosmological singularity as a consequence of the theorem about the absence of the massless limit of massive vector fields in quantum theory. This singularity can be removed by taking into account the collision processes leading to a thermalization of the created particles. The cosmic microwave background (CMB) temperature T=(M_W^2H_0)^{1/3} ~ 2.7 K occurs as an integral of motion for the universe in the stiff state. We show that this temperature can be attained by the CMB radiation being the final product of the decay of primordial bosons. The effect of anomalous nonconservation of baryon number due to the polarization of the Dirac sea vacuum by these primordial bosons is considered.

hep-th↗

arXiv2001

Cosmological Particle Creation and Baryon Number Violation in a Conformal Unified Theory

We consider a conformal unified theory as the basis of conformal-invariant cosmological model where the permanent rigid state of the universe is compatible with the primordial element abundance and supernova data. We show that the cosmological creation of vector Z and W bosons, in this case, is sufficient to explain the CMB temperature (2.7 K). The primordial bosons violate the baryon number in the standard model as a result of anomalous nonconservation of left-handed currents and a nonzero squeezed vacuum expectation value of the topological Chern-Simons functional.

hep-th↗

arXiv2001

Cosmological Creation of Vector Bosons and Fermions

The cosmological creation of primordial vector bosons and fermions is described in the Standard Model of strong and electro-weak interactions given in a space-time with the relative standard of measurement of geometric intervals. Using the reparametrization - invariant perturbation theory and the holomorphic representation of quantized fields we derive equations for the Bogoliubov coefficients and distribution functions of created particles. The main result is the intensive cosmological creation of longitudinal Z and W bosons (due to their mass singularity) by the universe in the rigid state. We introduce the hypothesis that the decay of the primordially created vector bosons is the origin of the Cosmic Microwave Background radiation.

gr-qc↗