arXiv subjects

Yu. L. Bolotin

Publications and source records attributed to Yu. L. Bolotin.

30 records · Page 2Linked to original sources

arXiv2014

A Thousand Problems in Cosmology: Horizons

This is one chapter of the collection of problems in cosmology, in which we assemble the problems, with solutions, that concern one of the most distinctive features of general relativity and cosmology---the horizons. The first part gives an elementary introduction into the concept in the cosmological context, then we move to more formal exposition of the subject and consider first simple, and then composite models, such as $Λ$CDM. The fourth section elevates the rigor one more step and explores the causal structure of different simple cosmological models in terms of conformal diagrams. The section on black holes relates the general scheme of constructing conformal diagrams for stationary black hole spacetimes. The consequent parts focus on more specific topics, such as the various problems regarding the Hubble sphere, inflation and holography. The full collection is available in the form of a wiki-based resource at universeinproblems.com. The cosmological community is welcome to contribute to its development.

physics.ed-ph↗

arXiv2013

A Thousand Problems in Cosmology: Interaction in the Dark Sector

This is one chapter of the collection of problems in cosmology, in which we assemble the problems that concern one of the most distinctive features of modern cosmology---the interaction in the Dark Sector. The evolution of any broadly applied model is accompanied by multiple generalizations that aim to resolve conceptual difficulties and to explain the ever-growing pool of observational data. In the case of Standard Cosmological Model one of the most promising directions of generalization is replacement of the cosmological constant with a more complicated, dynamic, form of dark energy and incorporation of interaction between the dark components---dark energy (DE) and dark matter (DM). Typically, DE models are based on scalar fields minimally coupled to gravity, and do not implement explicit coupling of the field to the background DM. However, there is no fundamental reason for this assumption in the absence of an underlying symmetry which would suppress the coupling. Given that we do not know the true nature of either DE or DM, we cannot exclude the possibility that there is some kind of coupling between them. Whereas interactions between DE and normal matter particles are heavily constrained by observations (e.g. in the solar system and gravitational experiments on Earth), this is not the case for DM particles. In other words, it is possible for the dark components to interact with each other while not being coupled to standard model particles. Therefore, the possibility of DE-DM interaction should be investigated with utmost gravity. This version contains only formulations of 117 problems. The full collection, with solutions included, is available in the form of a wiki-based resource at universeinproblems.com. The cosmological community is welcome to contribute to its development.

physics.ed-ph↗

arXiv2013

A Thousand Problems in Cosmology. Chapter 4: Black holes

The fourth chapter of the collection of problems in cosmology, devoted to black holes. Consists of basic introduction, sections on Schwarzschild and Kerr black holes, a section on particles' motion and collisions in general black hole space-times, and the astrophysical part. This version contains only formulations of 137 problems. The full collection, with solutions included, is available in the form of a wiki-based resource at www.universeinproblems.com. The cosmological community is welcome to contribute to its development.

physics.ed-ph↗

arXiv2012

Expanding Universe: slowdown or speedup?

The kinematics and dynamic interpretation of the cosmological expansion is reviewed in a widely accessible manner with emphasis on the acceleration aspect. Virtually all the approaches that can in principle account for the accelerated expansion of the Universe are reviewed, including dark energy as an item in the energy budget of the Universe; modified Einstein equations; and, on a fundamentally new level, the use of the holographic principle.

astro-ph.CO↗

arXiv2011

Holographic Dynamics as Way to Solve the Basic Cosmological Problems

We review recent results on the cosmological models based on the holographic principle which were proposed to explain the most of the problems occurring in the Standard Cosmological Model. It is shown that these models naturally solve the cosmological constant problem and coincidence problem. Well-documented cosmic acceleration at the present time was analyzed in the light of holographic dark energy. In particular, we showed that in the model of Universe consisting of dark matter interacting with a scalar field on the agegraphic background can explain the transient acceleration. We also study the impact of ideas on the physics of entangled states in these cosmological models. Entanglement entropy of the universe gives holographic dark energy with the equation of state consistent with current observational data.

astro-ph.CO↗

arXiv2009

Over-barrier decay of the mixed state

Classical escape in 2D Hamiltonian systems with the mixed state has been studied numerically and analytically. The wide class of potentials with the mixed state is presented by polinomial potentials. In potentials, where the mixed state could be realized, i.e. the phase space contains regions of both regular and chaotic motion, escape problem has a number of new features. In particular, some local minima become a trap with number of particles depending on energy and other values that characterize the ensemble of particles. Choosing the form of initial ensemble one chooses the set of parameters that determine the number of trapped particles.

nlin.CD↗

arXiv2008

Decay of the Mixed States

We study the classical escape from local minima for 2d multi-well Hamiltonian systems, realizing the mixed state. We show that escape from such local minima has a diversity of principally new features, representing an interesting topic for conceptual understanding of chaotic dynamics and applications.

nlin.CD↗

arXiv2006

Geometrical approach for description of the mixed state in multi-well potentials

We use so-called geometrical approach in description of transition from regular motion to chaotic in Hamiltonian systems with potential energy surface that has several local minima. Distinctive feature of such systems is coexistence of different types of dynamics (regular or chaotic) in different wells at the same energy Mixed state reveals unique opportunities in research of quantum manifestations of classical stochasticity. Application of traditional criteria for transition to chaos (resonance overlap criterion, negative curvature criterion and stochastic layer destruction criterion) is inefficient in case of potentials with complex topology. Geometrical approach allows considering only configuration space but not phase space when investigating stability. Trajectories are viewed as geodesics of configuration space equipped with suitable metric. In this approach all information about chaos and regularity consists in potential function. The aim of this work is to determine what details of geometry of potential lead to chaos in Hamiltonian systems using geometrical approach. Numerical calculations are executed for potentials that are relevant with lowest umbilical catastrophes.

nlin.CD↗

arXiv2003

Signatures of Quantum Chaos in Wave Functions Structure for Multi-well 2D Potentials

We propose a new approach to investigation of quantum manifestations of classical stochasticity (QMCS) in wave functions structure, which can be realized in potentials with two and more local minima. The main advantage of the proposed approach is the possibility to detect QMCS in comparison not different wave functions, but different parts of the same wave function. Efficiency of the approach is demonstrated for two potentials: surface quadrupole oscillations (QO) and lower umbillic catastrophe (UC) $D_5$.

nlin.CD↗

arXiv2001

Quadrupole Oscillations as Paradigm of the Chaotic Motion in Nuclei. Part 2

The present communication is a continuation of the review, the first part of which was presented in nucl-th/0109033. The second part dealswith the manifistation of Chaotic dynamics at quantum level. The variations of statistical properties of energy spectrum in the process of R-C-R transition have been studied in detail. We proved that the type of the classical motion is correlated with the structure of the eigenfunctions of highly excited states in the R-C-R transition. Shell structure destruction induced by the increase of nonintegrable perturbation was analyzed.

nucl-th↗

arXiv2001

Quadrupole Oscillations as Paradigm of the Chaotic Motion in Nuclei. Part 1

We have presented a complete description of classical dynamics generated by the Hamiltonian of quadrupole nuclear oscillations and identified those peculiarities of quantum dynamics that can be interpreted as quantum manifestations of classical stochasticity. Particular attention has been given to investigation of classical dynamics in the potential energy surface with a few local minima. A new technique is suggested for determination of the critical energy of the transition to chaos. It is simpler than criteria of transition to chaos connected with one or another version of overlap resonances criterion. We have numerically demonstrated that for potential with a localized unstable region motion becomes regular at the high energy again, i.e. transition regularity-chaos-regularity {R - C - R} takes place for these potentials. The variations of statistical properties of energy spectrum in the process of {R - C - R) transition have been studied in detail. We proved that the type of the classical motion is correlated with the structure of the eigenfunctions of highly excited states in the (R - C - R) transition. Shell structure destruction induced by the increase of nonintegrable perturbation was analyzed.

nucl-th↗

arXiv2001

Stochastic Resonance in a Periodically Modulated Dissipative Nuclear Dynamics

A fission decay of highly excited periodically driven compound nuclei is considered in the framework of Langevin approach. We have used residual-time distribution (RTD) as the tool for studying of dynamic features in a presence of periodic perturbation. The structure of RTD essentially depends on the relation between Kramers decay rate and the frequency of the periodic perturbation. In particular, intensity of the first peak in RTD has a sharp maximum at certain nuclear temperature depending on the frequency of the periodic perturbation. This maximum should be considered as first-hand manifestation of stochastic resonance in nuclear dynamics.

nlin.CD↗