Estimation of the shear viscosity at finite net-baryon density from A+A collision data at sNN=7.7−200\sqrt{s_\mathrm{NN}} = 7.7-200 GeV

Hybrid approaches based on relativistic hydrodynamics and transport theory have been successfully applied for many years for the dynamical description of heavy ion collisions at ultrarelativistic energies. In this work a new viscous hybrid model employing the hadron transport approach UrQMD for the early and late non-equilibrium stages of the reaction, and 3+1 dimensional viscous hydrodynamics for the hot and dense quark-gluon plasma stage is introduced. This approach includes the equation of motion for finite baryon number, and employs an equation of state with finite net-baryon density to allow for calculations in a large range of beam energies. The parameter space of the model is explored, and constrained by comparison with the experimental data for bulk observables from SPS and the phase I beam energy scan at RHIC. The favored parameter values depend on energy, but allow to extract the effective value of the shear viscosity coefficient over entropy density ratio $\eta/s$ in the fluid phase for the whole energy region under investigation. The estimated value of $\eta/s$ increases with decreasing collision energy, which may indicate that $\eta/s$ of the quark-gluon plasma depends on baryochemical potential $\mu_B$.Comment: minor changes in the text, results for constant eta*T/w added. Version accepted for publication in Phys. Rev.

Femtoscopy correlations of kaons in Pb+PbPb + Pb collisions at LHC within hydrokinetic model

We provide, within the hydrokinetic model, a detailed investigation of kaon interferometry in $Pb+Pb$ collisions at LHC energy ($\sqrt{s_{NN}} = 2.76$ TeV). Predictions are presented for 1D interferometry radii of $K^0_SK^0_S$ and $K^{\pm}K^{\pm}$ pairs as well as for 3D femtoscopy scales in out, side and long directions. The results are compared with existing pion interferometry radii. We also make predictions for full LHC energy.Comment: 12 pages, 6 figure

Эволюционные операторы популяционных алгоритмов глобальной оптимизации. Опыт систематизации

There are a large number of examples of using the population-based algorithms (P-algorithms) to have a successful solution for complex practical tasks of global optimization, for instance, problems of computer-aided design, synthesis of complex chemical compounds, optimal control of dynamic systems, etc. P-algorithms are also successfully used in multi-criteria optimization, when a preliminary construction of some Pareto set (front) approximation is required. P-algorithms are numerous and very diverse – over 100 such algorithms are known, and new algorithms continue to appear. In this connection, the problem of systematizing expressive means of P-algorithms is of relevance. We consider one of the components of this problem that is the problem of classification of the search operators of P-algorithms.The paper formulates a global optimization problem and a general scheme of the P-algorithms to solve it. This multilevel classification of the main search operators of P-algorithms at the highest level of the hierarchy identifies the following operators: initialization of the population and the end of the search; coding of individuals; randomization; selection; crossing; population management; local search.These operators at the next hierarchical level are divided into deterministic and stochastic ones. Further, we distinguish static, dynamic program and dynamic adaptive operators. The following classification levels are "operator dependent", that is, generally speaking, different for each operator. We reveal the essence of these operators and give the use cases in various P-algorithms.Although the paper uses the names of operators such as selection, crossing, our orientation is not only to evolutionary algorithms. A description scheme of operators presented in this paper can be used to determine any population-based algorithms.The work development expects extending a set of operators presented, and, above all, using this set and a set of basic essences of population algorithms, the formalization of which was earlier proposed by the author, systematizing the most known algorithms of this class.Известно большое число примеров успешного решения с помощью популяционных алгоритмов (П-алгоритмов) сложных практических задач глобальной оптимизации, например, задач автоматизированного проектирования, синтеза сложных химических соединений, оптимального управления динамическими системами и т.д. П-алгоритмы также успешно используются в многокритериальной оптимизации, когда требуется предварительное построение некоторой аппроксимации множества (фронта) Парето этой задачи. П-алгоритмы многочисленны и весьма разнообразны – известно более 100 таких алгоритмов, и продолжают появляться новые алгоритмы. В этой связи актуальной является проблема систематизации выразительных средств П-алгоритмов. Рассматриваем одну из составляющих этой проблемы – проблему систематизации поисковых операторов П-алгоритмов.Представляем постановку задачи глобальной оптимизации и общую схему П-алгоритмов ее решения. Предлагаем многоуровневую классификацию основных поисковых операторов П-алгоритмов. Эта классификация на верхнем уровне иерархии выделяет следующие операторы: инициализация популяции и окончание поиска; кодирование особей; рандомизация; селекция; скрещивание; управление популяцией; локальный поиск. Указанные операторы на следующем иерархическом уровне подразделяются на детерминированные и стохастические. Далее различаем статические, динамические программные и динамические адаптивные операторы. Следующие классификационные уровни являются «операторозависимыми», то есть, вообще говоря, различны для каждого из операторов. Раскрываем суть этих операторов, приводим варианты использования в различных П-алгоритмах.Хотя в работе используются такие наименования операторов, как селекция, скрещивание, мы ориентируемся не только на эволюционные алгоритмы. Представленная в работе схема описания операторов может быть использована для определения любых популяционных алгоритмов.В развитие работы планируется расширить представленный набор операторов и, главное, с помощью этого набора и набора основных сущностей популяционных алгоритмов, формализация которых предложена автором ранее, систематизировать наиболее известные алгоритмы этого класса

Equivariant pretheories and invariants of torsors

In the present paper we introduce and study the notion of an equivariant pretheory: basic examples include equivariant Chow groups, equivariant K-theory and equivariant algebraic cobordism. To extend this set of examples we define an equivariant (co)homology theory with coefficients in a Rost cycle module and provide a version of Merkurjev's (equivariant K-theory) spectral sequence for such a theory. As an application we generalize the theorem of Karpenko-Merkurjev on G-torsors and rational cycles; to every G-torsor E and a G-equivariant pretheory we associate a graded ring which serves as an invariant of E. In the case of Chow groups this ring encodes the information concerning the motivic J-invariant of E and in the case of Grothendieck's K_0 -- indexes of the respective Tits algebras.Comment: 23 pages; this is an essentially extended version of the previous preprint: the construction of an equivariant cycle (co)homology and the spectral sequence (generalizing the long exact localization sequence) are adde

Hydrokinetic predictions for femtoscopy scales in A+A collisions in the light of recent ALICE LHC results

A study of energy behavior of the pion spectra and interferometry scales is carried out for the top SPS, RHIC and for LHC energies within the hydrokinetic approach. The main mechanisms that lead to the paradoxical, at first sight, dependence of the interferometry scales with an energy growth, in particular, a decrease $R_{out}/R_{side}$ ratio, are exposed. The hydrokinetic predictions for the HBT radii at LHC energies are compared with the recent results of the ALICE experiment.Comment: Based on the talks given at the Sixth Workshop on Particle Correlations and Femtoscopy, BITP, Kiev, September 14 - 18, 2010 and GSI/EMMI Seminar, January 14, 201

Russian specialized periodicals in culture as a modern communicative channel

The key factor of modern society development is mass media, and nowadays its demanded business model is the translation of advertising informatio