### Regular Series

#### Vol. 48 (2017), No. 9, pp. 1457 – 1544

Open Charm Production in Central Pb+Pb Collisions at the CERN SPS: Statistical Model Estimates

Acta Phys. Pol. B 48, 1461 (2017)

page 1461 •

abstract

Charm particle production in nucleus–nucleus collisions at the CERN SPS energies is considered within a statistical approach. Namely, the Statistical Model of the Early Stage is used to calculate the mean multiplicity of charm particles in central Pb+Pb collisions. A small number of produced charm particles necessitates the use of the exact charm conservation law. The model predicts a rapid increase of mean charm multiplicity as a function of collision energy. The mean multiplicity calculated for central Pb+Pb collisions at the center-of-mass energy per nucleon pair $\sqrt {s_{NN}}=17.3$ GeV exceeds significantly the experimental upper limit. Thus, in order to describe open charm production model parameters and/or assumptions should be revised.

Extra Lepton Pair Emission Corrections to Drell–Yan Processes in PHOTOS and SANC

Acta Phys. Pol. B 48, 1469 (2017)

page 1469 •

abstract

In the paper, we present results for the final-state emissions of lepton pairs in decays of heavy intermediate states such as $Z$ boson. Short presentations of PHOTOS and SANC algorithms and physics assumptions are given. Numerical distributions of relevance for LHC observables are shown. They are used in discussions of systematic errors in the predictions of pair emissions as implemented in the two programs. Suggestions for the future works are given. Present results confirm, that for the precision of 0.3% level, in simulation of the final state, the pair emissions can be avoided. For the precision of 0.1–0.2%, the results obtained with the presented programs should be sufficient. To cross precision tag of 0.1%, the further work is however required.

Version corrected according to Erratum Acta Phys. Pol. B 48, 2119 (2017)

Production of Dirac Particles in External Electromagnetic Fields

Acta Phys. Pol. B 48, 1493 (2017)

page 1493 •

abstract

Pair creation of spin-$\frac {1}{2}$ particles in Minkowski spacetime is investigated by obtaining exact solutions of the Dirac equation in the presence of electromagnetic fields and using them for determining the Bogoliubov coefficients. The resulting particle creation number density depends on the strength of the electric and magnetic fields.

Langevin Diffusion Coefficients Ratio in STU Model with Higher Derivative Corrections

Acta Phys. Pol. B 48, 1507 (2017)

page 1507 •

abstract

In this article, we study Langevin diffusion coefficients for the five-dimensional $\mathcal {N}=2$ STU model in the presence of higher derivative corrections. We obtained the effect of black hole charge, corresponding to the chemical potential, on the Langevin diffusion coefficients ratio. We confirm universal behavior of transverse-to-longitudinal ratio of coefficients.

Electro-magnetohydrodynamic Peristaltic Pumping of a Biviscosity Fluid Between Two Coaxial Deformable Tubes Through a Porous Medium

Acta Phys. Pol. B 48, 1515 (2017)

page 1515 •

abstract

This article aims at analyzing the electro-magnetohydrodynamic (EMHD) flow of a biviscosity fluid in a peristaltic endoscope and through a porous medium. Both the inner and outer tubes have sinusoidal wave traveling down their walls where there is a coupling between the occlusion of the outer tube and the radius ratio. The analytical solutions are found under long wavelength and low Reynolds number assumptions. The influences of the electrical field strength parameter $H$, Hartmann number $M$, upper limit apparent viscosity coefficient $\beta$, Darcy number Da, occlusion $\phi$ and the radius ratio $n$ on the axial velocity $w$, pressure gradient $\frac {\partial p}{\partial z}$, pressure rise $\Delta p$, and on mechanical efficiency $E$ are discussed through graphs. The results show that $E$ increases with increasing all parameters except the Hartmann number. Moreover, the peristaltic pumping regions, the pressure rise for zero flow rate, and the flow rate in the absence of a pressure rise are graphically discussed.

On the Effect of Quorum Sensing and Delay in Coupled Nonlinear Degenerate Optical Parametric Oscillators

Acta Phys. Pol. B 48, 1529 (2017)

page 1529 •

abstract

Complex dynamical structures inherent in degenerate optical parametric oscillator (DOPO) system are studied in detail. The system under consideration is actually the temporal part of the original DOPO system. A host of fixed points and the corresponding route to chaos are analysed. In the process, several forms of attractors and bifurcation patterns are seen. The stability zones are enumerated with the help of the bi-parametric Lyapunov plots or shrimp structures. Lastly, we have analysed the behaviour of two such coupled systems for the analysis of different modes of synchronization. The coupling is chosen in different ways. One is the direct one, the other through quorum sensing and lastly through delayed quorum sensing. It is observed that introduction of delay effects the time to achieve synchronization. In each case, the stability and other properties are analysed.

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