Multi-particle Production and Thermalization in High-Energy QCD

We argue that multi-particle production in high energy hadron and nuclear collisions can be considered as proceeding through the production of gluons in the background classical field. In this approach we derive the gluon spectrum immediately after the collision and find that at high energies it is parametrically enhanced by ln(1/x) with respect to the quasi-classical result (x is the Bjorken variable). We show that the produced gluon spectrum becomes thermal (in three dimensions) with an effective temperature determined by the saturation momentum Qs, T= c Qs/2pi during the time ~1/T; we estimate c=sqrt{2pi}/2 ~ 1.2. Although this result by itself does not imply that the gluon spectrum will remain thermal at later times, it has an interesting applications to heavy ion collisions. In particular, we discuss the possibility of Bose-Einstein condensation of the produced gluon pairs and estimate the viscosity of the produced gluon system.Comment: 25 pages, 4 figures; typos fixed; discussions expanded; we added a new section IV in which we argue that at high energies the production mechanism discussed in the paper is parametrically enhanced by ln(1/x) with respect to the quasi-classical resul

Numerical investigation of high-pressure combustion in rocket engines using Flamelet/Progress-variable models

The present paper deals with the numerical study of high pressure LOx/H2 or LOx/hydrocarbon combustion for propulsion systems. The present research effort is driven by the continued interest in achieving low cost, reliable access to space and more recently, by the renewed interest in hypersonic transportation systems capable of reducing time-to-destination. Moreover, combustion at high pressure has been assumed as a key issue to achieve better propulsive performance and lower environmental impact, as long as the replacement of hydrogen with a hydrocarbon, to reduce the costs related to ground operations and increase flexibility. The current work provides a model for the numerical simulation of high- pressure turbulent combustion employing detailed chemistry description, embedded in a RANS equations solver with a Low Reynolds number k-omega turbulence model. The model used to study such a combustion phenomenon is an extension of the standard flamelet-progress-variable (FPV) turbulent combustion model combined with a Reynolds Averaged Navier-Stokes equation Solver (RANS). In the FPV model, all of the thermo-chemical quantities are evaluated by evolving the mixture fraction Z and a progress variable C. When using a turbulence model in conjunction with FPV model, a probability density function (PDF) is required to evaluate statistical averages of chemical quantities. The choice of such PDF must be a compromise between computational costs and accuracy level. State- of-the-art FPV models are built presuming the functional shape of the joint PDF of Z and C in order to evaluate Favre-averages of thermodynamic quantities. The model here proposed evaluates the most probable joint distribution of Z and C without any assumption on their behavior.Comment: presented at AIAA Scitech 201

Pair production by boost-invariant fields in comoving coordinates

We derive the pair-production probability in a constant electric field in Rindler coordinates in a quasi-classical approximation. Our result is different from the pair-production probability in an inertial frame (Schwinger formula). In particular, it exhibits non-trivial dependence on rapidity and deviation from Gaussian behavior at small transverse momenta. Our results can be important for analysis of particle production in heavy-ion collisions.Comment: 12 pages, 2 figures. Discussion added and typos fixe

Factors controlling interannual variability of vertical organic matter export and phytoplankton bloom dynamics – a numerical case-study for the NW Mediterranean Sea

Mid-latitude spring blooms of phytoplankton show considerable year-to-year variability in timing, spatial extent and intensity. It is still unclear to what degree the bloom variability is connected to the magnitude of the vertical flux of organic matter. A coupled three-dimensional hydrodynamic-biogeochemical model is used to relate interannual variability in phytoplankton spring-bloom dynamics to variability in the vertical export of organic matter in the NW Mediterranean Sea. Simulation results from 2001 to 2010, validated against remote-sensing chlorophyll, show marked interannual variability in both timing and shape of the bloom. Model results show a tendency for the bloom to start later after cold and windy winters. However, the onset of the bloom occurs often when the mixed layer is still several hundred metres deep while the heat flux is already approaching zero and turbulent mixing is low. Frequency and intensity of wind episodes control both the timing and development of the bloom and the consequent export flux of organic matter. The wintertime flux is greater than zero and shows relatively low interannual variability. The magnitude of the interannual variability is mainly determined in March when the frequency of windy days positively correlates with the export flux. Frequent wind-driven mixing episodes act to increase the export flux and, at the same time, to interrupt the bloom. Perhaps counterintuitively, our analysis shows that years with discontinuous, low-chlorophyll blooms are likely to have higher export flux than years with intense uninterrupted blooms. The NW Mediterranean shows strong analogy with the North Atlantic section within the same latitude range. Hence, our results may also be applicable to this quantitatively more important area of the world ocean

A Parametrization of Bipartite Systems Based on SU(4) Euler Angles

In this paper we give an explicit parametrization for all two qubit density matrices. This is important for calculations involving entanglement and many other types of quantum information processing. To accomplish this we present a generalized Euler angle parametrization for SU(4) and all possible two qubit density matrices. The important group-theoretical properties of such a description are then manifest. We thus obtain the correct Haar (Hurwitz) measure and volume element for SU(4) which follows from this parametrization. In addition, we study the role of this parametrization in the Peres-Horodecki criteria for separability and its corresponding usefulness in calculating entangled two qubit states as represented through the parametrization.Comment: 23 pages, no figures; changed title and abstract and rewrote certain areas in line with referee comments. To be published in J. Phys. A: Math. and Ge

Realization of compact Lie algebras in K\"ahler manifolds

The Berezin quantization on a simply connected homogeneous K\"{a}hler manifold, which is considered as a phase space for a dynamical system, enables a description of the quantal system in a (finite-dimensional) Hilbert space of holomorphic functions corresponding to generalized coherent states. The Lie algebra associated with the manifold symmetry group is given in terms of first-order differential operators. In the classical theory, the Lie algebra is represented by the momentum maps which are functions on the manifold, and the Lie product is the Poisson bracket given by the K\"{a}hler structure. The K\"{a}hler potentials are constructed for the manifolds related to all compact semi-simple Lie groups. The complex coordinates are introduced by means of the Borel method. The K\"{a}hler structure is obtained explicitly for any unitary group representation. The cocycle functions for the Lie algebra and the Killing vector fields on the manifold are also obtained