Active-to-absorbing state phase transition in the presence of fluctuating environments: Weak and strong dynamic scaling

We investigate the scaling properties of phase transitions between survival and extinction (active-to-absorbing state phase transition, AAPT) in a model, that by itself belongs to the directed percolation (DP) universality class, interacting with a spatio-temporally fluctuating environment having its own non-trivial dynamics. We model the environment by (i) a randomly stirred fluid, governed by the Navier-Stokes (NS) equation, and (ii) a fluctuating surface, described either by the Kardar-Parisi-Zhang (KPZ) or the Edward-Wilkinson (EW) equations. We show, by using a one-loop perturbative field theoretic set up, that depending upon the spatial scaling of the variance of the external forces that drive the environment (i.e., the NS, KPZ or EW equations), the system may show {\em weak} or {\em strong dynamic scaling} at the critical point of active to absorbing state phase transitions. In the former case AAPT displays scaling belonging to the DP universality class, whereas in the latter case the universal behavior is different.Comment: 17 pages, 2 figures, accepted in PR

Energy and momentum deposited into a QCD medium by a jet shower

Hard partons moving through a dense QCD medium lose energy by radiative emissions and elastic scatterings. Deposition of the radiative contribution into the medium requires rescattering of the radiated gluons. We compute the total energy loss and its deposition into the medium self-consistently within the same formalism, assuming perturbative interaction between probe and medium. The same transport coefficients that control energy loss of the hard parton determine how the energy is deposited into the medium; this allows a parameter free calculation of the latter once the former have been computed or extracted from experimental energy loss data. We compute them for a perturbative medium in hard thermal loop (HTL) approximation. Assuming that the deposited energy-momentum is equilibrated after a short relaxation time, we compute the medium's hydrodynamical response and obtain a conical pattern that is strongly enhanced by showering.Comment: 4 pages, 3 figures, revtex4, intro modified, typos correcte

Yang-Mills Radiation in Ultra-relativistic Nuclear Collisions

The classical Yang-Mills radiation computed in the McLerran-Venugopalan model is shown to be equivalent to the gluon bremsstrahlung distribution to lowest order in pQCD. The classical distribution is also shown to match smoothly onto the conventional pQCD mini-jet distribution at a scale characteristic of the initial parton transverse density of the system. The atomic number and energy dependence of that scale is computed from available structure function information. The limits of applicability of the classical Yang-Mills description of nuclear collisions at RHIC and LHC energies are discussed.Comment: 21 pages (Latex) including 2 postscript figures via psfi

Final state interaction in kaons decays

The kaons decays to the pairs of charged and neutral pions are considered in the framework of the non-relativistic quantum mechanics. The general expressions for the decay amplitudes to the two different channels accounting for the strong interaction between pions are obtained. The developed approach allows one to estimate the contribution of terms of any order in strong interaction and correctly takes into account the electromagnetic interaction between the pions in the final state.Comment: 8 page

Prompt photon hadroproduction at high energies in the k_T-factorization approach

We consider the prompt photon production at high energy hadron colliders in the framework of k_T-factorization approach. The unintegrated quark and gluon distributions in a proton are determined using the Kimber-Martin-Ryskin prescription. The conservative error analisys is performed. We investigate both inclusive prompt photon and prompt photon and associated muon production rates. In Standard Model such events come mainly due to Compton scattering process where the final heavy (charm or bottom) quark produces a muon. The theoretical results are compared with recent experimental data taken by the D0 and CDF collaborations at Fermilab Tevatron. Our analysis also covers the azimuthal correlations between produced prompt photon and muon which can provide an important information about non-collinear parton evolution in a proton. Finally, we extrapolate the theoretical predictions to CERN LHC energies.Comment: 27 pages, 13 figure

Signals of confinement in Green functions of SU(2) Yang-Mills theory

The vortex picture of confinement is employed to explore the signals of confinement in Yang-Mills Green functions. By using SU(2) lattice gauge theory, it has been well established that the removal of the center vortices from the lattice configurations results in the loss of confinement. The running coupling constant, the gluon and the ghost form factors are studied in Landau gauge for both cases, the full and the vortex removed theory. In the latter case, a strong suppression of the running coupling constant and the gluon form factor at low momenta is observed. At the same time, the singularity of the ghost form factor at vanishing momentum disappears. This observation establishes an intimate correlation between the ghost singularity and confinement. The result also shows that a removal of the vortices generates a theory for which Zwanziger's horizon condition for confinement is no longer satisfied.Comment: 4 pages, 4 figure

NeXSPheRIO results on azimuthal anisotropy in Au-Au collisions at 200A GeV

In this work, we present the results obtained by the hydrodynamic code NeXSPheRIO on anisotropic flows. In our calculation, we made use of event-by-event fluctuating initial conditions, and chemical freeze-out was explicitly implemented. We studied directed flow, elliptic flow and forth harmonic coefficient for various hadrons at different centrality windows for Au+Au collisions at 200 AGeV. The results are discussed and compared with experimental data from RHIC.Comment: 6 pages and 6 figures, sqm2008 contributio

Medium-modified evolution of multiparticle production in jets in heavy-ion collisions

The energy evolution of medium-modified average multiplicities and multiplicity fluctuations in quark and gluon jets produced in heavy-ion collisions is investigated from a toy QCD-inspired model. In this model, we use modified splitting functions accounting for medium-enhanced radiation of gluons by a fast parton which propagates through the quark gluon plasma. The leading contribution of the standard production of soft hadrons is found to be enhanced by the factor $\sqrt{N_s}$ while next-to-leading order (NLO) corrections are suppressed by $1/\sqrt{N_s}$, where the nuclear parameter $N_s>1$ accounts for the induced-soft gluons in the hot medium. The role of next-to-next-to-leading order corrections (NNLO) is studied and the large amount of medium-induced soft gluons is found to drastically affect the convergence of the perturbative series. Our results for such global observables are cross-checked and compared with their limits in the vacuum and a new method for solving the second multiplicity correlator evolution equations is proposed.Comment: 21 pages and 8 figures, typo corrections, references adde

Low energy onset of nuclear shadowing in photoabsorption

The early onset of nuclear shadowing in photoabsorption at low photon energies has recently been interpreted as a possible signature of a decrease of the rho meson mass in nuclei. We show that one can understand this early onset within simple Glauber theory if one takes the negative real part of the rho N scattering amplitudes into account, corresponding to a higher effective mass of the rho meson in nuclear medium.Comment: REVTEX, 9 pages, including 4 eps figure

Parity doubling in particle physics

Parity doubling in excited hadrons is reviewed. Parity degeneracy in hadrons was first experimentally observed 40 years ago. Recently new experimental data on light mesons caused much excitement and renewed interest to the phenomenon, which still remains to be enigmatic. The present retrospective review is an attempt to trace the history of parity doubling phenomenon, thus providing a kind of introduction to the subject. We begin with early approaches of 1960s (Regge theory and dynamical symmetries) and end up with the latest trends (manifestations of broader degeneracies and AdS/QCD). We show the evolution of various ideas about parity doubling. The experimental evidence for this phenomenon is scrutinized in the non-strange sector. Some experiments of 1960s devoted to the search for missing non-strange bosons are re-examined and it is argued that results of these experiments are encouraging from the modern perspective.Comment: Version to appear in Int. J. Mod. Phys. A, 63 pages, 9 figure