Flash of photons from the early stage of heavy-ion collisions

The dynamics of partonic cascades may be an important aspect for particle production in relativistic collisions of nuclei at CERN SPS and BNL RHIC energies. Within the Parton-Cascade Model, we estimate the production of single photons from such cascades due to scattering of quarks and gluons q g -> q gamma, quark-antiquark annihilation q qbar -> g gamma, or gamma gamma, and from electromagnetic brems-strahlung of quarks q -> q gamma. We find that the latter QED branching process plays the dominant role for photon production, similarly as the QCD branchings q -> q g and g -> g g play a crucial role for parton multiplication. We conclude therefore that photons accompanying the parton cascade evolution during the early stage of heavy-ion collisions shed light on the formation of a partonic plasma.Comment: 4 pages including 3 postscript figure

Secondary phi meson peak as an indicator of QCD phase transition in ultrarelativistic heavy ion collisions

In a previous paper, we have shown that a double phi peak structure appears in the dilepton invariant mass spectrum if a first order QCD phase transition occurs in ultrarelativistic heavy ion collisions. Furthermore, the transition temperature can be determined from the transverse momentum distribution of the low mass phi peak. In this work, we extend the study to the case that a smooth crossover occurs in the quark-gluon plasma to the hadronic matter transition. We find that the double phi peak structure still exists in the dilepton spectrum and thus remains a viable signal for the formation of the quark-gluon plasma in ultrarelativistic heavy ion collisions.Comment: 8 pages, 9 uuencoded postscript figures included, Latex, LBL-3572

Examining the Personal and Institutional Determinants of Research Productivity in Hospitality and Tourism Management

The transition toward a post-capitalist knowledge-oriented economy has resulted in an increasingly competitive academic environment, where the success of faculty is dependent on their research productivity. This study examines the personal and institutional determinants of the quantity and quality of the research productivity of hospitality and tourism management faculty in US institutions. A survey of 98 faculty found that a different set of determinants impact the quantity and quality aspects of research productivity. Also, institutional determinants were found to play a larger role, indicating the need for administrators to strive for a culture that is supportive of and an infrastructure that is conducive to their faculty’s research success. The authors use the field of hospitality and tourism management as a case study to develop a holistic and cohesive framework for knowledge worker productivity that can guide the evaluation, hiring, and development of researchers

Out of equilibrium quantum field dynamics of an initial thermal state after a change in the external field

The effects of the initial temperature in the out of equilibrium quantum field dynamics in the presence of an homogeneous external field are investigated. We consider an initial thermal state of temperature T for a constant external field J. A subsequent sign flip of the external field, J to -J, gives rise to an out of equilibrium nonperturbative quantum field dynamics. The dynamics is studied here for the symmetry broken lambda(Phi^2)^2 scalar N component field theory in the large N limit. We find a dynamical effective potential for the expectation value that helps to understand the dynamics. The dynamics presents two regimes defined by the presence or absence of a temporal trapping close to the metastable equilibrium position of the potential. The two regimes are separated by a critical value of the external field that depends on the initial temperature. The temporal trapping is shorter for larger initial temperatures or larger external fields. Parametric resonances and spinodal instabilities amplify the quantum fluctuations in the field components transverse to the external field. When there is a temporal trapping this is the main mechanism that allows the system to escape from the metastable state for large N. Subsequently backreaction stops the growth of the quantum fluctuations and the system enters a quasiperiodic regime.Comment: LaTeX, 19 pages, 12 .eps figures, improved version to appear in Phys Rev

A QCD space-time analysis of quarkonium formation and evolution in hadronic collisions

The production of heavy quarkonium as QQbar bound-states in hadron-hadron collisions is considered within the framework of a space-time description, combining parton-cascade evolution with a coalescence model for bound-state formation. The `hard' production of the initial QQbar, directly or via gluon fragmentation and including both color-singlet and color-octet contributions, is calculated from the PQCD cross-sections. The subsequent development of the QQbar system is described within a space-time generalization of the DGLAP parton-evolution formalism in position- and momentum-space. The actual formation of the bound-states is accomplished through overlap of the QQbar pair and a spectrum of quarkonium wave-functions. This coalescence can only occur after sufficent gluon radiation reduces the QQbar relative velocity to a value commensurate with the non-relativistic kinematics of these bound systems. The presence of gluon participants in the cascade then is both necessary and leads to the natural inclusion of both color-singlet and color-octet mechanisms. The application of this approach to pp (ppbar) collisions from sqrt(s)= 30 GeV - 14 TeV reveals very decent agreement with available data from ISR and Tevatron - without the necessity of introducing fit parameters. Moreover, production probabilities are calculated for a complete spectrum of charmonium and bottonium states, with the relative significance compared to open charm (bottom) production. An analysis of the space-time development is carried through which sheds light on the relevance of gluon radiation and color-structure, suggesting a correponding experimental investigation.Comment: 37 pages including 16 postscript figure

Non-equilibrium dynamics in quantum field theory at high density: the tsunami

The dynamics of a dense relativistic quantum fluid out of thermodynamic equilibrium is studied in the framework of the Phi^4 scalar field theory in the large N limit. The time evolution of a particle distribution in momentum space (the tsunami) is computed. The effective mass felt by the particles in such a high density medium equals the tree level mass plus the expectation value of the squared field. The case of negative tree level squared mass is particularly interesting. In such case dynamical symmetry restoration as well as dynamical symmetry breaking can happen. Furthermore, the symmetry may stay broken with vanishing asymptotic squared mass showing the presence of out of equilibrium Goldstone bosons. We study these phenomena and identify the set of initial conditions that lead to each case. We compute the equation of state which turns to depend on the initial state. Although the system does not thermalize, the equation of state for asymptotically broken symmetry is of radiation type. We compute the correlation functions at equal times. The two point correlator for late times is the sum of different terms. One stems from the initial particle distribution. Another term accounts for the out of equilibrium Goldstone bosons created by spinodal unstabilities when the symmetry is asymptotically broken.Both terms are of the order of the inverse of the coupling for distances where causal signals can connect the two points. The contribution of the out of equilibrium Goldstones exhibits scaling behaviour in a generalized sense.Comment: LaTex, 49 pages, 15 .ps figure

Virtual Meson Cloud of the Nucleon and Intrinsic Strangeness and Charm

We have applied the Meson Cloud Model (MCM) to calculate the charm and strange antiquark distribution in the nucleon. The resulting distribution, in the case of charm, is very similar to the intrinsic charm momentum distribution in the nucleon. This seems to corroborate the hypothesis that the intrinsic charm is in the cloud and, at the same time, explains why other calculations with the MCM involving strange quark distributions fail in reproducing the low x region data. From the intrinsic strange distribution in the nucleon we have extracted the strangeness radius of the nucleon, which is in agreement with other meson cloud calculations.Comment: 9 pages RevTex, 4 figure

Electromagnetic transition form factors of negative parity nucleon resonances

We have calculated the transition form factors for the electromagnetic excitation of the negative parity resonances of the nucleon using different models previously proposed and we discuss their results and limits by comparison with experimental data.Comment: 13 pages, 6 figures, to be published on Journal of Physics

Performance Analysis of Throughput Efficient Switch-over between FSO and mmW Links

Free Space Optics (FSO) links provide usage of high bandwidth and the flexibility of wireless communication links. However, weather patterns like fog and heavy snow fall limit the availability of FSO. Another technology providing similar properties regarding offered data rates and flexibility of setup is Millimeter Wave Technology (mmW), operating at several tens of GHz. In this case, heavy rain limits mmW link availability. A combination of both technologies had been proved to be very effective to achieve very high availability. Different hybrid architectures of these two links and switch-over techniques had been proposed in the recent years. All of these techniques require redundant transmission on either both transmission links or waste bandwidth of backup link when main FSO link is operational. In this paper, a switch-over between these technologies is proposed, to maintain high availability without the loss of transmission bandwidth. The performance of this switch-over has been simulated for more than one year measured availability data for hybrid network of mmW link and FSO link. The switch over behavior has also been simulated for fog, rain and snow events. It has been shown that the availability with switch-over reaches the redundant link availability but switchover can save more than 90% redundant transmission and increase the hybrid network throughput significantly

Effect of gluon-exchange pair-currents on the ratio G(E(P))/G(M(P))

The effect of one-gluon-exchange (OGE) pair-currents on the ratio $\mu_p G_E^p/G_M^p$ for the proton is investigated within a nonrelativistic constituent quark model (CQM) starting from $SU(6) \times O(3)$ nucleon wave functions, but with relativistic corrections. We found that the OGE pair-currents are important to reproduce well the ratio $\mu_p G_E^p/G_M^p$. With the assumption that the OGE pair-currents are the driving mechanism for the violation of the scaling law we give a prediction for the ratio $\mu_n G_E^n/G_M^n$ of the neutron.Comment: 5 pages, 4 figure