A relativistic quark model for the Omega- electromagnetic form factors

We compute the Omega- electromagnetic form factors and the decuplet baryon magnetic moments using a quark model application of the Covariant Spectator Theory. Our predictions for the Omega- electromagnetic form factors can be tested in the future by lattice QCD simulations at the physical strange quark mass.Comment: 13 pages, 5 figure

Finite Temperature Quark Confinement

Confinement may be more easily demonstrated at finite temperature using the Polyakov loop than at zero temperature using the Wilson loop. A natural mechanism for confinement can arise via the coupling of the adjoint Polyakov loop to F_{mu nu}^2. We demonstrate this mechanism with a one-loop calculation of the effective potential for SU(2) gluons in a background field consisting of a non-zero color magnetic field and a non-trivial Polyakov loop. The color magnetic field drives the Polyakov loop to non-trivial behavior, and the Polyakov loop can remove the well-known tachyonic mode associated with the Saviddy vacuum. Minimizing the real part of the effective potential leads to confinement, as determined by the Polyakov loop. Unfortunately, we cannot arrange for simultaneous stability and confinement for this simple class of field configurations. We show for a large class of abelian background fields that at one loop tachyonic modes are necessary for confinement.Comment: 15 pages, 7 figures, RevTe

On the frequency of oscillations in the pair plasma generated by a strong electric field

We study the frequency of the plasma oscillations of electron-positron pairs created by the vacuum polarization in an uniform electric field with strength E in the range 0.2 Ec < E < 10 Ec. Following the approach adopted in [1] we work out one second order ordinary differential equation for a variable related to the velocity from which we can recover the classical plasma oscillation equation when E -> 0. Thereby, we focus our attention on its evolution in time studying how this oscillation frequency approaches the plasma frequency. The time-scale needed to approach to the plasma frequency and the power spectrum of these oscillations are computed. The characteristic frequency of the power spectrum is determined uniquely from the initial value of the electric field strength. The effects of plasma degeneracy and pair annihilation are discussed.Comment: to appear in Physics Letters

The order, shape and critical point for the quark-gluon plasma phase transition

The order, shape and critical point for the phase transition between the hadronic matter and quark-gluon plasma are considered in a thermodynamical consistent approach. The hadronic phase is taken as Van der Waals gas of all the known hadronic mass spectrum particles $m_H\le 2.0$ GeV as well as Hagedorn bubbles which correspond hadronic states with mass spectrum $m_H> 2.0$ GeV. The density of states for Hagedorn bubbles is derived by calculating the microcanonical ensemble for a bag of quarks and gluons with specific internal color-flavor symmetry. The mixed-grand and microcanonical ensembles are derived for massless and massive flavors. We find Hagedorn bubbles are strongly suppressed in the dilute hadronic matter and they appear just below the line of the phase transition. The order of the phase transition depends on Hagedorn bubble's internal color-flavor structure and the volume fluctuation as well. On the other hand, the highly compressed hadronic matter undergoes a smooth phase transition from the gas of known mass spectrum hadrons to another one dominated by Hagedorn bubbles with specific internal color-flavor structure before the phase transition to quark-gluon plasma takes place at last. The phase transition is found a first order for the intermediate and large chemical potentials. The existence of the tri-critical point depends on the modification of the bubble's internal structure specified by a phenomenological parameter $\gamma\propto\mu_B$ in the medium.Comment: 69 pages, 10 figure

Bottom and Charm Production at LHC and RHIC

We study $b\bar{b}$ and $c\bar{c}$ production and the influence of nuclear shadowing at LHC and RHIC energies. We find a significant reduction in the production cross section of both charm and bottom at RHIC and LHC. Bound states such as $\Upsilon$ and $J/\Psi$ are suppressed by this reduction in the charm production cross sections. Therefore, $J/\Psi$ suppression may not be useful as a signature for the quark gluon plasma.Comment: 8 pages latex (single spaced), 4 postscript figures, title changed, minor modifications, submitted to PL

Photon production from a thermalized quark gluon plasma: quantum kinetics and nonperturbative aspects

We study the production of photons from a quark gluon plasma in local thermal equilibrium by introducing a non-perturbative formulation of the real time evolution of the density matrix. The main ingredient is the real time effective action for the electromagnetic field to $\mathcal{O}(\alpha_{em})$ and to all orders in $\alpha_s$. The real time evolution is completely determined by the solution of a \emph{classical stochastic} non-local Langevin equation which provides a Dyson-like resummation of the perturbative expansion. The Langevin equation is solved in closed form by Laplace transform in terms of the thermal photon polarization. A quantum kinetic description emerges directly from this formulation. We find that photons with $k \lesssim 200 ~{Mev}$ \emph{thermalize} as plasmon quasiparticles in the plasma on time scales $t \sim 10-20 ~{fm}/c$ which is of the order of the lifetime of the QGP expected at RHIC and LHC. We then obtain the direct photon yield to lowest order in $\alpha_{em}$ and to leading logarithmic order in $\alpha_s$ in a \emph{uniform} expansion valid at all time. The yield during a QGP lifetime $t \sim 10 ~{fm}/c$ is systematically larger than that obtained with the equilibrium formulation and the spectrum features a distinct flattening for $k \gtrsim 2.5 ~{Gev}$. We discuss the window of reliability of our results, the theoretical uncertainties in \emph{any} treatment of photon emission from a QGP in LTE and the shortcomings of the customary S-matrix approach.Comment: 31 pages. To appear in Nucl. Phys. A. New section (VII) with response to and criticism of hep-ph/031222

Wigner's DD-matrix elements for SU(3)SU(3) - A Generating Function Approach

A generating function for the Wigner's $D$-matrix elements of $SU(3)$ is derived. From this an explicit expression for the individual matrix elements is obtained in a closed form.Comment: RevTex 3.0, 22 pages, no figure

Deterministic Preparation of a Tunable Few-Fermion System

Systems consisting of few interacting fermions are the building blocks of matter with atoms and nuclei being the most prominent examples. We have created an artificial few-body quantum system with complete control over the system's quantum state using ultracold fermionic atoms in an optical dipole trap. We deterministically prepare ground state systems consisting of one to ten particles with fidelities of ~ 90%. We can tune the inter-particle interactions to arbitrary values using a Feshbach resonance and have observed the interaction-induced energy shift for a pair of repulsively interacting atoms. With this work, quantum simulation of strongly correlated fewbody systems has become possible. In addition, these microscopic quantum systems can be used as building blocks for scalable quantum information processing.Comment: 8 pages, 6 figure

SQM 2006: Theory Summary and Perspectives

In this write-up of my SQM 2006 Theory Summary talk I focus on a selection of key contributions which I consider to have a large impact on the current status of the field of strangeness physics or which may have the potential to significantly advance strangeness -- or in general flavor physics -- in the near future.Comment: 16 pages, 4 figures, SQM 2006 proceedings. Revised version containing two modifications to the transport theory sectio

Indoleamine 2,3-dioxygenase 1 (IDO1) activity in leukemia blasts correlates with poor outcome in childhood acute myeloid leukemia

Microenvironmental factors contribute to the immune dysfunction characterizing acute myeloid leukemia (AML). Indoleamine 2,3-dioxygenase 1 (IDO1) is an interferon (IFN)-γ-inducible enzyme that degrades tryptophan into kynurenine, which, in turn, inhibits effector T cells and promotes regulatory T-cell (Treg) differentiation. It is presently unknown whether childhood AML cells express IDO1 and whether IDO1 activity correlates with patient outcome. We investigated IDO1 expression and function in 37 children with newly diagnosed AML other than acute promyelocytic leukemia. Blast cells were cultured with exogenous IFN-γ for 24 hours, followed by the measurement of kynurenine production and tryptophan consumption. No constitutive expression of IDO1 protein was detected in blast cells from the 37 AML samples herein tested. Conversely, 19 out of 37 (51%) AML samples up-regulated functional IDO1 protein in response to IFN-γ. The inability to express IDO1 by the remaining 18 AML samples was not apparently due to a defective IFN-γ signaling circuitry, as suggested by the measurement of signal transducer and activator of transcription 3 (STAT3) phosphorylation. Coimmunoprecipitation assays indicated the occurrence of physical interactions between STAT3 and IDO1 in AML blasts. In line with this finding, STAT3 inhibitors abrogated IDO1 function in AML blasts. Interestingly, levels of IFN-γ were significantly higher in the bone marrow fluid of IDO-expressing compared with IDO-nonexpressing AMLs. In mixed tumor lymphocyte cultures (MTLC), IDO-expressing AML blasts blunted the ability of allogeneic naïve T cells to produce IFN-γ and promoted Treg differentiation. From a clinical perspective, the 8-year event-free survival was significantly worse in IDO-expressing children (16.4%, SE 9.8) as compared with IDO-nonexpressing ones (48.0%, SE 12.1; p=0.035). These data indicate that IDO1 expression by leukemia blasts negatively affects the prognosis of childhood AML. Moreover, they speak in favor of the hypothesis that IDO can be targeted, in adjunct to current chemotherapy approaches, to improve the clinical outcome of children with AML