274 research outputs found
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 GeV as well as Hagedorn
bubbles which correspond hadronic states with mass spectrum 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
in the medium.Comment: 69 pages, 10 figure
Bottom and Charm Production at LHC and RHIC
We study and 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 and are suppressed by this reduction in the charm
production cross sections. Therefore, 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 and to all
orders in . 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
\emph{thermalize} as plasmon quasiparticles in the plasma on time scales 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
and to leading logarithmic order in in a
\emph{uniform} expansion valid at all time. The yield during a QGP lifetime is systematically larger than that obtained with the
equilibrium formulation and the spectrum features a distinct flattening for . 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 -matrix elements for - A Generating Function Approach
A generating function for the Wigner's -matrix elements of 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
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