22 research outputs found
Schwinger Mechanism for Gluon Pair Production in the Presence of Arbitrary Time Dependent Chromo-Electric Field
We study Schwinger mechanism for gluon pair production in the presence of
arbitrary time-dependent chromo-electric background field with
arbitrary color index =1,2,...8 in SU(3) by directly evaluating the path
integral. We obtain an exact expression for the probability of non-perturbative
gluon pair production per unit time per unit volume and per unit transverse
momentum from arbitrary . We show that the
tadpole (or single gluon) effective action does not contribute to the
non-perturbative gluon pair production rate . We find
that the exact result for non-perturbative gluon pair production is independent
of all the time derivatives where
and has the same functional dependence on two casimir invariants
and as the constant
chromo-electric field result with the replacement: . This
result may be relevant to study the production of a non-perturbative
quark-gluon plasma at RHIC and LHC.Comment: 13 pages latex, Published in European Physical Journal
A kinetic approach to eta' production from a CP-odd phase
The production of (eta,eta')- mesons during the decay of a CP-odd phase is
studied within an evolution operator approach. We derive a quantum kinetic
equation starting from the Witten-DiVecchia-Veneziano Lagrangian for
pseudoscalar mesons containing a U_A(1) symmetry breaking term. The non-linear
vacuum mean field for the flavour singlet pseudoscalar meson is treated as a
classical, self-interacting background field with fluctuations assumed to be
small. The numerical solution provides the time evolution of momentum
distribution function of produced eta'- mesons after a quench at the
deconfinement phase transition. We show that the time evolution of the momentum
distribution of the produced mesons depend strongly on the shape of the
effective potential at the end of the quench, exhibiting either parametric or
tachyonic resonances. Quantum statistical effects are essential and lead to a
pronounced Bose enhancement of the low momentum states.Comment: 10 pages, latex, epsfig, 6 figure
Closed-Time Path Integral Formalism and Medium Effects of Non-Equilibrium QCD Matter
We apply the closed-time path integral formalism to study the medium effects
of non-equilibrium gluon matter. We derive the medium modified resummed gluon
propagator to the one loop level in non-equilibrium in the covariant gauge. The
gluon propagator we derive can be used to remove the infrared divergences in
the secondary parton collisions to study thermalization of minijet parton
plasma at RHIC and LHC.Comment: Final version, To appear in Physical Review D, Minor modification,
reference adde
Phase Space Description of the Leading Order Quark and Gluon Production from a Space-Time Dependent Chromofield
We derive source terms for the production of quarks and gluons from the QCD
vacuum in the presence of a space-time dependent external chromofield A_{cl} to
the order of S^{(1)}. We found that the source terms for the parton production
processes A_{cl} -> q\bar{q} and A_{cl},A_{cl}A_{cl} -> gg also include the
annihilation processes q\bar{q} -> A_{cl} and gg -> A_{cl},A_{cl}A_{cl}. The
source terms we derive are applicable for the description of the production of
partons with momentum p larger rhan gA which itself must be larger than
\Lambda_{QCD}. We observe that these source terms for the production of partons
from a space-time dependent chromofield can be used to study the production and
equilibration of the quark-gluon plasma during the very early stages of an
ultrarelativistic heavy-ion collision.Comment: 30 pages latex (single spaced), 7 eps figures, Revised Version, To
appear in Physical Review
Infrared Behaviour of The Gluon Propagator in Non-Equilibrium Situations
The infrared behaviour of the medium modified gluon propagator in
non-equilibrium situations is studied in the covariant gauge using the
Schwinger-Keldysh closed-time path formalism. It is shown that the magnetic
screening mass is non-zero at the one loop level whenever the initial gluon
distribution function is non isotropic with the assumption that the
distribution function of the gluon is not divergent at zero transverse
momentum. For isotropic gluon distribution functions, such as those describing
local equilibrium, the magnetic mass at one loop level is zero which is
consistent with finite temperature field theory results. Assuming that a
reasonable initial gluon distribution function can be obtained from a
perturbative QCD calculation of minijets, we determine these out of equilibrium
values for the initial magnetic and Debye screening masses at energy densities
appropriate to RHIC and LHC. We also compare the magnetic masses obtained here
with those obtained using finite temperature lattice QCD methods at similar
temperatures at RHIC and LHC.Comment: 21 pages latex, 4 figures, final version to be published in Phys.
Rev.
PD-1/PD-L1 blockers in NSCLC brain metastases: Challenging paradigms and clinical practice
Immune checkpoint inhibitors (ICI) have revolutionized the management of advanced non-small cell lung cancer (NSCLC). However, most pivotal phase III trials systematically excluded patients with active brain metastases, precluding the generalization of the results. Although theoretically restricted from crossing the blood-brain barrier, the novel pharmacokinetic/pharmacodynamic profiles of anti-PD-1/PD-L1 drugs have prompted studies to evaluate their activity in patients with NSCLC with active central nervous system (CNS) involvement. Encouraging results have suggested that ICI could be active in the CNS in selected patients with driver-negative advanced NSCLC with high PD-L1 expression and low CNS disease burden. Single-agent CNS response rates around 30% have been reported. Beyond this particular setting, anti-PD-1/PD-L1 antibodies have been evaluated in patients receiving local therapy for brain metastases (BM), addressing concerns about potential neurologic toxicity risks associated with radiotherapy, more specifically, radionecrosis (RN). Accordingly, a variety of clinical and imaging strategies are being appropriately developed to evaluate tumor response and to rule out pseudoprogression or radionecrosis. Our purpose is to critically summarize the advances regarding the role of systemic anti-PD-1/PD-L1 antibodies for the treatment of NSCLC BM. Data were collected from the PubMed database, reference lists, and abstracts from the latest scientific meetings. Recent reports suggest anti-PD-1/PD-L1 agents are active in a subset of patients with NSCLC with BM showing acceptable toxicity. These advances are expected to change soon the management of these patients but additional research is required to address concerns regarding radionecrosis and the appropriate sequencing of local and systemic therapy combinations