50,526 research outputs found
Strangeness Equilibration at GSI Energies
We develop the notion of "broad-band equilibration" in heavy-ion processes
involving dense medium. Given density-dependent \Km-masses we show that the
equilibration at GSI energies claimed to hold in previous treatments down to
, can be replaced by a broad-band equilibration in which the
\Km-meson and hyperons are produced in an essentially constant ratio
independent of density. There are experimental indications that this also holds
for AGS energies. We then proceed to argue that {\it both} and must
get lighter in dense medium at some density due to the
decoupling of the vector mesons. As a consequence, kaon condensation in compact
stars could take place {\it before} chiral restoration since the sum of bare
quark masses in the kaon should lie below . Another consequence of the
decoupling vector interactions is that the quasi-particle picture involving
(quasi)quarks, presumably ineffective at low densities, becomes more
appropriate at higher densities as chiral restoration is approached.Comment: 16 pages, latex with 2 eps figures. Abstract rewritten and references
update
Darboux Transformation of the Green Function for the Dirac Equation with the Generalized Potential
We consider the Darboux transformation of the Green functions of the regular
boundary problem of the one-dimensional stationary Dirac equation. We obtained
the Green functions of the transformed Dirac equation with the initial regular
boundary conditions. We also construct the formula for the unabridged trace of
the difference of the transformed and the initial Green functions of the
regular boundary problem of the one-dimensional stationary Dirac equation. We
illustrate our findings by the consideration of the Darboux transformation for
the Green function of the free particle Dirac equation on an interval.Comment: 14 pages,zip. file: Latex, 1 figure. Typos corrected, the figure
replace
Cervical Cancer-Associated Human Papillomavirus 16 E7 Oncoprotein Inhibits Induction of Anti-Cancer Immunity by a CD4+ T Cell Dependent Mechanism
Attempts to develop therapeutic vaccines against cervical cancer have been proven difficult. One of the major causes of the failure is due to the use of the wrong mouse models based on transplantable tumours in testing the efficacy of vaccines. Now that a transgenic epithelial mouse model has been developed to closely mimic cervical cancer, the mechanisms needed to eliminate this type of cancer could be studied. The E7 oncoprotein of Human Papillomavirus (HPV) is the most expressed HPV protein in cervical cancers and its continuous production is essential to maintain the cancerous state and therefore the obvious target in the development of vaccines. Skin grafts expressing the HPV 16 E7 protein (E7 autografts) are not spontaneously rejected from an MHC matched immunocompetent host. Interestingly, simultaneous placement of an MHC mismatched skin (allograft) next to an E7 autograft results in the E7 autograft rejection. However when the allograft also expresses E7, the E7 autograft is rejected more slowly. Autograft rejection requires CD8+ T cells, and is accelerated by removal of CD4+ T cells after placement of the E7 expressing allograft, suggesting induction of an E7 specific CD4+ regulatory T cell population by the E7 expressing allograft. This observation may have implications in designing effective vaccines and immunotherapy against cervical cancers in women
Long-lived domain wall plasmons in gapped bilayer graphene
Topological domain walls in dual-gated gapped bilayer graphene host edge
states that are gate- tunable and valley polarized. Here we predict that
plasmonic collective modes can propagate along these topological domain walls
even at zero bulk density, and possess a markedly different character from that
of bulk plasmons. Strikingly, domain wall plasmons are extremely long-lived,
with plasmon lifetimes that can be orders of magnitude larger than the
transport scattering time in the bulk. While most pronounced at low
temperatures, long domain wall plasmon lifetimes persist even at room
temperature with values up to a few picoseconds. Domain wall plasmons possess a
rich phenomenology including a wide range of frequencies (up to the
mid-infrared), tunable sub-wavelength electro-magnetic confinement lengths, as
well as a valley polarization for forward/backward propagating modes. Its
unusual features render them a new tool for realizing low-dissipation
plasmonics that transcend the restrictions of the bulk
S matrix of collective field theory
By applying the Lehmann-Symanzik-Zimmermann (LSZ) reduction formalism, we
study the S matrix of collective field theory in which fermi energy is larger
than the height of potential. We consider the spatially symmetric and
antisymmetric boundary conditions. The difference is that S matrices are
proportional to momenta of external particles in antisymmetric boundary
condition, while they are proportional to energies in symmetric boundary
condition. To the order of , we find simple formulas for the S matrix
of general potential. As an application, we calculate the S matrix of a case
which has been conjectured to describe a "naked singularity".Comment: 19 page, LaTe
Kaluza-Klein masses of bulk fields with general boundary conditions in AdS
Recently bulk Randall-Sundrum theories with the gauge group have drawn a lot of interest as an alternative to
electroweak symmetry breaking mechanism. These models are in better agreement
with electroweak precision data since custodial isospin symmetry on the IR
brane is protected by the extended bulk gauge symmetry. We comprehensively
study, in the S^1/\ZZ orbifold, the bulk gauge and fermion fields with the
general boundary conditions as well as the bulk and localized mass terms.
Master equations to determine the Kaluza-Klein (KK) mass spectra are derived
without any approximation, which is an important basic step for various
phenomenologies at high energy colliders. The correspondence between orbifold
boundary conditions and localized mass terms is demonstrated not only in the
gauge sector but also in the fermion sector. As the localized mass increases,
the first KK fermion mass is shown to decrease while the first KK gauge boson
mass to increase. The degree of gauge coupling universality violation is
computed to be small in most parameter space, and its correlation with the mass
difference between the top quark and light quark KK mode is also studied.Comment: 25 pages with 10 figures, Final version accepted by PR
Influence of Primary Cosmic Radiation Mass Composition on the Estimation of Eas Energy
At the Yakutsk EAS array E_em is determined by using measurements of EAS
Cherenkov light flux and charged particle flux. It is known from calculations
that these characteristics depend on a sort of primary particle and, therefore,
the estimation of E_em depends on a primary particle mass. In the work the
dependence of the E_em/E_0 ratio on the energy is given and experimental data
are compared with calculations by the QGSJET model. The calculations have been
carried out for the primary proton and iron nucleus. The average calculated
meaning of the value of E_em/E_0 ratio (between the proton and iron nucleus)
within experimental errors is in agreement with experimental data that doesnt
contradict to the mixed mass composition of primary cosmic radiation.Comment: 19th European Cosmic Ray Symposium. Aug 30 - Sep 3 2004, Florence,
Italy. 3 pages, 1 figure. Subbmitted for publication in International Journal
of Modern Physics
q-Deformation of W(2,2) Lie algebra associated with quantum groups
An explicit realization of the W(2,2) Lie algebra is presented using the
famous bosonic and fermionic oscillators in physics, which is then used to
construct the q-deformation of this Lie algebra. Furthermore, the quantum group
structures on the q-deformation of this Lie algebra are completely determined.Comment: 12 page
Pion electromagnetic form factor at finite temperature
Temperature effects on the electromagnetic couplings of pions in hot hadronic
matter are studied with an effective chiral Lagrangian. We show that the
Ward-Takahashi identity is satisfied at non-zero temperature in the soft pion
limit. The in-medium electromagnetic form factor of the pion is obtained in the
time-like region and shown to be reduced in magnitude, especially near the
vector-meson resonance region. Finally, we discuss the consequences of this
medium effect on dilepton production from hot hadronic matter.Comment: 29 pages (LaTex) + 11 figure
Quark Orbital Angular Momentum in the Baryon
Analytical and numerical results, for the orbital and spin content carried by
different quark flavors in the baryons, are given in the chiral quark model
with symmetry breaking. The reduction of the quark spin, due to the spin
dilution in the chiral splitting processes, is transferred into the orbital
motion of quarks and antiquarks. The orbital angular momentum for each quark
flavor in the proton as a function of the partition factor and the
chiral splitting probability is shown. The cancellation between the spin
and orbital contributions in the spin sum rule and in the baryon magnetic
moments is discussed.Comment: 26 pages, 3 figures, revised version with minor eq. no and ref. no.
corrections. Discussion on the spin and a new ref. are adde
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