481 research outputs found
Classical stability of U(1)_A domain walls in dense matter QCD
It was recently shown that there exists metastable U(1)_A domain wall
configurations in high-density QCD (\mu >> 1 GeV). In the following we will
assess the stability of such non-trivial field configurations at intermediate
densities (\mu < 1 GeV). The existence of such configurations at intermediate
densities could have interesting consequences for the physics of neutron stars
with high core density.Comment: 13 pages, 2 Postscript figures, typos correcte
Thermodynamics of non-local materials: extra fluxes and internal powers
The most usual formulation of the Laws of Thermodynamics turns out to be
suitable for local or simple materials, while for non-local systems there are
two different ways: either modify this usual formulation by introducing
suitable extra fluxes or express the Laws of Thermodynamics in terms of
internal powers directly, as we propose in this paper. The first choice is
subject to the criticism that the vector fluxes must be introduced a posteriori
in order to obtain the compatibility with the Laws of Thermodynamics. On the
contrary, the formulation in terms of internal powers is more general, because
it is a priori defined on the basis of the constitutive equations. Besides it
allows to highlight, without ambiguity, the contribution of the internal powers
in the variation of the thermodynamic potentials. Finally, in this paper, we
consider some examples of non-local materials and derive the proper expressions
of their internal powers from the power balance laws.Comment: 16 pages, in press on Continuum Mechanics and Thermodynamic
Meson-loop contributions to the quark condensate from the instanton vacuum
We investigate the quark condensate of the QCD vacuum within the instanton
vacuum model. We calculate the meson-loop contributions to the dynamical quark
mass and quark condensate to -, -, and -order corrections. We find that the meson (especially pion)
loops provide substantial contributions to the dynamical quark mass and as a
result to the quark condensate. The results indicate that the
corrections should be reconsidered in the systematical way. The present results
are consistent with those from chiral perturbation theory.Comment: Final version accepted for publication in Phys. Lett. B. The title
was changed. Small corrections were adde
Testing the principle of equivalence by supernova neutrinos
We study the possible impact of the neutrino oscillation which could be
induced by a tiny violation of equivalence principle (VEP) for neutrinos
emitted from supernova driven by gravitational collapse. Due to the absence of
any significant indication of neutrino oscillation in the SN1987A data, we
obtain sever bounds on relevant VEP parameters \delta \gamma\lsim O(10^{-31})
for massless or degenerated neutrinos and \delta \gamma \lsim O(10^{-16})\times
[\Delta m^2/10^{-5} eV^2] for massive neutrinos.Comment: Revtex, 16 pages, 4 figure
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Advanced thermally stable jet fuels: Technical progress report, October 1994--December 1994
There are five tasks within this project on thermally stable coal-based jet fuels. Progress on each of the tasks is described. Task 1, Investigation of the quantitative degradation chemistry of fuels, has 5 subtasks which are described: Literature review on thermal stability of jet fuels; Pyrolytic and catalytic reactions of potential endothermic fuels: cis- and trans-decalin; Use of site specific {sup 13}C-labeling to examine the thermal stressing of 1-phenylhexane: A case study for the determination of reaction kinetics in complex fuel mixtures versus model compound studies; Estimation of critical temperatures of jet fuels; and Surface effects on deposit formation in a flow reactor system. Under Task 2, Investigation of incipient deposition, the subtask reported is Uncertainty analysis on growth and deposition of particles during heating of coal-derived aviation gas turbine fuels; under Task 3, Characterization of solid gums, sediments, and carbonaceous deposits, is subtask, Studies of surface chemistry of PX-21 activated carbon during thermal degradation of jet A-1 fuel and n-dodecane; under Task 4, Coal-based fuel stabilization studies, is subtask, Exploratory screening and development potential of jet fuel thermal stabilizers over 400 C; and under Task 5, Exploratory studies on the direct conversion of coal to high quality jet fuels, are 4 subtasks: Novel approaches to low-severity coal liquefaction and coal/resid co-processing using water and dispersed catalysts; Shape-selective naphthalene hydrogenation for production of thermally stable jet fuels; Design of a batch mode and a continuous mode three-phase reactor system for the liquefaction of coal and upgrading of coal liquids; and Exploratory studies on coal liquids upgrading using mesopores molecular sieve catalysts. 136 refs., 69 figs., 24 tabs
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Advanced thermally stable jet fuels: Technical progress report, July 1994--September 1994
There are five tasks within this project on thermally stable coal-based jet fuels. Progress on each of the tasks is described. Task 1, Investigation of the quantitative degradation chemistry of fuels, has 3 subtasks which are described: Pyrolysis of n-alkylbenzenes; Thermal decomposition of n-tetradecane in near-critical region; and Re-examining the effects of reactant and inert gas pressure on tetradecane pyrolysis--Effect of cold volume in batch reactor. Under Task 2, Investigation of incipient deposition, the subtask reported is Uncertainty analysis on growth and deposition of particles during heating of coal-derived aviation gas turbine fuels; under Task 3, Investigation of the quantitative degradation chemistry of fuels, is subtask, Effects of high surface area activated carbon and decalin on thermal degradation of jet A-1 fuel and n-dodecane; under Task 4, Coal-based fuel stabilization studies, is subtask, Screening potential jet fuel stabilizers using the model compound dodecane; and under Task 5, Exploratory studies on the direct conversion of coal to high quality jet fuels, is subtask, Shape-selective naphthalene hydrogenation for production of thermally stable jet fuels. 25 refs., 64 figs., 22 tabs
Drum vortons in high density QCD
Recently it was shown that high density QCD supports of number of topological
defects. In particular, there are U(1)_Y strings that arise due to K^0
condensation that occurs when the strange quark mass is relatively large. The
unique feature of these strings is that they possess a nonzero K^+ condensate
that is trapped on the core. In the following we will show that these strings
(with nontrivial core structure) can form closed loops with conserved charge
and currents trapped on the string worldsheet. The presence of conserved
charges allows these topological defects, called vortons, to carry angular
momentum, which makes them classically stable objects. We also give arguments
demonstrating that vortons carry angular momentum very efficiently (in terms of
energy per unit angular momentum) such that they might be the important degrees
of freedom in the cores of neutron stars.Comment: 11 pages, accepted for publication in Physical Review
Lorentz-violating effects on topological defects generated by two real scalar fields
The influence of a Lorentz-violation on soliton solutions generated by a
system of two coupled scalar fields is investigated. Lorentz violation is
induced by a fixed tensor coefficient that couples the two fields. The
Bogomol'nyi method is applied and first-order differential equations are
obtained whose solutions minimize energy and are also solutions of the
equations of motion. The analysis of the solutions in phase space shows how the
stability is modified with the Lorentz violation. It is shown explicitly that
the solutions preserve linear stability despite the presence of Lorentz
violation. Considering Lorentz violation as a small perturbation, an analytical
method is employed to yield analytical solutions.Comment: (9 pages, 11 figures
Magnetic moments of antidecuplet pentaquarks
We analyze the magnetic moment of the exotic pentaquarks of the flavor
antidecuplet in the constituent quark model for the case in which the ground
state is in an orbital L(p)=0(+) or a L(p)=1(-) state. We derive sum rules for
the magnetic moments. The magnetic moment of the Theta(1540) is found to be
0.38, 0.09 and 1.05 mu_N for J(p)=1/2(-), 1/2(+) and 3/2(+), respectively,
which is compared with the results obtained in other approaches.Comment: 15 pages, 1 figure, 3 tables. Revised version, extended introduction
and discussion, accepted for publication in Physics Letters
Axion-like particles as ultra high energy cosmic rays?
If Ultra High Energy Cosmic Rays (UHECRs) with E>4 10^{19} eV originate from
BL Lacertae at cosmological distances as suggested by recent studies, the
absence of the GZK cutoff can not be reconciled with Standard-Model particle
properties. Axions would escape the GZK cutoff, but even the coherent
conversion and back-conversion between photons and axions in large-scale
magnetic fields is not enough to produce the required flux. However, one may
construct models of other novel (pseudo)scalar neutral particles with
properties that would allow for sufficient rates of particle production in the
source and shower production in the atmosphere to explain the observations. As
an explicit example for such particles we consider SUSY models with light
sgoldstinos.Comment: 5 pages, 2 postscript figures, ref. adde
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