1,165,620 research outputs found
Casimir force for cosmological domain walls
We calculate the vacuum fluctuations that may affect the evolution of
cosmological domain walls. Considering domain walls, which are classically
stable and have interaction with a scalar field, we show that explicit symmetry
violation in the interaction may cause quantum bias that can solve the
cosmological domain wall problem.Comment: 15 pages, 2figure
Cooling force on ions in a magnetized electron plasma
Electron cooling is a well-established method to improve the phase space
quality of ion beams in storage rings. In the common rest frame of the ion and
the electron beam the ion is subjected to a drag force and it experiences a
loss or a gain of energy which eventually reduces the energy spread of the ion
beam. A calculation of this process is complicated as the electron velocity
distribution is anisotropic and the cooling process takes place in a magnetic
field which guides the electrons. In this paper the cooling force is calculated
in a model of binary collisions (BC) between ions and magnetized electrons, in
which the Coulomb interaction is treated up to second-order as a perturbation
to the helical motion of the electrons. The calculations are done with the help
of an improved BC theory which is uniformly valid for any strength of the
magnetic field and where the second-order two-body forces are treated in the
interaction in Fourier space without specifying the interaction potential. The
cooling force is explicitly calculated for a regularized and screened potential
which is both of finite range and less singular than the Coulomb interaction at
the origin. Closed expressions are derived for monochromatic electron beams,
which are folded with the velocity distributions of the electrons and ions. The
resulting cooling force is evaluated for anisotropic Maxwell velocity
distributions of the electrons and ions.Comment: 22 pages, 10 figure
Inconsistencies in the MIT bag model of hadrons
It is shown that what is commonly referred to as the MIT `bag' model of
hadrons is thermodynamically wrong: The adiabatic conditions between pressure
and temperature, and between pressure and volume imply the third, an adiabatic
relation between temperature and volume. Consequently, the bag model is
destitute of any predictive power since it reduces to a single adiabatic state.
The virial theorems proposed by the MIT group are shown to be the result of the
normal power density of states of a non-degenerate gas and not the exponential
density of states of the Hagedorn mass spectrum. A number of other elementary
misconceptions and inaccuracies are also pointed out.Comment: 9 page
What is the Temperature Dependence of the Casimir Force between Real Metals?
The situation with the temperature corrections to the Casimir force between
real metals of finite conductivity is reported. It is shown that the plasma
dielectric function is well adapted to the Lifshitz formula and leads to
reasonable results for real conductors. The Drude dielectric function which
describes media with dissipation is found not to belong to the application
range of the Lifshitz formula at nonzero temperature. For Drude metals the
special modification of the zero-frequency term of this formula is suggested.
The contradictory results on the subject in recent literature are analysed and
explained.Comment: 10 pages, 1 figure, Contribution to the 5th Workshop on Quantum Field
Theory under the Influence of External Conditions, Leipzig, Germany, 10-14
Sep 200
The Fundamental Commutator For Massless Particles
It is discussed that the usual Heisenberg commutation relation (CR) is not a
proper relation for massless particles and then an alternative is obtained. The
canonical quantization of the free electromagnetic(EM)fields based on the field
theoretical generalization of this alternative is carried out. Without imposing
the normal ordering condition,the vacuum energy is automatically zero.This can
be considered as a solution to the EM fields vacuum catastrophe and a step
toward managing the cosmologial constant problem at least for the EM fields
contribution to the state of vacuum.Comment: 12 pages,no figures,To appear in Mod.Phys.Ltt.
Investigations into the BFKL Mechanism with a Running QCD Coupling
We present approximations of varying degree of sophistication to the integral
equations for the (gluon) structure functions of a hadron (``the partonic flux
factor'') in a model valid in the Leading Log Approximation with a running
coupling constant. The results are all of the BFKL-type, i.e. a power in the
Bjorken variable x_B^{-\lambda} with the parameter \lambda determined from the
size \alpha_0 of the ``effective'' running coupling \bar{\alpha}\equiv
3\alpha_s/\pi= \alpha_0/\log(k_{\perp}^2) and varying depending upon the
treatment of the transverse momentum pole. We also consider the implications
for the transverse momentum (k_{\perp}) fluctuations along the emission chains
and we obtain an exponential falloff in the relevant \kappa\equiv
\log(k_{\perp}^2)-variable, i.e. an inverse power (k_{\perp}^2)^{-(2+\lambda)}
with the same parameter \lambda. This is different from the BFKL-result for a
fixed coupling, where the distributions are Gaussian in the \kappa-variable
with a width as in a Brownian motion determined by ``the length'' of the
emission chains, i.e. \log(1/x_B). The results are verified by a realistic
Monte Carlo simulation and we provide a simple physics motivation for the
change.Comment: 24 pages, 10 supplementary files, submitted to Physical Review
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