8,454 research outputs found
The energy partitioning of non-thermal particles in a plasma: or the Coulomb logarithm revisited
The charged particle stopping power in a highly ionized and weakly to
moderately coupled plasma has been calculated to leading and next-to-leading
order by Brown, Preston, and Singleton (BPS). After reviewing the main ideas
behind this calculation, we use a Fokker-Planck equation derived by BPS to
compute the electron-ion energy partitioning of a charged particle traversing a
plasma. The motivation for this application is ignition for inertial
confinement fusion -- more energy delivered to the ions means a better chance
of ignition, and conversely. It is therefore important to calculate the
fractional energy loss to electrons and ions as accurately as possible, as this
could have implications for the Laser Megajoule (LMJ) facility in France and
the National Ignition Facility (NIF) in the United States. The traditional
method by which one calculates the electron-ion energy splitting of a charged
particle traversing a plasma involves integrating the stopping power dE/dx.
However, as the charged particle slows down and becomes thermalized into the
background plasma, this method of calculating the electron-ion energy splitting
breaks down. As a result, the method suffers a systematic error of order T/E0,
where T is the plasma temperature and E0 is the initial energy of the charged
particle. In the case of DT fusion, for example, this can lead to uncertainties
as high as 10% or so. The formalism presented here is designed to account for
the thermalization process, and in contrast, it provides results that are
near-exact.Comment: 10 pages, 3 figures, invited talk at the 35th European Physical
Society meeting on plasma physic
Matter-Antimatter Asymmetry Induced by a Running Vacuum Coupling
We show that a CP-violating interaction induced by a derivative coupling
between the running vacuum and a non-conserving baryon current may dynamically
break CPT and trigger baryogenesis through an effective chemical potential. By
assuming a non-singular class of running vacuum cosmologies which provides a
complete cosmic history (from an early inflationary de Sitter stage to the
present day quasi-de Sitter acceleration), it is found that an acceptable
baryon asymmetry is generated for many different choices of the model
parameters. It is interesting that the same ingredient (running vacuum energy
density) addresses several open cosmological questions/problems: avoids the
initial singularity, provides a smooth exit for primordial inflation,
alleviates both the coincidence and the cosmological constant problems, and,
finally, is also capable of explaining the generation of matter-antimatter
asymmetry in the very early Universe.Comment: 6 pages two column format, 1 table. Published version EPJ
Spectral Analysis of the Stromlo-APM Survey I. Spectral Properties of Galaxies
We analyze spectral properties of 1671 galaxies from the Stromlo-APM survey,
selected to have 15 < b_J < 17.15 and having a mean redshift z = 0.05. This is
a representative local sample of field galaxies, so the global properties of
the galaxy population provide a comparative point for analysis of more distant
surveys. We measure Halpha, Oii 3727, Sii 6716, 6731, Nii 6583 and Oi 6300
equivalent widths and the D_4000 break index. The 5A resolution spectra use an
8 arcsec slit, which typically covers 40-50% of the galaxy area. We find no
evidence for systematic trends depending on the fraction of galaxy covered by
the slit, and further analysis suggests that our spectra are representative of
integrated galaxy spectra.
We classify spectra according to their Halpha emission, which is closely
related to massive star formation. Overall we find 61% of galaxies are Halpha
emitters with rest-frame equivalent widths EW(Halpha) >= 2A. The emission-line
galaxy (ELG) fraction is smaller than seen in the CFRS at z = 0.2 and is
consistent with a rapid evolution of Halpha luminosity density. The ELG
fraction, and EW(Halpha), increase at fainter absolute magnitudes, smaller
projected area and smaller D_4000. In the local Universe, faint, small galaxies
are dominated by star formation activity, while bright, large galaxies are more
quiescent. This picture of the local Universe is quite different from the
distant one, where bright galaxies appear to show rapidly-increasing activity
back in time.
(Abridged)Comment: 40 pages, 25 figures, MNRAS, in pres
Temperature equilibration in a fully ionized plasma: electron-ion mass ratio effects
Brown, Preston, and Singleton (BPS) produced an analytic calculation for
energy exchange processes for a weakly to moderately coupled plasma: the
electron-ion temperature equilibration rate and the charged particle stopping
power. These precise calculations are accurate to leading and next-to-leading
order in the plasma coupling parameter, and to all orders for two-body quantum
scattering within the plasma. Classical molecular dynamics can provide another
approach that can be rigorously implemented. It is therefore useful to compare
the predictions from these two methods, particularly since the former is
theoretically based and the latter numerically. An agreement would provide both
confidence in our theoretical machinery and in the reliability of the computer
simulations. The comparisons can be made cleanly in the purely classical
regime, thereby avoiding the arbitrariness associated with constructing
effective potentials to mock up quantum effects. We present here the classical
limit of the general result for the temperature equilibration rate presented in
BPS. We examine the validity of the m_electron/m_ion --> 0 limit used in BPS to
obtain a very simple analytic evaluation of the long-distance, collective
effects in the background plasma.Comment: 14 pages, 4 figures, small change in titl
Localization of Interacting Fields in Five-Dimensional Braneworld Models
We study localization properties of fundamental fields which are coupled to
one another through the gauge mechanism both in the original Randall-Sundrum
(RS) and in the modified Randall-Sundrum (MRS) braneworld models:
scalar-vector, vector-vector, and spinor-vector configuration systems. For this
purpose we derive conditions of localization, namely the finiteness of
integrals over the extra coordinate in the action of the system considered. We
also derive field equations for each of the systems and then obtain their
solutions corresponding to the extra dimension by a separation of variable
method for every field involved in each system. We then insert the obtained
solutions into the conditions of localization to seek whether or not the
solutions are in accordance with the conditions of localization. We obtain that
not all of the configuration systems considered are localizable on the brane of
the original RS model while, on the contrary, they are localizable on the MRS
braneworld model with some restrictions. In terms of field localizability on
the brane, this result shows that the MRS model is much better than the
original RS model.Comment: 20 pages revtex4. No figures. Published in IJMP
Charged Particle Motion in a Highly Ionized Plasma
A recently introduced method utilizing dimensional continuation is employed
to compute the energy loss rate for a non-relativistic particle moving through
a highly ionized plasma. No restriction is made on the charge, mass, or speed
of this particle. It is, however, assumed that the plasma is not strongly
coupled in the sense that the dimensionless plasma coupling parameter
g=e^2\kappa_D/ 4\pi T is small, where \kappa_D is the Debye wave number of the
plasma. To leading and next-to-leading order in this coupling, dE/dx is of the
generic form g^2 \ln[C g^2]. The precise numerical coefficient out in front of
the logarithm is well known. We compute the constant C under the logarithm
exactly for arbitrary particle speeds. Our exact results differ from
approximations given in the literature. The differences are in the range of 20%
for cases relevant to inertial confinement fusion experiments. The same method
is also employed to compute the rate of momentum loss for a projectile moving
in a plasma, and the rate at which two plasmas at different temperatures come
into thermal equilibrium. Again these calculations are done precisely to the
order given above. The loss rates of energy and momentum uniquely define a
Fokker-Planck equation that describes particle motion in the plasma. The
coefficients determined in this way are thus well-defined, contain no arbitrary
parameters or cutoffs, and are accurate to the order described. This
Fokker-Planck equation describes the longitudinal straggling and the transverse
diffusion of a beam of particles. It should be emphasized that our work does
not involve a model, but rather it is a precisely defined evaluation of the
leading terms in a well-defined perturbation theory.Comment: Comments: Published in Phys. Rep. 410/4 (2005) 237; RevTeX, 111
Pages, 17 Figures; Transcription error corrected in temperature equilibration
rate (3.61) and (12.44) which replaces \gamma-2 by \gamma-
Effective 't Hooft-Polyakov monopoles from pure SU(3) gauge theory
The well known topological monopoles originally investigated by 't Hooft and
Polyakov are known to arise in classical Yang-Mills-Higgs theory. With a pure
gauge theory it is known that the classical Yang-Mills field equation do not
have such finite energy configurations. Here we argue that such configurations
may arise in a semi-quantized Yang-Mills theory, where the original gauge
group, SU(3), is reduced to a smaller gauge group, SU(2), and with some
combination of the coset fields of the SU(3) to SU(2) reduction acting as
effective scalar fields. The procedure is called semi-quantized since some of
the original gauge fields are treated as quantum degrees of freedom, while
others are postulated to be effectively described as classical degrees of
freedom. Some speculation is offer on a possible connection between these
monopole configurations and the confinement problem, and the nucleon spin
puzzle.Comment: one error is correcte
Journey to Beatrice
Originally published in 1977. This volume recovers the allegory in Dante's Divine Comedy and presumes that readers' deficient knowledge of or interest in allegory have led to misinterpretations of Dante's poem. None of the dozens of commentaries on the Comedy published in the first half of the twentieth century was concerned with allegory more than sporadically, says Singleton, and so these treatments directed readers' attention to the merest disjecta membra of that continuous dimension of the poem. From Singleton's perspective, the allegory of the Comedy is an imitation of Biblical allegory, which was acknowledged by thinkers in the Middle Ages but not by intellectuals during and following the Renaissance. Singleton attempts to restore the allegorical elements to the foreground of interpreting the Comedy
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