4,327 research outputs found
Field-dependent diamagnetic transition in magnetic superconductor
The magnetic penetration depth of single crystal
was measured down to 0.4 K in dc fields up
to 7 kOe. For insulating , Sm spins order at the
N\'{e}el temperature, K, independent of the applied field.
Superconducting ( K) shows a
sharp increase in diamagnetic screening below which varied from
4.0 K () to 0.5 K ( 7 kOe) for a field along the c-axis. If the
field was aligned parallel to the conducting planes, remained
unchanged. The unusual field dependence of indicates a spin freezing
transition that dramatically increases the superfluid density.Comment: 4 pages, RevTex
Electron cyclotron maser emission mode coupling to the z-mode on a longitudinal density gradient in the context of solar type III bursts
Copyright 2012 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. This article appeared in Physics of Plasmas 19, 110702 (2012) and may be found at .supplemental material at http://astro.qmul.ac.uk/~tsiklauri/sp.htmlsupplemental material at http://astro.qmul.ac.uk/~tsiklauri/sp.htm
Exclusive production of meson in proton-proton collisions at high energies
First we calculate cross section for the reaction
from the threshold to very large energies. At low energies the pion exchange is
the dominant mechanism. At large energies the experimental cross section can be
well described within the -factorization approach by adjusting
light-quark constituent mass. Next we calculate differential distributions for
the reaction at RHIC, Tevatron and LHC energies for the
first time in the literature. We consider photon-pomeron (pomeron-photon),
photon-pion (pion-photon) as well as diffractive hadronic bremsstrahlung
mechanisms. The latter are included in the meson/reggeon exchange picture with
parameters fixed from the known phenomenology. Interesting rapidity
distributions are predicted. The hadronic bremsstrahlung contributions dominate
at large (forward, backward) rapidities. At small energies the photon-pomeron
contribution is negligible compared to the bremsstrahlung contributions. It
could be, however, easily identified at large energies at midrapidities.
Absorptions effects are included and discussed. Our predictions are ready for
verification at RHIC and LHC.Comment: 21 pages, 14 figure
Light vector meson photoproduction at large t
We have studied in perturbative QCD all independent helicity amplitudes
describing the photoproduction of light vector mesons at large . We found a
new hard production mechanism which is related to the possibility for a real
photon to fluctuate into a massless pair in a chiral-odd spin
configuration. Each helicity amplitude is given as a sum of a usual chiral-even
contribution (when the helicities of quark and antiquark are antiparallel) and
this additional chiral-odd part (where the helicities of quark and antiquark
are parallel). The chiral-odd contribution is large, it leads to a dominance of
the non spin-flip amplitude in a very broad region of intermediately high
. All amplitudes are expressed in terms of short distance asymptotics of
the light-cone wave functions of vector meson (photon). We demonstrate that for
each helicity amplitude there exists a soft non-factorizable contribution. We
give arguments that for dominant non spin-flip helicity amplitude the relative
contribution of the soft nonfactorizable interactions is numerically not large.Comment: 21 pages LATEX, 2 .eps figures, the colour factor of chiral-odd
contributions is corrected, qualitative results remain unchange
Some combinatorial identities related to commuting varieties and Hilbert schemes
In this article we explore some of the combinatorial consequences of recent results relating the isospectral commuting variety and the Hilbert scheme of points in the plane
The dependence of the hard diffractive photoproduction of vector meson or photon and the range of pQCD validity
We consider two coupled problems.
We study the dependence on photon virtuality for the semihard
quasi--elastic photoproduction of neutral vector mesons on a quark, gluon or
real photon (at
GeV)). To this end we calculate the corresponding amplitudes (in an
analytical form) in the lowest nontrivial approximation of perturbative QCD. It
is shown that the amplitude for the production of light meson varies very
rapidly with the photon virtuality near .
We estimate the bound of the pQCD validity region for such processes. For the
real incident photon the obtained bound for the meson production is very
high. This bound decreases fast with the increase of , and we expect that
the virtual photoproduction at HERA gives opportunity to test the pQCD results.
The signature of this region is discussed. For the hard Compton effect the pQCD
should work good at not too high , and this effect seems measurable
at HERA.Comment: ReVTeX, 36 pages, 5 Postscript figures, uses epsf.st
Gravitational Laser Back-Scattering
A possible way of producing gravitons in the laboratory is investigated. We
evaluate the cross section electron + photon electron + graviton
in the framework of linearized gravitation, and analyse this reaction
considering the photon coming either from a laser beam or from a Compton
back-scattering process.Comment: 11 pages, 2 figures (available upon request), RevTeX, IFT-P.03/9
Discovery limits for Techni-Omega production in Collisions
In a strongly-interacting electroweak sector with an isosinglet vector state,
such as the techni-omega, , the direct coupling
implies that an can be produced by fusion in
collisions. This is a unique feature for high energy or
colliders operating in an mode. We consider the processes and , both of which proceed via
an intermediate . We find that at a 1.5 TeV linear collider
operating in an mode with an integrated luminosity of 200 fb,
we can discover an for a broad range of masses and widths.Comment: To appear in the Proceedings of the 29th International Conference on
High Energy Physics, Vancouver, July 1998, 5 pages, Latex, 7 postscript
figure
The effect of electron beam pitch angle and density gradient on solar type III radio bursts
Copyright 2012 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. This article appeared in Physics of Plasmas 19, 112903 (2012) and may be found at .supplemental material at http://astro.qmul.ac.uk/~tsiklauri/sp.htmlsupplemental material at http://astro.qmul.ac.uk/~tsiklauri/sp.htm
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