291 research outputs found
Electron Temperature Fluctuations Associated with the Weakly Coherent Mode in the Edge of I-mode Plasmas
The Paradox of Virtual Dipoles in the Einstein Action
The functional integral of pure Einstein 4D quantum gravity admits abnormally
large and long-lasting "dipolar fluctuations", generated by virtual sources
with the property Int d^4x Sqrt{g(x)} Tr T(x) = 0. These fluctuations would
exist also at macroscopic scales, with paradoxical consequences. We set out
their general features and give numerical estimates of possible suppression
processes.Comment: LaTeX, 5 pages; reference adde
Decay constants, light quark masses and quark mass bounds from light quark pseudoscalar sum rules
The flavor and pseudoscalar correlators are investigated using
families of finite energy sum rules (FESR's) known to be very accurately
satisfied in the isovector vector channel. It is shown that the combination of
constraints provided by the full set of these sum rules is sufficiently strong
to allow determination of both the light quark mass combinations ,
and the decay constants of the first excited pseudoscalar mesons in
these channels. The resulting masses and decay constants are also shown to
produce well-satisfied Borel transformed sum rules, thus providing non-trivial
constraints on the treatment of direct instanton effects in the FESR analysis.
The values of and obtained are in good agreement with the
values implied by recent hadronic decay analyses and the ratios obtained
from ChPT. New light quark mass bounds based on FESR's involving weight
functions which strongly suppress spectral contributions from the excited
resonance region are also presented.Comment: 28 pages, 10 figure
Transverse depinning in strongly driven vortex lattices with disorder
Using numerical simulations we investigate the transverse depinning of moving
vortex lattices interacting with random disorder. We observe a finite
transverse depinning barrier for vortex lattices that are driven with high
longitudinal drives, when the vortex lattice is defect free and moving in
correlated 1D channels. The transverse barrier is reduced as the longitudinal
drive is decreased and defects appear in the vortex lattice, and the barrier
disappears in the plastic flow regime. At the transverse depinning transition,
the vortex lattice moves in a staircase pattern with a clear transverse
narrow-band voltage noise signature.Comment: 4 pages, 4 figure
Dynamic Ordering and Transverse Depinning of a Driven Elastic String in a Disordered Media
We examine the dynamics of an elastic string interacting with quenched
disorder driven perpendicular and parallel to the string. We show that the
string is the most disordered at the depinning transition but with increasing
drive partial ordering is regained. For low drives the noise power is high and
we observe a 1/f^2 noise signature crossing over to a white noise character
with low power at higher drives. For the parallel driven moving string there is
a finite transverse critical depinning force with the depinning transition
occuring by the formation of running kinks.Comment: 4 pages, 4 postscript figure
Observations of Core Toroidal Rotation Reversals in Alcator C-Mod Ohmic L-mode Plasmas
Direction reversals of intrinsic toroidal rotation have been observed in Alcator C-Mod ohmic L-mode plasmas following modest electron density or toroidal magnetic field ramps. The reversal process occurs in the plasma interior, inside of the q = 3/2 surface. For low density plasmas, the rotation is in the co-current direction, and can reverse to the counter-current direction following an increase in the electron density above a certain threshold. Reversals from the co- to counter-current direction are correlated with a sharp decrease in density fluctuations with k(R) >= 2 cm(-1) and with frequencies above 70 kHz. The density at which the rotation reverses increases linearly with plasma current, and decreases with increasing magnetic field. There is a strong correlation between the reversal density and the density at which the global ohmic L-mode energy confinement changes from the linear to the saturated regime
On the longitudinal contributions to hadronic tau decay
A number of recent determinations of using hadronic decay data
involve inclusive analyses based on the so-called spectral weights. We
show here that the OPE representations of the longitudinal contributions
appearing in these analyses, which are already known to be poorly converging,
have in addition an unphysical dependence which produces a significant
unphysical decrease in with increasing . We also show how, using
additional sum rule constraints, the decay constants of the excited resonances
in the strange scalar and pseudoscalar channels may be determined, allowing one
to evaluate the longitudinal spectral contributions to the sum rules.
Taking into account the very-accurately known and pole contributions,
we find that longitudinal contributions can be determined with an accuracy at
the few % level, and hence reliably subtracted, leaving an analysis for
involving the sum of longitudinal and transverse contributions, for which the
OPE representation is much better converged.Comment: 20 pages, no figure
Gravitational Collapse in Generalized Vaidya Space-Time for Lovelock Gravity Theory
In this work, we have assumed the generalized Vaidya solution in Lovelock
theory of gravity in -dimensions. It has been shown that Gauss-Bonnet
gravity, dimensionally continued Lovelock gravity and pure Lovelock gravity can
be constructed by suitable choice of parameters. We have investigated the
occurrence of singularities formed by the gravitational collapse in above three
particular forms of Lovelock theory of gravity. The dependence of the nature of
singularity on the existence of radial null geodesic for Vaidya space-time has
been specially considered. In all the three models, we have shown that the
nature of singularities (naked singularity or black hole) completely depend on
the parameters. Choices of various parameters are shown in tabular form. In
Gauss-Bonnet gravity theory, it can be concluded that the possibility of naked
singularity increases with increase in dimensions. In dimensionally continued
Lovelock gravity, the naked singularity is possible for odd dimensions for
several values of parameters. In pure Lovelock gravity, only black hole forms
due to the gravitational collapse for any values of parameters. It has been
shown that when accretion is taking place on a collapsing object, it is highly
unlikely to get a black hole. Finally on considering the phantom era in the
expanding universe it is observed that there is no possibility of formation of
a black hole if we are in the Gauss-Bonnet gravity considering the accreting
procedure upon a collapsing object.Comment: 11 page
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