3,627 research outputs found
The Matter and the Pseudoscalar Densities in Lattice QCD
The matter and the pseudoscalar densities inside a hadron are calculated via
gauge-invariant equal-time correlation functions. A comparison is made between
the charge charge and the matter density distributions for the pion, the rho,
the nucleon and the within the quenched theory, and with two
flavours of dynamical quarks.Comment: Typos corrected; 13 pages, 16 figure
The variation of relative magnetic helicity around major flares
We have investigated the variation of magnetic helicity over a span of
several days around the times of 11 X-class flares which occurred in seven
active regions (NOAA 9672, 10030, 10314, 10486, 10564, 10696, and 10720) using
the magnetograms taken by the Michelson Doppler Imager (MDI) on board the Solar
and Heliospheric Observatory (SOHO). As a major result we found that each of
these major flares was preceded by a significant helicity accumulation over a
long period (0.5 to a few days). Another finding is that the helicity
accumulates at a nearly constant rate and then becomes nearly constant before
the flares. This led us to distinguish the helicity variation into two phases:
a phase of monotonically increasing helicity and the following phase of
relatively constant helicity. As expected, the amount of helicity accumulated
shows a modest correlation with time-integrated soft X-ray flux during flares.
However, the average helicity change rate in the first phase shows even
stronger correlation with the time-integrated soft X-ray flux. We discuss the
physical implications of this result and the possibility that this
characteristic helicity variation pattern can be used as an early warning sign
for solar eruptions
Strange meson-nucleon states in the quark potential model
The quark potential model and resonating group method are used to investigate
the bound states and/or resonances. The model potential consists of
the t-channel and s-channel one-gluon exchange potentials and the confining
potential with incorporating the QCD renormalization correction and the
spin-orbital suppression effect in it. It was shown in our previous work that
by considering the color octet contribution, use of this model to investigate
the low energy elastic scattering leads to the results which are in pretty
good agreement with the experimental data. In this paper, the same model and
method are employed to calculate the masses of the bound systems.
For this purpose, the resonating group equation is transformed into a standard
Schr\"odinger equation in which a nonlocal effective interaction
potential is included. Solving the Schr\"odinger equation by the variational
method, we are able to reproduce the masses of some currently concerned
states and get a view that these states possibly exist as
molecular states. For the system, the same calculation gives no support to
the existence of the resonance which was announced
recently.Comment: 15 pages, 4 figure
Quenched Charmed Meson Spectra using Tadpole Improved Quark Action on Anisotropic Lattices
Charmed meson charmonium spectra are studied with improved quark actions on
anisotropic lattices. We measured the pseudo-scalar and vector meson dispersion
relations for 4 lowest lattice momentum modes with quark mass values ranging
from the strange quark to charm quark with 3 different values of gauge coupling
and 4 different values of bare speed of light . With the bare
speed of light parameter tuned in a mass-dependent way, we study the mass
spectra of , , ,
, and mesons.
The results extrapolated to the continuum limit are compared with the
experiment and qualitative agreement is found.Comment: 8 pages, 2 figures, latex fil
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Formation of current sheets in magnetohydrostatic atmospheres (MHS)
It is demonstrated that a 2-D magnetic field configuration in a magnetohydrostatic equilibrium without any null point can be deformed into a configuration with current sheets, i.e., tangential discontinuities, either by temperature change or by footpoint displacement. The magnetohydrostatic solutions by Low, which have a quadrupolar field geometry, are chosen as our initial configurations. When the whole atmosphere is uniformly heated, the expansion of plasma is more effective in the outer flux tubes than in the inner ones. The expanding plasma pushes out the field lines in each bipolar region so that a current sheet of a finite length is formed where the lines from each region come into contact. The resulting pressure profile at the base has pressure maxima at the center of each bipolar regions. The smooth equilibrium solution with the same pressure distribution contains and X-point. If the pressure is initially higher in the outer tubes than in the inner ones, cooling of the atmosphere can also lead to current sheet formation. As the pressure scale height decreases by cooling, the magnetic field pressure dominates the plasma pressure in the upper part of the flux tubes. The subsequent expansion of field lines creates a tangential discontinuity. If resistivity is considered in this weak equilibrium state, magnetic reconnection results in a new Kippenhahn-Sch{umlt u}ITER type field configuration with a magnetic island. It is expected that a prominence can stably reside within the magnetic island. When the field footpoints undergo a shearing motion with a continuous shearing profile, a current sheet can be reformed beyond a critical amount of shear. Our results suggest that the formation of a current sheet and the subsequent magnetic reconnection can be ubiquitous in the solar atmosphere. The resulting field configurations are quite favorable for prominence formation
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Conceptual study of electron ripple injection for tokamak transport control
A non-intrusive method for inducing radial electric field based on electron ripple injection is under development by the Princeton CDX-U group. The radial electric field is known to play an important role in the L-H and H-VH mode transition according to the recent theoretical and experimental research. It is therefore important to develop a non-intrusive tool to control the radial electric field profile in tokamak plasmas. The present technique utilizes externally-applied local magnetic ripple fields to trap electrons at the edge, allowing them to penetrate towards the plasma center via {gradient}B and curvature drifts, causing the flux surfaces to charge up negatively. Electron cyclotron resonance heating is utilized to increase the trapped population and the electron drift velocity by raising the perpendicular energy of trapped electrons. In order to quantify the effects of cyclotron resonance heating on electrons, the temperature anisotropy of resonant electrons in a tokamak plasma is calculated. For the calculation of anisotropic temperatures, energy moments of the bounce-averaged Fokker-Planck equation with a bi-Maxwellian distribution function for heated electrons are solved, assuming a moderate wave power and a constant quasilinear diffusion coefficient. Simulation using a guiding-center orbit model have been performed to understand the behavior of suprathermal electrons in the presence of ripple fields. Examples for CDX-U and ITER parameters are given
The continuum limit of quark number susceptibilities
We report the continuum limit of quark number susceptibilities in quenched
QCD. Deviations from ideal gas behaviour at temperature T increase as the
lattice spacing is decreased from T/4 to T/6, but a further decrease seems to
have very little effect. The measured susceptibilities are 20% lower than the
ideal gas values, and also 10% below the hard thermal loop (HTL) results. The
off-diagonal susceptibility is several orders of magnitude smaller than the HTL
results. We verify a strong correlation between the lowest screening mass and
the susceptibility. We also show that the quark number susceptibilities give a
reasonable account of the Wroblewski parameter, which measures the strangeness
yield in a heavy-ion collision.Comment: 8 pages, 5 figure
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