34,630 research outputs found
The Anisotropy of MHD Alfv\'{e}nic Turbulence
We perform direct 3-dimensional numerical simulations for magnetohydrodynamic
(MHD) turbulence in a periodic box of size threaded by strong uniform
magnetic fields. We use a pseudo-spectral code with hyperviscosity and
hyperdiffusivity to solve the incompressible MHD equations. We analyze the
structure of the eddies as a function of scale. A straightforward calculation
of anisotropy in wavevector space shows that the anisotropy is scale-{\it
independent}. We discuss why this is {\it not} the true scaling law and how the
curvature of large-scale magnetic fields affects the power spectrum and leads
to the wrong conclusion. When we correct for this effect, we find that the
anisotropy of eddies depends on their size: smaller eddies are more elongated
than larger ones along {\it local} magnetic field lines. The results are
consistent with the scaling law proposed by Goldreich and Sridhar (1995, 1997). Here
(and ) are wavenumbers measured relative to
the local magnetic field direction. However, we see some systematic deviations
which may be a sign of limitations to the model, or our inability to fully
resolve the inertial range of turbulence in our simulations.Comment: 13 pages (11 NEW figures), ApJ, in press (Aug 10, 2000?
Sufficient Conditions for Starlike Functions Associated with the Lemniscate of Bernoulli
Let -1\leq B<A\leq 1. Condition on \beta, is determined so that 1+\beta
zp'(z)/p^k(z)\prec(1+Az)/(1+Bz)\;(-1<k\leq3) implies p(z)\prec \sqrt{1+z}.
Similarly, condition on \beta is determined so that 1+\beta zp'(z)/p^n(z) or
p(z)+\beta zp'(z)/p^n(z)\prec\sqrt{1+z}\;(n=0, 1, 2) implies
p(z)\prec(1+Az)/(1+Bz) or \sqrt{1+z}. In addition to that condition on \beta is
derived so that p(z)\prec(1+Az)/(1+Bz) when p(z)+\beta
zp'(z)/p(z)\prec\sqrt{1+z}. Few more problems of the similar flavor are also
considered
Baryon Masses in Partially Quenched Heavy Hadron Chiral Perturbation Theory
The masses of baryons containing a heavy quark are calculated to
next-to-leading order in partially quenched heavy hadron chiral perturbation
theory. Calculations are performed for three light flavors in the isospin limit
and additionally for two light non-degenerate flavors. The results presented
are necessary for extrapolating lattice QCD and partially quenched lattice QCD
calculations of the heavy hadron masses.Comment: 20 pages, 2 figures, RevTex
Compressible Sub-Alfvenic MHD turbulence in Low-beta Plasmas
We present a model for compressible sub-Alfvenic isothermal
magnetohydrodynamic (MHD) turbulence in low-beta plasmas and numerically test
it. We separate MHD fluctuations into 3 distinct families - Alfven, slow, and
fast modes. We find that, production of slow and fast modes by Alfvenic
turbulence is suppressed. As a result, Alfven modes in compressible regime
exhibit scalings and anisotropy similar to those in incompressible regime. Slow
modes passively mimic Alfven modes. However, fast modes show isotropy and a
scaling similar to acoustic turbulence.Comment: 4 pages, 8 figures, Phys. Rev. Lett., in pres
Wilsonian effective action for SU(2) Yang-Mills theory with Cho-Faddeev-Niemi-Shabanov decomposition
The Cho-Faddeev-Niemi-Shabanov decomposition of the SU(2) Yang-Mills field is
employed for the calculation of the corresponding Wilsonian effective action to
one-loop order with covariant gauge fixing. The generation of a mass scale is
observed, and the flow of the marginal couplings is studied. Our results
indicate that higher-derivative terms of the color-unit-vector
field are necessary for the description of topologically stable knotlike
solitons which have been conjectured to be the large-distance degrees of
freedom.Comment: 15 pages, no figures, v2: minor improvements, one reference added,
version to appear in PR
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