23,159 research outputs found
Energy dependence of a vortex line length near a zigzag of pinning centers
A vortex line, shaped by a zigzag of pinning centers, is described here
through a three-dimensional unit cell containing two pinning centers positioned
symmetrically with respect to its center. The unit cell is a cube of side
, the pinning centers are insulating spheres of radius , taken
within the range to , being the coherence length. We
calculate the free energy density of these systems in the framework of the
Ginzburg-Landau theory.Comment: Submitted to Braz. Jour. Phys. (http://www.sbfisica.org.br/bjp) 11
pages, 6 figures, 1 table, LaTex 2
Paramagnetic excited vortex states in superconductors
We consider excited vortex states, which are vortex states left inside a
superconductor once the external applied magnetic field is switched off and
whose energy is lower than of the normal state. We show that this state is
paramagnetic and develop here a general method to obtain its Gibbs free energy
through conformal mapping. The solution for any number of vortices in any cross
section geometry can be read off from the Schwarz - Christoffel mapping. The
method is based on the first order equations used by A. Abrikosov to discover
vortices.Comment: 14 pages, 7 figure
Vector form factor in K_l3 semileptonic decay with two flavors of dynamical domain-wall quarks
We calculate the vector form factor in K \to \pi l \nu semileptonic decays at
zero momentum transfer f_+(0) from numerical simulations of two-flavor QCD on
the lattice. Our simulations are carried out on 16^3 \times 32 at a lattice
spacing of a \simeq 0.12 fm using a combination of the DBW2 gauge and the
domain-wall quark actions, which possesses excellent chiral symmetry even at
finite lattice spacings. The size of fifth dimension is set to L_s=12, which
leads to a residual quark mass of a few MeV. Through a set of double ratios of
correlation functions, the form factor calculated on the lattice is accurately
interpolated to zero momentum transfer, and then is extrapolated to the
physical quark mass. We obtain f_+(0)=0.968(9)(6), where the first error is
statistical and the second is the systematic error due to the chiral
extrapolation. Previous estimates based on a phenomenological model and chiral
perturbation theory are consistent with our result. Combining with an average
of the decay rate from recent experiments, our estimate of f_+(0) leads to the
Cabibbo-Kobayashi-Maskawa (CKM) matrix element |V_{us}|=0.2245(27), which is
consistent with CKM unitarity. These estimates of f_+(0) and |V_{us}| are
subject to systematic uncertainties due to the finite lattice spacing and
quenching of strange quarks, though nice consistency in f_+(0) with previous
lattice calculations suggests that these errors are not large.Comment: 23 pages, 11 figures, 7 tables, RevTeX4; v3: one table added, results
and conclusions unchanged, final version to appear in Phys.Rev.
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