39,074 research outputs found
The rare decay B --> X_s l^+ l^- to NNLL precision for arbitrary dilepton invariant mass
We present a new phenomenological analysis of the inclusive rare decay . In particular, we present the first calculation of the NNLL
contributions due to the leading two-loop matrix elements, evaluated for
arbitrary dilepton invariant mass. This allows to obtain the first NNLL
estimates of the dilepton mass spectrum and the lepton forward-backward
asymmetry in the high region, and to provide an
independent check of previously published results in the low region. The numerical impact of these NNLL corrections in the
high-mass region () amounts to -13% in the
integrated rate, and leads to a reduction of the scale uncertainty to .
The impact of non-perturbative contributions in this region is also discussed
in detail.Comment: 40 pages, 12 figures. v2: extended phenomenological discussion;
results unchanged; published versio
Nonlinear Aggregation-Diffusion Equations: Radial Symmetry and Long Time Asymptotics
We analyze under which conditions equilibration between two competing
effects, repulsion modeled by nonlinear diffusion and attraction modeled by
nonlocal interaction, occurs. This balance leads to continuous compactly
supported radially decreasing equilibrium configurations for all masses. All
stationary states with suitable regularity are shown to be radially symmetric
by means of continuous Steiner symmetrization techniques. Calculus of
variations tools allow us to show the existence of global minimizers among
these equilibria. Finally, in the particular case of Newtonian interaction in
two dimensions they lead to uniqueness of equilibria for any given mass up to
translation and to the convergence of solutions of the associated nonlinear
aggregation-diffusion equations towards this unique equilibrium profile up to
translations as
Influence of low-level Pr substitution on the superconducting properties of YBa2Cu3O7-delta single crystals
We report on measurements on Y1-xPrxBa2Cu3O7-delta single crystals, with x
varying from 0 to 2.4%. The upper and the lower critical fields, Hc2 and Hc1,
the Ginzburg-Landau parameter and the critical current density, Jc(B), were
determined from magnetization measurements and the effective media approach
scaling method. We present the influence of Pr substitution on the pinning
force density as well as on the trapped field profiles analyzed by Hall probe
scanning.Comment: 4 pages, 5 figures, accepted for publication in J. Phys. Conf. Se
In-plane thermal conductivity of large single crystals of Sm-substituted (YSm)BaCuO
We have investigated the in-plane thermal conductivity of
large single crystals of optimally oxygen-doped
(Y,Sm)BaCuO (=0, 0.1, 0.2 and 1.0)
and YBa(CuZn)O(=0.0071) as functions
of temperature and magnetic field (along the c axis). For comparison, the
temperature dependence of for as-grown crystals with the
corresponding compositions are presented.
The nonlinear field dependence of for all crystals was observed
at relatively low fields near a half of . We make fits of the
data to an electron contribution model, providing both the mean
free path of quasiparticles and the electronic thermal conductivity
, in the absence of field. The local lattice distortion due to the
Sm substitution for Y suppresses both the phonon and electron contributions. On
the other hand, the light Zn doping into the CuO planes affects solely
the electron component below , resulting in a substantial decrease in
.Comment: 7 pages,4 figures,1 tabl
Unimpeded tunneling in graphene nanoribbons
We studied the Klein paradox in zigzag (ZNR) and anti-zigzag (AZNR) graphene
nanoribbons. Due to the fact that ZNR (the number of lattice sites across the
nanoribbon (N is even) and AZNR (N is odd) configurations are indistinguishable
when treated by the Dirac equation, we supplemented the model with a
pseudo-parity operator whose eigenvalues correctly depend on the sublattice
wavefunctions for the number of carbon atoms across the ribbon, in agreement
with the tight-binding model. We have shown that the Klein tunneling in zigzag
nanoribbons is related to conservation of the pseudo-parity rather than
pseudo-spin in infinite graphene. The perfect transmission in the case of
head-on incidence is replaced by perfect transmission at the center of the
ribbon and the chirality is interpreted as the projection of the pseudo-parity
on momentum at different corners of the Brillouin zone
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