370 research outputs found
Decay constants of the heavy-light mesons from the field correlator method
Meson Green's functions and decay constants in different
channels are calculated using the Field Correlator Method. Both,
spectrum and , appear to be expressed only through universal
constants: the string tension , , and the pole quark masses.
For the -wave states the calculated masses agree with the experimental
numbers within MeV. For the and mesons the values of are equal to 210(10) and 260(10) MeV, respectively, and their ratio
=1.24(3) agrees with recent CLEO experiment. The values MeV are obtained for the , , and mesons
with the ratio =1.19(2) and =1.14(2). The decay constants
for the first radial excitations as well as the decay constants
in the vector channel are also calculated. The difference of
about 20% between and , and directly follows
from our analytical formulas.Comment: 37 pages, 10 tables, RevTeX
Effect of the sample geometry on the second magnetization peak in single crystalline BaKBiO thick film
Magnetization hysteresis loop measurements performed on a single
crystalline BaKBiO superconducting thick film reveal
pronounced sample geometry dependence of the "second magnetization peak" (SMP),
i.e. a maximum in the width of occurring at the field .
In particular, it is found that the SMP vanishes decreasing the film dimension.
We argue that the observed sample geometry dependence of the SMP cannot be
accounted for by models which assume a vortex pinning enhancement as the origin
of the SMP. Our results can be understood considering the thermomagnetic
instability effect and/or non-uniform current distribution at
in large enough samples.Comment: 8 pages 3 figure
Masses of heavy baryons in the relativistic quark model
The masses of the ground state heavy baryons consisting of two light (u,d,s)
and one heavy (c,b) quarks are calculated in the heavy-quark--light-diquark
approximation within the constituent quark model. The light quarks, forming the
diquark, and the light diquark in the baryon are treated completely
relativistically. The expansion in v/c up to the second order is used only for
the heavy (b and c) quarks. The diquark-gluon interaction is taken modified by
the form factor describing the light diquark structure in terms of the diquark
wave functions. An overall reasonable agreement of the obtained predictions
with available experimental data and previous theoretical results is found.Comment: 13 pages, 2 figures, version published in Phys. Rev.
Spin Glass Phase in Spin-Density-Wave Cr–Co Alloys
A spin glass (SG) phase was observed in the spin-density wave (SDW) alloys Cr1−xCox at high Co concentrations (x≥13%). After zero-field cooling, the temperature dependence of the magnetization M(T) of Cr0.87Co0.13 and Cr0.85Co0.15, measured in an applied field H=100 Oe with a SQUID magnetometer, exhibits a low T maximum, characteristic of a SG. Cooling in the measuring field, however, gives quite a different behavior. The field dependence of the magnetization M(H) is nonlinear, with a pronounced hysteresis. A strong time relaxation M(t) is also an indication of a SG phase. SG in Cr1−xCox is formed at high impurity concentrations, possibly due to clustering of the magnetic impurities
Core-Core Dynamics in Spin Vortex Pairs
We investigate magnetic nano-pillars, in which two thin ferromagnetic
nanoparticles are separated by a nanometer thin nonmagnetic spacer and can be
set into stable spin vortex-pair configurations. The 16 ground states of the
vortex-pair system are characterized by parallel or antiparallel chirality and
parallel or antiparallel core-core alignment. We detect and differentiate these
individual vortex-pair states experimentally and analyze their dynamics
analytically and numerically. Of particular interest is the limit of strong
core-core coupling, which we find can dominate the spin dynamics in the system.
We observe that the 0.2 GHz gyrational resonance modes of the individual
vortices are replaced with 2-6 GHz range collective rotational and vibrational
core-core resonances in the configurations where the cores form a bound pair.
These results demonstrate new opportunities in producing and manipulating spin
states on the nanoscale and may prove useful for new types of ultra-dense
storage devices where the information is stored as multiple vortex-core
configurations
Relativistic Description of Exclusive Semileptonic Decays of Heavy Mesons
Using quasipotential approach, we have studied exclusive semileptonic decays
of heavy mesons with the account of relativistic effects. Due to more complete
relativistic description of the quark more precise expressions for
semileptonic form factors are obtained. Various differential distributions in
exclusive semileptonic decays of heavy mesons are calculated. It is argued that
consistent account of relativistic effects and HQET motivated choice of the
parameters of quark-antiquark potential allow to get reliable value for the
ratio in the decay as well as the
ratio~. All calculated branching
ratios are in accord with available experimental data.Comment: 18 pages, LATEX, 2 figures inclosed + 4 Postscript figure
- …