27,193 research outputs found
Itinerant and localized magnetism on the triangular lattice: sodium rich phases of NaCoO
We study the interplay between correlation, itinerant ferromagnetism and
local moment formation on the electron doped triangular lattice of sodium
cobaltates NaCoO. We find that strong correlation renormalizes the
Stoner criterion and stabilizes the paramagnetic state for .
For , ferromagnetic (FM) order emerges. The enhanced Na dopant potential
fluctuations play a crucial role in the sodium rich phases and lead to an
inhomogeneous FM state, exhibiting nonmagnetic Co patches,
antiferromagnetic (AF) correlated regions, and FM clusters with AF domains.
Hole doping the band insulator at x=1 leads to the formation of local moments
near the Na vacancies and AF correlated magnetic clusters. We explain recent
observations by neutron, SR, and NMR experiments on the evolution of the
magnetic properties in the sodium rich phases.Comment: revtex4 file, 5 pages, 3 figures, published versio
Nonfactorizable decay and QCD factorization
We study the unexpectedly large rate for the factorization-forbidden decay
within the QCD factorization approach. We use a non-zero
gluon mass to regularize the infrared divergences in vertex corrections. The
end-point singularities arising from spectator corrections are regularized and
carefully estimated by the off-shellness of quarks. We find that the
contributions arising from the vertex and leading-twist spectator corrections
are numerically small, and the twist-3 spectator contribution with chiral
enhancement and linear end-point singularity becomes dominant. With reasonable
choices for the parameters, the branching ratio for decay is
estimated to be in the range , which is compatible with
the Belle and BaBar data.Comment: Appendix added; it is emphasized that in the dominant twist-3
spectator corrections the end-point singularity contributions may be
estimated by the off-shellness of the charm quark (by the binding energy in
charmonium) and the gluon (by the transverse momentum of the light quark in
the kaon
A density version of Waring-Goldbach problem
In this paper, we study a density version of the Waring-Goldbach problem.
Suppose that A is a subset of the primes, and the lower density of A in the
primes is larger than 1/2. Let k be a positive integer other than 1, 2, 4, 8,
and 9. We prove that every sufficiently large natural number n satisfying the
necessary congruence condition can be expressed as a sum of s terms of the k-th
powers of primes from set A, where s is a positive integer dependent on k
- β¦