16,816 research outputs found
V_{us} from hyperon semileptonic decays
A model-independent determination of the CKM matrix element V_{us} from five
measured strangeness-changing hyperon semileptonic decays is performed. Flavor
SU(3) symmetry breaking effects in the leading vector and axial-vector form
factors are analyzed in the framework of the 1/N_c expansion of QCD. A fit to
experimental data allows one to extract the value V_{us}=0.2199\pm 0.0026,
which is comparable to the one from K_{e3} decays. This reconciliation is
achieved through second-order symmetry breaking effects of a few percent in the
form factors f_1, which increase their magnitudes over their SU(3) predictions.Comment: 23 pages, Revtex4, 12 tables, no figure
Law, Liberty and the Rule of Law (in a Constitutional Democracy)
In the hunt for a better--and more substantial--awareness of the “law,” The author intends to analyze the different notions related to the “rule of law” and to criticize the conceptions that equate it either to the sum of “law” and “rule” or to the formal assertion that “law rules,” regardless of its relationship to certain principles, including both “negative” and “positive” liberties. Instead, he pretends to scrutinize the principles of the “rule of law,” in general, and in a “constitutional democracy,” in particular, to conclude that the tendency to reduce the “democratic principle” to the “majority rule” (or “majority principle”), i.e. to whatever pleases the majority, as part of the “positive liberty,” is contrary both to the “negative liberty” and to the “rule of law” itself
Radiative corrections to all charge assignments of heavy quark baryon semileptonic decays
In semileptonic decays of spin-1/2 baryons containing heavy quarks up to six
charge assignments for the baryons and lepton are possible. We show that the
radiative corrections to four of these possibilities can be directly obtained
from the final results of the two possibilities previously studied. There is no
need to recalculate integrals over virtual or real photon momentum or any
traces.Comment: 15 pages, 2 figures, RevTex. Extended discussion. Final version to
appear in Physical Review
One-loop vertex integrals in heavy-particle effective theories
We give a complete analytical computation of three-point one-loop integrals
with one heavy propagator, up to the third tensor rank, for arbitrary values of
external momenta and masses.Comment: 10 pages, Latex, to appear in J. Phys.
Breaking a Chaotic Cryptographic Scheme Based on Composition Maps
Recently, a chaotic cryptographic scheme based on composition maps was
proposed. This paper studies the security of the scheme and reports the
following findings: 1) the scheme can be broken by a differential attack with
chosen-plaintext, where is the size of
plaintext and is the number of different elements in plain-text; 2) the
scheme is not sensitive to the changes of plaintext; 3) the two composition
maps do not work well as a secure and efficient random number source.Comment: 9 pages, 7 figure
Decoherence from internal degrees of freedom for cluster of mesoparticles : a hierarchy of master equations
A mesoscopic evolution equation for an ensemble of mesoparticles follows
after the elimination of internal degrees of freedom. If the system is composed
of a hierarchy of scales, the reduction procedure could be worked repeatedly
and the characterization of this iterating method is carried out. Namely, a
prescription describing a discrete hierarchy of master equations for the
density operator is obtained. Decoherence follows from the irreversible
coupling of the systems, defined by mesoscopic variables, to internal degrees
of freedom. We discuss briefly the existence of systems with the same dynamics
laws at different scales. We made an explicit calculation for an ensemble of
particles with internal harmonic interaction in an external anharmonic field.
New conditions related to the semiclassical limit for mesoscopic systems
(Wigner-function) are conjectured.Comment: 19 pages, 0 figures, late
Localization Properties of the Periodic Random Anderson Model
We consider diagonal disordered one-dimensional Anderson models with an
underlying periodicity. We assume the simplest periodicity, i.e., we have
essentially two lattices, one that is composed of the random potentials and the
other of non-random potentials. Due to the periodicity special resonance
energies appear, which are related to the lattice constant of the non-random
lattice. Further on two different types of behaviors are observed at the
resonance energies. When a random site is surrounded by non-random sites, this
model exhibits extended states at the resonance energies, whereas otherwise all
states are localized with, however, an increase of the localization length at
these resonance energies. We study these resonance energies and evaluate the
localization length and the density of states around these energies.Comment: 4 page
Methane activation and exchange by titanium-carbon multiple bonds
We demonstrate that a titanium-carbon multiple bond, specifically an alkylidyne ligand in the transient complex, (PNP)Ti≡C^(t)Bu (A) (PNP^− = N[2-P(CHMe_2)_(2)-4-methylphenyl]_2), can cleanly activate methane at room temperature with moderately elevated pressures to form (PNP)Ti=CHtBu(CH_3). Isotopic labeling and theoretical studies suggest that the alkylidene and methyl hydrogens exchange, either via tautomerization invoking a
methylidene complex, (PNP)Ti=CH_(2)(CH_(2)^(t)Bu), or by forming the methane adduct (PNP)Ti≡C^(t)Bu(CH_4). The thermal, fluxional and chemical behavior of (PNP)Ti=CH^(t)Bu(CH_3) is also presented in this study
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