5,232 research outputs found
Comment on "On the -Anomaly in Betaine Calcium Chloride Dihydrate"
Recently, Hlinka and Ishibashi [J. Phys. Soc. Jpn. 67, 495 (1998)] discussed
the -anomaly in betaine calcium chloride dihydrate (BCCD) in a Landau-type
approach. We comment on the shortcomings of this approach and discuss the
-anomaly in the framework of a microscopical pseudo spin model based on a
realistic description of BCCD in terms of symmetry-adapted local modes.Comment: 2 pages, RevTex, submitted to J. Phys. Soc. Jp
Model-Independent Properties of the B-Meson Distribution Amplitude
The operator product expansion is used to obtain model-independent
predictions for the first two moments of the renormalized B-meson light-cone
distribution amplitude phi_+(omega,mu), defined with a cutoff omega<Lambda_UV.
The leading hadronic power corrections are given in terms of the parameter
Lambda(bar)=m_B-m_b. From the cutoff dependence of the zeroth moment an
analytical expression for the asymptotic behavior of the distribution amplitude
is derived, which exhibits a negative radiation tail for omega>>mu. By solving
the evolution equation for the distribution amplitude, an integral
representation for phi_+(omega,mu) is obtained in terms an initial function
phi_+(omega,mu_0) defined at a lower renormalization scale. A realistic model
of the B-meson light-cone distribution amplitude is proposed, which satisfies
the moment relations and has the correct asymptotic behavior. This model
provides an estimate for the first inverse moment and the associated parameter
lambda_B.Comment: 8 pages, 5 figures; problem in Figure 4 fixed, references updated;
version to appear in Phys. Rev.
New Bound on gamma from B^+- -> pi K Decays
A bound on the angle gamma of the unitarity triangle is derived using
experimental information on the CP-averaged branching ratios for the rare
decays B^+- -> pi^+- K^0 and B^+- -> pi^0 K^+-. The theoretical description is
cleaner than the Fleischer-Mannel analysis of the decays B^+- -> pi^+- K^0 and
B^0 -> pi^-+ K^+- in that the two decay rates differ only in a single isospin
amplitude, which has a simple structure in the SU(3) limit. As a consequence,
electroweak penguin contributions and strong rescattering effects can be taken
into account in a model-independent way. The resulting bound excludes values of
cos(gamma) around 0.6 and is thus largely complementary to indirect constraints
derived from a global analysis of the unitarity triangle.Comment: minor corrections, version to appear in Physics Letters
Probing the density dependence of the symmetry potential with peripheral heavy-ion collisions
The peripheral heavy-ion collisions of at are studied by means of the Improved Quantum Molecular Dynamics
Model(ImQMD). It is shown that the slope of the average N/Z ratio of emitted
nucleons vs impact parameters for these reactions is very sensitive to the
density dependence of the symmetry energy. Our study also shows that the yields
of and decrease with impact parameters and slope of the yield
of vs impact parameters as well as the ratio of Y()/Y()
depend on the symmetry potential strongly for peripheral heavy-ion collisions.Comment: 10 pages,6 figures, accepted by Phys.Rev.
Low temperature phase diagram and critical behaviour of the four-state chiral clock model
The low temperature behaviour of the four-state chiral clock () model
is reexamined using a systematic low temperature series expansion of the free
energy. Previously obtained results for the low temperature phases are
corrected and the low temperature phase diagram is derived. In addition, the
phase transition from the modulated region to the high temperature paraphase is
shown to belong to the universality class of the 3d-XY model.Comment: 17 pages in ioplppt style, 3 figure
Extracting , and from Inclusive and Decays
Using recent results for nonperturbative contributions to the and
meson inclusive semileptonic widths, a model independent extraction of \vbc,
and is made from the experimentally measured and lifetimes
and semileptonic branching ratios. Constraining the parameters of the HQET at
\CO(1/m_Q^2) by the semileptonic width, \vbc is found to lie in the
range .040<\vbc< 0.057. The and quark masses are not well constrained
due to uncertainty in the relevant scale of . These results assume
the validity of perturbative QCD at the low scales relevant to semileptonic
charm decay. Without making this assumption, somewhat less stringent bounds on
from decay alone may be obtained.Comment: (revised version - contains a more detailed discussion of the
uncertainty in our results from the uncertainty in the scale of \alpha_s) 12
pages, 5 figures included, uses harvmac.tex and epsf.tex, UCSD/PTH 93-25,
UTPT 93-21, CMU-HEP 93-1
Exploring CP Violation through B Decays
The B-meson system provides many strategies to perform stringent tests of the
Standard-Model description of CP violation. In this brief review, we discuss
implications of the currently available B-factory data on the angles alpha,
beta and gamma of the unitarity triangle, emphasize the importance of Bs
studies at hadronic B experiments, and discuss new, theoretically clean
strategies to determine gamma.Comment: 22 pages, 4 figures, invited brief review for Modern Physics Letters
Long-Distance Dominance of the CP Asymmetry in B->X_{s,d}+gamma Decays
We show that in the Standard Model the parametrically leading (by a factor
1/alpha_s) contribution to the inclusive CP asymmetry in B->X_{s,d}+gamma
decays arises from a long-distance effect in the interference of the
electromagnetic dipole amplitude with the amplitude for an up-quark penguin
transition accompanied by soft gluon emission. This contribution is governed by
a single hadronic parameter Lambda_{17}^u related to a matrix elements of a
non-local operator. In view of current experimental data, a future precision
measurement of the flavor-averaged CP asymmetry in B->X_s+gamma will signal the
presence of new physics only if a value below -2% is found. A cleaner probe of
new physics is offered by the difference of the CP asymmetries in charged
versus neutral B-meson decays.Comment: 4 page
Infrared singularities of scattering amplitudes in perturbative QCD
An exact formula is derived for the infrared singularities of dimensionally
regularized scattering amplitudes in massless QCD with an arbitrary number of
legs, valid at any number of loops. It is based on the conjecture that the
anomalous-dimension matrix of n-jet operators in soft-collinear effective
theory contains only a single non-trivial color structure, whose coefficient is
the cusp anomalous dimension of Wilson loops with light-like segments. Its
color-diagonal part is characterized by two anomalous dimensions, which are
extracted to three-loop order from known perturbative results for the quark and
gluon form factors. This allows us to predict the three-loop coefficients of
all 1/epsilon^k poles for an arbitrary n-parton scattering amplitudes,
generalizing existing two-loop results.Comment: 4 pages; v2: typo in eq. (12) fixed, references updated; v3:
additional term in (12
Hyperfine Interactions in Charm and Bottom Systems
Hyperfine interactions in the light meson and baryon sectors are generalized
to the charm and bottom systems. It is pointed out that an attempt to increase
the value of the wave function at the origin to account for the unusual ratio
of to the lifetimes could spoil the good agreement among
the baryon and meson hyperfine mass-splitting. Including spin effects and
taking phase space differences into account we predict that the decay rate of
the can be increased relative to that of the meson by about
7%.Comment: 10 pages, plain Latex, no figures. A new isospin argument has been
adde
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