25 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
Renormalization of the baryon axial vector current in large-N_c chiral perturbation theory
The baryon axial vector current is computed at one-loop order in heavy baryon
chiral perturbation theory in the large-N_c limit, where N_c is the number of
colors. Loop graphs with octet and decuplet intermediate states cancel to
various orders in N_c as a consequence of the large-N_c spin-flavor symmetry of
QCD baryons. These cancellations are explicitly shown for the general case of
N_f flavors of light quarks. In particular, a new generic cancellation is
identified in the renormalization of the baryon axial vector current at
one-loop order. A comparison with conventional heavy baryon chiral perturbation
theory is performed at the physical values N_c=3, N_f=3.Comment: REVTex4, 29 pages, 2 figures, 6 tables. Equations (32) and (81)
corrected. Some typos fixed. Results and conclusions remain unchange
Numerical precision radiative corrections to the Dalitz plot of baryon semileptonic decays including the spin-momentum correlation of the decaying and emitted baryons
We calculate the radiative corrections to the angular correlation between the
polarization of the decaying and the direction of the emitted spin one-half
baryons in the semileptonic decay mode. The final results are presented, first,
with the triple integration of the bremsstrahlung photon ready to be performed
numerically and, second, in an analytical form. A third presentation of our
results in the form of numerical arrays of coefficients to be multiplied by the
quadratic products of form factors is discussed. This latter may be the most
practical one to use in Monte Carlo simulations. A series of crosschecks is
performed. Previous results to order (alpha/pi)(q/M_1) for the decays of
unpolarized baryons are reviewed, too, where q is the momentum transfer and M_1
is the mass of the decaying baryon. This paper is self-contained and organized
to make it accessible and reliable in the analysis of the Dalitz plot of
precision experiments involving heavy quarks and is not compromised to fixing
the form factors at predetermined values. It is assumed that the real photons
are kinematically discriminated. Otherwise, our results have a general
model-independent applicability.Comment: 34 pages, 4 tables, no figures. Some sections have been shortened.
Conclusions remain unchange
Radiative corrections to the Dalitz plot of K_{l3}^\pm decays
We calculate the model-independent radiative corrections to the Dalitz plot
of K_{l3}^\pm decays to order (\alpha/\pi)(q/M_1), where q is the momentum
transfer and M_1 is the mass of the kaon. The final results are presented,
first, with the triple integration over the variables of the bremsstrahlung
photon ready to be performed numerically and, second, in an analytical form.
These two forms are useful to crosscheck on one another and with other
calculations. This paper is organized to make it accessible and reliable in the
analysis of the Dalitz plot of precision experiments and is not compromised to
fixing the form factors at predetermined values. It is assumed that the real
photons are kinematically discriminated. Otherwise, our results have a general
model-independent applicability.Comment: RevTex4, 38 pages, 5 figures, 5 tables; some typos corrected;
discussion extended to compare with other result
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
SU(3) symmetry breaking in hyperon semileptonic decays
Flavor SU(3) symmetry breaking in the hyperon semileptonic decay form-factors
is analyzed using the 1/N expansion. A detailed comparison with experimental
data shows that corrections to f_1 are approximately 10%, which agrees with
theoretical expectations. Corrections to g_1 are compatible with first-order
symmetry breaking. A fit to the experimental data allows one to predict the g_1
form factor for Xi^0 -> Sigma^+ decay. The proton matrix element of the T^8
component of the axial current (which is equal to 3F-D in the SU(3) symmetry
limit) is found to be approximately 0.34.Comment: 18 pages (revtex). Discussion of theory errors added. Two redundant
parameters for symmetry breaking in f1 deleted. Central values for the fits
remain unchanged, but some of the errors are modifie
Contributions of SU(3) higher-order interaction operators to rotational bands in the interacting boson model
Rotational bands are commonly used in the analysis of the spectra of atomic nuclei. The early version of the interacting boson model of Arima and Iachello has been foundational to the description of rotations in nuclei. The model is based on a unitary spectrum generating algebra U(6) and an orthogonal (angular momentum) symmetry algebra SO(3). A solvable limit of the model contains SU(3) in its dynamical symmetry chain. The corresponding Hamiltonian is written as a linear combination of linear and quadratic Casimir invariants of all the algebras in the chain. The limit of exact dynamical symmetry, however, is rarely fulfilled by realistic systems, so the symmetry needs be broken. A suitable mechanism to do so is the partial dynamical symmetry approach. Prompted by these facts, the aim of this work is to construct higher-order SU(3) interaction terms in both the limit of exact and broken symmetry, which can be used in the description of rotational bands of nuclei. For this task, a systematic algebraic approach, loosely referred here to as the projection operator technique, will be extensively used to obtain those operators that make up the n-body terms in the corresponding Hamiltonians. This novel technique is thus proved to be quite efficient for these purposes