3,828 research outputs found
A Critical Reassessment of Q7 and Q8 Matrix Elements
We compare recent theoretical determinations of weak matrix elements of the
electroweak penguin operators Q7 and Q8. We pay special attention to the
renormalization scheme dependence of these determinations as well as to the
influence of higher dimension operators in the different approaches.Comment: 11 pages, latex; minor change
Vanishing chiral couplings in the large-N_C resonance theory
The construction of a resonance theory involving hadrons requires
implementing the information from higher scales into the couplings of the
effective Lagrangian. We consider the large-Nc chiral resonance theory
incorporating scalars and pseudoscalars, and we find that, by imposing LO
short-distance constraints on form factors of QCD currents constructed within
this theory, the chiral low-energy constants satisfy resonance saturation at
NLO in the 1/Nc expansion.Comment: 5 pages, 2 figures. Version published in Physical Review D. Some
equations to facilitate the discussion have been adde
Research in Aeronomy Semiannual Progress Report, 1 Oct. 1965 - 31 Mar. 1966
Theoretical and experimental studies in aeronomy dealing with direct measurements of ionospheric density and drifts by Nike-Apache and other rocket
An example of resonance saturation at one loop
We argue that the large-Nc expansion of QCD can be used to treat a Lagrangian
of resonances in a perturbative way. As an illustration of this we compute the
L_10 coupling of the Chiral Lagrangian by integrating out resonance fields at
one loop. Given a Lagrangian and a renormalization scheme, this is how in
principle one can answer in a concrete and unambiguous manner questions such as
at what scale resonance saturation takes place.Comment: 9 pages, 5 figures. Enlarged discussion, results unchanged. To be
published in Phys. Rev.
Contributions of order to form factors and unitarity of the CKM matrix
The form factors for the semileptonic decay are computed to
order in generalized chiral perturbation theory. The main difference
with the standard expressions consists in contributions quadratic in
quark masses, which are described by a single divergence-free low-energy
constant, . A new simultaneous analysis is presented for the CKM matrix
element , the ratio , decay rates and the
scalar form factor slope . This framework easily accommodates the
precise value for deduced from superallowed nuclear -decays
Baryon chiral perturbation theory with virtual photons and leptons
We construct the general pion-nucleon SU(2) Lagrangian including both virtual
photons and leptons for relativistic baryon chiral perturbation theory up to
fourth order. We include the light leptons as explicit dynamical degrees of
freedom by introducing new building blocks which represent these leptons.Comment: 11 page
Performance of Geant4 in simulating semiconductor particle detector response in the energy range below 1 MeV
Geant4 simulations play a crucial role in the analysis and interpretation of
experiments providing low energy precision tests of the Standard Model. This
paper focuses on the accuracy of the description of the electron processes in
the energy range between 100 and 1000 keV. The effect of the different
simulation parameters and multiple scattering models on the backscattering
coefficients is investigated. Simulations of the response of HPGe and
passivated implanted planar Si detectors to \beta{} particles are compared to
experimental results. An overall good agreement is found between Geant4
simulations and experimental data
Thin-disk laser pump schemes for large number of passes and moderate pump source quality
Novel thin-disk laser pump layouts are proposed yielding an increased number
of passes for a given pump module size and pump source quality. These novel
layouts result from a general scheme which bases on merging two simpler pump
optics arrangements. Some peculiar examples can be realized by adapting
standard commercially available pump optics simply by intro ducing an
additional mirror-pair. More pump passes yield better efficiency, opening the
way for usage of active materials with low absorption. In a standard multi-pass
pump design, scaling of the number of beam passes brings ab out an increase of
the overall size of the optical arrangement or an increase of the pump source
quality requirements. Such increases are minimized in our scheme, making them
eligible for industrial applicationsComment: 16 pages, 9 figure
Perturbative and nonperturbative renormalization of anomalous quark triangles
Anomalous quark triangles with one axial and two vector currents are studied
in special kinematics when one of the vector currents carries a soft momentum.
According to the Adler-Bardeen theorem the anomalous longitudinal part of the
triangle is not renormalized in the chiral limit. We derive a new
nonrenormalization theorem for the transversal part of the triangle. This
nonrenormalization, in difference with the longitudinal part, holds on only
perturbatively. At the nonperturbative level we use the operator product
expansion and the pion dominance in the longitudinal part to determine the
magnetic susceptibility of the quark condensate, .Comment: Revtex, 9 pages, 1 figure. A few references are added, discussion is
extende
Explicit Results for the Anomalous Three Point Function and Non-Renormalization Theorems
Two-loop corrections for the correlator of the singlet axial and vector
currents in QCD are calculated in the chiral limit for arbitrary momenta.
Explicit calculations confirm the non-renormalization theorems derived recently
by Vainshtein and Knecht et.al. We find that as in the one-loop case also at
the two loops the correlator has only 3 independent form-factors instead
of 4. From the explicit results we observe that the two-loop correction to the
correlator is equal to the one-loop result times the constant factor C_2(R)
alpha_s/pi in the MSbar scheme. This holds for the full correlator, for the
anomalous longitudinal as well as for the non- anomalous thansversal
amplitudes. The finite overall alpha_s dependent constant has to be normalized
away by renormalizing the axial current according to Witten's
algebraic/geometrical constraint on the anomalous Ward identity. Our
observations, together with known facts, suggest that in perturbation theory
the correlator is proportional to the one-loop term to all orders and
that the non- renormalization theorem of the Adler-Bell-Jackiw anomaly carries
over to the full correlator.Comment: 10 pages, 2 Postscript figures, uses axodraw.st
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