6,109 research outputs found
Explicit generating functional for pions and virtual photons
We construct the explicit one-loop functional of chiral perturbation theory
for two light flavours, including virtual photons. We stick to contributions
where 1 or 2 mesons and at most one photon are running in the loops. With the
explicit functional at hand, the evaluation of the relevant Green functions
boils down to performing traces over the flavour matrices. For illustration, we
work out the pi+ pi- -> pi0 pi0 scattering amplitude at threshold at order p^4,
e^2p^2.Comment: 20 pages, 2 figures; version accepted for publication, minor
typographical changes, acknowledgments adde
Approximating chiral SU(3) amplitudes
We construct large-N_c motivated approximate chiral SU(3) amplitudes of
next-to-next-to-leading order. The amplitudes are independent of the
renormalization scale. Fitting lattice data with those amplitudes allows for
the extraction of chiral coupling constants with the correct scale dependence.
The differences between approximate and full amplitudes are required to be at
most of the order of N^3LO contributions numerically. Applying the approximate
expressions to recent lattice data for meson decay constants, we determine
several chiral couplings with good precision. In particular, we obtain a value
for F_0, the meson decay constant in the chiral SU(3) limit, that is more
precise than all presently available determinations.Comment: 19 pages, 4 figures, improved presentation, results unchanged,
version to appear in EPJ
The pionic beta decay in chiral perturbation theory
Within the framework of chiral perturbation theory with virtual photons and
leptons, we present an updated analysis of the pionic beta decay including all
electromagnetic contributions of order e**2 p**2. We discuss the extraction of
the Cabibbo-Kobayashi-Maskawa matrix element |Vud| from experimental data. The
method employed here is consistent with the analogous treatment of the Kl3
decays and the determination of |Vus|.Comment: 8 pages, 1 figure, latex file, uses EPJC macro
Chiral Perturbation Theory with Virtual Photons and Leptons
We construct a low-energy effective field theory which allows the full
treatment of isospin-breaking effects in semileptonic weak interactions. To
this end, we enlarge the particle spectrum of chiral perturbation theory with
virtual photons by including also the light leptons as dynamical degrees of
freedom. Using super-heat-kernel techniques, we determine the additional
one-loop divergences generated by the presence of virtual leptons and give the
full list of associated local counterterms. We illustrate the use of our
effective theory by applying it to the decays pi -> l nu_{l} and K -> l nu_{l}.Comment: 22 pages, no figure
The effect of forcing on the spatial structure and spectra of chaotically advected passive scalars
The stationary distribution of passive tracers chaotically advected by a
two-dimensional large-scale flow is investigated. The tracer field is force by
resetting the value of the tracer in certain localised regions. This problem is
mathematically equivalent to advection in open flows and results in a fractal
tracer structure. The spectral exponent of the tracer field is different from
that for a passive tracer with the usual additive forcing (the so called
Batchelor spectrum) and is related to the fractal dimension of the set of
points that have never visited the forcing regions. We illustrate this
behaviour by considering a time-periodic flow whose effect is equivalent to a
simple two-dimensional area-preserving map. We also show that similar structure
in the tracer field is found when the flow is aperiodic in time.Comment: 7 pages, 9 figure
Radiative corrections to K_{l3} decays
We present a complete calculation of the K_{l3} decays K^+ --> pi^0 l^+ nu_l
and K^0 --> pi^- l^+ nu_l to O(p^4, (m_d-m_u) p^2, e^2 p^2) in chiral
perturbation theory with virtual photons and leptons. We introduce the concept
of generalized form factors and kinematical densities in the presence of
electromagnetism, and propose a possible treatment of the real photon emission
in K^+_{l3} decays. We illustrate our results by applying them to the
extraction of the Kobayashi--Maskawa matrix element |V_{us}| from the
experimental K^+_{e3} decay parameters.Comment: 13 page
Isospin violation in epsilon'
On the basis of a next-to-leading-order calculation in chiral perturbation
theory, the first complete analysis of isospin breaking for direct CP violation
in K^0 -> 2 pi decays is performed. We find a destructive interference between
three different sources of isospin violation in the CP violation parameter
epsilon'. Within the uncertainties of large-N_c estimates for the low-energy
constants, the isospin violating correction for epsilon' is below 15 %.Comment: 4 page
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