164 research outputs found
The double radiative annihilation of the heavy-light fermion bound states
We consider the double-radiative decays of heavy-light QED and QCD atoms,
and . Especially,
we take under scrutiny contributions coming from operators that vanish on the
free-quark mass shell. We show that by field redefinitions these operators are
converted into contact terms attached to the bound state dynamics. A net
off-shell contribution is suppressed with respect to the effect of the well
known flavour-changing magnetic-moment operator by the bound-state binding
factor. The negligible off-shellness of the weakly bound QED atoms becomes more
relevant for strongly bound QCD atoms. We analyze this off-shellness in
model-approaches to QCD, one of them enabling us to keep close contact to the
related effect in QED. We also comment on the off-shell effect in the
corresponding process , and discuss possible
hindering of the claimed beyond-standard-model discovery in this decay mode.Comment: 24 pages, 5 figures; to be published in Fizika
On Distinguishing Non-Standard Interactions from Radiative Corrections in Neutrino-Electron Scattering
We present a contribution of higher order to neutrino-electron scattering
that is a charged-current counterpart of both the anomalous axial-vector
triangle and possible non-standard interaction contributions. It arises in the
standard model with massive neutrinos, and renormalizes the nondiagonal
axial-vector form-factor at low energies. We show that, due to the small size
of radiative corrections, the neutrino-electron scattering still provides a
discovery potential for some of the non-standard neutrino interactions proposed
in the literature.Comment: 9 pages, 3 figures, change in title and context of the consideration,
results of radiative corrections unchange
New physics in \epsilon' from chromomagnetic contributions and limits on Left-Right symmetry
New physics in the chromomagnetic flavor changing transition s->dg* can avoid
the strong GIM suppression of the Standard Model and lead to large
contributions to CP-violating observables, in particular to the epsilon'
parameter, that we address here. We discuss the case of the Left-Right
symmetric models, where this contribution implies bounds on the phases of the
right-handed quark mixing matrix, or in generic models with large phases a
strong bound on the Left-Right symmetry scale. To the leading order, a numeric
formula for epsilon' as a function of the short-distance coefficients for a
wide class of models of new physics is given.Comment: 12 pages, Eq. 12 and related numerics amende
On the color suppressed contribution to $\bar{B_{d}^0} \rightarrow \, \pi^0 \pi^{0}
The decay modes of the type are dynamically
different. For the case there is a
substantial factorized contribution which dominates. In contrast, the decay
mode has a small factorized
contribution, being proportional to a small Wilson coefficient combination.
However, for the decay mode there
is a sizeable nonfactorizable (color suppressed) contribution due to soft (long
distance) interactions, which dominate the amplitude. We estimate the branching
ratio for the mode in the heavy
quark limit for the - quark. In order to estimate color suppressed
contributions we treat the energetic light () quark within a variant of
Large Energy Effective Theory combined with a recent extension of chiral quark
models in terms of model- dependent gluon condensates. We find that our
calculated color suppressed amplitude is suppressed by a factor of order
with respect to the factorizable amplitude, as it should
according to QCD-factorization. Further, for reasonable values of the
constituent quark mass and the gluon condensate, the calculated nonfactorizable
amplitude for can easily
accomodate the experimental value. Unfortunately, the color suppressed
amplitude is very sensitive to the values of these model dependent parameters.
Therefore fine-tuning is necessary in order to obtain an amplitude compatible
with the experimental result for .
A possible link to the triangle anomaly is discussed.Comment: The submitted Latex version correspond to 23 pages in ps-version and
contains 4 figure
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