6,006 research outputs found
Law of large numbers for branching symmetric Hunt processes with measure-valued branching rates
We establish weak and strong law of large numbers for a class of branching
symmetric Hunt processes with the branching rate being a smooth measure with
respect to the underlying Hunt process, and the branching mechanism being
general and state-dependent. Our work is motivated by recent work on strong law
of large numbers for branching symmetric Markov processes by Chen-Shiozawa [J.
Funct. Anal., 250, 374--399, 2007] and for branching diffusions by
Engl\"ander-Harris-Kyprianou [Ann. Inst. Henri Poincar\'e Probab. Stat., 46,
279--298, 2010]. Our results can be applied to some interesting examples that
are covered by neither of these papers
A General Analysis of Wtb anomalous Couplings
We investigate new physics effects on the Wtb effective couplings in a
model-independent manner. The new physics effects are summarized as four
independent couplings , , and . Using
single-top-quark productions and W-helicity fraction measurements at the LHC
and Tevatron, we perform a global fit to impose constraints on top quark
effective couplings. We introduce a set of parameters , , and
to study the correlations among Wtb effective couplings. We show that (i)
improving the measurements of and is important in
constraining the correlation of and ; (ii)
and are anti-correlated, which is sensitive to all the
experiments; (iii) and are also anti-correlated, which is
sensitive to the W-helicity measurements; (iv) the correlation between
and is sensitive to the precision of , and
measurements. The effective Wtb couplings are studied in three kinds of
new physics models: models, vector-like
quark models and Littlest Higgs model with and without T-parity. The Wtb
couplings in the left-right model and the un-unified model are sensitive to the
ratio of gauge couplings when the new heavy gauge boson's mass () is
less than several hundred GeV, but the constraint is loose if TeV.
The Wtb couplings in vector-like quark models and the Littlest Higgs models are
sensitive to the mixing angles of new heavy particles and SM particles. We also
include the constraints of the oblique T-parameter and Zbb couplings which
impose much tighter constraints on the mixing angles. We show that the Wtb
coupling constraints become relevant if the precision of single top production
cross section measurements could be reduced to 1\% relative to the SM
predictions in future.Comment: Chin. Phys. C in pres
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