11 research outputs found
Towards next-to-next-to-leading-log accuracy for the width difference in the system: fermionic contributions to order and
We calculate a class of three-loop Feynman diagrams which contribute to the
next-to-next-to-leading logarithmic approximation for the width difference
in the system. The considered diagrams
contain a closed fermion loop in a gluon propagator and constitute the order
, where is the number of light quarks. Our results entail
a considerable correction in that order, if is expressed in
terms of the pole mass of the bottom quark. If the scheme is
used instead, the correction is much smaller. As a result, we find a decrease
of the scheme dependence. Our result also indicates that the usually quoted
value of the NLO renormalization scale dependence underestimates the
perturbative error.Comment: We corrected a typographical mistake in Eq. (4.18), made larger axis
labels in Fig.2. Version accepted by JHE
Forward-backward Asymmetry and New Physics
The forward-backward asymmetry in
decay is a sensitive probe of New Physics. Previous studies have focused on the
sensitivity in the position of the zero. However, the short distance effective
couplings are in principle complex, as illustrated by
decay within the Standard Model. Allowing the effective couplings to be
complex, but keeping the and rate
constraints, we find the landscape for to be far richer than from entertaining just sign flips,
which can be explored by future high statistics experiments.Comment: RevTex 4 pages including 5 eps figures; Minor changes made,
references adde
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Towards the NNLL Precision in the Decay
The present NLL prediction for the decay rate of the rare inclusive process {bar B} {yields} X{sub s}{gamma} has a large uncertainty due to the charm mass renormalization scheme ambiguity. We estimate that this uncertainty will be reduced by a factor of 2 at the NNLL level. This is a strong motivation for the on-going NNLL calculation, which will thus significantly increase the sensitivity of the observable {bar B} {yields} X{sub s}{gamma} to possible new degrees of freedom beyond the SM. We also give a brief status report of the NNLL calculation