4,520 research outputs found
Renormalization of Velocity-Changing Dimension-Five Operators in the Heavy-Quark Effective Theory
We study the renormalization of operators of the type in the heavy-quark effective theory (HQET). We construct the
combinations of such operators that are renormalized multiplicatively, and
calculate their velocity-dependent anomalous dimensions at the one-loop order.
We then show that the virial theorem of the HQET is not renormalized, and that
in the limit of equal velocities the anomalous dimension of the chromo-electric
operator vanishes to all orders in perturbation theory. This implies an exact
relation between renormalization constants, which may help in a future
calculation of the two-loop anomalous dimension of the chromo-magnetic
operator.Comment: 9 pages, 1 figur
Comment on "On the -Anomaly in Betaine Calcium Chloride Dihydrate"
Recently, Hlinka and Ishibashi [J. Phys. Soc. Jpn. 67, 495 (1998)] discussed
the -anomaly in betaine calcium chloride dihydrate (BCCD) in a Landau-type
approach. We comment on the shortcomings of this approach and discuss the
-anomaly in the framework of a microscopical pseudo spin model based on a
realistic description of BCCD in terms of symmetry-adapted local modes.Comment: 2 pages, RevTex, submitted to J. Phys. Soc. Jp
Higher-order estimates of the chromomagnetic moment of a heavy quark
The leading beta_0^(n-1) alpha_s^n terms in the Wilson coefficient and
anomalous dimension of the chromomagnetic operator in the heavy-quark effective
Lagrangian are summed to all orders of perturbation theory. The perturbation
series for the anomalous dimension is well behaved, while that for the Wilson
coefficient exhibits a divergent behaviour already in low orders, caused by a
nearby infrared renormalon singularity. The resulting ambiguity is commensurate
with terms of order 1/m^2 in the effective Lagrangian, whose corresponding
ultraviolet renormalons are identified. An excellent approximation for the
scheme-invariant Wilson coefficient at next-to-next-to-leading order in
renormalization-group improved perturbation theory is obtained.Comment: 16 pages, 3 figures embedde
Note on Tests of the Factorization Hypothesis and the Determination of Meson Decay Constants
We discuss various tests of the factorization hypothesis making use of the
close relationship between semi-leptonic and factorized nonleptonic decay
amplitudes. It is pointed out that factorization leads to truely
model-independent predictions for the ratio of nonleptonic to semi-leptonic
decay rates, if in the nonleptonic decay a spin one meson of arbitrary mass or
a pion take the place of the lepton pair. Where the decay constants of those
mesons are known, these predictions represent ideal tests of the factorization
hypothesis. In other cases they may be used to extract the decay constants.
Currently available data on the decays are shown to be in excellent agreement with
the factorization results. A weighted average of the four independent values
for the QCD coefficient extracted from the data gives
suggesting that it may be equal to the Wilson coefficient evaluated
at the scale .Comment: (9 pages, ReVTeX, no figures), HD-THEP-92-3
Violations of Local Duality in the Heavy Quark Sector
We examine the origin of possible failures of the quark-hadron local duality.
In particular, we consider a correlator of two currents comprising heavy quark
operators, and compare the evaluation by the Operator Product Expansion with
the result obtained inserting an infinite set of hadronic states, in the N_c to
infinity limit. Whereas the smeared spectral functions agree with each other,
their local behaviour is different. The difference manifests itself in the form
of a term O(Lambda/epsilon) (epsilon being the residual energy) that is not
present in the expansion in powers of Lambda/epsilon predicted by the OPE.Comment: Latex, 14 pages, 1 figur
Non-perturbative Effects in
The rare decay provides excellent prospects for precision
tests of Standard Model flavour dynamics. The process can be computed in
perturbation theory with small uncertainty. However, in order to ensure a
reliable theoretical prediction, also potentially important effects from
non-perturbative QCD have to be controlled with sufficient accuracy. The
present article summarizes recent developments related to this topic.Comment: Invited Talk presented at the QCD Euroconference 98, Montpellier, 2-8
July 1998, 7 pages, 1 figur
Two-loop hybrid renormalization of local dimension-4 heavy-light operators
The renormalization of local dimension-4 operators containing a heavy and a
light quark field at scales below the heavy-quark mass is discussed, using the
formalism of the heavy-quark effective theory. The anomalous dimensions of
these operators and their mixing are calculated to two-loop order. Some
phenomenological applications are briefly discussed.Comment: 11 pages, 2 figure
A High-Statistics Lattice Calculation of and in the meson
We present a high-statistics lattice calculation of the kinetic energy
of the heavy quark inside the -meson and of the
chromo-magnetic term , related to the -- mass splitting,
performed in the HQET. Our results have been obtained from a numerical
simulation based on 600 gauge field configurations generated at , on
a lattice volume and using, for the meson correlators, the
results obtained with the SW-Clover improved lattice action for the
light quarks. For the kinetic energy we found ~GeV, which
is interesting for phenomenological applications. We also find GeV, corresponding to GeV, which is about one half of the experimental value. The origin
of the discrepancy with the experimental number needs to be clarified.Comment: 26 pages, latex, 5 figure
Long-range two-body final-state interactions and direct CP asymmetry in {B}^{+}\to{\pi}^{+} {K}^{0} decay
We present a calculation of the direct CP asymmetry, , for the
process including the effects of long-range inelastic
final-state interactions (FSI). We admit three channels in our calculation:
, and . The strong
scattering is described in terms of Pomeron and Regge exchanges. We find that
the direct CP asymmetry is enhanced by a factor of as a result of FSI,
but remains well short of the claims of (10 - 20)% in recent literature. A
critical assessment of papers claiming large CP asymmetries is also presented.Comment: 21 pages, latex, no figures. Added the charge-exchange channel
{B}^{+}\to {\pi}^{0} {K}^{+}. Expanded the discussion section. To be
published in Phys. Rev.
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