487 research outputs found
Uraltsev Sum Rule in Bakamjian-Thomas Quark Models
We show that the sum rule recently proved by Uraltsev in the heavy quark
limit of QCD holds in relativistic quark models \`a la Bakamjian and Thomas,
that were already shown to satisfy Isgur-Wise scaling and Bjorken sum rule.
This new sum rule provides a {\it rationale} for the lower bound of the slope
of the elastic IW function obtained within the BT
formalism some years ago. Uraltsev sum rule suggests an inequality
. This difference is interpreted in the BT
formalism as due to the Wigner rotation of the light quark spin, independently
of a possible LS force. In BT models, the sum rule convergence is very fast,
the state giving the essential contribution in most of the
phenomenological potential models. We underline that there is a serious
problem, in the heavy quark limit of QCD, between theory and experiment for the
decays , independently of any model
calculation.Comment: 16 pages, Late
Remarks on sum rules in the heavy quark limit of QCD
We underline a problem existing in the heavy quark limit of QCD concerning
the rates of semileptonic B decays into P-wave mesons, where (wide states) or (narrow states). The leading order
sum rules of Bjorken and Uraltsev suggest , in contradiction with experiment. The same trend follows also from a sum
rule for the subleading curent matrix element correction .
The problem is made explicit in relativistic quarks models \`a la Bakamjian and
Thomas, that give a transparent physical interpretation of the latter as due,
not to a force, but to the Wigner rotation of the light quark spin.
We point out moreover that the selection rule for decay constants of states, , predicts, assuming the model of factorization,
the opposite hierarchy .Comment: Contribution to the International Europhysics Conference on HEP,
Budapest, July 2001 (presented by L. Oliver); 5 page
One Interesting New Sum Rule Extending Bjorken's to order {1/m_Q}
We explicitly check quark-hadron duality to order
for decays in the limit including ground state
and orbitally excited hadrons. Duality occurs thanks to a new sum rule which
expresses the subleading HQET form factor or, in other notations,
in terms of the infinite mass limit form factors and some level
splittings. We also demonstrate the sum rule, which is not restricted to the
condition , applying OPE to the longitudinal axial component
of the hadronic tensor without neglecting the subleading contributions
to the form factors. We argue that this method should produce a new class of
sum rules, depending on the current, beyond Bjorken, Voloshin and the known
tower of higher moments. Applying OPE to the vector currents we find another
derivation of the Voloshin sum rule. From independent results on we
derive a sum rule which involves only the and
form factors and the corresponding level splittings. The
latter strongly supports a theoretical evidence that the semileptonic decay
into narrow orbitally-excited resonances dominates over the decay into the
broad ones, in apparent contradiction with some recent experiments. We discuss
this issue.Comment: 9 page
Duality in the non-relativistic harmonic oscillator quark model in the Shifman-Voloshin limit : a pedagogical example
The detailed way in which duality between sum of exclusive states and the
free quark model description operates in semileptonic total decay widths, is
analysed. It is made very explicit by the use of the non relativistic harmonic
oscillator quark model in the SV limit, and a simple interaction current with
the lepton pair. In particular, the Voloshin sum rule is found to eliminate the
mismatches of order .Comment: 11 pages, Latex2e, AMS-LaTe
Study of internal structures of 9,10Be and 10B in scattering of 4He from 9Be
A study of inelastic scattering and single-particle transfer reactions was
performed by an alpha beam at 63 MeV on a 9$Be target. Angular distributions of
the differential cross sections for the 9Be(4He,4He')9Be*, 9Be(4He,3He)10Be and
9Be(4He,t)10B reactions were measured. Experimental angular distributions of
the differential cross sections for the ground state and a few low-lying states
were analyzed in the framework of the optical model, coupled channels and
distorted-wave Born approximation. An analysis of the obtained spectroscopic
factors was performed.Comment: 16 pages, 7 figures, 3 tables, regular paper, mispritns are corrected
in new versio
Spatial distributions in static heavy-light mesons: a comparison of quark models with lattice QCD
Lattice measurements of spatial distributions of the light quark bilinear
densities in static mesons allow to test directly and in detail the wave
functions of quark models. These distributions are gauge invariant quantities
directly related to the spatial distribution of wave functions. We make a
detailed comparison of the recent lattice QCD results with our own quark
models, formulated previously for quite different purposes. We find a striking
agreement not only between our two quark models, but also with the lattice QCD
data for the ground state in an important range of distances up to about 4/GeV.
Moreover the agreement extends to the L=1 states [j^P=(1/2)^+]. An explanation
of several particular features completely at odds with the non-relativistic
approximation is provided. A rather direct, somewhat unexpected and of course
approximate relation between wave functions of certain quark models and QCD has
been established.Comment: 40 pages, 5 figures (version published in PRD
The structure of the atomic helium trimers: Halos and Efimov states
The Faddeev equations for the atomic helium-trimer systems are solved
numerically with high accuracy both for the most sophisticated realistic
potentials available and for simple phenomenological potentials. An efficient
numerical procedure is described. The large-distance asymptotic behavior,
crucial for weakly bound three-body systems, is described almost analytically
for arbitrary potentials. The Efimov effect is especially considered. The
geometric structures of the bound states are quantitatively investigated. The
accuracy of the schematic models and previous computations is comparable, i.e.
within 20% for the spatially extended states and within 40% for the smaller
^4He-trimer ground state.Comment: 32 pages containing 7 figures and 6 table
semileptonic decay in covariant quark models \`a la Bakamjian Thomas
Once chosen the dynamics in one frame, for example the rest frame, the
Bakamjian and Thomas method allows to define relativistic quark models in any
frame. These models have been shown to provide, in the heavy quark limit, fully
covariant current form factors as matrix elements of the quark current
operator. They also verify the Isgur-Wise scaling and give a slope parameter
for all the possible choices of the dynamics. In this paper we
study the excited states and derive the general formula, valid for any
dynamics, for the scaling invariant form factors and
. We also check the Bjorken-Isgur-Wise sum rule already
demonstrated elsewhere in this class of models.Comment: 14 pages, Latex2e, AMS-LaTe
Regularization of a three-body problem with zero-range potentials
We propose a coordinate-space regularization of the three-body problem with
zero-range potentials. We include the effective range and the shape parameter
in the boundary condition of the zero-range potential. The proposed extended
zero-range model is tested against atomic helium trimers and is shown to
provide an adequate quantitative description of these systems
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