589 research outputs found
On P-wave meson decay constants in the heavy quark limit of QCD
In previous work it has been shown that, either from a sum rule for the
subleading Isgur-Wise function or from a combination of Uraltsev and
Bjorken SR, one infers for -wave states . This implies, in the heavy quark limit of QCD, a hierarchy
for the {\it production} rates of -states that seems at
present to be contradicted by experiment. It was also shown that the decay
constants of -states vanish in the heavy quark limit of
QCD, . Assuming the {\it model} of factorization in the
decays , one expects the opposite hierarchy for
the {\it emission} rates , since
-states are coupled to vacuum. Moreover, using Bjorken SR and previously
discovered SR involving heavy-light meson decay constants and IW functions, one
can prove that the sums ,
(where and
are the decay constants of -states and
-states) are divergent. This situation seems to be realized in the
relativistic quark models \`a la Bakamjian and Thomas, that satisfy HQET and
predict decays constants and that do not decrease
with the radial quantum number .Comment: 7 pages, Late
Heavy-to-Light Form Factors in the Final Hadron Large Energy Limit: Covariant Quark Model Approach
We prove the full covariance of the heavy-to-light weak current matrix
elements based on the Bakamjian-Thomas construction of relativistic quark
models, in the heavy mass limit for the parent hadron and the large energy
limit for the daughter one. Moreover, this quark model representation of the
heavy-to-light form factors fulfills the general relations that were recently
argued to hold in the corresponding limit of QCD, namely that there are only
three independent form factors describing the B -> pi (rho) matrix elements, as
well as the factorized scaling law sqrt(M)z(E) of the form factors with respect
to the heavy mass M and large energy E. These results constitute another good
property of the quark models \`a la Bakamjian-Thomas, which were previously
shown to exhibit covariance and Isgur-Wise scaling in the heavy-to-heavy case.Comment: 11 pages, LaTex2e, no figur
Bound on the curvature of the Isgur-Wise function of the baryon semileptonic decay Lambda_b -> Lambda_c + l + nu
In the heavy quark limit of QCD, using the Operator Product Expansion, the
formalism of Falk for hadrons or arbitrary spin, and the non-forward amplitude,
as proposed by Uraltsev, we formulate sum rules involving the Isgur-Wise
function of the baryon transition , where the light cloud has for both
initial and final baryons. We recover the lower bound for the slope
obtained by Isgur et al., and we
generalize it by demonstrating that the IW function is an
alternate series in powers of , i.e. . Moreover, exploiting systematically the sum rules, we get an improved
lower bound for the curvature in terms of the slope, . This
bound constrains the shape of the Isgur-Wise function and it will be compelling
in the analysis of future precise data on the differential rate of the baryon
semileptonic decay , that
has a large measured branching ratio, of about 5%.Comment: 16 page
Explicit form of the Isgur-Wise function in the BPS limit
Using previously formulated sum rules in the heavy quark limit of QCD, we
demonstrate that if the slope rho^2 = -xi'(1) of the Isgur-Wise function xi(w)
attains its lower bound 3/4, then all the derivatives (-1)^L xi^(L)(1) attain
their lower bounds (2L+1)!!/2^(2L), obtained by Le Yaouanc et al. This implies
that the IW function is completely determined, given by the function xi(w) =
[2/(w+1)]^(3/2). Since the so-called BPS condition proposed by Uraltsev implies
rho^2 = 3/4, it implies also that the IW function is given by the preceding
expression.Comment: 19 page
Sum rules for leading and subleading form factors in Heavy Quark Effective Theory using the non-forward amplitude
Within the OPE, we the new sum rules in Heavy Quark Effective Theory in the
heavy quark limit and at order 1/m_Q, using the non-forward amplitude. In
particular, we obtain new sum rules involving the elastic subleading form
factors chi_i(w) (i = 1,2, 3) at order 1/m_Q that originate from the L_kin and
L_mag perturbations of the Lagrangian. To the sum rules contribute only the
same intermediate states (j^P, J^P) = ((1/2)^-, 1^-), ((3/2)^-, 1^-) that enter
in the 1/m_Q^2 corrections of the axial form factor h_(A_1)(w) at zero recoil.
This allows to obtain a lower bound on -delta_(1/m^2)^(A_1) in terms of the
chi_i(w) and the shape of the elastic IW function xi(w). An important
theoretical implication is that chi'_1(1), chi_2(1) and chi'_3(1) (chi_1(1) =
chi_3(1) = 0 from Luke theorem) must vanish when the slope and the curvature
attain their lowest values rho^2->3/4, sigma^2->15/16. These constraints should
be taken into account in the exclusive determination of |V_(cb)|.Comment: Invited talk to the International Workshop on Quantum Chromodynamics
: Theory and Experiment, Conversano (Bari, Italy), 16-20 June 200
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