共查询到20条相似文献,搜索用时 31 毫秒
1.
《Nuclear Physics B》1995,434(3):619-646
By bosonization of an extended NJL model we derive an effective meson theory which describes the interplay between chiral symmetry and heavy quark dynamics. This effective theory is worked out in the low-energy regime using the gradient expansion. The resulting effective lagrangian describes strong and weak interactions of heavy B and D mesons with pseudoscalar Goldstone bosons and light vector and axial-vector mesons. Heavy meson weak decay constants, coupling constants and the Isgur-Wise function are predicted in terms of the model parameters partially fixed from the light quark sector. Explicit SU(3)F symmetry breaking effects are estimated and, if possible, confronted with experiment. 相似文献
2.
J. Portolés P.D. Ruiz-Femenía 《The European Physical Journal C - Particles and Fields》2002,24(3):439-446
We analyze new contributions to the theoretical input in heavy quark sum rules and we show that the general theory of singularities
of perturbation theory amplitudes yields the method to handle these specific features. In particular we study the inclusion
of heavy quark radiation by light quarks at and of non-symmetric correlators at . Closely related with this is that we also propose a solution to the construction of moments of the spectral densities at
where the presence of massless contributions invalidates the standard approach. We circumvent this problem through a new
definition of the moments, providing an infrared safe and consistent procedure.
Received: 11 February 2002 / Revised version: 14 March 2002 / Published online: 22 May 2002 相似文献
3.
We analyze the phenomenon of heavy quark condensation within the framework of the QCD sum rule approach. We discuss two alternative expansions for massive quark condensates. The first one (heavy to light quark expansion), introduced by Broadhurst and Generalis, establishes a connection between the heavy and light quark worlds. The other one (heavy quark expansion) is valid when only heavy quark systems are considered. As a byproduct we have obtained the coefficients of \(\left\langle {\bar qq} \right\rangle \) , \(\left\langle {\bar qGq} \right\rangle \) , 〈G 2〉 and 〈G 3〉 for all bilinear currents. 相似文献
4.
5.
S. Groote J. G. Körner A. A. Pivovarov 《The European Physical Journal C - Particles and Fields》2008,58(3):355-382
We present an analysis of the static properties of heavy baryons at next-to-leading order in the perturbative expansion of
QCD. We obtain analytical next-to-leading order three-loop results for the two-point correlators of baryonic currents with
one finite-mass quark field for a variety of quantum numbers of the baryonic currents. We consider both the massless limit
and the HQET limit of the correlator as special cases of the general finite-mass formula and find agreement with previous
results. We present closed-form expressions for the moments of the spectral density. We determine the residues of physical
baryon states using sum-rule techniques. 相似文献
6.
The method of systematical expansion in the inverse powers of the heavy quark masses of the weak current matrix elements between heavy meson states is developed in the framework of the relativistic quark model based on the quasipotential approach in quantum field theory. The comparison of the first and second order terms of this expansion with the structure predicted by the heavy quark effective theory imposes strong constraints on the form of the long-range confining potential of quark-antiquark interaction. It is found that the confinig $q\bar q$ potential is effectively vector, while scalar potential is anticonfining and helps to reproduce the correct nonrelativistic limit. At large distances quarks have nonperturbative anomalous chromomagnetic moments. The obtained values of the potential parameters are in accord with the ones found in our previous consideration of meson masses and decay rates. We calculate the Isgur-Wise function. The first and the second order form factors within 1/m Q expansion. 相似文献
7.
M. Jamin J.A. Oller A. Pich 《The European Physical Journal C - Particles and Fields》2002,24(2):237-243
In this work, the mass of the strange quark is calculated from QCD sum rules for the divergence of the strangeness-changing
vector current. The phenomenological scalar spectral function which enters the sum rule is determined from our previous work
on strangeness-changing scalar form factors [1]. For the running strange mass in the scheme, we find . Making use of this result and the light quark mass ratios obtained from chiral perturbation theory, we are also able to
extract the masses of the lighter quarks and . We then obtain and . In addition, we present an updated value for the light quark condensate.
Received: 18 October 2001 / Revised version: 22 January 2002 / Published online: 12 April 2002 相似文献
8.
O'Donnell P.J. Xu Q.P. Tung H.K.K. 《The European Physical Journal C - Particles and Fields》1999,10(2):313-317
Corrections to the exact heavy–quark symmetry results are expected to come from the inverse powers of the heavy-quark mass.
We show, by an explicit calculation using the quark model, that the breaking of the spin symmetry is suppressed by other kinematic
effects even when the quark masses are not heavy.
Received: 21 January 1999 / Published online: 20 May 1999 相似文献
9.
In a previous paper, we have shown how to systematically determine the low-energy structure of the Green functions in QCD. The present article extends this framework to expansions in the mass of the strange quark. We construct the generating functional of U(3)×U(3) which allows us to calculate the Green functions up to and including terms of order p4 (at fixed radio mquark/p2) in terms of a few coupling constants which chiral symmetry leaves undetermined. We calculate the first non-leading term in the quark mass expansion of the order parameters
, and of the masses and decay constants in the pseudoscalar octet. The three coupling constants which are not fixed by experimental low-energy information are estimated by invoking large-Nc arguments. 相似文献
10.
The contributions to the coefficient functions of the quark and the mixed quark-gluon condensate to mesonic correlators are calculated for the first time to all orders in the quark masses, and to lowest order in the strong coupling constant. Existing results on the coefficient functions of the unit operator and the gluon condensate are reviewed. The proper factorization of short- and long-distance contributions in the operator product expansion is discussed in detail. It is found that to accomplish this task rigorously the operator product expansion has to be performed in terms ofnon-normal-ordered condensates. The resulting coefficient functions are improved with the help of the renormalization group. The scale invariant combination of dimension 5 operators, including mixing with the mass operator, which is needed for the renormalization group improvement, is calculated in the leading order.Supported by the German Bundesministerium für Forschung und Technologie, under the contract 06 TM 761 相似文献
11.
The decay widths for the radiative decays of heavy baryons are calculated in the heavy quark effective theory. Introducing
the interpolating fields for heavy baryons we obtain the transition matrix elements and the corresponding decay widths. Considering
theSU(6) flavor-spin wave functions for heavy baryons, the coupling constants are calculated in the nonrelativistic quark model.
Since the masses of the heavy baryons are not available, we have taken the predicted bag model masses. We find our results
are quite different from that of the heavy quark bag model calculations. 相似文献
12.
A. Cabo Montes de Oca M. Rigol Madrazo 《The European Physical Journal C - Particles and Fields》2002,23(2):289-300
A recently proposed modified perturbative expansion for QCD incorporating gluon condensation is employed to evaluate the
quark and gluon self-energy corrections in first approximation. The results predict mass values of 1/3 of the nucleon mass
for the light quarks u, d, and s and a monotonously growing variation with the current mass. The only phenomenological input is that is evaluated up to order as a function of the unique parameter C defining the modified propagator, and then C is fixed to give a current estimate of . The light quarks u and d as a result are found to be confined and the s, c, b and t ones show damped propagation modes, suggesting a model for the large differences in stability between the nucleons and the
higher resonances. The above properties of quark modes diverge from the fully confinement result following from the similar
gluon propagator previously considered by Munczek and Nemirovski. On the other hand, the condensate effects on the gluon self-energy
furnish a tachyonic mass shell as predicted by the Fukuda analysis of gluon condensation in QCD.
Received: 28 September 2001 / Revised version: 15 November 2001 / Published online: 8 February 2002 相似文献
13.
The radiative decays of heavy mesons are considered in heavy quark symmetry formalism. Introducing the interpolating fields
for the heavy mesons we obtain the transition matrix element and the corresponding decay widths in the heavy quark symmetry
limits. The Isgur-Wise function present in the expression is determined by ISGW quark model. The results obtained agree reasonably
well with other estimations. 相似文献
14.
We calculate three-loop corrections to correlation functions of heavy-quark currents in the low- and high-energy regions. We present 30 coefficients both in the low-energy and the high-energy expansion of the scalar and the vector correlator with non-diagonal flavour structure. In addition we compute 30 coefficients in the high-energy expansion of the diagonal vector, axial-vector, scalar and pseudo-scalar correlators. Possible applications of our new results are improvements of lattice-based quark-mass determinations and the approximate reconstruction of the full momentum dependence of the correlators. 相似文献
15.
By making use of the path integral duality transformation, we derive the string representation for the partition function
of an extended Dual Abelian Higgs Model containing gauge fields of external currents of electrically charged particles. By
the same method, we obtain the corresponding representations for the generating functionals of gauge field and monopole current
correlators. In the case of bilocal correlators, the obtained results are found to be in agreement with the dual Meissner
scenario of confinement and the Stochastic Model of the QCD vacuum.
Received: 28 September 1998 / Revised version: 18 November 1998 / Published online: 11 March 1999 相似文献
16.
D. Gromes 《The European Physical Journal C - Particles and Fields》2001,20(3):523-530
We decompose the quark propagator in the presence of an arbitrary gluon field with respect to a set of Dirac matrices. The
four-dimensional integrals which arise in first order perturbation theory are rewritten as line-integrals along certain field
lines, together with a weighted integration over the various field lines. It is then easy to transform the propagator into
a form involving path ordered exponentials. The resulting expression is non-perturbative and has the correct behavior under
Lorentz transformations, gauge transformations and charge conjugation. Furthermore it coincides with the exact propagator
in first order of the coupling g. No expansion with respect to the inverse quark mass is involved, the expression can even be used for vanishing mass. For
large mass the field lines concentrate near the straight line connection and simple results can be obtained immediately.
Received: 31 March 2001 / Revised version: 3 May 2001 / Published online: 8 June 2001 相似文献
17.
We study the weak vector and axial-vector form factors of first- and second-class currents for the semileptonic octet baryon
decays in the spirit of the chiral quark model. Our results for the weak magnetism form factors are consistent with the conserved
vector current (CVC) results. The induced pseudotensor form factors, which are highly model dependent, are small. The overall
performance of the chiral quark model is quite good and in general agreement with existing experimental data.
Received: 9 March 1998 / Published online: 12 August 1998 相似文献
18.
The structure of the quark propagator of QCD in a confining background is not known. We make an ansatz for it, as hinted by a particular mechanism for confinement, and analyze its implications in the meson and baryon correlators. We connect the various terms in the Källen-Lehmann representation of the quark propagator with appropriate combinations of hadron correlators, which may ultimately be calculated in lattice QCD. Furthermore, using the positivity of the path integral measure for vector like theories, we reanalyze some mass inequalities in our formalism. A curiosity of the analysis is that, the exotic components of the propagator (axial and tensor), produce terms in the hadron correlators which, if not vanishing in the gauge field integration, lead to violations of fundamental symmetries. The non observation of these violations implies restrictions in the space-time structure of the contributing gauge field configurations. In this way, lattice QCD can help us analyze the microscopic structure of the mechanisms for confinement.Supported in part by CICYT (AEN91-0234) and DGICYT grant (PB91-0119-C02-01) 相似文献
19.
K.G. Chetyrkin M. Steinhauser 《The European Physical Journal C - Particles and Fields》2001,21(2):319-338
The non-diagonal correlators of vector and scalar currents are considered at three-loop order in QCD. The full mass dependence
is computed in the case where one of the quarks is massless and the other one carries mass M. We exploit the decoupling relations between the full theory and the heavy quark effective theory (HQET) in order to obtain
the logarithmic parts of the leading threshold terms. With the help of conformal mapping and Padé approximation numerical
estimates for the non-logarithmic terms are extracted which in turn lead to a prediction of the correlator in HQET at order
. As applications of the vector and scalar correlator we consider the single-top-quark production via the process and the decay rate of a charged Higgs boson into hadrons, respectively. In both cases the computed NLO corrections are shown
to be numerically much less important than the leading ones. On the contrary, the NLO order QCD corrections to the HQET sum
rule for the leptonic decay rate of a heavy-light meson proves to be comparable to the leading one.
Received: 19 June 2001 / Published online: 10 August 2001 相似文献
20.
H.David Politzer 《Nuclear Physics B》1976,117(2):397-406
The behavior of effective, scale dependent quark masses in the chiral limit is studied using the operator product expansion. Their relation to current and constituent quark masses is clarified. Current correlation functions are examined as an example of separating effects of spontaneous and explicit chiral symmetry breaking. 相似文献