摘要:

TheNC→ ∞ limit of QCD gives a useful approximation scheme to the physical hadronic world. A brief overview of the mesonic sector is presented. The large‐NCconstraints on the low‐energy couplings of Chiral Perturbation Theory are summarized and the role of unitarity corrections is discussed. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570555

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We assume that QCD can be described in a certain kinematical regime by an effective string theory. This hadronic string must couple to background chiral fields in a chirally invariant manner, taking into account the true chirally non‐invariant QCD vacuum. By requiring conformal symmetry of the string and the unitarity constraint on chiral fields we reconstruct the equations of motion for the latter ones. These provide a consistent background for the propagation of the string. By further requiring locality of the effective action we recover the Lagrangian of non‐linear sigma model of pion interactions. The prediction is totally unambiguous and parameter‐free. The estimated chiral structural constants of Gasser and Leutwyler fit very well the phenomenological values. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570556

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We write a set of dispersion relations for the &Kgr; → &pgr;&pgr; amplitude in which the weak Hamiltonian carries momentum. A soft pion theorem relates this amplitude to the &Kgr; → &pgr; amplitude, and can be used to determine one of the two subtraction constants — the second constant is at present known only to leading order in chiral perturbation theory. We solve the dispersion relations numerically and express the result in terms of the unknown higher order corrections to this subtraction constant. We present preliminary results of an analysis of the effect of inelastic channels. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570557

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Meson‐Baryon Interactions can be successfully described using both Chiral Symmetry and Unitarity. Thes‐wave meson‐baryon scattering amplitude is analyzed in a Bethe‐Salpeter coupled channel formalism incorporating Chiral Symmetry in the potential. Two body coupled channel unitarity is exactly preserved. The needed two particle irreducible matrix amplitude is taken from lowest order Chiral Perturbation Theory in a relativistic formalism. Off‐shell behavior is parameterized in terms of low energy constants. The relation to the heavy baryon limit is discussed. The position of the complex poles in the second Riemann sheet of the scattering amplitude determine masses and widths baryonic resonances of theN(1535),N(1670), &Lgr;(1405) and &Lgr;(1670) resonances which compare well with accepted numbers. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570558

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We analyze the masses of the negative paritySU(6)70‐plet baryons using the 1/Ncexpansion to order 1/Ncand to first order inSU(3) breaking. At this level of precision there are twenty predictions which include the well known Gell‐Mann Okubo and equal spacing relations together with four new relations involvingSU(3) breaking splittings in differentSU(3) multiplets. Although the breaking ofSU(6) symmetry occurs at zeroth order in 1/Nc, it turns out to be small. The dominant source of the breaking is the hyperfine interaction which is of order 1/Nc. The spin‐orbit interaction, of zeroth order in 1/Nc, is entirely fixed by the splitting between the singlet states &Lgr;(1405) and &Lgr;(1520), and the spin‐orbit puzzle is solved by the presence of other zeroth order operators involving flavor exchange. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570559

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The method which allows for asymptotic expansion of the one‐loop effective actionW= lndetAis formulated. The positively defined elliptic operatorA = U+M2depends on the external classical fields taking values in the Lie algebra of the internal symmetry groupG. Unlike the standard method of Schwinger ‐ DeWitt, the more general case with the nongenerate mass matrixM= diag(m1,m2, &ellip;) is considered. The first coefficients of the new asymptotic series are calculated and their relationship with the Seeley ‐ DeWitt coefficients is clarified. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570560

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The ’t Hooft six quark flavor mixing interaction (Nf= 3) is bosonized by the path integral method. The considered complete Lagrangian is constructed on the basis of the combined ’t Hooft andU(3) ×U(3) extended chiral four fermion Nambu — Jona‐Lasinio interactions. The method of the steepest descents is used to derive the effective mesonic Lagrangian. Additionally to the known lowest order stationary phase (SP) result of Reinhardt and Alkofer we obtain the contribution from the small quantum fluctuations of bosonic configurations around their stationary phase trajectories. Fluctuations give rise to multivalued solutions of the gap equations. Using the gap equations we construct the effective potential, from which the structure of the vacuum can be settled. We obtain that from the several extremal solutions, only one is a minimum. The others are either maxima or a saddle point. The effective potential reveals furthermore the existence of logartithmically divergent attractive wells at certain field expectation values, signalizing caustic regions. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570561

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Recently, the relatively old speculation that the physical QCD vacuum might be a kind of dual superconductor, in which color‐magnetic monopoles have condensed, seems to have received some “experimental” confirmation in lattice calculations. The lattice calculations do not dictate, however, the form of the effective low‐energy theory. And indeed, a rather wide panoply of possible effective theories has been proposed. The purpose of this talk is to review them in order to contrast their properties. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570562

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Effective hadron models commonly require the computation of functional determinants. In the static case these are one‐loop vacuum polarization energies, known as Casimir energies. In this talk I will present general methods to efficiently compute renormalized one‐loop vacuum polarization energies and energy densities and apply these methods to construct soliton solutions within a variational approach. This calculational method is particularly useful to study singular limits that emerge in the discussion of theclassicalCasimir problem which is usually posed as the response of a fluctuating quantum field to externally imposed boundary conditions. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570563

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We report on our recent progress in the generation of resonant behavior in unitarized meson‐meson scattering amplitudes obtained from Chiral Perturbation Theory. These amplitudes provide simultaneously a remarkable description of the resonance region up to 1.2 GeV as well as the low energy region, since they respect the chiral symmetry expansion. By studying the position of the poles in these amplitudes it is possible to determine the mass and width of the associated resonances, as well as to get a hint on possible classification schemes, that could be of interest for the spectroscopy of the scalar sector. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1570564

出版商:AIP    

年代:1903

数据来源: AIP