Meson dominance of hadron form factors and large-N_{c} phenomenology (original) (raw)

Hadron form factors and large- N c phenomenology

EPJ Web of Conferences, 2014

The half width rule provides a way to consider 1/N c corrections to hadronic models containing resonances. Consequences of such ideas for hadron form factors and Regge trajectories are explored, with special emphasis on the possibility to describe the spectrum of light and heavy unflavored vector mesons in a universal way.

A Study on the Form Factors of Hadrons

JOURNAL OF ADVANCES IN PHYSICS, 2016

The form factors of the heavy mesons like Bc+ , ηb, B0s, F+, B0 , D, ψ, ϕ, proton and also deuteron are investigated in the framework of the statistical model for low momentum transfer Q in the range 0.01 ≤ Q2 ≤ 0.1 GeV2.It has been observedthat the heavy-light flavour mesonic form factors show a scaling behavior in the aforesaid low Q2 range. The proton form factor also shows almost scaling in the aforesaid range whereas the deuteron form factor shows a clear violation indicating large contribution from sea quarks and gluon sector.

Nucleon form factors from a covariant quark core: Limits in their description

The European Physical Journal A - Hadrons and Nuclei, 2003

In treating the relativistic 3-quark problem, a dressed-quark propagator parameterization is used which is compatible with recent lattice data and pion observables. Furthermore 2-quark correlations are modeled as a series of quark loops in the scalar and axialvector channel. The resulting reduced Faddeev equations are solved for nucleon and delta. Nucleon electromagnetic form factors are calculated in a fully covariant and gauge-invariant scheme. Whereas the proton electric form factor G E and the nucleon magnetic moments are described correctly, the neutron electric form factor and the ratio G E /G M for the proton appear to be quenched. The influence of vector mesons on the form factors is investigated which amounts to a 25 % modification of the electromagnetic proton radii within this framework.

Applicability of perturbative QCD and NLO power corrections for the pion form factor

Physical Review D, 2002

In many years ago, Isgur and Llewellyn Smith addressed that PQCD is inapplicable to exclusive processes , such as the pion form factor. The main problem is that the asymptotic of PQCD is only about one fourth of the experimental value . We reexamine this PQCD deep problem. By including NLO power corrections to the pion form factor, we may arrive at a perturbative explanation for the data. The key realization is that we need to interprete that the strong interaction coupling constant involved in the PQCD result should be taken as an effective coupling constant under nonperturbative QCD vaccum. This implies that one can equally identify the relevant scale for the effective coupling constant as the factorization scale about 1 GeV. We also find that the average momentum fraction variable locates about 0.5, which is in favor of the asymptotic pion wave function. By employing photon-pion form factor with NLO power corrections to factorize out the nonperturbative effects involved in the effective coupling constant, we can extract an effective running coupling constant, which represents an effective coupling involving in the hard scattering subprocesses. The difference between the effective running coupling constant and the usual perturbative running coupling constant (Λ QCD = 0.3 GeV) is very small for Q 2 > 1 GeV 2 . The effective running coupling constant αs/π is smaller than 0.2 for Q 2 > 1 GeV 2 . This directly showes that PQCD is applicable to exclusive processes at energy Q 2 > 1 GeV 2 . In summary, with NLO power corrections, PQCD can completely explain the Q 2 spectrum of pion form factor.

Hadron resonances, large Nc, and the half-width rule

2012

We suggest using the half-width rule to make an estimate of the 1/Nc errors in hadronic models containing resonances. We show simple consequences ranging from the analysis of meson Regge trajectories, the hadron resonance gas at finite temperature and generalized hadronic form factors.

Role of mesons in the electromagnetic form factors of the nucleon

Physical Review C, 2010

The roles played by mesons in the electromagnetic form factors of the nucleon are explored using as a basis a model containing vector mesons with coupling to the continuum together with the asymptotic Q 2 behavior of perturbative QCD. Specifically, the vector dominance model (GKex) developed by E. L. Lomon is employed, as it is known to be very successful in representing the existing high-quality data published to date. An analysis is made of the experimental uncertainties present when the differences between the GKex model and the data are expanded in orthonormal basis functions. A main motivation for the present study is to provide insight into how the various ingredients in this model yield the measured behavior, including discussions of when dipole form factors are to be expected or not, of which mesons are the major contributors, for instance, at low Q 2 or large distances, and of what effects are predicted from coupling to the continuum. Such insights are first discussed in momentum space, followed by an analysis of how different and potentially useful information emerges when both the experimental and theoretical electric form factors are Fourier transformed to coordinate space. While these Fourier transforms should not be interpreted as "charge distributions," nevertheless the roles played by the various mesons, especially those which are dominant at large or small distance scales, can be explored via such experiment-theory comparisons.

Scalar form factors of light mesons

Physics Letters B, 2004

The scalar radius of the pion plays an important role in χPT, because it is related to one of the basic effective coupling constants, viz. the one which controls the quark mass dependence of F π at one loop. In a recent Letter, Ynduráin derives a robust lower bound for this radius, which disagrees with earlier determinations. We show that such a bound does not exist: the "derivation" relies on an incorrect claim. Moreover, we discuss the physics of the form factors associated with the operatorsūu, dd andss and show that their structure in the vicinity of the KK threshold is quite different. Finally, we draw attention to the fact that the new data on the slope of the scalar K 3 form factor confirm a recent, remarkably sharp theoretical prediction.

Meson form factors and the quark-level linear /sigma model

Nucl Phys a, 2003

The quark-level linear σ model (LσM) is employed to compute a variety of electromagnetic and weak observables of light mesons, including pion and kaon form factors and charge radii, charged-pion polarizabilities, semileptonic weak K ℓ3 decay, semileptonic weak radiative pion and kaon form factors, radiative decays of vector mesons, and nonleptonic weak K 2π decay. The agreement of all these predicted observables with experiment is striking. In passing, the tight link between the LσM and vector-meson dominance is shown. Some conclusions are drawn on the LσM in connection with lattice and renormalization-group approaches to QCD.