Linear meson and baryon trajectories in AdS/QCD

An approximate holographic dual of QCD is constructed and shown to reproduce the empirical linear trajectories of universal slope on which the square masses of radially and orbitally excited hadrons join. Conformal symmetry breaking and other IR effects are described exclusively by deformations of the anti-de Sitter background metric. The predictions for the light hadron spectrum include new relations between ground state masses and trajectory slopes and are in good overall agreement with experimental data.Comment: 4 page

The Strangeness Radius and Magnetic Moment of the Nucleon Revisited

We update Jaffe's estimate of the strange isoscalar radius and magnetic moment of the nucleon. We make use of a recent dispersion--theoretical fit to the nucleon electromagnetic form factors and an improved description of symmetry breaking in the vector nonet. We find $\mu_s = -0.24 \pm 0.03$~n.m. and $r_s^2 = 0.21 \pm 0.03$~fm$^2$. The strange formfactor $F_2^s (t)$ follows a dipole with a cut--off mass of 1.46~GeV, $F_2^s (t)= \mu_s (1-t/2.14 \, {\rm GeV}^2 )^{-2}$. These numbers should be considered as upper limits on the strange vector current matrix--elements in the nucleon.Comment: 8 pp, LaTeX, uses epsf, 1 figure in separate fil

Scalar Spectrum from a Dynamical Gravity/Gauge model

We show that a Dynamical AdS/QCD model is able to reproduce the linear Regge trajectories for the light-flavor sector of mesons with high spin and also for the scalar and pseudoscalar ones. In addition the model has confinement by the Wilson loop criteria and a mass gap. We also calculate the decay amplitude of scalars into two pion in good agreement to the available experimental data.Comment: Presented in the 4th International Workshop on Astronomy and Relativistic Astrophysic

K* nucleon hyperon form factors and nucleon strangeness

A crucial input for recent meson hyperon cloud model estimates of the nucleon matrix element of the strangeness current are the nucleon-hyperon-K* (NYK*) form factors which regularize some of the arising loops. Prompted by new and forthcoming information on these form factors from hyperon-nucleon potential models, we analyze the dependence of the loop model results for the strange-quark observables on the NYK* form factors and couplings. We find, in particular, that the now generally favored soft N-Lambda-K* form factors can reduce the magnitude of the K* contributions in such models by more than an order of magnitude, compared to previous results with hard form factors. We also discuss some general implications of our results for hadronic loop models.Comment: 9 pages, 8 figures, new co-author, discussion extended to the momentum dependence of the strange vector form factor

Meson-Baryon-Baryon Vertex Function and the Ward-Takahashi Identity

Ohta proposed a solution for the well-known difficulty of satisfying the Ward-Takahashi identity for a photo-meson-baryon-baryon amplitude ($\gamma$MBB) when a dressed meson-baryon-baryon (MBB) vertex function is present. He obtained a form for the $\gamma$MBB amplitude which contained, in addition to the usual pole terms, longitudinal seagull terms which were determined entirely by the MBB vertex function. He arrived at his result by using a Lagrangian which yields the MBB vertex function at tree level. We show that such a Lagrangian can be neither hermitian nor charge conjugation invariant. We have been able to reproduce Ohta's result for the $\gamma$MBB amplitude using the Ward-Takahashi identity and no other assumption, dynamical or otherwise, and the most general form for the MBB and $\gamma$MBB vertices. However, contrary to Ohta's finding, we find that the seagull terms are not robust. The seagull terms extracted from the $\gamma$MBB vertex occur unchanged in tree graphs, such as in an exchange current amplitude. But the seagull terms which appear in a loop graph, as in the calculation of an electromagnetic form factor, are, in general, different. The whole procedure says nothing about the transverse part of the ($\gamma$MBB) vertex and its contributions to the amplitudes in question.Comment: A 20 pages Latex file and 16 Postscript figures in an uuencoded format. Use epsf.sty to include the figures into the Latex fil

Mesonic Spectrum from a Dynamical Gravity/Gauge model

Within a formulation of a Dynamical AdS/QCD model we calculate the spectrum of light flavored mesons. The background fields of the model correspond to an IR deformed Anti de Sitter metric coupled to a dilaton field. Confinement comes as a consequence of the dilaton dynamics coupled to gravity. Additionally to the Regge-like spectrum of light- scalar, vector and higher spin mesons, we obtain the decay width of scalar mesons into two pions.Comment: Talk given at Light Cone 2009: Relativistic Hadronic and Particle Physics (LC 2009), Sao Jose dos Campos, Brazil, 8-13 Jul 2009

Strange form factors in the context of SAMPLE, HAPPEX, and A4 experiments

The strange properties of the nucleon are investigated within the framework of the SU(3) chiral quark-soliton model assuming isospin symmetry and applying the symmetry conserving SU(3) quantization. We present the form factors $G^0_{E,M}(Q^2)$, $G^Z_M(Q^2)$ and the electric and magnetic strange form factors $G^s_{E,M}(Q^2)$ incorporating pion and kaon asymptotics. The results show a fairly good agreement with the recent experimental data from the SAMPLE and HAPPEX collaborations. We also present predictions for future measurements including the A4 experiment at MAMI (Mainz).Comment: 10 pages with four figures. RevTeX4 is used. Few lines are changed. Accepted for publication in Phys.Rev.

Hadrons in AdS/QCD models

We discuss applications of gauge/gravity duality to describe the spectrum of light hadrons. We compare two particular 5-dimensional approaches: a model with an infrared deformed Anti-de Sitter metric and another one based on a dynamical AdS/QCD framework with back-reacted geometry in a dilaton/gravity background. The models break softly the scale invariance in the infrared region and allow mass gap for the field excitations in the gravity description, while keeping the conformal property of the metric close to the four-dimensional boundary. The models provide linear Regge trajectories for light mesons, associated with specially designed infrared gravity properties. We also review the results for the decay widths of the f0's into two pions, as overlap integrals between mesonic string amplitudes, which are in qualitative agreement with data