arXiv subjects

Enrique Ruiz Arriola

Publications and source records attributed to Enrique Ruiz Arriola.

At least 91 records · Page 5Linked to original sources

arXiv2011

Transversity Form Factors and Generalized Parton Distributions of the pion in chiral quark models

The transversity Generalized Parton Distributions (tGPDs) and related transversity form factors of the pion are evaluated in chiral quark models, both local (Nambu--Jona-Lasinio) and nonlocal, involving a momentum-dependent quark mass. The obtained tGPDs satisfy all a priori formal requirements, such as the proper support, normalization, and polynomiality. We evaluate generalized transversity form factors accessible from the recent lattice QCD calculations. These form factors, after the necessary QCD evolution, agree very well with the lattice data, confirming the fact that the spontaneously broken chiral symmetry governs the structure of the pion also in the case of the transversity observables.

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arXiv2011

Generalized Quark Transversity Distribution of the Pion in Chiral Quark Models

The transversity generalized parton distributions (tGPDs) of the the pion, involving matrix elements of the tensor bilocal quark current, are analyzed in chiral quark models. We apply the nonlocal chiral models involving a momentum-dependent quark mass, as well as the local Nambu--Jona-Lasinio with the Pauli-Villars regularization to calculate the pion tGPDs, as well as related quantities following from restrained kinematics, evaluation of moments, or taking the Fourier-Bessel transforms to the impact-parameter space. The obtained distributions satisfy the formal requirements, such as proper support and polynomiality, following from Lorentz covariance. We carry out the leading-order QCD evolution from the low quark-model scale to higher lattice scales, applying the method of Kivel and Mankiewicz. We evaluate several lowest-order generalized transversity form factors, accessible from the recent lattice QCD calculations. These form factors, after evolution, agree properly with the lattice data, in support of the fact that the spontaneously broken chiral symmetry is the key element also in the evaluation of the transversity observables.

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arXiv2010

Scalar-isoscalar states, gravitational form factors, and dimension-2 condensates in a large-Nc Regge approach

Scalar-isoscalar states are analyzed within the large-Nc Regge approach. We find that the lightest f0(600) scalar-isoscalar state fits very well into the pattern of the radial Regge trajectory. We confirm the obtained mass values from an analysis of the pion and nucleon spin-0 gravitational form factors, recently measured on the lattice. We find that a simple two-state model suggests a meson nature of f0(600), and a glueball nature of f0(980), which naturally explains the ratios of various coupling constants. Finally, matching to the OPE requires a fine-tuned mass condition of the vanishing dimension-2 condensate in the Regge approach with infinitely many scalar-isoscalar states.

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arXiv2010

Transversity relations, chiral and holographic models, and pion wave functions from lattice QCD

We analyze the equal-time Bethe-Salpeter quark wave functions of the pion in various models. We discuss how the quenched lattice QCD results with delocalized pion interpolators can be identified with the coarse grained wave functions, typical of low-energy effective models. Actually, we find that one-loop chiral quark models predict that pseudoscalar and tensor wave functions have the same shape, while the axial component is more extended. These facts are accurately confirmed by the lattice. We also show how the transversity information, relevant for the light-cone physics, can be straightforwardly obtained from the equal-time rest-frame lattice calculations. This remarkable relation provides a way to extract, for instance, the equal-time holographic wave functions and compare them, quite favorably, to the lattice calculations.

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arXiv2010

Pion transition form factor in the Regge approach

We explore the BaBar puzzle within the Regge approach. After reviewing the chiral quark models in applications to PDF and PDA of the pion, we argue that variants of these models, fulfilling the chiral anomaly, may in fact violate the second Terazawa-West unitarity bound, which is based on unverified assumptions for the real part of the amplitude. Consequently, the transition form factor need not vanish at large values of the photon virtuality. Then we show that the experimental data may be properly explained with incomplete vector-meson dominance in a simple model with one state, as well as in more sophisticated radial Regge models including infinitely many states. We also consider the experimental constraint from the rare Z -> pi0 gamma decay, which is comfortably satisfied in our approach. Finally, we point out that the photon momentum asymmetry parameter may noticeably influence the precision fits to the data.

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arXiv2010

Transversity form factors of the pion in chiral quark models

The transversity form factors of the pion, involving matrix elements of bilocal tensor currents, are evaluated in chiral quark models, both in the local Nambu--Jona-Lasinio with the Pauli-Villars regularization, as well as in nonlocal models involving momentum-dependent quark mass. After suitable QCD evolution the agreement with recent lattice calculations is very good, in accordance to the fact that the spontaneously broken chiral symmetry governs the dynamics of the pion. Meson dominance of form factors with expected meson masses also works properly, conforming to the parton-hadron duality in the considered process.

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arXiv2010

Pion transition form factor in the Regge approach and incomplete vector-meson dominance

The concept of incomplete vector-meson dominance and Regge models is applied to the transition form factor of the pion. First, we argue that variants of the chiral quark model fulfilling the chiral anomaly may violate the Terazawa-West unitarity bounds, as these bounds are based on unverified assumptions for the real parts of the amplitudes, precluding a possible presence of polynomial terms. A direct consequence is that the transition form factor need not necessarily vanish at large values of the photon virtuality. Moreover, in the range of the BaBar experiment, the Terazawa-West bound is an order of magnitude above the data, thus is of formal rather than practical interest. Then we demonstrate how the experimental data may be properly explained with incomplete vector-meson dominance in a simple model with one state, as well as in more sophisticated Regge models. Generalizations of the simple Regge model along the lines of Dominguez result in a proper description of the data, where one may adjust the parameters in such a way that the Terazawa-West bound is satisfied or violated. We also impose the experimental constraint from the Z -> pi0 gamma decay. Finally, we point out that the photon momentum asymmetry parameter may noticeably influence the precision analysis.

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arXiv2010

Scalar-isoscalar states in the large-Nc Regge approach

Scalar-isoscalar states (0++) are investigated within the large-Nc Regge approach. We elaborate on the consequences of including the lightest f0(600) scalar-isoscalar state into such an analysis, where the position of f0(600) fits very well into the pattern of the radial Regge trajectory. Furthermore, we point out that the pion and nucleon spin-0 gravitational form factors, recently measured on the lattice, provide valuable information on the low-mass spectrum of the scalar-isoscalar states on the basis of the scalar-meson dominance in the spin-0 channel. Through the fits to these data we find m_sigma= 450-600 MeV. We compare the predictions of various fits and methods. An analysis of the QCD condensates in the two-point correlators provides further constraints on the parameters of the scalar-isoscalar sector. We find that a simple two-state model suggests a meson nature of f0(600), and a glueball nature of f0(980), which naturally explains the ratios of various coupling constants. Finally, we note that the fine-tuned condition of the vanishing dimension-2 condensate in the Regge approach with infinitely many scalar-isoscalar states yields a reasonable value for the mass of the lighest glueball state.

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arXiv2009

Pion wave function from lattice QCD vs. chiral quark models

We analyze the equal-time Bethe-Salpeter quark wave function of the pion obtained from a quenched lattice QCD calculation with delocalized quark interpolators. We find that the result agrees remarkably well with the predictions of the Nambu--Jona-Lasinio model in all channels. We choose the quenched lattice QCD, since it is closer to the large-Nc limit of the Nambu--Jona-Lasinio model. We also show how transversity information, relevant for the light-cone physics, can be obtained from our equal-time rest-frame lattice calculations.

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arXiv2009

Gravitational, electromagnetic, and transition form factors of the pion

Results of the Spectral Quark Model for the gravitational, electromagnetic, and transition form factors of the pion are discussed. In this model both the parton distribution amplitude and the parton distribution function are flat, in agreement with the transverse lattice calculations at low renormalization scales. The model predictions for the gravitational form factor are compared to the lattice data, with good agreement. We also find a remarkable relation between the three form factors, holding within our model, which besides reproducing the anomaly, provides a relation between radii which is reasonably well fulfilled. Comparison with the CELLO, CLEO, and BaBar data for the transition form factor is also considered.

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arXiv2009

Application of chiral quarks to high-energy processes and lattice QCD

Results of the chiral quark models for the soft matrix elements involving pions and photons, relevant for high-energy processes, are reviewed. We discuss quantities related to the generalized parton distributions of the pion: the parton distribution functions, the parton distribution amplitudes, and the generalized form factors. The model predictions are compared to the data or lattice simulations, with good agreement. The QCD evolution from the low quark model scale up to the experimental scales is a crucial ingredient of the approach.

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arXiv2009

Photon interactions and chiral dynamics

Twist-2 components of the real and virtual photon distribution amplitudes are evaluated in several chiral quark models. The results, obtained at the quark model scale, are then evolved to higher scales, probed in experiments or in lattice QCD. We also analyze the related form factors and coupling constants. Our results are a genuine dynamical prediction, following from the chiral dynamics.

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arXiv2009

From chiral quark models to high-energy processes

We show the results of low-energy chiral quark models for soft matrix elements involving pions and photons. Such soft elements, upon convolution with the hard matrix elements, are relevant in various high-energy processes. We focus on quantities related to the generalized parton distributions of the pion: the parton distribution functions, the parton distribution amplitudes, and the generalized form factors. Wherever possible, the model predictions are confronted with the data or lattice simulations, where surprisingly good agreement is achieved. The QCD evolution from the low quark model scale up to the scale of the data is crucial for this agreement.

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arXiv2009

A note on the QCD evolution of generalized form factors

Generalized form factors of hadrons are objects appearing in moments of the generalized parton distributions. Their leading-order DGLAP-ERBL QCD evolution is exceedingly simple and the solution is given in terms of matrix triangular structures of linear equations where the coefficients are the evolution ratios. We point out that this solution has a practical importance in analyses where the generalized form factors are basic objects, e.g., the lattice-gauge studies or models. It also displays general features of their evolution.

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arXiv2008

Gravitational and higher-order form factors of the pion in chiral quark models

The gravitational form factor of the pion is evaluated in two chiral quark models and confronted to the recent full-QCD lattice data. We find good agreement for the case of the Spectral Quark Model, which builds in the vector-meson dominance for the charge form factor. We derive a simple relation between the gravitational and electromagnetic form factors, holding in the considered quark models in the chiral limit. The relation implies that the gravitational mean squared radius is half the electromagnetic one. We also analyze higher-order quark generalized form factors of the pion, related to higher moments in the symmetric Bjorken X-variable of the generalized parton distribution functions, and discuss their perturbative QCD evolution, needed to relate the quark-model predictions to the lattice data. The values of the higher-order quark form factors at t=0, computed on the lattice, also agree with our quark model results within the statistical and method uncertainties.

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arXiv2008

Pion electromagnetic form factor, perturbative QCD, and large-Nc Regge models

We present a construction of the pion electromagnetic form factor where the transition from large-Nc Regge vector meson dominance models with infinitely many resonances to perturbative QCD is built in explicitly. The construction is based on an appropriate assignment of residues to the Regge poles, which fulfills the constraints of the parton-hadron duality and perturbative QCD. The model contains a slowly falling off non-perturbative contribution which dominates over the perturbative QCD radiative corrections for the experimentally accessible momenta. The leading order and next-to-leading order calculations show a converging pattern which describes the available data within uncertainties, while the onset of asymptotic QCD takes place at extremely high momenta, Q ~ 10^3-10^4 GeV. The method can be straightforwardly extended to study other form factors where the perturbative QCD result is available.

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arXiv2008

Generalized parton distributions of the pion

Generalized Parton Distributions of the pion are evaluated in chiral quark models with the help of double distributions. As a result the polynomiality conditions are automatically satisfied. In addition, positivity constraints, proper normalization and support, sum rules, and soft pion theorems are fulfilled. We obtain explicit expressions holding at the low-energy quark-model scale, which exhibit no factorization in the t-dependence. The crucial QCD evolution of the quark-model distributions is carried out up to experimental or lattice scales. The obtained results for the Parton Distribution Function and the Parton Distribution Amplitude describe the available experimental and lattice data, confirming that the quark-model scale is low, around 320 MeV.

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arXiv2008

Generalized parton distributions of the pion in chiral quark models and their QCD evolution

We evaluate Generalized Parton Distributions of the pion in two chiral quark models: the Spectral Quark Model and the Nambu-Jona-Lasinio model with a Pauli-Villars regularization. We proceed by the evaluation of double distributions through the use of a manifestly covariant calculation based on the alpha representation of propagators. As a result polynomiality is incorporated automatically and calculations become simple. In addition, positivity and normalization constraints, sum rules and soft pion theorems are fulfilled. We obtain explicit formulas, holding at the low-energy quark-model scale. The expressions exhibit no factorization in the t-dependence. The QCD evolution of those parton distributions is carried out to experimentally or lattice accessible scales. We argue for the need of evolution by comparing the Parton Distribution Function and the Parton Distribution Amplitude of the pion to the available experimental and lattice data, and confirm that the quark-model scale is low, about 320 MeV.

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