Search

We present a comprehensive analysis of the SU(3) octet and decuplet baryon masses and $\sigma$-terms using high-precision lattice QCD data and chiral SU(3) effective theory with finite range regularization. The effects of various systematic uncertainties, including from the scale setting of the lattice data and the regularization prescriptions, are quantified. We find the pion-nucleon and strange nucleon $\sigma$-terms to be $\sigma_{\pi N} = 44(3)(3)$ MeV and $\sigma_{N s} = 50(6)(1)$ MeV, respectively. The results provide constraints on the energy-momentum tensor mass decompositions of the SU(3) octet and decuplet baryons, where we find the trace anomaly and quark/gluon energies decrease for strange baryons due to their larger strange $\sigma$-terms., Comment: 12 pages, 6 figures

The issue of resulting in the same physical observables with different current components, in particular from the minus current, has been challenging in the light-front quark model (LFQM) even for the computation of the two-point functions such as meson decay constants. At the level of one-body current matrix element computation, we show the uniqueness of pseudoscalar and vector meson decay constants using all available components including the minus component of the current in the LFQM consistent with the Bakamjian-Thomas construction. Regardless of the current components, the polarization vectors, and the reference frames, the meson decay constants are uniquely determined in the non-interacting constituent quark and antiquark basis while the interactions of the constituents are added to the meson mass operator in the LFQM.

Light-front time-ordered amplitudes are investigated in the virtual scalar meson production process in (1+1) dimensions using the scalar field model extended from the conventional Wick-Cutkosky model. There is only one Compton form factor (CFF) in the (1+1)-dimensional computation of the virtual meson production process, and we compute both the real and imaginary parts of the CFF for the entire kinematic regions of Q2>0 and t<0. We then analyze the contribution of each and every light-front time-ordered amplitude to the CFF as a function of Q2 and t. In particular, we discuss the significance of the “cat’s ears” contributions for gauge invariance and the validity of the “handbag dominance” in the formulation of the generalized parton distribution (GPD) function used typically in the analysis of deeply virtual meson production processes. We explicitly derive the GPD from the “handbag” light-front time-ordered amplitudes in the −t/Q2≪1 limit and verify that the integrations of the GPD over the light-front longitudinal momentum fraction for the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi and Efremov-Radyushkin-Brodsky-Lepage regions correspond to the valence and nonvalence contributions of the electromagnetic form factor that we have recently reported [Phys. Rev. D 103, 076002 (2021)]. We also discuss the correspondence of the GPD to the parton distribution function for the analysis of the deep inelastic lepton-hadron scattering process and the utility of the new light-front longitudinal spatial variable z˜.

The helicity-dependent strange quark distribution in the proton, $\Delta s$, is calculated in a nonlocal chiral SU(3) effective field theory. The hadronic proton to meson plus octet or decuplet baryon splitting functions are derived at the one-loop level, with loop integrals rendered finite by correlation functions introduced in the nonlocal Lagrangian. Within the convolution framework, the proton strange helicity distribution is obtained using spin-flavor symmetry to constrain the input valence quark distributions in the hadronic intermediate states. The polarized strange quark distribution is found to be quite small, with the lowest moment of $\Delta s$ negative, but consistent with recent global QCD analyses., Comment: 23 pages, 4 figures

We calculate the spin-averaged generalized parton distributions (GPDs) of sea quarks in the proton at zero skewness from nonlocal covariant chiral effective theory, including one-loop contributions from intermediate states with pseudoscalar mesons and octet and decuplet baryons. A relativistic regulator is generated from the nonlocal Lagrangian where a gauge link is introduced to guarantee local gauge invariance, with additional diagrams from the expansion of the gauge link ensuring conservation of electric charge and strangeness. Flavor asymmetries for sea quarks at zero and finite momentum transfer, as well as strange form factors, are obtained from the calculated GPDs, and results compared with phenomenological extractions and lattice QCD., 71 pages, 10 figures

We present a review of recent applications of nonlocal chiral effective theory to hadron structure studies. Starting from a nonlocal meson--baryon effective chiral Lagrangian, we show how the introduction of a correlation function representing the finite extent of hadrons regularizes the meson loop integrals and introduces momentum dependence in vertex form factors in a gauge invariant manner. We apply the framework to the calculation of nucleon electromagnetic form factors, unpolarized and polarized parton distributions, as well as transverse momentum dependent distributions and generalized parton distributions. Assuming that the nonlocal behavior is a general property of all interactions, we also discuss the application to the lepton anomalous magnetic moment in nonlocal QED., Comment: 97 pages, 32 figures

We discuss the electroproduction of a pseudoscalar (0-+) meson or a scalar (0++) meson off the scalar target. The most general formulation of the differential cross section for the 0-+ or 0++ meson process involves only one or two hadronic form factors, respectively, on a scalar target. The Rosenbluth-type separation of the differential cross section provides the explicit relation between the hadronic form factors and the different parts of the differential cross section in a completely model-independent manner. The absence of the beam spin asymmetry for the pseudoscalar meson production provides a benchmark for the experimental data analysis. The measurement of the beam spin asymmetry for the scalar meson production may also provide a unique opportunity not only to explore the imaginary part of the hadronic amplitude in the general formulation but also to examine the significance of the chiral-odd generalized parton distribution (GPD) contribution in the leading-twist GPD formulation.

We perform the first global QCD analysis of pion valence, sea quark, and gluon distributions within a Bayesian Monte Carlo framework with threshold resummation on Drell-Yan cross sections at next-to-leading log accuracy. Exploring various treatments of resummation, we find that the large-$x$ asymptotics of the valence quark distribution $\sim (1-x)^{\beta_v}$ can differ significantly, with $\beta_v$ ranging from $\approx 1$ to $> 2.5$ at the input scale. Regardless of the specific implementation, however, the resummation induced redistribution of the momentum between valence quarks and gluons boosts the total momentum carried by gluons to $\approx 40\%$, increasing the gluon contribution to the pion mass to $\approx 40$ MeV., Comment: 6 pages, 3 figures

The self-energies of the full set of flavor SU(3) octet and decuplet baryons are computed within a relativistic chiral effective theory framework. The leading nonanalytic chiral behavior is derived for the octet and decuplet masses, and a finite-range regularization consistent with Lorentz and gauge invariance is applied to account for the finite size of the baryons. Using a four-dimensional dipole form factor, the relative importance of various meson-baryon loop contributions to the self-energies is studied numerically as a function of the dipole range parameter and meson mass, and comparison is made between the relativistic results and earlier approximations within the heavy baryon limit., 42 pages, 7 figures

We investigate the electromagnetic form factor $F(q^2)$ of the meson by using the solvable $��^{3}$ scalar field model in $(1+1)$ dimensions. As the transverse rotations are absent in $(1+1)$ dimensions, the advantage of the light-front dynamics (LFD) with the light-front time $x^+ = x^0 + x^3$ as the evolution parameter is maximized in contrast to the usual instant form dynamics (IFD) with the ordinary time $x^0$ as the evolution parameter. In LFD, the individual $x^+$-ordered amplitudes contributing to $F(q^2)$ are invariant under the boost, i.e., frame-independent, while the individual $x^0$-ordered amplitudes in IFD are not invariant under the boost but dependent on the reference frame. The LFD allows to get the analytic result for the one-loop triangle diagram which covers not only the spacelike ($q^{2}0$). Using the analytic results, we verify that the real and imaginary parts of the form factor satisfy the dispersion relations in the entire $q^{2}$ space. Comparing with the results in $(3+1)$ dimensions, we discuss the transverse momentum effects on $F(q^2)$ . We also discuss the longitudinal charge density in terms of the boost invariant variable $\tilde z = p^+ x^-$ in LFD., 15 pages, 12 figures; Slight changes have been made in the title and abstract. Version to appear in Phys. Rev. D

The ’t Hooft model, i.e., the two-dimensional quantum chromodynamics in the limit of infinite number of colors, is interpolated by an angle parameter δ between δ=0 for the instant form dynamics (IFD) and δ=π/4 for the light-front dynamics (LFD). With this parameter δ, we formulate the interpolating mass gap equation which takes into account the nontrivial vacuum effect on the bare fermion mass to find the dressed fermion mass. Our interpolating mass gap solutions not only reproduce the previous IFD result at δ=0 as well as the previous LFD result at δ=π/4 but also link them together between the IFD and LFD results with the δ parameter. We find the interpolation angle independent characteristic energy function which satisfies the energy-momentum dispersion relation of the dressed fermion, identifying the renormalized fermion mass function and the wave function renormalization factor. The renormalized fermion condensate is also found independent of δ, indicating the persistence of the nontrivial vacuum structure even in the LFD. Using the dressed fermion propagator interpolating between IFD and LFD, we derive the corresponding quark-antiquark bound-state equation in the interpolating formulation verifying its agreement with the previous bound-state equations in the IFD and LFD at δ=0 and δ=π/4, respectively. The mass spectra of mesons bearing the feature of the Regge trajectories are found independent of the δ-parameter reproducing the previous results in LFD and IFD for the equal mass quark and antiquark bound states. The Gell-Mann-Oakes-Renner relation for the pionic ground-state in the zero fermion mass limit is confirmed indicating that the spontaneous breaking of the chiral symmetry occurs in the ’t Hooft model regardless of the quantization for 0≤δ≤π/4. We obtain the corresponding bound-state wave functions and discuss their reference frame dependence with respect to the frame independent LFD result. Applying them for the computation of the so-called quasi-parton distribution functions now in the interpolating formulation between IFD and LFD, we note a possibility of utilizing not only the reference frame dependence but also the interpolation angle dependence to get an alternative effective approach to the LFD-like results.

We discuss the electroproduction of a spinless meson, i.e. pseudoscalar (0−+) or scalar (0++) meson, off the scalar target. The most general formulation of the differential cross section for the 0−+ or 0++ meson process involves only one or two hadronic form factors, respectively, on a scalar target. The Rosenbluth-type separation of the differential cross section provides the explicit relation between the hadronic form factors and the different parts of the differential cross section in a completely model-independent manner. The absence of the beam spin asymmetry for the pseudoscalar meson production provides a benchmark for the experimental data analysis. The measurement of the beam spin asymmetry for the scalar meson production may also provide a unique opportunity not only to explore the imaginary part of the hadronic amplitude in the general formulation but also to examine the significance of the chiral-odd generalized parton distribution (GPD) contribution in the leading-twist GPD formulation.

The Ward-Takahashi identity in quantum electrodynamics ($QED_4$), first considered by J. C. Ward and Y. Takahashi, correlates the wave function renormalization for the electron to its vertex renormalization function. It guarantees the cancellation of ultraviolet (UV) divergences to all orders of perturbation theory. Since the QED in the light-front gauge is a constrained theory that brings a more demanding UV renormalization program due to the inevitable non-local terms, we check the Ward-Takahashi identity to the one-loop level, using the Mandelstam-Leibbrandt prescription to handle the characteristic light-front poles that appear in the Feynman integrals. Our calculations for the vertex correction and inverse electron propagators show that the strict light-front part contributions do indeed satisfy the Ward-Takahashi identity to one-loop order.

We study the pion electromagnetic half-off-shell form factors $F_1$ and $F_2$ using an exactly solvable manifestly covariant model of a $(3+1)$ dimensional fermion field theory. The model provides a three-dimensional imaging of $F_1$ and $F_2$ as a function of $(Q^2,t)$, which are constrained by the Ward-Takahashi identity. The normalization of the charge form factor $F_1$ is fixed by $F_1(Q^2=0, t=m^2_\pi)=1$ while the other form factor $F_2$ vanishes, i.e. $F_2(Q^2, t=m^2_\pi)=0$ for any value of $Q^2$ due to the time-reversal invariance of the strong interaction. The new form factor defined by $g(Q^2,t)=F_2(Q^2,t)/(t- m^2_\pi)$ is however measurable in the on-mass-shell limit. We note that $g(Q^2=0, t=m^2_\pi)$ is related with the pion charge radius.

We study the suppression of non-planar diagrams in a scalar QCD model of a meson system in $3+1$ space-time dimensions due to the inclusion of the color degrees of freedom. As a prototype of the color-singlet meson, we consider a flavor-nonsinglet system consisting of a scalar-quark and a scalar-antiquark with equal masses exchanging a scalar-gluon of a different mass, which is investigated within the framework of the homogeneous Bethe-Salpeter equation. The equation is solved by using the Nakanishi representation for the manifestly covariant bound-state amplitude and its light-front projection. The resulting non-singular integral equation is solved numerically. The damping of the impact of the cross-ladder kernel on the binding energies are studied in detail. The color-suppression of the cross-ladder effects on the light-front wave function and the elastic electromagnetic form factor are also discussed. As our results show, the suppression appears significantly large for $N_c=3$, which supports the use of rainbow-ladder truncations in practical nonperturbative calculations within QCD., 12 pages, 7 figures. To appear in Physics Letters B

We propose a medium-modified holographic-hadron dynamics suitable for the study of symmetric nuclear matter, with a key property of a simple law for the evolution of the five dimensional mass with the scalar background field. We show that the model satisfies symmetric nuclear matter constraints, namely, incompressibility and density dependence of the pressure, with only three free adjustable parameters fitted to the free nucleon mass and the nuclear matter saturation properties. We found that the holographic nucleon swells and the UV behavior of the associated string amplitude is damped, with the scaling property at short distances softened. Both effects can also generate observable consequences reflecting an average leakage of partons to the nuclear medium when density is increased, in the route towards the deconfinement of the internal nucleon degrees of freedom. Keywords: AdS/QCD models, Nuclear matter, Equations of state

We compute the helicity-dependent strange quark distribution in the proton in the framework of chiral effective theory. Starting from the most general chiral SU(3) Lagrangian that respects Lorentz and gauge invariance, we derive the complete set of hadronic splitting functions at the one meson loop level, including the octet and decuplet rainbow, tadpole, Kroll-Ruderman and octet-decuplet transition configurations. By matching hadronic and quark level operators, we obtain generalized convolution formulas for the quark distributions in the proton in terms of hadronic splitting functions and quark distributions in the hadronic configurations, and from these derive model-independent relations for the leading nonanalytic behavior of their moments. Within the limits of parameters of the Pauli-Villars regulators derived from inclusive hyperon production, we find that the polarized strange quark distribution is rather small and mostly negative., Comment: 43 pages, 4 figures, 1 table

We explore the link between the chiral symmetry of QCD and the numerical results of the light-front quark model, analyzing both the two-point and three-point functions of the pion. Including the axial-vector coupling as well as the pseudoscalar coupling in the light-front quark model, we discuss the implication of the chiral anomaly in describing the pion decay constant, the pion-photon transition form factor and the electromagnetic form factor of the pion. In constraining the model parameters, we find that the chiral anomaly plays a critical role and the analysis of $F_{\pi\gamma}(Q^2)$ in timelike region is important. Our results indicate that the constituent quark picture is effective for the low and high $Q^2$ ranges implementing the quark mass evolution effect as $Q^2$ grows., Comment: 13 pages, 7 figures, update abstract, typo corrected, version to appear in Physical Review D

The two-dimensional quantum chromodynamics (QCD2) in the limit of infinite number of colors, known as ‘t Hooft model, was originally formulated in the Light Front Dynamics (LFD). The theory is exactly solvable, while still bearing some resemblance to the four-dimensional real world QCD in aspects such as confinement and mass g ap, as well as the spontaneous breaking of chiral symmetry. The work in the Instant Form Dynamics (IFD) was done in 1978 by Bars and Green. The quark- antiquark bound state equation was derived and solved in each of the two forms, i.e., ‘t Hooft equation and Bars-Green equations, respectively, and they give the same discrete meson mass spectrum independent of the quantization form as expected. Introducing an interpolation angle parameter δ, in this work, we link the two distinct forms of dynamics, IFD and LFD, by letting the space-time axes rotate from the ordinary equal-time form {t, x} to the light front{x+,x−}, as δ varies from 0 to π/4. We unify the ‘t Hooft and Bars-Green equations into one formula, and by numerically solving it we confirm the independence of the meson mass spectra on the interpolation angle δ. We note that the quark condensate is quantization angle independent. This indicates a non-trivial vacuum structure even in the light-front form.

Talk from the Strong QCD from Hadron Structure Experiments Workshop 2019

We investigate the pion electromagnetic half off-shell form factors, which parametrize the matrix element of the charged pion electromagnetic current with one leg off-mass-shell and the other leg on-mass-shell, using an exactly solvable manifestly covariant model of a $(3+1)$ dimensional fermion field theory. The model provides a 3D imaging of the two off-shell pion form factors $F_1$ and $F_2$ as a function of $(Q^2,t)$, which are related to each other satisfying the Ward-Takahashi identity. The normalization of the renormalized charge form factor $F_1$ is fixed by $F_1(Q^2=0, t=m^2_\pi)=1$ while the other form factor $F_2$ vanishes, i.e. $F_2(Q^2, t=m^2_\pi)=0$ for any value of $Q^2$ due to the time-reversal invariance of the strong interaction. We define the new form factor $g(Q^2,t)=F_2(Q^2,t)/(t-m^2_\pi)$ and find that $g(Q^2,t)$ can be measurable in the on-mass-shell limit. In particular, $g(Q^2=0, t=m^2_\pi)$ is related with the pion charge radius. We also compare our form factors with the data extracted from the pion electroproduction reaction for both the off-shell region ($t, Comment: typo corrected; revision for the discussion in Sec. III.; 11pages, 10 figures; version to appear in Physical Review D

We study the twist-2 distribution amplitudes (DAs) and the decay constants of pseudoscalar light ($\pi$, $K$) and heavy ($D$, $D_s$, $B$, $B_s$) mesons as well as the longitudinally and transversely polarized vector light ($\rho$, $K^*$) and heavy ($D^*$, $D_s^*$, $B^*$, $B_s^*$) mesons in the light-front quark model with the Coulomb plus exponential-type confining potential $V_{\rm {exp}} = a + b e^{\alpha r}$ in addition to the hyperfine interaction. We first compute the mass spectra of ground state pseudoscalar and vector light and heavy mesons and fix the model parameters necessary for the analysis, applying the variational principle with the trial wave function up to the first three lowest order harmonic oscillator (HO) wave functions $\Phi(x, \textbf{k}_\bot) = \sum_{n=1}^{3} c_n \phi_{nS}$. We then obtain the numerical results for the corresponding decay constants of light and heavy mesons. We estimate the DAs, analyze their variation as a function of momentum fraction and compute the first six $\xi$-moments of the $B$ and $D$ mesons as well. We compare our results with the available experimental data as well as with the other theoretical model predictions., Comment: 32 pages, 9 figures

Using recently derived results for one-loop hadronic splitting functions from a nonlocal implementation of chiral effective theory, we study the contributions from pseudoscalar meson loops to flavor asymmetries in the proton. Constraining the parameters of the regulating functions by inclusive production of $n$, $\Delta^{++}$, $\Lambda$ and $\Sigma^{*+}$ baryons in $pp$ collisions, we compute the shape of the light antiquark asymmetry $\bar{d}-\bar{u}$ in the proton and the strange asymmetry $s-\bar{s}$ in the nucleon sea. With these constraints, the magnitude of the $\bar{d}-\bar{u}$ asymmetry is found to be compatible with that extracted from the Fermilab E866 Drell-Yan measurement, with no indication of a sign change at large values of $x$, and an integrated value in the range $\langle \bar d-\bar u \rangle \approx 0.09-0.17$. The $s-\bar s$ asymmetry is predicted to be positive at $x > 0$, with compensating negative contributions at $x=0$, and an integrated $x$-weighted moment in the range $\langle x (s-\bar s) \rangle \approx (0.9-2.5) \times 10^{-3}$., Comment: 43 pages, 8 figures

The number of Compton form factors of a scalar hadron is known to be three. It may be expected that depending on the structure of that hadron, it may occur that in some kinematical regimes the observables are only sensitive to one dominant form factor. Here we show in a particular kinematic situation that one may perform an experiment that unequivocally answers the question whether other form factors besides the anticipated dominant one can be neglected or not.

We report our investigation on the doubly virtual transition form factors (TFFs) ${F}_{\mathrm{P}{\ensuremath{\gamma}}^{*}}({Q}_{1}^{2},{Q}_{2}^{2})$ for the $\mathrm{P}\ensuremath{\rightarrow}{\ensuremath{\gamma}}^{*}({q}_{1}){\ensuremath{\gamma}}^{*}({q}_{2})(\mathrm{P}={\ensuremath{\pi}}^{0},\ensuremath{\eta},{\ensuremath{\eta}}^{\ensuremath{'}})$ transitions using the light-front quark model (LFQM). Performing a LF calculation in the exactly solvable manifestly covariant Bethe-Salpeter (BS) model as the first illustration, we use the ${q}_{1}^{+}=0$ frame and find that both LF and manifestly covariant calculations produce exactly the same results for ${F}_{\mathrm{P}{\ensuremath{\gamma}}^{*}}({Q}_{1}^{2},{Q}_{2}^{2})$. This confirms the absence of the LF zero mode in the doubly virtual TFFs. We then map this covariant BS model to the standard LFQM using the more phenomenologically accessible Gaussian wave function provided by the LFQM analysis of meson mass spectra. For the numerical analyses of ${F}_{\mathrm{P}{\ensuremath{\gamma}}^{*}}({Q}_{1}^{2},{Q}_{2}^{2})$, we compare our LFQM results with the available experimental data and the perturbative QCD (pQCD) and vector meson dominance (VMD) model predictions. As $({Q}_{1}^{2},{Q}_{2}^{2})\ensuremath{\rightarrow}\ensuremath{\infty}$, our LFQM result for doubly virtual TFF is consistent with the pQCD prediction, i.e., ${F}_{\mathrm{P}{\ensuremath{\gamma}}^{*}}({Q}_{1}^{2},{Q}_{2}^{2})\ensuremath{\sim}1/({Q}_{1}^{2}+{Q}_{2}^{2})$, while it differs greatly from the result of the VMD model, which behaves as ${F}_{\mathrm{P}{\ensuremath{\gamma}}^{*}}^{\mathrm{VMD}}({Q}_{1}^{2},{Q}_{2}^{2})\ensuremath{\sim}1/({Q}_{1}^{2}{Q}_{2}^{2})$. Our LFQM prediction for ${F}_{{\ensuremath{\eta}}^{\ensuremath{'}}{\ensuremath{\gamma}}^{*}}({Q}_{1}^{2},{Q}_{2}^{2})$ shows an agreement with the very recent experimental data obtained from the BABAR Collaboration for the ranges of $2l({Q}_{1}^{2},{Q}_{2}^{2})l60\text{ }\text{ }{\mathrm{GeV}}^{2}$.

We perform the first global QCD analysis of parton distribution functions (PDFs) in the pion, combining $\pi A$ Drell-Yan data with leading neutron electroproduction from HERA within a Monte Carlo approach based on nested sampling. Inclusion of the HERA data allows the pion PDFs to be determined down to much lower values of $x$, with relatively weak model dependence from uncertainties in the chiral splitting function. The combined analysis reveals that gluons carry a significantly higher pion momentum fraction, $\sim 30\%$, than that inferred from Drell-Yan data alone, with sea quarks carrying a somewhat smaller fraction, $\sim 15\%$, at the input scale. Within the same effective theory framework, the chiral splitting function and pion PDFs can be used to describe the $\bar d-\bar u$ asymmetry in the proton., Comment: This article will appear in Physical Review Letters; 4 figures

The light-front quark model analysis of the meson-photon transition form factor $F_{P\gamma} (Q^2)$ amenable both for the spacelike region ($Q^2 >0$) and the timelike region ($Q^2

Made available in DSpace on 2018-12-11T17:20:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-09-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) U.S. Department of Energy We discuss the interpolation between the instant form dynamics (IFD) and the light-front dynamics (LFD) proposed by Dirac in 1949 and present its application to quantum electrodynamics (QED). Our analysis clarifies any conceivable confusion in the prevailing notion of the equivalence between the IFD at infinite momentum frame and the LFD. Entwining the fermion propagator interpolation with our previous works of the interpolating helicity spinors and the electromagnetic gauge field interpolation, we fasten the bolts and nuts necessary to launch the interpolating QED at least in the tree level. Department of Physics North Carolina State University, Box 8202 First Leads Inc. Instituto de Física Teórica-UNESP Universidade Estadual Paulista, Rua Doutor Bento Teobaldo Ferraz, 271 - Bloco II, Várzea da Barra Funda Department of Physics La Sierra University, 4500 Riverwalk Pkwy Instituto de Física Teórica-UNESP Universidade Estadual Paulista, Rua Doutor Bento Teobaldo Ferraz, 271 - Bloco II, Várzea da Barra Funda FAPESP: 2014/20892-2 U.S. Department of Energy: DE-FG02-03ER41260

Using deeply virtual Compton scattering as a tool to study the structure of hadrons in an exclusive process, one expresses the amplitudes in terms of invariant quantities: the Compton form factors. In this paper the sensitivity of the hadronic part of the cross section to the Compton form factors is determined.

We investigate the $(\pi^0,\eta, \eta')\to \gamma^*\gamma$ transitions both for the spacelike region and the timelike region using the light-front quark model (LFQM). In particular, we present the new direct method to explore the timelike region without resorting to mere analytic continuation from the spacelike region to the timelike region. Our direct calculation in timelike region shows the complete agreement not only with the analytic continuation result from the spacelike region but also with the result from the dispersion relation between the real and imaginary parts of the form factor.

Due to the angular condition in the light-front dynamics (LFD), the extraction of the electromagnetic form factors for spin-1 particles can be uniquely determined taking into account implicitly non-valence and/or the zero-mode contributions to the matrix elements of the electromagnetic current. No matter which matrix elements of the electromagnetic current is used to extract the electromagnetic form factors, the same unique result is obtained. As physical observables, the electromagnetic form factors obtained from matrix elements of the current in LFD must be equal to those obtained in the instant form calculations. Recently, the Babar collaboration \cite{Aubert2008} has analyzed the reaction $e^+ e^-\rightarrow \rho^+ + \rho^-$ at $\sqrt{s}=10.58 GeV$ to measure the cross section as well as the ratios of the helicity amplitudes $F_{\lambda'\lambda}$. We present our recent analysis of the Babar data for the rho meson considering the angular condition in LFD to put a stringent test on the onset of asymptotic perturbative QCD and predict the energy regime where the subleading contributions are still considerable., Comment: 7 pages, 4 figures, Few-Body latex style. Contribuition to the Light-Cone 2017, 18-22 September, 2017, Mumbai, India. Submitted to Few-Body Systems

We present a new formulation of pseudoscalar meson loop corrections to nucleon parton distributions within a nonlocal covariant chiral effective field theory, including contributions from SU(3) octet and decuplet baryons. The nonlocal Lagrangian, constrained by requirements of local gauge invariance and Lorentz-invariant ultraviolet regularization, generates additional interactions associated with gauge links. We use these to compute the full set of proton $\to$ meson + baryon splitting functions, which in general contain on-shell and off-shell contributions, in addition to $\delta$-function terms at zero momentum, along with nonlocal contributions associated with the finite size of the proton. We illustrate the shapes of the various local and nonlocal functions numerically using a simple example of a dipole regulator., Comment: 43 pages, 6 figures, version to appear in Phys. Rev. D

When deeply virtual Compton scattering is used as a tool to study the structure of hadrons in an exclusive process, one way to analyze this process is to express the amplitudes in terms of generalized parton distributions (GPDs). The definition of the latter quantities requires a special kinematics, that cannot always be realized in experiments. Therefore, one may use the expression of the scattering amplitudes in terms of the invariant Compton form factors (CFFs) as a stepping stone to finding the GPDs. In a simple case we illustrate the influences of making approximations in the extraction of CFFs on the values obtained.