The axial-vector form factor of the nucleons is studied at a finite temperature using the holographic soft-wall model with the thermal dilaton field. We use the bulk interaction action known from the zero temperature case and apply the profile functions of fields thermalized by the interaction with the thermal dilaton field. The dependence of the axial form factor on the square of the transferred momentum and the temperature is plotted for the ground and excited states of the nucleons.
The axial-vector form factor of the nucleons is considered in the framework of hard-wall model of holographic QCD. A new interaction term between the bulk gauge and matter fields was included into the interaction Lagrangian. We obtain the axial-vector form factor of nucleons in the boundary QCD from the bulk action using AdS/CFT correspondence. The momentum square dependence of the axial-vector form factor is analysed numerically.
We study the helicity-independent generalized parton distributions of nucleons in the zero skewness case, based on a particular light-front quark model derived in a soft-wall AdS/QCD approach.
We calculate the hypercharge and flavor singlet axial couplings related to the spin of the nucleon in a constituent quark model. In addition to the standard one-body axial currents, the model includes two-body axial exchange currents. The latter are necessary to satisfy the Partial Conservation of Axial Current (PCAC) condition. For both axial couplings we find significant corrections to the standard quark model prediction. Exchange currents reduce the valence quark contribution to the nucleon spin and afford an interpretation of the missing nucleon spin as orbital angular momentum carried by …
The axial strange form factor $F^s_A$ of the nucleon is assumed to be dominated at low momentum transfer by the isoscalar axial vector mesons $f_1(1285)$ and $f_1(1420)$. The importance of the $a_0πN$-triangular vertex correction is demonstrated.
It is shown that the specific space distribution of the nucleon axial charge may lead to the significant reduction of the cross section of the reaction $p+p\to D+e^++ν$ and may provide the mechanism to explain observed deficit of solar neutrinos.
In the framework of the soft-wall model of AdS/QCD we calculated the $ρ$ meson nucleon coupling constant. Bulk-to boundary propagators for the free vector and spinor fields are presented, whose boundary values correspond to $ρ$ meson and to the nucleon respectively. The interaction Lagrangian between these fields is written in the bulk of AdS space and includes magnetic type interactions as well. Using the AdS/CFT correspondence from the bulk interaction action we derived the $g_{ρNN}$ coupling constant in the boundary QCD. We found that the soft-wall model result for the $g_{ρNN}$ constant is…
We have analyzed axial-vector current-current correlation functions between one-nucleon states to calculate the singlet axial-vector coupling constant of the nucleon. The octet-octet and the octet-singlet current correlators, investigated in this work, do not require any use of instanton effects. The QCD and hadronic parameters used for the evaluation of correlators have been varied by (10 - 20)%. The value of the singlet axial-vector coupling constant of the nucleon obtained from this analysis is consistent with its current determination from experiments and QCD theory.
Measurements of the polarization of the final proton in elastic e-p scattering drastically changed our knowledge about the electromagnetic form factors of the proton. Here we present our results of the calculation of the polarization of the final nucleon in charged current quasi-elastic neutrino nucleon scattering. Relations which connect the axial form factor with the polarization, the cross section and the electromagnetic form factors of the nucleon are derived. Measurements of the polarization of the nucleon in the high-statistics short baseline neutrino experiments (or in near detectors of…
We study the temperature dependence of the $a_1$ meson-nucleon coupling constant in the framework of the soft-wall AdS/QCD model with thermal dilaton field. Profile functions for the axial-vector and fermion fields in the AdS-Schwarzschild metric are presented. It is constructed an interaction Lagrangian for the fermion-axial-vector-thermal dilaton fields system in the bulk of space-time. From this Lagrangian integral representation for the $g_{a_1NN}$ coupling constant is derived. The temperature dependence of this coupling constant is numerically analyzed.
The axial charges of the nucleon and the well-established N* resonances are studied within a consistent framework. For the first time the axial charges of the N* resonances are produced for the relativistic constituent quark model. The axial charge of the nucleon is predicted close to experiment, and the ones of N*(1535) and N*(1650), the only cases where such a comparison is possible, agree well with results from quantum chromodynamics on the lattice that have recently become available. The relevance of the magnitudes of the N* axial charges for the low-energy behavior of quantum chromodynami…
It is shown that the QCD anomaly may lead to an abnormal mixing behavior of the axial vector mesons similar to the pseudoscalar mesons. These mixing effects, involving a gluonic axial vector state, generate a non-vanishing strange quark component in the nucleon. They reduce the matrix element of the singlet axial vector in comparison to the value obtained in a naive quark model. The results are in agreement with the data obtained in the polarized lepton-nucleon scattering experiments.
Using the most general form of the baryon current, nucleon form factors, induced by isovector and isoscalar axial-vector currents, are studied in the framework of light cone QCD sum rule approach. Comparison of our results on form factors with the existing results and lattice calculations are presented.
We have calculated the polarization of the final nucleon in charged current quasi-elastic ν-N scattering. We show that the longitudinal and transverse polarizations, as well as their ratio exhibit simple dependence on the axial form factor and their sensitivity to the axial mass is much stronger than that of the cross section. This suggests that measurements of the polarization of the nucleon in the high-statistics neutrino experiments could provide important information on the axial form factor.
We apply the perturbative chiral quark model (PCQM) at one loop to analyze the axial form factor of the nucleon. This chiral quark model is based on an effective Lagrangian, where baryons are described by relativistic valence quarks and a perturbative cloud of Goldstone bosons as dictated by chiral symmetry. We apply the formalism to obtain analytical expressions for the axial form factor of the nucleon, which is given in terms of fundamental parameters of low-energy pion-nucleon physics (weak pion decay constant, strong pion-nucleon form factor) and of only one model parameter (radius of the …
We study the axial-vector form factor of the nucleons at constant and homogenous isospin chemical potential using holographic QCD. Nucleon mass splitting in such isospin medium is taken into account. According to AdS/CFT correspondence, the critical value of the isospin chemical potential μ_I equals to UV- boundary value of the time component of the bulk gauge field. We calculate the axial-vector form factor of the proton and neutron in such background in the framework of the hard-wall model and plot the form factors for the isospin chemical potential critical value μ_I=m_π.
Renormalization of the axial vector currents due to Goldstone loops is studied in a simple extension of Manohar - Georgi chiral quark model which incorporates $U(1)_A$ anomaly effects. The polarized strage quark sea in the polarized nucleon results from different renormalization of the flavor singlet and octet currents and is in reasonable agreement with the experiment.
The theoretical and experimental status of the isovector axial-vector current form factors G_A(q^2) and G_P(q^2) of the nucleon is reviewed. We also describe a new calculation of these form factors in manifestly Lorentz-invariant chiral perturbation theory (ChPT) with the inclusion of axial-vector mesons as explicit degrees of freedom.
With twisted boundary conditions on the quark fields, we study nucleon matrix elements of the axial current utilizing twisted heavy baryon chiral perturbation theory. One can explore the momentum transfer dependence of the axial form factors more easily than by using ordinary lattice quantized momenta alone. As examples, we derive expressions for the nucleon axial radius and pseudoscalar form factor.
We analize the influence of nuclear effects on the determination of the nucleon axial mass from nuclear cross sections. Our work is based on a formalism widely applied to describe electron-nucleus scattering data in the impulse approximation regime. The results of numerical calculations show that correlation effects, not taken into account by the relativistic Fermi gas model, sizably affect the $Q^2$-dependence of the cross section. However, their inclusion does not appear to explain the large values of the axial mass recently reported by the K2K and MiniBooNE collaborations.
We investigate three different axial-vector form factors of the nucleon, $G_A^{0}$, $G_A^3$, $G_A^8$, within the framework of the SU(3) chiral quark-soliton model, emphasizing their strangeness content. We take into account the rotational $1/N_c$ and linear strange quark ($m_s$) contributions using the symmetry-conserving SU(3) quantization and assuming isospin symmetry. The strange axial-vector form factor is also obtained and they all are discussed in the context of the parity-violating scattering of polarized electrons off the nucleon and its relevance to the strange vector form factors.
We analyze the nucleon axial-vector coupling to two loops in chiral perturbation theory. We show that chiral extrapolations based on this representation require lattice data with pion masses below 300 MeV.
The nucleon axial vector form factor is investigated in a light-cone quark spectator diquark model, in which Melosh rotations are applied to both the quark and vector diquark. It is found that this model gives a very good description of available experimental data and the results have very little dependence on the parameters of the model. The relation between the nucleon axial constant and the anomalous magnetic moment of nucleons is also discussed.
Using the expansion of the baryon wave function in a series of products of single quark bispinors (Dirac orbitals), the nonsinglet axial and tensor charge of the nucleon are calculated. The leading term yields ${G_A}/{G_V} = 1.27$ and in good agreement with experiment. Calculation is essentially parameter-free and depends on the string tension $σ$ and $α_s$, fixed at standard values. The importance of lower Dirac bispinor component, yielding 18% to the wave function normalization is stressed.
The value of the nucleon's flavour-singlet axial-charge extracted from polarised deep inelastic scattering is sensitive to the value of the octet axial-charge g_A^8 which is usually taken from an analysis of hyperon beta-decays within the framework of SU(3) symmetry, namely 0.58 \pm 0.03. Using the Cloudy Bag model we find that the value of g_A^8 is reduced by as much as 20% below the usual phenomenological value. This increases the value of the flavour singlet axial charge (g_A^0|_inv) derived from deep inelastic data and significantly reduces the difference between it and g_A^8.
It is well established that the nucleon form factors can be related to Generalized Parton Distributions (GPDs) through sum-rules. On the other hand, GPDs can be expressed in terms of Parton Distribution Functions (PDFs) according to Diehl's model. In this work, we use this model to calculate polarized GPDs for quarks ($\widetilde{H}_q$) using the available polarized PDFs obtained from the experimental data, and then study the axial form factor of nucleon. We determine parameters of the model using standard $χ^2$ analysis of experimental data. It is shown that some parameters should be readjust…
We compute finite-volume corrections to nucleon matrix elements of the axial-vector current. We show that knowledge of this finite-volume dependence --as well as that of the nucleon mass-- obtained using lattice QCD will allow a clean determination of the chiral-limit values of the nucleon and Delta-resonance axial-vector couplings.
We study the momentum and the quark mass dependence of the axial nucleon to Delta(1232) transition form factors in the framework of non-relativistic chiral effective field theory to leading-one-loop order. The outcome of our analysis provides a theoretical guidance for chiral extrapolations of lattice QCD results with dynamical fermions.
We review the current status of experimental and theoretical understanding of the axial nucleon structure at low and moderate energies. Topics considered include (quasi)elastic (anti)neutrino-nucleon scattering, charged pion electroproduction off nucleons and ordinary as well as radiative muon capture on the proton.
We use a continuum quark+diquark approach to the nucleon bound-state problem in relativistic quantum field theory to deliver parameter-free predictions for the nucleon axial and induced pseudoscalar form factors, $G_A$ and $G_P$, and unify them with the pseudoscalar form factor $G_5$ or, equivalently, the pion-nucleon form factor $G_{πNN}$. We explain how partial conservation of the axial-vector current and the associated Goldberger-Treiman relation are satisfied once all necessary couplings of the external current to the building blocks of the nucleon are constructed consistently; in particul…
It is shown that the strong volume-dependence of the axial charge of the nucleon seen in lattice QCD calculations can be understood quantitatively in terms of the pion-induced interactions between neighbouring nucleons. The associated wave function renormalization leads to an increased suppression of the axial charge as the strength of the interaction increases, either because of a decrease in lattice size or in pion mass.
We report a theoretical study of the axial Nucleon to Delta(1232) ($N\toΔ$) transition form factors up to one-loop order in relativistic baryon chiral perturbation theory. We adopt a formalism in which the $Δ$ couplings obey the spin-3/2 gauge symmetry and, therefore, decouple the unphysical spin-1/2 fields. We compare the results with phenomenological form factors obtained from neutrino bubble chamber data and in quark models.
In frame of a phenomenological approach based on Compton-like Feynman amplitudes, we study the annihilation channel in antiproton nucleon collisions with production of a single charged or neutral pion and a lepton-antilepton pair. These reactions allow to access nucleon and axial electromagnetic form factors in time-like region and offer a unique possibility to study the kinematical region below two nucleon threshold. The differential cross section in an experimental set-up where the pion is fully detected is given with explicit dependence on the relevant nucleon form factors. The possibility …
We calculate the stress tensor, or energy-momentum tensor, form factors of the pion and of axial vector mesons in the chiral limit of a hard wall AdS/CFT model of QCD. One (of the two) pion gravitational form factors is directly related to the second moment of the pion generalized parton distribution, thus providing a sum rule for the latter. As was also the case for vector mesons, both the pion and the axial vector mesons appear strikingly more compact measured by the gravitational form factor than by the electromagnetic form factor.
The nucleon axial form factor is a dominant contribution to errors in neutrino oscillation studies. Lattice QCD calculations can help control theory errors by providing first-principles information on nucleon form factors. In these proceedings, we present preliminary results on a blinded calculation of $g_A$ and the axial form factor using HISQ staggered baryons with 2+1+1 flavors of sea quarks. Calculations are done using physical light quark masses and are absolutely normalized. We discuss fitting form factor data with the model-independent $z$ expansion parametrization.
Within the semibosonized SU(3)-NJL model the mass splittings of baryons and the axial vector coupling constants of the nucleon are evaluated. The mass splittings of the hyperons are reproduced with great accuracy if second order corrections in $m_s$ are taken into account. New corrections to the axial vector currents coming from the subleading terms in the $1/N_c$ expansion are shown to be non-vanishing and substantially improving the phenomenological predictions for axial quantities. Finally the numerical values for the $g_{\rm A}$'s are $g_A^{(0)}=0.37$, $g_A^{(3)}=1.38$ and $g_A^{(8)}=0.31$…
In the present work we study the effect of the scalar spin coupling of constituent quarks on the nucleon electroweak properties by introducing a valence light-front wave function with two momentum scales. By comparing the results obtained with the one scale and two scale wave function models, we have found that the last one has shown a reasonable description of the static observables and $μ_pG_{Ep}/G_{Mp}$ ratio in which the position of the zero appears around 10~[GeV/c]$^2$ or for higher squared momentum transfers. We have also shown results for the axial-vector coupling $g_{A}$ and the nucle…
Using the light front wave functions for the nucleons in a quark model in AdS/QCD, we calculate the nucleon electromagnetic form factors. The flavor decompositions of the nucleon form factors are calculated from the GPDs in this model. We show that the nucleon form factors and their flavor decompositions calculated in AdS/QCD are in agreement with experimental data.
Results for the proton and neutron electric and magnetic form factors as well as the nucleon axial form factor are presented for constituent quark models, based on either one-gluon-exchange and Goldstone-boson-exchange dynamics. The calculations are performed in a covariant framework using the point-form approach to relativistic quantum mechanics. The only input to the calculations is the nucleon wave function of the corresponding constituent quark model. A comparison is given to results of the instanton-induced constituent quark model treated with the Bethe-Salpeter equation.
We present a study of electroexcitation of nucleon resonances with higher spins, in a soft-wall AdS/QCD model, comparing our results with existing data from the CLAS Collaboration at JLab, from MAMI, and other experiments.
The extrapolation of nucleon axial charge $g_A$ is investigated within the framework of heavy baryon chiral effective field theory. The intermediate octet and decuplet baryons are included in the one loop calculation. Finite range regularization is applied to improve the convergence in the quark-mass expansion. The lattice data from three different groups are used for the extrapolation. At physical pion mass, the extrapolated $g_A$ are all smaller than the experimental value.
The contribution of axial anomaly to charge symmetry breaking in pion-nucleon coupling constants is calculated within instanton model for QCD vacuum. It has been demonstrated that the contribution is large and allows to explain Nolen-Schiffer anomaly.
New short baseline neutrino experiments open new possibilities of high precision study of different neutrino processes. We present here results of the calculation of the polarization of final nucleon in elastic NC ν_μ(\barν_μ)-nucleon scattering. In a numerical analysis the sensitivity to the different choices of the axial and axial strange form factors is examined. Measurements of the polarization of the final proton in elastic e-p scattering drastically changed our knowledge about the electromagnetic form factors of the proton. From measurement of the nucleon polarization in the NC elastic s…
Three-quark nucleon interpolating fields in QCD have well-defined SU_L(2) x SU_R(2) and U_A(1) chiral transformation properties. Mixing of the [(1,1/2) + (1/2,1)] chiral multiplet with one of [(1/2,0) + (0,1/2)] or [(0,1/2) + (1/2,0)] representation can be used to fit the isovector axial coupling g_A(1) and thus predict the isoscalar axial coupling g_A(0) of the nucleon, in reasonable agreement with experiment. We also use a chiral meson-baryon interaction to calculate the masses and one-pion-interaction terms of J=1/2 baryons belonging to the [(0,1/2) + (1/2,0)] and [(1,1/2) + (1/2,1)] chiral…
We study further the soft-wall AdS/QCD model with a cubic potential for the bulk scalar. We analyze the spectra of pseudoscalar, scalar, vector and axial-vector mesons. We also study the spin-1/2 nucleon spectrum and the pion-nucleon coupling. All of them have a good agreement with the experimental data.
We present a comparative study of nucleon structure such as electromagnetic form factors, transverse charge and magnetization densities in three different models within AdS/QCD framework.
We compute the axial and pseudoscalar form factors of the nucleon in the Dyson-Schwinger approach. To this end, we solve a covariant three-body Faddeev equation for the nucleon wave function and determine the matrix elements of the axialvector and pseudoscalar isotriplet currents. Our only input is a well-established and phenomenologically successful ansatz for the nonperturbative quark-gluon interaction. As a consequence of the axial Ward-Takahashi identity that is respected at the quark level, the Goldberger-Treiman relation is reproduced for all current-quark masses. We discuss the timelike…
Calculation of ratio of the nucleon axial and vector coupling constants $G_A/G_V$ in the framework of the quasipotential quark model has been performed. It was shown that in this model $G_A/G_V$ is defined by the ratio of the corresponding quark axial and and vector coupling constants $g_A/g_V$ and by the dimensionless parameter describing the relativistic relative quark motion and vanishing in the nonrelativistic limit. This relativistic parameter also defines nucleon magnetic moments. Thus we obtain relations independent of the form of the wave function: $G_A/G_V=(g_A/g_V)5(μ^p-1)/6$, $μ^p=(…
In this manuscript, a unified approach to hadron physics from holographic point of view is described. After introduction of a general setup for meson-nucleon system based on the bottom-up approach of QCD (AdS/QCD), as an illustration, we specifically examine meson-nucleon couplings. This is an example of the notion we call "holographic unification" in hadron physics.
We show that the nucleon spectrum in a hard-wall AdS/QCD model can be improved by use of a relatively large IR cutoff. All of the spin-1/2 nucleon masses listed in PDG can be fit quite well within 11%. The average error is remarkably only 4.66%.
In light of the improved precision of the experimental measurements and enormous theoretical progress, the nucleon form factors have been evaluated with an aim to understand how the static properties and dynamical behavior of nucleons emerge from the theory of strong interactions between quarks. We have analysed the vector and axial-vector nucleon form factors ($G^{p,n}_{E,M}(Q^2)$ and $G^{p,n}_{A}(Q^2)$) using the spin observables in the chiral constituent quark model ($χ$CQM) which has made a significant contribution to the unraveling of the internal structure of the nucleon in the nonpertur…
A thermal QCD Finite Energy Sum Rule (FESR) is used to obtain the temperature dependence of the axial-vector coupling of the nucleon, $g_{A}(T)$. We find that $g_{A}(T)$ is essentially independent of $T$, in the very wide range $0 \leq T \leq 0.9 T_{c}$, where $T_{c}$ is the critical temperature. While $g_{A}$ at T=0 is $q^{2}$-independent, it develops a $q^{2}$ dependence at finite temperature. We then obtain the mean square radius associated with $g_{A}$ and find that it diverges at $T=T_{c}$, thus signalling quark deconfinement. As a byproduct, we study the temperature dependence of the Gol…
We calculate the proton's magnetic moment $μ_p$ and its axial-vector coupling $g_A$ as a function of its Dirac radius $R_1$ using a relativisitic three-quark model formulated on the light-cone. The relationship between $μ_p$ and $g_A$ is found to be independent of the assumed form of the light-cone wavefunction. At the physical radius $R_1=0.76$ fm, one obtains the experimental values for both $μ_p$ and $g_A$, and the helicity carried by the valence $u$ and $d$ quarks are each reduced by a factor $\simeq 0.75$ relative to their non-relativistic values. At large proton radius, $μ_p$ and $g_A$ a…
We perform a full next-to-leading analysis of the the available experimental data on the polarized structure function g_1 of the nucleon, and give a precise determination of its singlet axial charge together with a thorough assessment of the theoretical uncertainties. We find that the data are now sufficient to separately determine first moments of the polarized quark and gluon distributions, and show in particular that the gluon contribution is large and positive.
We use light-front Holography to estimate the valence quark and the meson cloud contributions to the nucleon axial form factor. The free couplings of the holographic model are determined by the empirical data and by the information extracted from lattice QCD. The holographic model provides a good description of the empirical data when we consider a meson cloud mixture of about 30\% in the physical nucleon state. The estimate of the valence quark contribution to the nucleon axial form factor compares well with the lattice QCD data for small pion masses. Our estimate of the meson cloud contribut…
The charged-current double differential neutrino cross section, measured by the MiniBooNE Collaboration, has been analyzed using a microscopical model that accounts for, among other nuclear effects, long range nuclear (RPA) correlations and multinucleon scattering. We find that MiniBooNE data are fully compatible with the world average of the nucleon axial mass in contrast with several previous analyses which have suggested an anomalously large value. We also discuss the reliability of the algorithm used to estimate the neutrino energy.
