Search

We introduce a new family of generalized parton distribution models able to fulfill by construction all the theoretical properties imposed by QCD. These models are built on standard parton distribution functions and extended to off-forward kinematics through a well-defined procedure. We apply this strategy on the pion, first handling a simple but insightful algebraic model, and then exploiting state-of-the-art computations obtained in continuum QCD. We compare these models with a more standard one relying on an xFitter extraction of the pion parton distribution functions. The results for both quark and gluon generalized parton distributions are presented and exploited for calculation of electromagnetic, gravitational, and Compton form factors. Results on the latter highlight the relevance of next-to-leading-order corrections, even in the so-called valence region, We are grateful to Qin-Tao Song for kindly providing us the GFF data obtained from pion GDA. We would like to thank P. Barry, H. Dutrieux, T. Meisgny, B. Pire, K. Raya, C. D. Roberts, P. Sznajder, and J. Wagner for interesting discussions and stimulating comments. This work is supported by the University of Huelva under Grant No. EPIT2020 (J. M. M. C.). F. S., J. R. Q., and J. S. acknowledge support from Ministerio de Ciencia e Innovación (Spain) under Grant No. PID2019–107844 GB-C22; Junta de Andaluca, under the 2014–2020 FEDER Contracts No. UHU-1264517, No. P18-1321FR-5057 and PAIDI FQM-370. This project was supported by the European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 824093. This work is supported in part in the framework of the GLUODYNAMICS project funded by the “P2IO LabEx (ANR-10-LABX-0038)” in the framework “Investissements d’Avenir” (ANR-11-IDEX0003-01) managed by the Agence Nationale de la Recherche (ANR), France

We reconstruct ghost and gluon spectral functions in 2 þ 1 flavor QCD with Gaussian process regression. This framework allows us to largely suppress spurious oscillations and other common reconstruction artifacts by specifying generic magnitude and length scale parameters in the kernel function. The Euclidean propagator data are taken from lattice simulations with domain wall fermions at the physical point. For the infrared and ultraviolet extensions of the lattice propagators as well as the low-frequency asymptotics of the ghost spectral function, we utilize results from functional computations in Yang-Mills theory and QCD. This further reduces the systematic error significantly. Our numerical results are compared against a direct real-time functional computation of the ghost and an earlier reconstruction of the gluon in Yang-Mills theory. The systematic approach presented in this work offers a promising route toward unveiling real-time properties of QCD, We thank A. Cyrol, F. Gao, L. Kades, J. Y. Lin, J. Papavassiliou, and A. Rothkopf for discussions. We thank P. Boucaud and F. De Soto for an earlier collaboration and for their help in the preparation of the lattice data. We are indebted to the RBC/ UKQCD Collaboration, especially to P. Boyle, N. Christ, Z. Dong, N. Garron, C. Jung, B. Mawhinney, and O. Witzel, for access to the lattices used in this work. We also thank the members of the fQCD Collaboration for discussions and collaborations on related subjects. J. R. Q. acknowledges the support of MICINN Grant No. PID2019-107844GB-C22. Numerical computations have used resources of CINES, GENCI IDRIS (Project No. 52271) and of the IN2P3 computing facility in France. This work is supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy Grant No. EXC 2181/ 1-390900948 (the Heidelberg STRUCTURES Excellence Cluster), under the Collaborative Research Centre SFB 1225 (ISOQUANT), EMMI, and BMBF Grant No. 05P18VHFCA

One of the biggest challenges in contemporary physics is understanding the origin and dynamics of the internal structure of hadrons which, at a fundamental level, is described by quantum chromodynamics (QCD). Taking great prominence amongst hadrons are pions and kaons which, despite being the lightest hadrons in nature, their very existence is intimately connected to those mechanisms responsible for almost all of the mass of the visible matter. In this manuscript we discuss many aspects of the pion and kaon structure via light front wave functions and generalized parton distributions, and a collection of other distributions and structural properties that are inferred therefrom., Comment: Invited plenary talk given at the 19th International Conference on Hadron Spectroscopy and Structure in memoriam Simon Eidelman (HADRON2021), 26-31 July (2021), Mexico City (Mexico). 8 pages, 6 figures

We present the first systematic feasibility study of accessing generalized parton distributions of the pion at an electron-ion collider through deeply virtual Compton scattering. Relying on state-of-the-art models for pion GPDs, we show that quarks and gluons interfere destructively, modulating the expected event rate and maximizing it when parton content is generated via radiation from valence dressed quarks. Moreover, gluons are found to induce a sign inversion for the beam-spin asymmetry in every model studied, being a clear signal for pinning down the regime of gluon superiority, We would like to thank P. Barry, H. Dutrieux, T. Meisgny, B. Pire, K. Raya, C. D. Roberts, D. Sokhan, Q.-T. Song, P. Sznajder, and J. Wagner for interesting discussions and stimulating comments. This work is supported by the University of Huelva under Grant No. EPIT-2020 (J.M.M. C.). F. S., J. R. Q., and J. S. acknowledge support from Ministerio de Ciencia e Innovación (Spain) underGrant No. PID2019–107844 GB-C22 and Junta de Andalucía, under the 2014-2020 FEDER Contracts No.UHU-1264517, No. P18-1321FR-5057 and No. PAIDI FQM-370. This project was supported by the European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 824093. This work is supported in part in the framework of the GLUODYNAMICS project funded by the “P2IO LabEx” (No. ANR-10-LABX-0038) in the framework “Investissements d’Avenir” (No. ANR-11- IDEX-0003-01) managed by the Agence Nationale de la Recherche (ANR), France

Describing hadronic structure is one of the most intriguing problems in physics. In this respect, generalized parton distributions (GPDs) constitute an outstanding tool, allowing to draw "three dimensional pictures" of hadron's inside. Starting from contemporary models for pion's GPDs fulfilling all constraints imposed by QCD, we compute Compton form factors (CFFs) of pions subjected to deeply virtual Compton scattering. We show the behaviour of CFFs to be gluon-dominated at EIC's kinematics. Finally we evaluate lepton-beam-spin asymmetries in the Sullivan process, demonstrating the existence of such and thus triggering optimism about the possibility of probing pion's 3D structure at electron-ion colliders., Comment: Proceedings of the 19th International Conference on Hadron Spectroscopy and Structure in memoriam Simon Eidelman (HADRON2021), 26-31 July (2021), Mexico City (Mexico). To appear in Suplemento de la Revista Mexicana de F\'isica

Talk from PIEIC 2020

It is recalled why, as already stated in a previous paper, there seems to be an inconsistency in identifying the non perturbative ZA,MOM as the renormalisation of the axial current, or equivalently, in setting as normalisation condition that the renormalised vertex=1 at p^2 = mu^2 at some renormalisation scale mu, where p is the momentum in the legs. Indeed, unlike the vector case, the Ward-Takahashi (WT) identity for the axial current is shown to imply both the renormalisation scale independence of ZA and a mu2 dependence of ZA,MOM. This mu^2 dependence is simply related to certain invariants in the pseudoscalar vertex and can persist in the chiral limit due to the spontaneous breaking of chiral symmetry (pion pole). It is seen clearly in the mu^2 dependence of some lattice calculations of ZA,MOM/ZV,MOM near the chiral limit., Comment: One reference added; some minor material errors corrected; no substantial change with respect to the first version

We compute the pion quark Generalized Parton Distribution H and quark Double Distributions F and G in a coupled Bethe-Salpeter and Dyson-Schwinger approach in terms of quark flavors or isospin states. We use simple analytic expressions inspired by the numerical resolution of Dyson-Schwinger and Bethe-Salpeter equations. We explicitly check the support and polynomiality properties, and the behavior under charge conjugation or time invariance of our model. We obtain analytic expressions for the pion Double Distributions and Generalized Parton Distribution at vanishing pion momentum transfer at a low scale. Our model compares very well to experimental pion form factor or Parton Distribution Function data. This paper is the first stage of a GPD-modeling program which will be pursued by incorporating more realistic solutions of the Bethe-Salpeter and Dyson-Schwinger equations., 20 pages, 9 figures

We argue that all evidences point towards a finite non-vanishing zero momentum renormalised lattice gluon propagator in the infinite volume limit. We argue that different simulations with different lattice setups end-up with fairly compatible results for the gluon propagator at zero momentum, with different positive slopes as a function of the inverse volume., Comment: 7 pages, no figures, comment

We discuss a non-perturbative lattice calculation of the ghost and gluon propagators in the pure Yang-Mills theory in Landau gauge. The ultraviolet behaviour is checked up to NNNLO yielding the value $\Lambda^{n_f=0}_{\ms}=269(5)^{+12}_{-9}\text{MeV}$, and we show that lattice Green functions satisfy the complete Schwinger-Dyson equation for the ghost propagator for all considered momenta. The study of the above propagators at small momenta showed that the infrared divergence of the ghost propagator is enhanced, whereas the gluon propagator seem to remain finite and non-zero. The result for the ghost propagator is consistent with the analysis of the Slavnov-Taylor identity, whereas, according to this analysis, the gluon propagator should diverge in the infrared, a result at odds with other approaches., Comment: To appear in the proceedings of the workshop "Hadron Structure and QCD: from LOW to HIGH energies" (St. Petersburg, Russia, 20-24 September 2005)

We study the infrared behaviour of the pure Yang-Mills correlators using relations that are well defined in the non-perturbative domain. These are the Slavnov-Taylor identity for three-gluon vertex and the Schwinger-Dyson equation for ghost propagator in the Landau gauge. We also use several inputs from lattice simulations. We show that lattice data are in serious conflict with a widely spread analytical relation between the gluon and ghost infrared critical exponents. We conjecture that this is explained by a singular behaviour of the ghost-ghost-gluon vertex function in the infrared. We show that, anyhow, this discrepancy is not due to some lattice artefact since lattice Green functions satisfy the ghost propagator Schwinger-Dyson equation. We also report on a puzzle concerning the infrared gluon propagator: lattice data seem to favor a constant non vanishing zero momentum gluon propagator, while the Slavnov-Taylor identity (complemented with some regularity hypothesis of scalar functions) implies that it should diverge., 25 pages, 7 figures; replaced version with some references adde and an enlarged discussion of the non-renormalization theorem; second replacement with improved figures and added references

Strong coupling constant computed in Landau gauge and MOM renormalization scheme from lattice two and three gluon Green Functions exhibits an unexpected behavior in the deep IR, showing a maximum value around $1 {\rm GeV}$. We analise this coupling below this maximum within a semiclassical approach, were gluon degrees of freedom at very low energies are described in terms of the classical solutions of the lagrangian, namely instantons. We provide some new results concerning the relationship between instantons and the low energy dynamics of QCD, by analising gluon two- and three-point Green functions separately and with the help of a cooling procedure to eliminate short range correlations., Comment: 4 pages, talk given at XXXX Rencontres de Moriond on QCD and Hadronic Interactions, La Thuile (Italy)

The running coupling constant can be estimated by computing gluon two- and three-point Green functions from the lattice. Computing in lattice implies working in a fixed gauge sector (Landau). An source of systematic uncertainty is then the contribution of non gauge-invariant condensates, as $$, generating power corrections that might still be important at very high energies. We study the impact of this gluon condensate on the analysis of gluon propagator and vertex lattice data and on the estimate of $\Lambda_{\bar{\rm MS}}$. We finally try a qualitative description of this gluon condensate through the instanton picture, Comment: Talk given in Moriond 2002