Strange-quark asymmetry in the proton in chiral effective theory

Abstract

We perform a comprehensive analysis of the strange-antistrange parton distribution function (PDF) asymmetry in the proton in the framework of chiral effective theory, including the full set of lowest order kaon loop diagrams with off-shell and contact interactions, in addition to the usual on-shell contributions previously discussed in the literature. We identify the presence of δ-function contributions to thes PDF at x = 0, with a corresponding valence-like component of the s-quark PDF at larger x, which allows greater flexibility for the shape of s −s. Expanding the moments of the PDFs in terms of the pseudoscalar kaon mass, we compute the leading nonanalytic behavior of the number and momentum integrals of the s ands distributions, consistent with the chiral symmetry of QCD. We discuss the implications of our results for the understanding of the NuTeV anomaly and for the phenomenology of strange quark PDFs in global QCD analysis.

Parton distributions from nonlocal chiral SU(3) effective theory: Flavor asymmetries

“…The operators B and T α appearing in Eqs. (11) and ( 15) can be written in terms of the SU(3) baryon octet fields B ij (which include N , Λ, Σ and Ξ fields) and decuplet baryon fields T ijk α (which include ∆, Σ * , Ξ * and Ω fields) using the relations [19,26]…”

“…For the numerical calculation of the meson-bayron splitting functions, earlier work used various regularization prescriptions, including sharp transverse momentum cutoffs, Pauli-Villars regularization, as well as phenomenological vertex form factors [19,20,[29][30][31][32]. At times the prescriptions have been imposed in rather ad hoc ways, without necessarily ensuring that the relevant symmetries, such as Lorentz, chiral, and local gauge symmetries, are necessarily respected.…”

“…In the previous paper [15], we presented the proton → pseudoscalar meson (φ) + baryon splitting functions for the intermediate octet (B) and decuplet (T ) baryon configurations in nonlocal chiral effective theory [16,17]. From the calculated splitting functions, the parton distribution functions (PDFs) of the nucleon are obtained as convolutions of these with PDFs of the intermediate state mesons and baryons [18][19][20]. Here we apply the results from [15] to compute, for the first time within the nonlocal theory, sea quark PDF asymmetries in the proton, including the light antiquark flavor asymmetry d − ū and the strange quark asymmetry s − s. Using SU(3) relations for the intermediate state hadron PDFs, the only parameters in the calculation of the asymmetries are the mass parameters appearing in the ultraviolet regulator functions.…”

Octet and decuplet baryon self-energies in relativistic SU(3) chiral effective theory

“…In other recent applications, careful treatment of chiral loops has been stressed in connection with the meson-baryon splitting functions needed for the calculation of parton distribution functions [27][28][29][30][31][32][33], and in particular the key role played by light-front zero-mode contributions [34][35][36][37][38]. Elsewhere, the effects of relativistic chiral corrections on electromag-netic form factors [39,40] and transverse momentum distributions [41] have recently been studied.…”

Pion structure function and SU(2) flavor asymmetry

“…This convolution expression (3.2) is the standard one used in calculations of chiral loop corrections in meson cloud models and its appearance in the effective chiral theory is made manifest recently [27]. As we discuss the efficacy of the pion exchange model [6] in Sec.…”