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Register a new userStrange quark helicity in the proton from chiral effective theory
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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.
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Beginning with precise data on the ratio of structure functions in deep inelastic scattering (DIS) from $^3$He and $^3$H, collected on the domain $0.19 leq x_B leq 0.83$, where $x_B$ is the Bjorken scaling variable, we employ a robust method for extrapolating such data to arrive at a model-independent result for the $x_B=1$ value of the ratio of neutron and proton structure functions. Combining this with information obtained in analyses of DIS from nuclei, corrected for target-structure dependence, we arrive at a prediction for the protons valence-quark ratio: $left. d_v/u_v right|_{x_Bto 1} = 0.230 (57)$. Requiring consistency with this result presents a challenge to many descriptions of proton structure.
We demonstrate that a nonzero strangeness contribution to the spacelike electromagnetic form factor of the nucleon is evidence for a strange-antistrange asymmetry in the nucleons light-front wave function, thus implying different nonperturbative contributions to the strange and antistrange quark distribution functions. A recent lattice QCD calculation of the nucleon strange quark form factor predicts that the strange quark distribution is more centralized in coordinate space than the antistrange quark distribution, and thus the strange quark distribution is more spread out in light-front momentum space. We show that the lattice prediction implies that the difference between the strange and antistrange parton distribution functions, $s(x)-bar{s}(x)$, is negative at small-$x$ and positive at large-$x$. We also evaluate the strange quark form factor and $s(x)-bar{s}(x)$ using a baryon-meson fluctuation model and a novel nonperturbative model based on light-front holographic QCD. This procedure leads to a Veneziano-like expression of the form factor, which depends exclusively on the twist of the hadron and the properties of the Regge trajectory of the vector meson which couples to the quark current in the hadron. The holographic structure of the model allows us to introduce unambiguously quark masses in the form factors and quark distributions preserving the hard scattering counting rule at large-$Q^2$ and the inclusive counting rule at large-$x$. Quark masses modify the Regge intercept which governs the small-$x$ behavior of quark distributions, therefore modifying their small-$x$ singular behavior. Both nonperturbative approaches provide descriptions of the strange-antistrange asymmetry and intrinsic strangeness in the nucleon consistent with the lattice QCD result.
The strong decays of charm-strange baryons up to N=2 shell are studied in a chiral quark model. The theoretical predictions for the well determined charm-strange baryons, $Xi_c^*(2645)$, $Xi_c(2790)$ and $Xi_c(2815)$, are in good agreement with the experimental data. This model is also extended to analyze the strong decays of the other newly observed charm-strange baryons $Xi_c(2930)$, $Xi_c(2980)$, $Xi_c(3055)$, $Xi_c(3080)$ and $Xi_c(3123)$. Our predictions are given as follows. (i) $Xi_c(2930)$ might be the first $P$-wave excitation of $Xi_c$ with $J^P=1/2^-$, favors the $|Xi_c ^2P_lambda 1/2^->$ or $|Xi_c ^4P_lambda 1/2^->$ state. (ii) $Xi_c(2980)$ might correspond to two overlapping $P$-wave states $|Xi_c ^2P_rho 1/2^->$ and $|Xi_c ^2P_rho 3/2^->$, respectively. The $Xi_c(2980)$ observed in the $Lambda_c^+bar{K}pi$ final state is most likely to be the $|Xi_c ^2P_rho 1/2^->$ state, while the narrower resonance with a mass $msimeq 2.97$ GeV observed in the $Xi_c^*(2645)pi$ channel favors to be assigned to the $|Xi_c ^2P_rho 3/2^->$ state. (iii) $Xi_c(3080)$ favors to be classified as the $|Xi_c S_{rhorho} 1/2^+>$ state, i.e., the first radial excitation (2S) of $Xi_c$. (iv) $Xi_c(3055)$ is most likely to be the first $D$-wave excitation of $Xi_c$ with $J^P=3/2^+$, favors the $|Xi_c ^2D_{lambdalambda} 3/2^+>$ state. (v) $Xi_c(3123)$ might be assigned to the $|Xi_c ^4D_{lambdalambda} 3/2^+>$, $|Xi_c ^4D_{lambdalambda} 5/2^+>$, or $|Xi_c ^2D_{rhorho} 5/2^+>$ state. As a by-product, we calculate the strong decays of the bottom baryons $Sigma_b^{pm}$, $Sigma_b^{*pm}$ and $Xi_b^*$, which are in good agreement with the recent observations as well.
We show that transverse-momentum-dependent parton distribution functions (TMDPDFs), important non-perturbative quantities for describing the properties of hadrons in high-energy scattering processes such as Drell-Yan and semi-inclusive deep-inelastic scattering with observed small transverse momentum, can be obtained from Euclidean QCD calculations in the framework of large-momentum effective theory (LaMET). We present a LaMET factorization of the Euclidean quasi-TMDPDFs in terms of the physical TMDPDFs and off-light-cone soft function at leading order in $1/P^z$ expansion, with the perturbative matching coefficient satisfying a renormalization group equation. We also discuss the implementation in lattice QCD with finite-length gauge links as well as the rapidity-regularization-independent factorization for Drell-Yan cross section.
We have systematically investigated the decuplet (T) to octet (B) baryon ($Trightarrow Bgamma$) transition magnetic moments to the next-to-next-to-leading order and electric quadruple moments to the next-to-leading order in the framework of the heavy baryon chiral perturbation theory. Our calculation includes the contributions from both the intermediate decuplet and octet baryon states in the loops. Our results show reasonably good convergence of the chiral expansion and agreement with the experimental data. The analytical expressions may be useful to the chiral extrapolation of the lattice simulations of the decuplet electromagnetic properties.
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