Various shadowing aspects of nuclear parton distributions are discussed in a partonmodel framework. We explain existing x dependent data of F 2 /F 2 , then the model is applied to a flavor asymmetry ū − d̄ in a nucleus, to shadowing in valence-quark distributions, and to nuclear dependence of Q evolution. First, we find that a finite nuclear ū−d̄ distribution could be possible due to nuclear inte...

We study the normalized difference between the solution u of a reaction–diffusion equation in a bounded interval [0,L], perturbed by a fast oscillating term arising as the solution of a stochastic reaction–diffusion equation with a strong mixing behavior, and the solution ū of the corresponding averaged equation. We assume the smoothness of the reaction coefficient and we prove that a central l...

As in the classical paper of Lax [L], we assume here that the system is strictly hyperbolic with each characteristic field either linearly degenerate or genuinely nonlinear. In this setting, the recent progress in the field has shown that within the class of initial data ū ∈ L ∩BV (R,R) having the total variation suitably small, the problem (1.1) (1.2) is well posed in L(R,R). Namely, as proved...

We present a calculation of the polarized ρ meson cloud in a nucleon using time-ordered perturbation theory in two different variants advocated in the literature. We calculate the induced difference between the distributions ∆d̄(x) and ∆ū(x). We use a recent lattice calculation to motivate an ansatz for the polarized valence quark distribution of the ρ meson. Our calculations show that the two t...

SU(2)-flavor-symmetry breaking in antiquark distributions of the nucleon was suggested by the New Muon Collaboration (NMC) in deep inelastic muon scattering. As an independent test, Drell-Yan data for the tungsten target have been used for examining the asymmetry. We investigate whether there exists significant modification of the ū− d̄ distribution in nuclei in a parton recombination model. It ...

We study the singular ordinary differential equation dU dt = 1 ζ(U) φs(U) + φns(U), (0.1) where U ∈ R , the functions φs ∈ R N and φns ∈ R N are of class C and ζ is a real valued C function. The equation is singular in the sense that ζ(U) can attain the value 0. We focus on the solutions of (0.1) that belong to a small neighbourhood of a point Ū such that φs(Ū) = φns(Ū) = ~0, ζ(Ū) = 0. We inves...

We study the d̄ ū asymmetry of the proton in a model approach recently developed, in which hadronic fluctuations of the nucleon are generated through gluon splitting and recombination mechanisms. Within this framework, it is shown that both d̄/ū and d̄− ū distributions in the proton can be consistently described by including only nucleon fluctuations to |πN〉 and |π∆〉 bound states. Predictions of t...