High--Resolution 3D Simulations of Relativistic Jets

We have performed high-resolution 3D simulations of relativistic jets with beam flow Lorentz factors up to 7, a spatial resolution of 8 cells per beam radius, and for up to 75 normalized time units to study the morphology and dynamics of 3D relativistic jets. Our simulations show that the coherent fast backflows found in axisymmetric models are not present in 3D models. We further find that when the jet is exposed to non-axisymmetric perturbations, (i) it does not display the strong perturbations found for 3D classical hydrodynamic and MHD jets (at least during the period of time covered by our simulations), and (ii) it does propagate according to the 1D estimate. Small 3D effects in the relativistic beam give rise to a lumpy distribution of apparent speeds like that observed in M87. The beam is surrounded by a boundary layer of high specific internal energy. The properties of this layer are briefly discussed.Comment: 15 pages, 4 figures. Accepted to be publish in the ApJ Letters. Tar+gzip documen

Breakdown of QCD Factorization for P-Wave Quarkonium Production at Low Transverse Momentum

Quarkonium production at low transverse momentum in hadron collisions can be used to extract Transverse-Momentum-Dependent(TMD) gluon distribution functions, if TMD factorization holds there. We show that TMD factorization for the case of P-wave quarkonium with $J^{PC}=0^{++}, 2^{++}$ holds at one-loop level, but is violated beyond one-loop level. TMD factorization for other P-wave quarkonium is also violated already at one-loop.Comment: Published version in Physics Letters B (2014), pp. 103-10

Transverse Momentum Dependent Factorization for Quarkonium Production at Low Transverse Momentum

Quarkonium production in hadron collisions at low transverse momentum $q_\perp \ll M$ with $M$ as the quarkonium mass can be used for probing transverse momentum dependent (TMD) gluon distributions. For this purpose, one needs to establish the TMD factorization for the process. We examine the factorization at the one-loop level for the production of $\eta_c$ or $\eta_b$. The perturbative coefficient in the factorization is determined at one-loop accuracy. Comparing the factorization derived at tree level and that beyond the tree level, a soft factor is, in general, needed to completely cancel soft divergences. We have also discussed possible complications of TMD factorization of p-wave quarkonium production.Comment: Title changed in the journal, published versio

Photon-meson transition form factors of light pseudoscalar mesons

The photon-meson transition form factors of light pseudoscalar mesons $\pi ^{0}$, $\eta$, and $\eta ^{\prime}$ are systematically calculated in a light-cone framework, which is applicable as a light-cone quark model at low $Q^{2}$ and is also physically in accordance with the light-cone pQCD approach at large $Q^{2}$. The calculated results agree with the available experimental data at high energy scale. We also predict the low $Q^{2}$ behaviors of the photon-meson transition form factors of $\pi ^{0}$, $\eta$ and $\eta ^{\prime }$, which are measurable in $e+A({Nucleus})\to e+A+M$ process via Primakoff effect at JLab and DESY.Comment: 22 Latex pages, 7 figures, Version to appear in PR

Proton spin in a light-cone chiral quark model

We discuss the spin structure of the proton in a light-cone treatment of the chiral quark model. Based on the fact that the quark helicity ($\Delta q$) measured in polarized deep inelastic scattering experiments is actually the quark spin defined in the light-cone formalism, rather than the quark spin ($\Delta q_{QM}$) defined in the conventionally quark model (or in the rest frame of the nucleon), we calculate the $x$-dependence of the polarized quark distribution functions $\Delta q(x)$, and the polarized structure functions $g_1 (x)$. Special attention is focused on the Melosh-Wigner rotation due to the transversal motions of quarks inside the nucleon and its effects on the bare quark input. It is shown that our results match the experimental data well.Comment: 11 latex pages, 8 figures, final version published in PR