arXiv subjects

F. Yuan

Publications and source records attributed to F. Yuan.

77 records · Page 5Linked to original sources

arXiv2004

Further Clues to the Nature of Composite LINER/HII Galaxies

We have analyzed new, archival and published high resolution radio and X-ray observations of a sample of composite LINER/HII galaxies known to exhibit AGN-like properties. Five of the 16 AGN candidates have milliarcsecond-scale detections and are found to display a compact, flat spectrum, high brightness temperature radio core, four of which also exhibit extended radio emission. Five of the eight AGN candidates with available high resolution X-ray observations were found to possess a hard X-ray nuclear source, two of which have no milliarcsecond radio detection. The combined high resolution radio and X-ray data yield a 50% detection rate of low luminosity AGN among the AGN candidates, which translates into a 12% detection rate for the entire composite LINER/HII sample. In the sources where the AGN has been unambiguously detected, the ionizing power of the AGN is not sufficient to generate the observed emission lines, unless the hard X-rays are heavily obscured. We attempt to apply a canonical advection-dominated accretion flow (ADAF) and jet model to the sample sources in order to explain the observed radio and X-ray emission. While ADAFs may be responsible for the observed emission in submillijansky radio cores like NGC 7331, they do not appear consistent with the radio emission observed in the milliarcsecond-scale radio detected cores; the latter sources are more likely to have an energetically important contribution from a radio-emitting jet.

astro-ph↗

arXiv2003

Anomalous c-axis charge dynamics in copper oxide materials

Within the t-J model, the c-axis charge dynamics of the copper oxide materials in the underdoped and optimally doped regimes is studied by considering the incoherent interlayer hopping. It is shown that the c-axis charge dynamics is mainly governed by the scattering from the in-plane fluctuation. In the optimally doped regime, the c-axis resistivity is a linear in temperatures, and shows the metallic-like behavior for all temperatures, while the c-axis resistivity in the underdoped regime is characterized by a crossover from the high temperature metallic-like behavior to the low temperature semiconducting-like behavior, which are consistent with experiments and numerical simulations.

cond-mat.str-el↗

arXiv2002

Final state interactions and gauge invariant parton distributions

Parton distributions contain factorizable final state interaction effects originating from the fast-moving struck quark interacting with the target spectators in deeply inelastic scattering. We show that these interactions give rise to gauge invariance of the transverse momentum-dependent parton distributions. As compared to previous analyses, our study demonstrates the existence of extra scaling contributions from transverse components of the gauge potential at the light-cone infinity. They form a transverse gauge link which is indispensable for restoration of the gauge invariance of parton distributions in the light-cone gauge where the gauge potential does not vanish asymptotically. Our finding helps to explain a number of features observed in a model calculation of structure functions in the light-cone gauge.

hep-ph↗

arXiv2002

Polarized J/psi production in deep inelastic scattering at HERA

We perform a calculation on the polarization of J/psi production in deep inelastic scattering in the HERA energy range. For the inclusive production distributions, we find that the color-singlet contributions are consistent with the experimental data in the major region of z (z>0.4). Only in low z regions, there are some hints of the need of the color-octet contributions to describe the experimental data. For the polarization of J/psi in DIS processes, we find the parameter alpha changes with Q^2. Especially, at higher Q^2, difference on alpha between color-singlet and color-octet contributions become more distinctive. In the two regions of lower and larger z, the polarization parameter alpha have different features. These properties can provide important information on the polarization mechanism for J/psi production.

hep-ph↗

arXiv2000

Color-singlet direct J/ψand ψ' production at Tevatron in the k_t factorization approach

Direct $J/ψ$ and $ψ'$ production rates at Tevatron are calculated in the $k_t$-factorization approach within the color-singlet model. In this approach, the production rates are enhanced by a factor of 20 compared to the naive collinear parton model. However, the theoretical predictions are still below the experimental data by at least one order of magnitude. This means that to explain charmonium productions at Tevatron, we still need to call for the contributions from color-octet channels or other production mechanisms.

hep-ph↗