199676816
Discovering the missing bright quasars at intermediate redshifts based on the optical/near-IR color selections
119181774
LAMOST Quasar Survey
The main objective of the Chinese LAMOST spectroscopic quasar survey is to discover 0.4 million new quasars from 1 million quasar candidates brighter than the magnitude limit i=20.5 in the next 5 years. This will hopefully provide the largest quasar sample for the further studies of AGN physics and cosmology. The improved quasar selection criteria based on the UKIDSS near-IR and SDSS optical colors are presented, and their advantages in uncovering the missing quasars in the quasar 'redshift desert' are demonstrated. In addition, some recent discoveries of new quasars during the LAMOST commissioning phase are presented.
124212752
Ultra-luminous Infrared galaxies in SDSS Data Release 6
14447660
The local stability of accretion disks with advection
The local stability of accretion disks with advection is studied together with the considerations of radial viscous force and thermal diffusion. For a geometrically thin, radiative cooling dominated disk, the thermal diffusion has nearly no effects on the thermal and viscous modes. The including of thermal diffusion, however, tends to stabilize the acoustic modes which, if without advection, are unstable if the disk is optically thick, radiation pressure dominated or optically thin, and are stable if the disk is optically thick, gas pressure dominated. The including of very little advection has significant effects on two acoustic modes. Independent on the optical depth, the instability of the outward propagating mode (O-mode) is enhanced and that of the inward propagating mode (I-mode) is damped if the disk is gas pressure dominated, while the instability of O-mode is damped and that of I-mode is enhanced if the disk is radiation pressure dominated. For a geometrically slim, advection-dominated disk, both the thermal and viscous modes, as well as I-mode, are always stable if the disk is optically thin. The including of thermal diffusion tends to make these modes more stable. However, the O-mode can become unstable when $q/m$ is very large ($q$ is the ratio of advective to viscous dissipated energy and $m$ the Mach number), even if the thermal diffusion is considered. On the other hand, if the advection-dominated disk is optically thick, we found there is no self-consistent acoustic modes in our local analyses. The thermal diffusion has no effect on the stable viscous mode but has a significant contribution to enhance the thermal instability.
117093043
EGRET GAMMA-RAY SOURCE 2EG J0809+5117, A QUASAR WITH REDSHIFT OF 1.14 ?
The low dispersion (400 Angstrom/mm) spectrum of the optical counterpart of a flat-spectrum radio source 87GB 080315.5+512613, which is one of two possible radio counterparts of 2EG J0809+5117, was obtained recently. The optical counterpart, which is 2.02 '' away from 87GB 080315.5+512613 and 19.3' away from 2EG J0809+5117, was identified as a quasar with redshift of 1.14. We noted that Matter et al. (1997) suggested the other radio counterpart 87GB 080459.4+495915 (OJ 508), which is 87.1' away from 2EG J0809+5117, is the more potential identification, though it was previously suggested to be the identification (with low confidence) of another nearby EGRET source 2EG J0807+4849. Our observation suggests that it is quite possible that 87GB 080315.5+512613 is the identification of 2EG J0809+5117 rather than 87GB 080459.4+495915. But we still can not exclude the possibility of 87GB 080459.4+495915 at present. Moreover, in order to determine whether or not 87GB 080315.5+512613 is a blazar type quasar, the optical polarization and variability measures of its optical counterpart are strongly encouraged.
450968
Studying the scalar bound states of KK system in Bethe-Salpeter formalism
We study the possible bound states of the KK system in the Bethe-Salpeter formalism in the ladder and instantaneous approximations. We find that the bound states exist. However, these bound states have very small decay widths. Therefore, besides the possible KK component, there may be some other structures in the observed f{sub 0}(980) and a{sub 0}(980)
118505094
Constraints on the leading-twist pion distribution amplitude from a QCD light-cone sum rule with chiral current
We present an improved analysis of the constraints on the first two Gegenbauer moments, a2π and a4π, of the pion’s leading-twist distribution amplitude from a QCD light-cone sum rule analysis of the B→π weak transition form factor f+(q2). A proper chiral current is adopted in QCD light-cone sum rules so as to eliminate the most uncertain twist-3 contributions to f+(q2), and then we concentrate our attention on the properties of the leading-twist pionic DA. A nearly model-independent f+(q2), based on the spectrum of B→πlν decays from BaBar, together with uncertainties, is adopted as the standard shape for f+(q2) for our discussion. From a minimum χ2-fit and by taking the theoretical uncertainties into account, we obtain a2π(1 GeV)=0.17−0.17+0.15 and a4π(1 GeV)=−0.06−0.22+0.20 at the 1σ confidence level for mb*∈[4.7,4,8] GeV.
18567598
Pion Electromagnetic Form Factor in the KT Factorization Formulae
Based on the light-cone (LC) framework and the kT factorization formalism, the transverse momentum effects and the different helicity components' contributions to the pion form factor Fπ(Q2) are recalculated. In particular, the contribution to the pion form factor from the higher helicity components (λ1 + λ2 = ±1), which come from the spin-space Wigner rotation, are analyzed in the soft and hard energy regions respectively. Our results show that the right power behavior of the hard contribution from the higher helicity components can only be obtained by fully keeping the kT dependence in the hard amplitude, and that the kT dependence in LC wavefunction affects the hard and soft contributions substantially. A model for the twist-3 wavefunction ψp(x,k⊥) of the pion has been constructed based on the moment calculation by applying the QCD sum rules, whose distribution amplitude has a better end-point behavior than that of the asymptotic one. With this model wavefunction, the twist-3 contributions including both the usual helicity components (λ1 + λ2 = 0) and the higher helicity components (λ1 + λ2 = ±1) to the pion form factor have been studied within the modified pQCD approach. Our results show that the twist-3 contribution drops fast and it becomes less than the twist-2 contribution at Q2~10GeV2. The higher helicity components in the twist-3 wavefunction will give an extra suppression to the pion form factor. When all the power contributions, which include higher order in αs, higher helicities, higher twists in DA and etc., have been taken into account, it is expected that the hard contributions will fit the present experimental data well at the energy region where pQCD is applicable.
119104596
B-meson wavefunction in the Wandzura–Wilczek approximation
The B-meson wavefunction has been studied with the help of the vacuum-to-meson matrix element of the non-local operators in the heavy quark effective theory. In order to obtain the Wandzura-Wilczek-type B-meson wavefunction, we solve the equations which are derived from the equation of motion of the light spectator quark in the B meson by using two different assumptions. Under the condition that omega(0) = 2 (Lambda) over bar, the solutions for the B-meson wavefunction in this paper agree well with the one obtained by directly taking the heavy quark limit m(b) -> infinity. Our results show that the equation of motion of the light spectator quark in the B meson can impose a strong constraint on the B-meson wavefunctions Psi(+/-)(omega, z(2)). Based on the obtained results, we claim that both its distribution amplitudes phi(B)(omega) and phi(B)(omega) are important for calculating the B meson decays. (c) 2005 Elsevier B.V. All rights reserved.
13937852
Strong decays of heavy baryons in the Bethe-Salpeter formalism
In this paper we study the properties of diquarks (composed of u and/or d quarks) in the Bethe-Salpeter (BS) formalism under the covariant instantaneous approximation. We calculate their BS wave functions and study their effective interaction with the pion. Using the effective coupling constant among the diquarks and the pion, in the heavy quark limit m{sub Q}{yields}{infinity}, we calculate the decay widths of {sigma}{sub Q}{sup (*)} (Q=c, b) in the BS formalism under the covariant instantaneous approximation and then give predictions of the decay widths {gamma}({sigma}{sub b}{sup (*)}{yields}{lambda}{sub b}+{pi})