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.
2132712
Inclinations and black hole masses of Seyfert 1 galaxies
A tight correlation between black hole mass (MBH) and central velocity dispersion (σ) has been found recently for both active and quiescent galaxies. By applying this correlation, we develop a simple method to derive the inclination angles for a sample of 11 Seyfert 1 galaxies that have both measured central velocity dispersions and black hole masses estimated by reverberation mapping. These angles, with a mean value of 36° that agrees well with the result obtained by fitting the iron Kα lines of Seyfert 1 galaxies observed with ASCA, provide further support to the orientation-dependent unification scheme of active galactic nuclei (AGNs). A positive correlation of the inclinations with observed FWHMs of the Hβ line and a possible anticorrelation with the nuclear radio loudness have been found. We conclude that more accurate knowledge of inclinations and broad-line region dynamics is needed to improve the black hole mass determination of AGNs with the reverberation mapping technique.
2227030
Testing the transition layer model of quasi-periodic oscillations in neutron star X-ray binaries
We compare the theoretical predictions of the transition layer model with some observational features of quasi-periodic oscillations (QPOs) in neutron star X-ray binaries. We found that the correlation between horizontal branch oscillation (HBO) frequencies and kilohertz (kHz) QPO frequencies, the difference between the low-frequency QPOs in atoll sources and HBOs in Z sources, and the correlation between the frequencies of low-frequency QPOs and break frequencies can be well explained by the transition layer model, provided the neutron star mass is around 1.4 M☉ and the angle between magnetosphere equator and accretion disk plane is around 6°. The observed decrease of peak separation between the two kHz QPO frequencies with the increase of the kHz QPO frequencies and the increase of QPO frequencies with the increase of inferred mass accretion rate are also consistent with the theoretical predictions of the transition layer model. In addition, we derive a simple equation that can be adopted to estimate the angle (δ) between magnetosphere equator and accretion disk plane by use of the simultaneously observed QPO frequency data. We estimate this angle, in the range of 4°-8°, for five Z sources and two atoll sources. The nearly constant δ value for each source, derived from the different sets of simultaneously observed QPO frequency data, provides a strong test of the theoretical model. Finally, we suggest that similar transition layer oscillations may be responsible for the observed QPOs in accretion-powered millisecond X-ray pulsars and Galactic black hole candidates.
11771360
The Nature of Linearly Polarized Millimeter and Submillimeter Emission in Sagittarius A
The linearly polarized millimeter and sub-millimeter emission in Sagittarius A* is produced within 10 Schwarzschild radii of the supermassive black hole at the Galactic Center and may originate from a hot magnetized accretion disk, where electrons are heated efficiently by turbulent plasma waves. I n such a scenario, the flux density and polarization are very sensitive to the electron heating rate and the inclination angle of disk, respectively, and the major axis of the submillimeter intrinsic polarization, which is aligned with the rotation axis of the disk, is perpendicular to the major axis of the polarized near-infrared emission. In combination with MHD simulations, which study the properties of the magnetic field and viscous stresses, the current spectral and polarization measurements give tight constraints on the model parameters. Simultaneous observations will be able to test the model.
118357880
ON THE STRUCTURE OF ACCRETION DISKS WITH OUTFLOWS
To study the outflows from accretion disks, we solve the set of hydrodynamic equations for accretion disks in spherical coordinates (rθ) to obtain the explicit structure along the θ-direction. Using self-similar assumptions in the radial direction, we change the equations to a set of ordinary differential equations about the θ-coordinate, which are then solved with symmetrical boundary conditions in the equatorial plane; the velocity field is then obtained. The α viscosity prescription is applied and an advective factor f is used to simplify the energy equation. The results display thinner, quasi-Keplerian disks for Shakura-Sunyaev disks; thicker, sub-Keplerian disks for advection-dominated accretion flows; and slim disks which are consistent with previous popular analytical models. However, an inflow region and an outflow region always exist, except when the viscosity parameter α is too large, which supports the results of some recent numerical simulation works. Our results indicate that the outflows should be common in various accretion disks and may be stronger in slim disks, where both advection and radiation pressure are dominant. We also present the structure's dependence on the input parameters and discuss their physical meanings. The caveats of this work and possible improvements for the future are discussed.
118517819
Quasar candidate selection and photometric redshift estimation based on SDSS and UKIDSS data
We present a sample of 8498 quasars with both SDSS ugriz optical and UKIDSS Y JHK near-IR photometric data. With this sample, we obtain the median colour-z relations based on 7400 quasars with magnitude uncertainties less than 0.1mag in all bands. By analyzing the quasar colours, we propose an empirical criterion in the Y K vs. g z colour-colour diagram to separate stars and quasars with redshift z < 4, and two other criteria for selecting high redshift quasars. Using the SDSS-UKIDSS colourz relations, we estimate the photometric redshifts of 8498 SDSS-UKIDSS quasars, and find that 85.0% of them are consistent with the spectroscopic redshifts within |�z| < 0.2, which leads to a significant increase of the photometric redshift accuracy than that based on the SDSS colour-z relations only. As two tests, we compare our colour selection criterion with a small UKIDSS/EDR quasar/star sample and a sample of 4671 variable sources in the SDSS Stripe 82 region with both SDSS and UKIDSS data. We find that they can be clearly divided into two classes (quasars and stars) by our criterion in the Y K vs. g z plot. We select 3834 quasar candidates from the variable sources with g < 20.5 in Stripe 82, 826 of them being SDSS quasars and the rest without SDSS spectroscopy. We estimate the photometric redshifts for 3519 quasar candidates with all UKIDSS Y JHK data and find an accuracy of 87.5% within |�z| < 0.2 with the spectroscopic redshifts of 819 SDSS-UKIDSS identified quasars among them. We demonstrate that even at the same spectroscopy limit as SDSS, with our criterion we can at least partially recover the missing quasars with z � 2.7 in SDSS. The SDSS identified quasars only take a small fraction (21.5%) of our quasar candidates selected from the variable sources in Stripe 82, indicating that a deeper spectroscopy is very promising in producing a much larger sample of quasars than SDSS. The implications of our current results to the future Chinese LAMOST quasar survey are also discussed.
118446028
Z0 boson decays to $B^{(*)}_{c}$ meson and its uncertainties
The planned new e+e− collider with high luminosity shall provide another useful platform to study the properties of the doubly heavy Bc meson in addition to the hadronic colliders as LHC and TEVATRON. In the ‘New Trace Amplitude Approach’, we calculate the production of the spin-singlet Bc and the spin-triplet $B^{*}_{c}$ mesons through the Z0 boson decays, where uncertainties for the production are also discussed. Our results show $\varGamma_{(^{1}S_{0})}=81.4^{+102.1}_{-40.5}$ KeV and $\varGamma_{(^{3}S_{1})}=116.4^{+163.9}_{-62.8}$ KeV, where the errors are caused by varying mb and mc within their reasonable regions.
118684122
Hadronic production of $\Xi_{cc}$ at a fixed-target experiment at the LHC
In the paper, we present a detailed discussion on the $\Xi_{cc}$ production at a fixed target experiment at the LHC (After@LHC). The doubly charmed baryon $\Xi_{cc}$ is produced via the channel, ${\rm Proton} + {\rm Proton}\to\Xi_{cc}+X$. In estimating its hadroproduction, we discuss three dominant subprocesses, e.g. $g+g\to \Xi_{cc} +\bar{c} +\bar{c}$, $g+c\to \Xi_{cc}+\bar{c}$ and $c+c\to \Xi_{cc}+g$. During the production, it shall first generate a binding diquark and then form the $\Xi_{cc}$ baryon by grabbing soft light-quarks or gluons. We observe that both the two diquark configurations $(cc)[^3S_1]_{\bf\bar 3}$ and $(cc)[^1S_0]_{\bf 6}$ can have sizable contributions to the $\Xi_{cc}$ production. Large number of $\Xi_{cc}$ events can be generated at the After@LHC, whose total production cross section is larger than that of the SELEX experiment by about thirty-five times. It may also possible to study the properties of $\Xi_{bc}$ at the After@LHC. More specifically, we shall have about $8.3 \times 10^6$ $\Xi_{cc}$ events/year and $1.8 \times 10^4$ $\Xi_{bc}$ events/year when its integrated luminosity approaches to $2$ fb$^{-1}$/year. Thus, in addition to SELEX and LHC, the After@LHC shall provide another useful platform for studying the baryon properties.
53650025
Heavy pseudoscalar leading-twist distribution amplitudes within QCD theory in background fields
In this paper, we study the leading-twist distribution amplitude (DA) of the heavy pseudoscalars (HPs), such as $$\eta _c$$ηc, $$\eta _b$$ηb, and $$B_c$$Bc, within the QCD theory in the background fields. New sum rules up to dimension-six condensates for both the HP decay constants and their leading-twist DA moments are presented. From the sum rules for the HP decay constants, we obtain $$f_{\eta _c} = 453 \pm 4\, \text {MeV}$$fηc=453±4MeV, $$f_{B_c} = 498 \pm 14 \,\text {MeV}$$fBc=498±14MeV, and $$f_{\eta _b} = 811 \pm 34 \,\text {MeV}$$fηb=811±34MeV. Based on the sum rules for the HPs’ leading-twist DA moments, we construct a new model for the $$\eta _c$$ηc, $$\eta _b$$ηb, and $$B_c$$Bc leading-twist DAs. Our present HP DA model is also adaptable for the light pseudoscalar DAs, such as the pion and kaon DAs. Thus, it shall be applicable for a wide range of QCD exclusive processes. As an application, we apply the $$\eta _c$$ηc leading-twist DA to calculate the $$B_c \rightarrow \eta _c$$Bc→ηc transition form factor $$f_+^{B_c \rightarrow \eta _c}(q^2)$$f+Bc→ηc(q2). At the maximum recoil region, we obtain $$f_+^{B_c \rightarrow \eta _c}(0) = 0.612^{+0.053}_{-0.052}$$f+Bc→ηc(0)=0.612-0.052+0.053. Furthermore we predict the branching ratio for the semi-leptonic decay $$B_c \rightarrow \eta _c l \nu $$Bc→ηclν and obtain $$\mathcal{B}(B_c \rightarrow \eta _c l \nu )=\left( 7.70^{+1.65}_{-1.48}\right) \times 10^{-3}$$B(Bc→ηclν)=7.70-1.48+1.65×10-3 for massless leptons, which is consistent with the light-cone sum rules estimation obtained in the literature.
119299163
SU(f)(3)-symmetry breaking effects of the B ---> K transition form-factor in the QCD light-cone sum rules
We present an improved calculation of the B{yields}K transition form factor with a chiral current in the QCD light-cone sum rule approach. Under the present approach, the most uncertain twist-3 contribution is eliminated. And the contributions from the twist-2 and the twist-4 structures of the kaon wave function are discussed, including the SU{sub f}(3)-breaking effects. One-loop radiative corrections to the kaonic twist-2 contribution together with the leading-order twist-4 corrections are studied. The SU{sub f}(3)-breaking effect is obtained, (F{sub +}{sup B{r_reversible}}{sup K}(0)/F{sub +}{sup B{r_reversible}}{sup {pi}}(0))=1.16{+-}0.03. By combining the light-cone sum rule results with the newly obtained perturbative QCD results that have been calculated up to O(1/m{sub b}{sup 2}) by Wu, Huang, and Fang [Eur. Phys. J. C 52, 561 (2007)], we present a consistent analysis of the B{yields}K transition form factor in the large and intermediate energy regions.
118512890
Radiative Corrections on the B → P Form Factors with Chiral Current in the Light-Cone Sum Rules
Based on the approach of the vector form factor F(B ->pi,K)(+)(q(2)) in our previous papers, we extend the calculation of the radiative corrections to the B -> P (P stands pi, K, and all light pseudoscalar mesons) scalar and tensor form factors F(B -> P)(0,T)(q(2)) with chiral current in the light-cone sum rules (LCSRs). The most uncertain twist-3 contributions to the B -> P form factors can be naturally eliminated through a properly designed correlator. We present the next-leading-order formulas of F(B -> P)(+,0,T)(q(2)) with the b-quark pole mass that is universal. It has been shown that our results are simpler and less uncertain under the same parameter regions since we only need to calculate the next-leading order on the twist-2 part from the obtained LCSR. Second, we obtain f(B ->pi)(+,0)(0)=0.260(-0.040)(+0.059), f(B ->pi)(T)(0)=0.276(-0.039)(+0.052), f(B -> K)(+,0)(0)=0.334(-0.069)(+0.094), and f(B -> K)(T)(0)=0.379(-0.077)(+0.092) at q(2)=0 and the SU(f)(3)-breaking effects are discussed too.