198177313
Weighing black holes in the universe
The determination of the mass of black holes in our universe is crucial to understand their physics nature but is a great challenge to scientists. In this paper I briefly review some methods that are currently used to estimate the mass of black holes, especially those in X-ray binary systems and in galactic nuclei. Our recent progress in improving the mass estimates of supermassive black holes in active galactic nuclei by involving some empirical relations is presented. Finally I point out the similarities and common physics in Galactic black hole X-ray binaries and active galactic nuclei, and demonstrate that the black hole mass estimation is very much helpful to understand the accretion physics around black holes.
2377462
Galaxy bulge formation: Interplay with dark matter halo and central supermassive black hole
We present a simple scenario where the formation of galactic bulges was regulated by the dark halo gravity and regulates the growth of the central supermassive black hole. Assuming the angular momentum is low, we suggest that bulges form in a runaway collapse due to the "gravothermal" instability once the central gas density or pressure exceeds a certain threshold. We emphasize that the threshold is nearly universal, set by the background NFW dark matter gravity gDM ~ 1.2 × 10-8 cm s-2 in the central cusps of halos. Unlike known thresholds for gradual formation of galaxy disks, we show that the universal "halo-regulated" star formation threshold for spheroids matches the very high star formation rate and star formation efficiency seen in high-redshift observations of central starburst regions. The starburst feedback also builds up a pressure shortly after the collapse. This large pressure could act both outward to halt further infall of gas from larger scales and inward to counter the Compton-thick wind launched from the central black hole in an Eddington accretion. Assuming the feedback balances inward and outward forces, our scenario naturally gives rise to the black hole-bulge relationships observed in the local universe.
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.
199676816
Discovering the missing bright quasars at intermediate redshifts based on the optical/near-IR color selections
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.
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.
118371472
Holographic entanglement entropy and thermodynamic instability of planar R-charged black holes
The holographic entanglement entropy of an infinite strip subsystem on the asymptotic AdS boundary is used as a probe to study the thermodynamic instabilities of planar R-charged black holes (or their dual field theories). We focus on the single-charge AdS black holes in $D=5$, which correspond to spinning D3-branes with one non-vanishing angular momentum. Our results show that the holographic entanglement entropy indeed exhibits the thermodynamic instability associated with the divergence of the specific heat. When the width of the strip is large enough, the finite part of the holographic entanglement entropy as a function of the temperature resembles the thermal entropy, as is expected. As the width becomes smaller, however, the two entropies behave differently. In particular, there exists a critical value for the width of the strip, below which the finite part of the holographic entanglement entropy as a function of the temperature develops a self-intersection. We also find similar behavior in the single-charge black holes in $D=4$ and $7$.
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.
118477643
Revisiting the Twist-3 Distribution Amplitudes of $K$ Meson within the QCD Background Field Approach
In the present paper, we investigate the kaon twist-3 distribution amplitudes (DAs) Kp,σ within the QCD background field approach. The SUf (3)-breaking effects are studied in detail under a systematical way, especially the sum rules for the moments of Kp,σ are obtained by keeping all the mass terms in the s-quark propagator consistently. After adding all the uncertainties in quadrature, the first two Gegenbauler moments of Kp,σ are a1K,p(1 GeV) = − 0.376+0.103−0.148, a2K,p(1 GeV) = 0.701+0.481−0.491, a1K,σ(1 GeV) = −0.160+0.051−0.074, and a2K,σ(1 GeV) = 0.369+0.163−0.149, respectively. Their normalization parameters μpK|1 GeV = 1.188+0.039−0.043 GeV and μσK|1 GeV = 1.021+0.036−0.055 GeV. A detailed discussion on the properties of Kp,σ moments shows that the higher-order s-quark mass terms can indeed provide sizable contributions. Furthermore, based on the newly obtained moments, a model for the kaon twist-3 wavefunction ΨKp,σ (x, k⊥) with a better end-point behavior is constructed, which shall be useful for perturbative QCD calculations. As a byproduct, we make a discussion on the properties of the pion twist-3 DAs.
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.
118599552
Some mass relations for mesons and baryons in Regge phenomenology
In the quasilinear Regge trajectory ansatz, some useful linear mass inequalities, quadratic mass inequalities, and quadratic mass equalities are derived for mesons and baryons. Based on these relations, mass ranges of some mesons and baryons are given. The masses of bc and ss belonging to the pseudoscalar, vector, and tensor meson multiplets are also extracted. The J{sup P} of the baryon {xi}{sub cc}{sup +}(3520) is assigned to be (1/2){sup +}. The parameters of the (1/2){sup +} and (3/2){sup +} SU(4) baryon trajectories are extracted and the masses of the orbital excited baryons lying on the (1/2){sup +} and (3/2){sup +} trajectories are estimated. The J{sup P} assignments of baryons {xi}{sub c}(2980), {xi}{sub c}(3055), {xi}{sub c}(3077), and {xi}{sub c}(3123) are discussed. The predictions are in reasonable agreement with the existing experimental data and those suggested in many other different approaches. The mass relations and the predictions may be useful for the discovery of the unobserved meson and baryon states and the J{sup P} assignment of these states.