16911559
Harmonic QPOs and Thick Accretion Disk Oscillations in BL Lac Object AO 0235 + 164
Periodic outbursts are observed in many AGNs and usually explained with a supermassive black hole binary (SMBHB) scenario. However, multiple periods are observed in some AGNs and cannot be explained with it. Here we analyze the periodicity of the radio light curves of AO 0235+164 at multi-frequencies and report the discovery of six QPOs in integer ratio 1:2:3:4:5:6 of QPO frequencies, of which the second with period P 2 = (5.46 ± 0.47) yr is the strongest. We fit the radio light curves and show that the initial phases of six QPOs have zero or π differences relative to each other. We suggest a harmonic relationship of QPOs. The centroid frequency, relative strength, harmonic relationship and relative initial phases of QPOs are independent of radio frequency. The harmonic QPOs are likely due to the quasi-periodic injection of plasma from an oscillating accretion disk into the jet. We estimate the supermassive black hole mass M BH ≃ (4.72 ± 2.04) × 10 8 M ⊙ and the accretion rate ˙ m ≃ 0.007. With the knowledge of accretion disk, it implies that the inner region of accretion disk of AO 0235+164 is a radiatively inefficient accretion flow. The oscillation accretion is due to the p-mode oscillation of the thick disk probably excited by a SMBHB. The theoretical predications of fundamental oscillation frequency and the harmonics are well consistent with the observations. Harmonic QPOs would be absent when the thick disk becomes geometrically thin due to the increase of accretion rate. We discuss the observations of AO 0235+164 basing on the SMBHB-thick disk oscillation scenario. – 2 –
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.
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.
199676816
Discovering the missing bright quasars at intermediate redshifts based on the optical/near-IR color selections
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.
62897747
Self-Consistency Requirements of the Renormalization Group for Setting the Renormalization Scale
In conventional treatments, predictions from fixed-order perturbative QCD calculations cannot be fixed with certainty due to ambiguities in the choice of the renormalization scale as well as the renormalization scheme. In this paper we present a general discussion of the constraints of the renormalization group (RG) invariance on the choice of the renormalization scale. We adopt the RG based equations, which incorporate the scheme parameters, for a general exposition of RG invariance, since they simultaneously express the invariance of physical observables under both the variation of the renormalization scale and the renormalization scheme parameters. We then discuss the self-consistency requirements of the RG, such as reflexivity, symmetry, and transitivity, which must be satisfied by the scale-setting method. The Principle of Minimal Sensitivity (PMS) requires the slope of the approximant of an observable to vanish at the renormalization point. This criterion provides a scheme-independent estimation, but it violates the symmetry and transitivity properties of the RG and does not reproduce the Gell-Mann-Low scale for QED observables. The Principle of Maximum Conformality (PMC) satisfies all of the deductions of the RG invariance - reflectivity, symmetry, and transitivity. Using the PMC, all non-conformal {βRi}-terms (R stands for an arbitrary renormalization scheme) in themore » perturbative expansion series are summed into the running coupling, and one obtains a unique, scale-fixed, scheme-independent prediction at any finite order. The PMC scales and the resulting finite-order PMC predictions are both to high accuracy independent of the choice of initial renormalization scale, consistent with RG invariance.« less
33191226
Fragmentation function and hadronic production of the heavy supersymmetric hadrons
The light top-squark $\widetilde{t}_1$ may be the lightest squark, and its lifetime may be ‘long enough’ in a kind of SUSY models that have not been ruled out yet experimentally, so colorless ‘supersymmetric hadrons (superhadrons)’ $(\widetilde{t}_1 \overline{q})$ (q is a quark excluding the t-quark) may be formed as long as the light top-squark $\widetilde{t}_1$ can be produced. The fragmentation function of $\widetilde{t}_1$ into heavy ‘supersymmetric hadrons (superhadrons)’ $(\widetilde{t}_1 \overline{Q})$ (Q̄=c̄ or b̄) and hadronic production of the superhadrons are investigated quantitatively. The fragmentation function is calculated precisely. Due to the difference in spin of the SUSY component, the asymptotic behavior of the fragmentation function is different from those of the existing ones. The fragmentation function is also applied to compute the production of heavy superhadrons at the hadronic colliders Tevatron and LHC in the so-called fragmentation approach. The resultant cross-section for the heavy superhadrons is too small to observe at Tevatron, but large enough at LHC, when all the relevant parameters in the SUSY models are taken within the favored region for the heavy superhadrons. The production of ‘light superhadrons’ $(\widetilde{t}_1 \overline{q})$ (q=u,d,s) is also roughly estimated with the same SUSY parameters. It is pointed out that the production cross-sections of the light superhadrons $(\widetilde{t}_1 \overline{q})$ may be much greater than those of the heavy superhadrons, so that even at Tevatron the light superhadrons may be produced in great quantities.
43275754
Eliminating the renormalization scale ambiguity for top-pair production using the principle of maximum conformality.
It is conventional to choose a typical momentum transfer of the process as the renormalization scale and take an arbitrary range to estimate the uncertainty in the QCD prediction. However, predictions using this procedure depend on the renormalization scheme, leave a nonconvergent renormalon perturbative series, and moreover, one obtains incorrect results when applied to QED processes. In contrast, if one fixes the renormalization scale using the principle of maximum conformality (PMC), all nonconformal {β(i)} terms in the perturbative expansion series are summed into the running coupling, and one obtains a unique, scale-fixed, scheme-independent prediction at any finite order. The PMC scale μ(R)(PMC) and the resulting finite-order PMC prediction are both to high accuracy independent of the choice of initial renormalization scale μ(R)(init), consistent with renormalization group invariance. As an application, we apply the PMC procedure to obtain next-to-next-to-leading-order (NNLO) predictions for the tt-pair production at the Tevatron and LHC colliders. The PMC prediction for the total cross section σ(tt) agrees well with the present Tevatron and LHC data. We also verify that the initial scale independence of the PMC prediction is satisfied to high accuracy at the NNLO level: the total cross section remains almost unchanged even when taking very disparate initial scales μ(R)(init) equal to m(t), 20m(t), and √s. Moreover, after PMC scale setting, we obtain A(FB)(tt)≃12.5%, A(FB)(pp)≃8.28% and A(FB)(tt)(M(tt)>450 GeV)≃35.0%. These predictions have a 1σ deviation from the present CDF and D0 measurements; the large discrepancy of the top quark forward-backward asymmetry between the standard model estimate and the data are, thus, greatly reduced.
118440734
Observational Constraints on Agegraphic Dark Energy
In this paper, we use the Type Ia supernova data as well as the CMB and LSS data to constrain the agegraphic dark energy model recently proposed by Cai. Due to its peculiar nature, the parameter $n$ of this model cannot be well constrained by the SNIa data, while the other parameter $\Omega_{m0}$ can be constrained to be $0.34\pm0.04$. When combined with CMB and LSS data, the range of $1\sigma$ confidence level for $n$ is greatly narrowed, albeit still very large. The best fit result is $\Omega_{m0}=0.28\pm0.02$, which is consistent with most observations like WMAP and SDSS, and $n=3.4$, of which a meaningful range of confidence level can not be obtained due to the fact that the contours are not closed. Despite of this result, we conclude that for $n>1$ this model is consistent with SNIa, CMB and LSS observations. Furthermore, the fitting results indicate a generalized definition for the agegraphic dark energy.
118447242
Heavy and light meson wavefunctions
We present a short review on the properties of heavy and light mesons’ light-cone wavefunctions (LCWFs), and their distribution amplitudes (DAs). The $$B$$B meson LCWFs can be treated by taking the heavy quark limit ($$m_b\rightarrow \infty $$mb→∞) and by using the heavy quark effective theory. Furthermore, we propose a simple model for the $$B$$B meson wavefunctions with 3-particle Fock states’ contributions, whose behaviors are controlled by two parameters $$\bar{\varLambda }$$Λ¯ and $$\delta $$δ. Using such model, the form factors $$F^{B\rightarrow \pi }_{+,0,{\text{T}}}$$F+,0,TB→π and $$F^{B\rightarrow K}_{+,0,{\text{T}}}$$F+,0,TB→K in large recoil region are studied up to $$\mathcal{O}(1/m_b^2)$$O(1/mb2) within the $$k_{{\mathrm{T}}}$$kT factorization approach. On the other hand, we adopt Brodsky-Huang-Lepage (BHL) prescription for constructing the WFs of the lighter pseudoscalars as $$\eta _c, D$$ηc,D-meson, pion, kaon, $$\eta ^{(\prime )}$$η(′) and etc. Such BHL-like model can be conveniently extended to construct the LCWFs for light scalar or vector mesons. Within such model the longitudinal distributions of those WFs are basically determined by a parameter $$B$$B, whose value can be determined via a global fit of experimental data.