118942465
The Arches Cluster Mass Function
We have analyzed H- and Ks-band images of the Arches cluster obtained using the NIRC2 instrument on Keck with the laser guide star adaptive optics (LGS AO) system. With the help of the LGS AO system, we were able to obtain the deepest ever photometry for this cluster and its neighborhood and derive the background-subtracted present-day mass function down to 1.3 M☉ for the 5''-9'' annulus of the cluster. We find that the previously reported turnover at 6 M☉ is simply due to a local bump in the mass function (MF), and that the MF continues to increase down to our 50% completeness limit (1.3 M☉) with a power-law exponent of Γ = -0.91 for the mass range of 1.3 < M/M☉ < 50. Our numerical calculations for the evolution of the Arches cluster show that the Γ-values for our annulus increase by 0.1-0.2 during the lifetime of the cluster and thus suggest that the Arches cluster initially had Γ of -1.0 to 1.1, which is only slightly shallower than the Salpeter value.
16004057
Spatial diffusion of stars in the inner galactic bulge
Star formation in the inner few hundred parsecs of the Galactic bulge occurs in a flattened molecular layer called the central molecular zone (CMZ). It has been suggested that star formation in the CMZ has been sustained for the lifetime of the Galaxy and that the resulting agglomeration of stars formed in the CMZ has resulted in the prominent r-2 stellar density cusp at the Galactic center having about the same physical extent as the CMZ. This "central cusp" is somewhat less flat than the CMZ; thus, the population of stars formed in the CMZ appears to have diffused out to larger latitudes. We hypothesize that such vertical diffusion is driven by the scattering of stars off the giant molecular clouds (GMCs) in the CMZ and perform numerical simulations of the scattering between stars and GMCs in the presence of the nonaxisymmetric background potential. The simulation results show that the timescale for an initially flattened stellar population to achieve an aspect ratio of the observed OH/IR stars in the inner bulge, 1-2 Gyr, agrees well with the estimated age of those OH/IR stars.
14620141
Evolution of Debris of a Tidally Disrupted Star by a Massive Black Hole: Development of a Hybrid Scheme of the SPH and TVD Methods
The evolution of the stellar debris after tidal disruption due to the super massive black hole's tidal force is difficult to solve numerically because of the large dynamical range of the problem. We developed an SPH (Smoothed Particle Hydrodynamics) - TVD (Total Variation Diminishing) hybrid code in which the SPH is used to cover a widely spread debris and the TVD is used to compute the stream collision more accurately. While the code in the present form is not sufficient to obtain desired resoultion, it could provide a useful tool in studying the aftermath of the stellar disruption by a massive black hole.
119489565
Core-Collapse Times of Two-Component Clusters
We examine the corecollapse times of isolated, two-mass-component star clusters using Fokker-Planck models. With initial condition of Plummer models, we find that the corecollapse times of clusters with M_1/M_2 >> 1 are well correlated with (N_1/N_2)^{1/2}(m_1/m_2)^{2} t_{rh}, where M_1/M_2 and m_1/m_2 are the light to heavy component total and individual mass ratios, respectively, N_1/N_2 is the number ratio, and t_{rh} is the initial half-mass relaxation time scale. We also find two-component cluster parameters that best match multi-component (thus more realistic) clusters with power-law mass functions.
119456102
Theoretical isochrones with extinction in the K band. II. J - K versus K
ABSTRACT We calculate theoretical isochrones in a consistent way for five filter pairs near the J and K band atmospheric windows ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $J-K$ \end{document} , \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcom...
13909300
The Stream-Stream Collision after the Tidal Disruption of a Star around a Massive Black Hole
A star can be tidally disrupted around a massive black hole. It is known that the debris forms a precessing stream, which may collide with itself. The stream collision is a key process in determining the subsequent evolution of the stellar debris: if the orbital energy is efficiently dissipated, the debris will eventually form a circular disk (or torus). In this paper, we have numerically studied such a stream collision resulting from the encounter between a 106 M☉ black hole and a 1 M☉ normal star with a pericenter radius of 100 R☉. A simple treatment for radiative cooling has been adopted for both optically thick and optically thin regions. We have found that approximately 10% to 15% of the initial kinetic energy of the streams is converted into thermal energy during the collision. The spread in angular momentum of the incoming stream is increased by a factor of 2 to 3, and such an increase, together with the decrease in kinetic energy, significantly helps the circularization process. The initial luminosity burst produced by the collision may reach as high as 1041 ergs s-1 in 104 s, after which the luminosity increases again (but slowly this time) to a steady value of a few 1040 ergs s-1 in a few times 105 s. The radiation from the system is expected to be close to Planckian, with an effective temperature of ~105 K.
119097342
Torsion as a dynamic degree of freedom of quantum gravity
The gauge approach to gravity based on the local Lorentz group with a general independent affine connection A?cd is developed. We consider SO(1, 3) gauge theory with a Lagrangian quadratic in curvature as a simple model of quantum gravity. The torsion is proposed to represent a dynamic degree of freedom of quantum gravity at scales above the Planckian energy. The Einstein?Hilbert theory is induced as an effective theory due to quantum corrections of torsion via generating a stable gravito-magnetic condensate. We conjecture that torsion possesses an intrinsic quantum nature and can be confined.
16412418
Expanding (3+1)-dimensional universe from a lorentzian matrix model for superstring theory in (9+1) dimensions.
We reconsider the matrix model formulation of type IIB superstring theory in (9+1)-dimensional space-time. Unlike the previous works in which the Wick rotation was used to make the model well defined, we regularize the Lorentzian model by introducing infrared cutoffs in both the spatial and temporal directions. Monte Carlo studies reveal that the two cutoffs can be removed in the large-N limit and that the theory thus obtained has no parameters other than one scale parameter. Moreover, we find that three out of nine spatial directions start to expand at some "critical time," after which the space has SO(3) symmetry instead of SO(9).
119231020
Maximally supersymmetric Yang-Mills in five dimensions in light-cone superspace
We formulate maximally supersymmetric Yang-Mills theory in five dimensions in light-cone superspace. The light-cone Hamiltonian is of the quadratic form and the theory can be understood as an oxidation of the $ \mathcal{N} = 4 $ Super Yang-Mills Theory in four dimensions. We specifically study three-point counterterms and show how these counterterms vanish on-shell. This study is a preliminary to set up the technique in order to study possible four-point counterterms.
2032494
Deconfinement phase transition in N=4 super Yang-Mills theory on R x S3 from supersymmetric matrix quantum mechanics.
We test the recent claim that supersymmetric matrix quantum mechanics with mass deformation preserving maximal supersymmetry can be used to study N=4 super Yang-Mills theory on R x S{3} in the planar limit. When the mass parameter is large, we can integrate out all of the massive fluctuations around a particular classical solution, which corresponds to R x S{3}. The resulting effective theory for the gauge field moduli at finite temperature reproduces the deconfinement phase transition in N=4 super Yang-Mills theory on R x S{3} at weak coupling. This transition was speculated to be a continuation of the conjectured phase transition at strong coupling, which corresponds to the Hawking-Page transition based on the gauge-gravity duality. At strong coupling, one can study the target theory by the new simulation method for supersymmetric matrix quantum mechanics.
17174387
N-flation: Observable predictions from the random matrix mass spectrum
We carry out numerical investigations of the perturbations in N-flation models where the mass spectrum is generated by random matrix theory. The tensor-to-scalar ratio and non-Gaussianity are already known to take the single-field values, and so the density perturbation spectral index is the main parameter of interest. We study several types of random field initial conditions and compute the spectral index as a function of mass spectrum parameters. Comparison with microwave anisotropy data from the Wilkinson Microwave Anisotropy Probe shows that the model is currently viable in the majority of its parameter space.