85,133 research outputs found
An accretion model for the growth of the central black hole associated with ionization instability in quasars
A possible accretion model associated with the ionization instability of
quasar disks is proposed to address the growth of the central black hole
harbored in the host galaxy.The mass ratio between black hole and its host
galactic bulge is a nature consequence of our model.Comment: submitted to ApJ, 15 page
Density oscillations in trapped dipolar condensates
We investigated the ground state wave function and free expansion of a
trapped dipolar condensate. We find that dipolar interaction may induce both
biconcave and dumbbell density profiles in, respectively, the pancake- and
cigar-shaped traps. On the parameter plane of the interaction strengths, the
density oscillation occurs only when the interaction parameters fall into
certain isolated areas. The relation between the positions of these areas and
the trap geometry is explored. By studying the free expansion of the condensate
with density oscillation, we show that the density oscillation is detectable
from the time-of-flight image.Comment: 7 pages, 9 figure
On the origin of kinematic distribution of the sub-parsec young stars in the Galactic center
Within a half-parsec from the Galactic center (GC), there is a population of
coeval young stars which appear to reside in a coherent disk. Surrounding this
dynamically-cool stellar system, there is a population of stars with a similar
age and much larger eccentricities and inclinations relative to the disk. We
propose a hypothesis for the origin of this dynamical dichotomy. Without
specifying any specific mechanism, we consider the possibility that both
stellar populations were formed within a disk some 6 Myr ago. But this orderly
structure was dynamically perturbed outside-in by an intruding object with a
mass ~10^4 Msun, which may be an intermediate-mass black hole (IMBH) or a dark
stellar cluster hosting an IMBH. We suggest that the perturber migrated inward
to ~0.15-0.3pc from the GC under the action of dynamical friction. Along the
way, it captured many stars in the outer disk region into its mean-motion
resonance, forced them to migrate with it, closely encountered with them, and
induced the growth of their eccentricity and inclination. But stars in the
inner regions of the disk retain their initial coplanar structure. We predict
that some of the inclined and eccentric stars surrounding the disk may have
similar Galactocentric semimajor axis. Future precision determination of their
kinematic distribution of these stars will not only provide a test for this
hypothesis but also evidences for the presence of an IMBH or a dark cluster at
the immediate proximity of the massive black hole at the GC. (abridged)Comment: 14 pages, including 13 figures, typo corrected, reference added, ApJ
in pres
Black Holes in Higher-Derivative Gravity
Extensions of Einstein gravity with higher-order derivative terms arise in
string theory and other effective theories, as well as being of interest in
their own right. In this paper we study static black-hole solutions in the
example of Einstein gravity with additional quadratic curvature terms. A
Lichnerowicz-type theorem simplifies the analysis by establishing that they
must have vanishing Ricci scalar curvature. By numerical methods we then
demonstrate the existence of further black-hole solutions over and above the
Schwarzschild solution. We discuss some of their thermodynamic properties, and
show that they obey the first law of thermodynamics.Comment: Typos corrected, discussion added, figure changed. 4 pages, 6 figure
Spectrum-generating Symmetries for BPS Solitons
We show that there exist nonlinearly realised duality symmetries that are
independent of the standard supergravity global symmetries, and which provide
active spectrum-generating symmetries for the fundamental BPS solitons. The
additional ingredient, in any spacetime dimension, is a single scaling
transformation that allows one to map between BPS solitons with different
masses. Without the inclusion of this additional transformation, which is a
symmetry of the classical equations of motion, but not the action, it is not
possible to find a spectrum-generating symmetry. The necessity of including
this scaling transformation highlights the vulnerability of duality multiplets
to quantum anomalies. We argue that fundamental BPS solitons may be immune to
this threat.Comment: References added. Latex, 29 page
Lichnerowicz Modes and Black Hole Families in Ricci Quadratic Gravity
A new branch of black hole solutions occurs along with the standard
Schwarzschild branch in -dimensional extensions of general relativity
including terms quadratic in the Ricci tensor. The standard and new branches
cross at a point determined by a static negative-eigenvalue eigenfunction of
the Lichnerowicz operator, analogous to the Gross-Perry-Yaffe eigenfunction for
the Schwarzschild solution in standard dimensional general relativity.
This static eigenfunction has two r\^oles: both as a perturbation away from
Schwarzschild along the new black-hole branch and also as a threshold unstable
mode lying at the edge of a domain of Gregory-Laflamme-type instability of the
Schwarzschild solution for small-radius black holes. A thermodynamic analogy
with the Gubser and Mitra conjecture on the relation between quantum
thermodynamic and classical dynamical instabilities leads to a suggestion that
there may be a switch of stability properties between the old and new
black-hole branches for small black holes with radii below the branch crossing
point.Comment: 33 pages, 8 figure
Dilatonic p-brane solitons
We find new 4-brane and 5-brane solitons in massive gauged , and
, supergravities. In each case, the solutions preserve half of the
original supersymmetry. These solutions make use of the metric and dilaton
fields only. We also present more general dilatonic -branes in
dimensions.Comment: 9 pages, Latex, no figure
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