40,844 research outputs found
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
Accurate numerical solution to the finite-size Dicke model
By using extended bosonic coherent states, a new technique to solve the Dicke
model exactly is proposed in the numerical sense. The accessible system size is
two orders of magnitude higher than that reported in literature. Finite-size
scaling for several observables, such as the ground-state energy, Berry phase,
and concurrence are analyzed. The existing discrepancy for the scaling exponent
of the concurrence is reconciled.Comment: 4 pages, 5 figures. Phys. Rev. A (in press, a Rapid Communication
Path integral Monte Carlo study of the interacting quantum double-well model: Quantum phase transition and phase diagram
The discrete time path integral Monte Carlo (PIMC) with a one-particle
density matrix approximation is applied to study the quantum phase transition
in the coupled double-well chain. To improve the convergence properties, the
exact action for a single particle in a double well potential is used to
construct the many-particle action. The algorithm is applied to the interacting
quantum double-well chain for which the zero-temperature phase diagram is
determined. The quantum phase transition is studied via finite-size scaling and
the critical exponents are shown to be compatible with the classical
two-dimensional (2D) Ising universality class -- not only in the order-disorder
limit (deep potential wells) but also in the displacive regime (shallow
potential wells).Comment: 17 pages, 7 figures; Accepted for publication in Phys. Rev.
Multipartite Entanglement Measures and Quantum Criticality from Matrix and Tensor Product States
We compute the multipartite entanglement measures such as the global
entanglement of various one- and two-dimensional quantum systems to probe the
quantum criticality based on the matrix and tensor product states (MPSs/TPSs).
We use infinite time-evolving block decimation (iTEBD) method to find the
ground states numerically in the form of MPSs/TPSs, and then evaluate their
entanglement measures by the method of tensor renormalization group (TRG). We
find these entanglement measures can characterize the quantum phase transitions
by their derivative discontinuity right at the critical points in all models
considered here. We also comment on the scaling behaviors of the entanglement
measures by the ideas of quantum state renormalization group transformations.Comment: 22 pages, 11 figure
Perturbation theorems for Hele-Shaw flows and their applications
In this work, we give a perturbation theorem for strong polynomial solutions
to the zero surface tension Hele-Shaw equation driven by injection or suction,
so called the Polubarinova-Galin equation. This theorem enables us to explore
properties of solutions with initial functions close to but are not polynomial.
Applications of this theorem are given in the suction or injection case. In the
former case, we show that if the initial domain is close to a disk, most of
fluid will be sucked before the strong solution blows up. In the later case, we
obtain precise large-time rescaling behaviors for large data to Hele-Shaw flows
in terms of invariant Richardson complex moments. This rescaling behavior
result generalizes a recent result regarding large-time rescaling behavior for
small data in terms of moments. As a byproduct of a theorem in this paper, a
short proof of existence and uniqueness of strong solutions to the
Polubarinova-Galin equation is given.Comment: 25 page
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