16,318 research outputs found
Evolution of Star Clusters near the Galactic Center: Fully Self-consistent N-body Simulations
We have performed fully self-consistent -body simulations of star clusters
near the Galactic center (GC). Such simulations have not been performed because
it is difficult to perform fast and accurate simulations of such systems using
conventional methods. We used the Bridge code, which integrates the parent
galaxy using the tree algorithm and the star cluster using the fourth-order
Hermite scheme with individual timestep. The interaction between the parent
galaxy and the star cluster is calculate with the tree algorithm. Therefore,
the Bridge code can handle both the orbital and internal evolutions of star
clusters correctly at the same time. We investigated the evolution of star
clusters using the Bridge code and compared the results with previous studies.
We found that 1) the inspiral timescale of the star clusters is shorter than
that obtained with "traditional" simulations, in which the orbital evolution of
star clusters is calculated analytically using the dynamical friction formula
and 2) the core collapse of the star cluster increases the core density and
help the cluster survive. The initial conditions of star clusters is not so
severe as previously suggested.Comment: 19 pages, 19 figures, accepted for publication in Ap
Mathematical Structure of Rabi Oscillations in the Strong Coupling Regime
In this paper we generalize the Jaynes--Cummings Hamiltonian by making use of
some operators based on Lie algebras su(1,1) and su(2), and study a
mathematical structure of Rabi floppings of these models in the strong coupling
regime. We show that Rabi frequencies are given by matrix elements of
generalized coherent operators (quant--ph/0202081) under the rotating--wave
approximation.
In the first half we make a general review of coherent operators and
generalized coherent ones based on Lie algebras su(1,1) and su(2). In the
latter half we carry out a detailed examination of Frasca (quant--ph/0111134)
and generalize his method, and moreover present some related problems.
We also apply our results to the construction of controlled unitary gates in
Quantum Computation. Lastly we make a brief comment on application to Holonomic
Quantum Computation.Comment: Latex file, 24 pages. I added a new section (Quantum Computation), so
this paper became self-contained in a certain sens
Scalar Glueball--Quarkonium Mixing and the Structure of the QCD Vacuum
We use Ward identities of broken scale invariance to infer the amount of
scalar glueball-- meson mixing from the ratio of quark and gluon
condensates in the QCD vacuum. Assuming dominance by a single scalar state, as
suggested by a phase-shift analysis, we find a mixing angle , corresponding to near-maximal mixing of the glueball and
components.Comment: 7 pages, LaTe
BRIDGE: A Direct-tree Hybrid N-body Algorithm for Fully Self-consistent Simulations of Star Clusters and their Parent Galaxies
We developed a new direct-tree hybrid N-body algorithm for fully
self-consistent N-body simulations of star clusters in their parent galaxies.
In such simulations, star clusters need high accuracy, while galaxies need a
fast scheme because of the large number of the particles required to model it.
In our new algorithm, the internal motion of the star cluster is calculated
accurately using the direct Hermite scheme with individual timesteps and all
other motions are calculated using the tree code with second-order leapfrog
integrator. The direct and tree schemes are combined using an extension of the
mixed variable symplectic (MVS) scheme. Thus, the Hamiltonian corresponding to
everything other than the internal motion of the star cluster is integrated
with the leapfrog, which is symplectic. Using this algorithm, we performed
fully self-consistent N-body simulations of star clusters in their parent
galaxy. The internal and orbital evolutions of the star cluster agreed well
with those obtained using the direct scheme. We also performed fully
self-consistent N-body simulation for large-N models (). In
this case, the calculation speed was seven times faster than what would be if
the direct scheme was used.Comment: 12 pages, 13 figures, Accepted for PAS
The unitary-model-operator approach to nuclear many-body problems
Microscopic nuclear structure calculations have been performed within the
framework of the unitary-model-operator approach. Ground-state and
single-particle energies are calculated for nuclei around ^{14}C, ^{16}O and
^{40}Ca with modern nucleon-nucleon interactions.Comment: 6 pages, 4 figures, Talk presented at the International Symposium on
Correlation Dynamics in Nuclei (CDN05), Jan. 1 - Feb. 4, 2005, Tokyo, Japa
Remarks on the Collective Quantization of the SU(2) Skyrme Model
We point out the question of ordering momentum operator in the canonical
\break quantization of the SU(2) Skyrme Model. Thus, we suggest a new
definition for the momentum operator that may solve the infrared problem that
appears when we try to minimize the Quantum Hamiltonian.Comment: 8 pages, plain tex, IF/UFRJ/9
The unitary-model-operator approach to nuclear many-body problems
Microscopic nuclear structure calculations have been performed within the
framework of the unitary-model-operator approach. Ground-state and
single-particle energies are calculated for nuclei around ^{14}C, ^{16}O and
^{40}Ca with modern nucleon-nucleon interactions.Comment: 6 pages, 4 figures, Talk presented at the International Symposium on
Correlation Dynamics in Nuclei (CDN05), Jan. 1 - Feb. 4, 2005, Tokyo, Japa
The unitary-model-operator approach to nuclear many-body problems
Microscopic nuclear structure calculations have been performed within the
framework of the unitary-model-operator approach. Ground-state and
single-particle energies are calculated for nuclei around ^{14}C, ^{16}O and
^{40}Ca with modern nucleon-nucleon interactions.Comment: 6 pages, 4 figures, Talk presented at the International Symposium on
Correlation Dynamics in Nuclei (CDN05), Jan. 1 - Feb. 4, 2005, Tokyo, Japa
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