40,116 research outputs found
Monopole Excitation to Cluster States
We discuss strength of monopole excitation of the ground state to cluster
states in light nuclei. We clarify that the monopole excitation to cluster
states is in general strong as to be comparable with the single particle
strength and shares an appreciable portion of the sum rule value in spite of
large difference of the structure between the cluster state and the
shell-model-like ground state. We argue that the essential reasons of the large
strength are twofold. One is the fact that the clustering degree of freedom is
possessed even by simple shell model wave functions. The detailed feature of
this fact is described by the so-called Bayman-Bohr theorem which tells us that
SU(3) shell model wave function is equivalent to cluster model wave function.
The other is the ground state correlation induced by the activation of the
cluster degrees of freedom described by the Bayman-Bohr theorem. We
demonstrate, by deriving analytical expressions of monopole matrix elements,
that the order of magnitude of the monopole strength is governed by the first
reason, while the second reason plays a sufficient role in reproducing the data
up to the factor of magnitude of the monopole strength. Our explanation is made
by analysing three examples which are the monopole excitations to the
and states in O and the one to the state in C.
The present results imply that the measurement of strong monopole transitions
or excitations is in general very useful for the study of cluster states.Comment: 11 pages, 1 figure: revised versio
Hydrodynamics of Internal Shocks in Relativistic Outflows
We study the hydrodynamical effects of two colliding shells, adopted to model
internal shocks in various relativistic outflows such as gamma-ray bursts and
blazars. We find that the density profiles are significantly affected by the
propagation of rarefaction waves. A split-feature appears at the contact
discontinuity of the two shells. The shell spreading with a few ten percent of
the speed of light is also shown to be a notable aspect. The conversion
efficiency of the bulk kinetic energy to internal one shows deviations from the
widely-used inelastic two-point-mass-collision model. Observational
implications are also shortly discussed.Comment: 6 pages, 4 figures, Proceeding of International Symposium on High
Energy Gamma-ray Astronomy (July 26-30, 2004, Heidelberg, Germany
Chiral dynamics of -hyperons in the nuclear medium
Using SU(3) chiral perturbation theory we calculate the density-dependent
complex mean field of a -hyperon in
isospin-symmetric nuclear matter. The leading long-range -interaction arises from one-kaon exchange and from two-pion exchange with a
- or a -hyperon in the intermediate state. We find from the
conversion process at nuclear matter saturation density
fm an imaginary single-particle potential of
MeV, in fair agreement with existing empirical
determinations. The genuine long-range contributions from iterated (second
order) one-pion exchange with an intermediate - or -hyperon
sum up to a moderately repulsive real single-particle potential of
MeV. Recently measured ) inclusive spectra
related to -formation in heavy nuclei give evidence for a
-nucleus repulsion of similar size. Our results suggest that the net
effect of the short-range -interaction on the -nuclear mean
field could be small.Comment: 7 pages, 2 figures, published in: Phys. Rev. C 71, 068201 (2005
On the Riemannian Penrose inequality with charge and the cosmic censorship conjecture
We note an area-charge inequality orignially due to Gibbons: if the outermost
horizon in an asymptotically flat electrovacuum initial data set is
connected then , where is the total charge and
is the area radius of . A consequence of this inequality is that for
connected black holes the following lower bound on the area holds: . In conjunction with the upper bound which is expected to hold always, this implies the natural
generalization of the Riemannian Penrose inequality: .Comment: 4 pages; 1st revision, added a generalization, added a reference; 2nd
revision, minor correction
Modified Laplace transformation method and its application to the anharmonic oscillator
We apply a recently proposed approximation method to the evaluation of
non-Gaussian integral and anharmonic oscillator. The method makes use of the
truncated perturbation series by recasting it via the modified Laplace integral
representation. The modification of the Laplace transformation is such that the
upper limit of integration is cut off and an extra term is added for the
compensation. For the non-Gaussian integral, we find that the perturbation
series can give accurate result and the obtained approximation converges to the
exact result in the limit ( denotes the order of perturbation
expansion). In the case of anharmonic oscillator, we show that several order
result yields good approximation of the ground state energy over the entire
parameter space. The large order aspect is also investigated for the anharmonic
oscillator.Comment: 26 pages including tables, Late
Mott transition and ferrimagnetism in the Hubbard model on the anisotropic kagom\'e lattice
Mott transition and ferrimagnetism are studied in the Hubbard model on the
anisotropic kagom\'e lattice using the variational cluster approximation and
the phase diagram at zero temperature and half-filling is analyzed. The
ferrimagnetic phase rapidly grows as the geometric frustration is relaxed, and
the Mott insulator phase disappears in moderately frustrated region, showing
that the ferrimagnetic fluctuations stemming from the relaxation of the
geometric frustration is enhanced by the electron correlations. In metallic
phase, heavy fermion behavior is observed and mass enhancement factor is
computed. Enhancement of effective spatial anisotropy by the electron
correlations is also confirmed in moderately frustrated region, and its effect
on heavy fermion behavior is examined.Comment: 5 pages, 6 figure
A Parametric Study of the Acoustic Mechanism for Core-Collapse Supernovae
We investigate the criterion for the acoustic mechanism to work successfully
in core-collapse supernovae. The acoustic mechanism is an alternative to the
neutrino-heating mechanism. It was proposed by Burrows et al., who claimed that
acoustic waves emitted by -mode oscillations in proto-neutron stars (PNS)
energize a stalled shock wave and eventually induce an explosion. Previous
works mainly studied to which extent the -modes are excited in the PNS. In
this paper, on the other hand, we investigate how strong the acoustic wave
needs to be if it were to revive a stalled shock wave. By adding the acoustic
power as a new axis, we draw a critical surface, an extension of the critical
curve commonly employed in the context of neutrino heating. We perform both 1D
and 2D parametrized simulations, in which we inject acoustic waves from the
inner boundary. In order to quantify the power of acoustic waves, we use the
extended Myers theory to take neutrino reactions into proper account. We find
for the 1D simulations that rather large acoustic powers are required to
relaunch the shock wave, since the additional heating provided by the secondary
shocks developed from acoustic waves is partially canceled by the neutrino
cooling that is also enhanced. In 2D, the required acoustic powers are
consistent with those of Burrows et al. Our results seem to imply, however,
that it is the sum of neutrino heating and acoustic powers that matters for
shock revival.Comment: 20 pages, 19 figures, accepted by Ap
Metastability of R-Charged Black Holes
The global stability of R-charged AdS black holes in a grand canonical
ensemble is examined by eliminating the constraints from the action, but
without solving the equations of motion, thereby constructing the reduced
action of the system. The metastability of the system is found to set in at a
critical value of the chemical potential which is conjugate to the R-charge.
The relation among the small black hole, large black hole and the instability
is discussed. The result is consistent with the metastability found in the
AdS/CFT-conjectured dual field theory. The "renormalized" temperature of AdS
black holes, which has been rather ad hoc, is suggested to be the boundary
temperature in the sense of AdS/CFT correspondence. As a byproduct of the
analysis, we find a more general solution of the theory and its properties are
briefly discussed.Comment: 36 pages, 7 figures, v2 is the published version. the exposition is
made slightly shorter and hopefully cleare
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