Anomalous shell effect in the transition from a circular to a triangular billiard

We apply periodic orbit theory to a two-dimensional non-integrable billiard system whose boundary is varied smoothly from a circular to an equilateral triangular shape. Although the classical dynamics becomes chaotic with increasing triangular deformation, it exhibits an astonishingly pronounced shell effect on its way through the shape transition. A semiclassical analysis reveals that this shell effect emerges from a codimension-two bifurcation of the triangular periodic orbit. Gutzwiller's semiclassical trace formula, using a global uniform approximation for the bifurcation of the triangular orbit and including the contributions of the other isolated orbits, describes very well the coarse-grained quantum-mechanical level density of this system. We also discuss the role of discrete symmetry for the large shell effect obtained here.Comment: 14 pages REVTeX4, 16 figures, version to appear in Phys. Rev. E. Qualities of some figures are lowered to reduce their sizes. Original figures are available at http://www.phys.nitech.ac.jp/~arita/papers/tricirc

Periodic-orbit approach to the nuclear shell structures with power-law potential models: Bridge orbits and prolate-oblate asymmetry

Deformed shell structures in nuclear mean-field potentials are systematically investigated as functions of deformation and surface diffuseness. As the mean-field model to investigate nuclear shell structures in a wide range of mass numbers, we propose the radial power-law potential model, V \propto r^\alpha, which enables a simple semiclassical analysis by the use of its scaling property. We find that remarkable shell structures emerge at certain combinations of deformation and diffuseness parameters, and they are closely related to the periodic-orbit bifurcations. In particular, significant roles of the "bridge orbit bifurcations" for normal and superdeformed shell structures are pointed out. It is shown that the prolate-oblate asymmetry in deformed shell structures is clearly understood from the contribution of the bridge orbit to the semiclassical level density. The roles of bridge orbit bifurcations in the emergence of superdeformed shell structures are also discussed.Comment: 20 pages, 23 figures, revtex4-1, to appear in Phys. Rev.

Transmission Phase of an Isolated Coulomb-Blockade Resonance

In two recent papers, O. Entin-Wohlman et al. studied the question: ``Which physical information is carried by the transmission phase through a quantum dot?'' In the present paper, this question is answered for an islolated Coulomb-blockade resonance and within a theoretical model which is more closely patterned after the geometry of the actual experiment by Schuster et al. than is the model of O. Entin-Wohlman et al. We conclude that whenever the number of leads coupled to the Aharanov-Bohm interferometer is larger than two, and the total number of channels is sufficiently large, the transmission phase does reflect the Breit-Wigner behavior of the resonance phase shift.Comment: 6 pages and one figur

Fast scintillation counter system and performance

An experimental study of the fast scintillation counter (FS) system to observe a shower disk structure at Mt. Norikura is described, especially the system performance and a pulse wave-form by a single charge particles. The photomultiplier tube (PT) pulse appears at the leading edge of the main pulse. To remove this PT-pulse from the main pulse, the frame of the scintillator vessel was changed. The fast triggering system was made to decrease the dead time which came from the use of the function of the self triggering of the storage oscilloscope (OSC). To provide a new field on the multi-parameter study of the cosmic ray showers, the system response of the FS system also improved as a result of many considerations

The structure of the shower disk observed at Mt. Norikura

The structure of the EAS shower disk, the arrival time distribution of charged particles at the core of the small or middle size shower, is measured at Mt. Norikura in Japan. Four fast scintillation counters with an area of 0.25 sq m and a fast trigger system are added to the Mt. Norikura EAS array for the study

Can Geometric Test Probe the Cosmic Equation of State ?

Feasibility of the geometric test as a probe of the cosmic equation of state of the dark energy is discussed assuming the future 2dF QSO sample. We examine sensitivity of the QSO two-point correlation functions, which are theoretically computed incorporating the light-cone effect and the redshift distortions, as well as the nonlinear effect, to a bias model whose evolution is phenomenologically parameterized. It is shown that the correlation functions are sensitive on a mean amplitude of the bias and not to the speed of the redshift evolution. We will also demonstrate that an optimistic geometric test could suffer from confusion that a signal from the cosmological model can be confused with that from a stochastic character of the bias.Comment: 11 pages, including 3 figures, accepted for publication in ApJ

Near Extremal Black Hole Entropy as Entanglement Entropy via AdS2/CFT1

We point out that the entropy of (near) extremal black holes can be interpreted as the entanglement entropy of dual conformal quantum mechanics via AdS2/CFT1. As an explicit example, we study near extremal BTZ black holes and derive this claim from AdS3/CFT2. We also analytically compute the entanglement entropy in the two dimensional CFT of a free Dirac fermion compactified on a circle at finite temperature. From this result, we clarify the relation between the thermal entropy and entanglement entropy, which is essential for the entanglement interpretation of black hole entropy.Comment: LaTeX, 32 pages, 7 figures; refinement in the organizatio

Novel phase transition and the pressure effect in YbFe2Al10-type CeT2Al10 (T=Fe, Ru, Os)

We have succeeded in growing single crystals of orthorhombic CeT2Al10 (T=Fe, Ru, Os) by Al self-flux method for the first time, and measured the electrical resistivity at pressures up to 8 GPa, the magnetic susceptibility and specific heat at ambient pressure. These results indicate that CeT2Al10 belongs to the heavy fermion compounds. CeRu2Al10 and CeOs2Al10 show a similar phase transition at T0 = 27.3 and 28.7 K, respectively. The temperature dependences in the ordered phases are well described by the thermally activated form, suggesting that partial gap opens over the Fermi surfaces below T0. When pressure is applied to CeRu2Al10, T0 disappears suddenly between 3 and 4 GPa, and CeRu2Al10 turns into a Kondo insulator, followed by a metal. The similarity of CeT2Al10 under respective pressures suggests a scaling relation by some parameter controlling the unusual physics in these compounds.Comment: 9 pages, 5 figure

Semiclassical theory of surface plasmons in spheroidal clusters

A microscopic theory of linear response based on the Vlasov equation is extended to systems having spheroidal equilibrium shape. The solution of the linearized Vlasov equation, which gives a semiclassical version of the random phase approximation, is studied for electrons moving in a deformed equilibrium mean field. The deformed field has been approximated by a cavity of spheroidal shape, both prolate and oblate. Contrary to spherical systems, there is now a coupling among excitations of different multipolarity induced by the interaction among constituents. Explicit calculations are performed for the dipole response of deformed clusters of different size. In all cases studied here the photoabsorption strength for prolate clusters always displays a typical double-peaked structure. For oblate clusters we find that the high--frequency component of the plasmon doublet can get fragmented in the medium size region ($N \sim 250$). This fragmentation is related to the presence of two kinds of three-dimensional electron orbits in oblate cavities. The possible scaling of our semiclassical equations with the valence electron number and density is investigated.Comment: 23 pages, 8 figures, revised version, includes discussion of scalin