Green's function method for strength function in three-body continuum

Practical methods to compute dipole strengths for a three-body system by using a discretized continuum are analyzed. New techniques involving Green's function are developed, either by correcting the tail of the approximate wave function in a direct calculation of the strength function or by using a solution of a driven Schroedinger equation in a summed expression of the strength. They are compared with the complex scaling method and the Lorentz integral transform, also making use of a discretized continuum. Numerical tests are performed with a hyperscalar three-body potential in the hyperspherical-harmonics formalism. They show that the Lorentz integral transform method is less practical than the other methods because of a difficult inverse transform. These other methods provide in general comparable accuracies.Comment: 22 pages, 8 figures, to appear in Progress of Theoretical Physic

Electric dipole response of 6^6He: Halo-neutron and core excitations

Electric dipole ($E1$) response of $^{6}$He is studied with a fully microscopic six-body calculation. The wave functions for the ground and excited states are expressed as a superposition of explicitly correlated Gaussians (CG). Final state interactions of three-body decay channels are explicitly taken into account. The ground state properties and the low-energy $E1$ strength are obtained consistently with observations. Two main peaks as well as several small peaks are found in the $E1$ strength function. The peak at the high-energy region indicates a typical macroscopic picture of the giant dipole resonance, the out-of-phase proton-neutron motion. The transition densities of the lower-lying peaks exhibit in-phase proton-neutron motion in the internal region, out-of-phase motion near the surface region, and spatially extended neutron oscillation, indicating a soft-dipole mode (SDM) and its vibrationally excited mode.Comment: 12 pages, 12 figures, to appear in Phys. Rev.

Alpha-cluster structure and density wave in oblate nuclei

Pentagon and triangle shapes in Si-28 and C-12 are discussed in relation with nuclear density wave. In the antisymmetrized molecular dynamics calculations, the $K^\pi=5^-$ band in Si-28 and the $K^\pi=3^-$ band in C-12 are described by the pentagon and triangle shapes, respectively. These negative-parity bands can be interpreted as the parity partners of the $K^\pi=0^+$ ground bands and they are constructed from the parity-asymmetric-intrinsic states. The pentagon and the triangle shapes originate in 7alpha and 3alpha cluster structures, respectively. In a mean-field picture, they are described also by the static one-dimensional density wave at the edge of the oblate states. In analysis with ideal alpha cluster models using Brink-Bloch cluster wave functions and that with a simplified model, we show that the static edge density wave for the pentagon and triangle shapes can be understood by spontaneous breaking of axial symmetry, i.e., the instability of the oblate states with respect to the edge density wave. The density wave is enhanced in the Z=N nuclei due to the proton-neutron coherent density waves, while it is suppressed in Z\ne N nuclei.Comment: 23 pages, 8 figure

16O+16O^{16}{\rm O} + ^{16}{\rm O} nature of the superdeformed band of 32S^{32}{\rm S} and the evolution of the molecular structure

The relation between the superdeformed band of $^{32}{\rm S}$ and $^{16}{\rm O} + ^{16}{\rm O}$ molecular bands is studied by the deformed-base antisymmetrized molecular dynamics with the Gogny D1S force. It is found that the obtained superdeformed band members of $^{32}{\rm S}$ have considerable amount of the $^{16}{\rm O} + ^{16}{\rm O}$ component. Above the superdeformed band, we have obtained two excited rotational bands which have more prominent character of the $^{16}{\rm O} + ^{16}{\rm O}$ molecular band. These three rotational bands are regarded as a series of $^{16}{\rm O} + ^{16}{\rm O}$ molecular bands which were predicted by using the unique $^{16}{\rm O}$ -$^{16}{\rm O}$ optical potentil. As the excitation energy and principal quantum number of the relative motion increase, the $^{16}{\rm O} + ^{16}{\rm O}$ cluster structure becomes more prominent but at the same time, the band members are fragmented into several states

Cosmic Neutrino Bound on the Dark Matter Annihilation Rate in the Late Universe

How large can the dark matter self-annihilation rate in the late universe be? This rate depends on (rho_DM/m_chi)^2 , where rho_DM/m_chi is the number density of dark matter, and the annihilation cross section is averaged over the velocity distribution. Since the clustering of dark matter is known, this amounts to asking how large the annihilation cross section can be. Kaplinghat, Knox, and Turner proposed that a very large annihilation cross section could turn a halo cusp into a core, improving agreement between simulations and observations; Hui showed that unitarity prohibits this for large dark matter masses. We show that if the annihilation products are Standard Model particles, even just neutrinos, the consequent fluxes are ruled out by orders of magnitude, even at small masses. Equivalently, to invoke such large annihilation cross sections, one must now require that essentially no Standard Model particles are produced.Comment: 4 pages, 2 figures; to appear in the proceedings of the TeV Particle Astrophysics II Workshop, Madison, Wisconsin, 28-31 Aug 200

Nucleon Flow and Fragment Flow in Heavy Ion Reactions

The collective flow of nucleons and that of fragments in the 12C + 12C reaction below 150 MeV/nucleon are calculated with the antisymmetrized version of molecular dynamics combined with the statistical decay calculation. Density dependent Gogny force is used as the effective interaction. The calculated balance energy is about 100 MeV/nucleon, which is close to the observed value. Below the balance energy, the absolute value of the fragment flow is larger than that of nucleon flow, which is also in accordance with data. The dependence of the flow on the stochastic collision cross section and its origin are discussed. All the results are naturally understood by introducing the concept of two components of flow: the flow of dynamically emitted nucleons and the flow of the nuclear matter which contributes to both the flow of fragments and the flow of nucleons due to the statistical decay.Comment: 20 pages, PostScript figures, LaTeX with REVTeX and EPSF, KUNS 121

Multifrequency Polarimetry of the Nrao 140 Jet: Possible Detection of a Helical Magnetic Field and Constraints on its Pitch Angle

We present results from multifrequency polarimetry of NRAO 140 using the Very Long Baseline Array. These observations allow us to reveal the distributions of both the polarization position angle and the Faraday rotation measure (RM). These distributions are powerful tools to discern the projected and line-of-sight components of the magnetic field, respectively. We find a systematic gradient in the RM distribution, with its sign being opposite at either side of the jet with respect to the jet axis. The sign of the RM changes only with the direction of the magnetic field component along the line of sight, so this can be explained by the existence of helical magnetic components associated with the jet itself. We derive two constraints for the pitch angle of the helical magnetic field from the distributions of the RM and the projected magnetic field; the RM distribution indicates that the helical fields are tightly wound, while that of the projected magnetic field suggests they are loosely wound around the jet axis. This inconsistency may be explained if the Faraday rotator is not cospatial with theemitting region. Our results may point toward a physical picture in which an ultra-relativistic jet (spine) with a loosely wound helical magnetic field is surrounded by a sub-relativistic wind layer (sheath) with a tightly wound helical magnetic field.Comment: 12 pages, 4 figures, ApJ, in pres

The {\alpha}-Decay Chains of the 287,288115^{287, 288}115 Isotopes using Relativistic Mean Field Theory

We study the binding energy, root-mean-square radius and quadrupole deformation parameter for the synthesized superheavy element Z = 115, within the formalism of relativistic mean field theory. The calculation is dones for various isotopes of Z = 115 element, starting from A = 272 to A = 292. A systematic comparison between the binding energies and experimental data is made.The calculated binding energies are in good agreement with experimental result. The results show the prolate deformation for the ground state of these nuclei. The most stable isotope is found to be 282115 nucleus (N = 167) in the isotopic chain. We have also studied Q{\alpha} and T{\alpha} for the {\alpha}-decay chains of $^{287, 288}$115.Comment: 12 Pages 6 Figures 3 Table