Emergence of nuclear clustering in electric-dipole excitations of 6^6Li

Nuclear clustering plays an important role, especially in the dynamics of light nuclei. The importance of the emergence of the nuclear clustering was discussed in the recent measurement of the photoabsorption cross sections as it offered the possibility of the coexistence of various excitation modes which are closely related to the nuclear clustering. To understand the excitation mechanism, we study the electric-dipole ($E1$) responses of $^6$Li with a fully microscopic six-body calculation. The ground-state wave function is accurately described with a superposition of correlated Gaussian (CG) functions with the aid of the stochastic variational method. The final-state wave functions are also expressed by a number of the CG functions including important configurations to describe the six-body continuum states excited by the $E1$ field. We found that the out-of-phase transitions occur due to the oscillations of the valence nucleons against the $^4$He cluster at the low energies around 10 MeV indicating ``soft'' giant-dipole-resonance(GDR)-type excitations, which are very unique in the $^6$Li system but could be found in other nuclear systems. At the high energies beyond $\sim 30$ MeV typical GDR-type transitions occur. The $^3$He-$^3$H clustering plays an important role to the GDR phenomena in the intermediate energy regions around 20 MeV.Comment: 13 pages, 10 figure

Nuclear surface diffuseness revealed in nucleon-nucleus diffraction

Nuclear surface provides useful information on nuclear radius, nuclear structure as well as properties of nuclear matter. We discuss the relationship between the nuclear surface diffuseness and elastic scattering differential cross section at the first diffraction peak of high-energy nucleon-nucleus scattering as an efficient tool in order to extract the nuclear surface information from limited experimental data involving short-lived unstable nuclei. The high-energy reaction is described by a reliable microscopic reaction theory, the Glauber model. Extending the idea of the black sphere model, we find one-to-one correspondence between the nuclear bulk structure information and proton elastic scattering diffraction peak. This implies that we can extract both the nuclear radius and diffuseness simultaneously, using the position of the first diffraction peak and its magnitude of the elastic scattering differential cross section. We confirm the reliability of this approach by using realistic density distributions obtained by a mean-field model.Comment: 12 pages, 12 figures, to appear in Phys. Rev.

Evidence for <i>L</i>-dependence generated by channel coupling: ¹⁶O scattering from ¹²C at 115.9 MeV

Background: In earlier work, inversion of S matrix for 330 MeV 16O on 12C resulted in highly undulatory potentials; the S matrix resulted from the inclusion of strong coupling to states of projectile and target nuclei. L-independent S-matrix equivalent potentials for other explicitly L-dependent potentials have been found to be undulatory. Purpose: To investigate the possible implications of the undulatory dynamic polarization potential for an underlying L dependence of the 16O on 12C optical potential. Methods: S matrix to potential, SL → V (r), inversion which yields local potentials that reproduce the elastic channel S matrix of coupled channel (CC) calculations, will be applied to the S matrix for 115.9 MeV 16O on 12C. Further, SL for explicitly L-dependent potentials are inverted and the resulting L-independent potentials are characterized and compared with the undulatory potentials found for 16O on 12C. Results: Some of the undulatory features exhibited by the potentials modified by channel coupling for 115.9 MeV 16O on 12C can be simulated by simple parameterized L-dependent potentials. Conclusions: The elastic scattering of 16O by 12C is a particularly favorable case for revealing the effective L dependence of the potential modified by channel coupling. Nevertheless, there is no reason to suppose that undularity is not a generic property leading in many cases to the choice: nucleus-nucleus potentials are (i) smooth and L-dependent, (ii) L-independent and undulatory, or (iii) both

Neutrino Induced 4He Break-up Reaction -- Application of the Maximum Entropy Method in Calculating Nuclear Strength Function

The maximum entropy method is examined as a new tool for solving the ill-posed inversion problem involved in the Lorentz integral transformation (LIT) method. As an example, we apply the method to the spin-dipole strength function of 4He. We show that the method can be successfully used for inversion of LIT, provided the LIT function is available with a sufficient accuracy.Comment: 5 pages, 2 figures. Poster presented by TM at the International Workshop on Neutrino-Nucleus Interaction in the Few-GeV Region (NuInt15), Novenber 16-21 2015, Osaka, Japa

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