Ab initio calculation of Li7 photodisintegration

The Li7 total photoabsorption cross section is calculated microscopically. As nucleon-nucleon interaction the semi-realistic central AV4' potential with S- and P-wave forces is taken. The interaction of the final 7-nucleon system is fully taken into account via the Lorentz Integral Transform (LIT) method. For the calculation of the LIT we use expansions in hyperspherical harmonics (HH) in conjunction with the HH effective interaction (EIHH) approach. The convergence of the LIT expansion is discussed in detail. The calculated cross section agrees quite well with the available experimental data, which cover an energy range from threshold up to 100 MeV.Comment: 11 pages with 3 figure

Superfluid to insulator phase transition in a unitary Fermi gas

We study the evolution of the energy gap in a unitary Fermi gas as a function of temperature. To this end we approximate the Fermi gas by the Hubbard lattice Hamiltonian and solve using the dynamical mean-field approximation. We have found that below the critical temperature, Tc, the system is a superfluid and the energy gap is decreasing monotonously. For temperatures above Tc the system is an insulator and the corresponding energy gap is monotonously increasing.Comment: 4 pages,4 figure

Dynamical mean-field approximation for unitary Fermi gas

Dynamical mean-field approximation with explicit pairing is utilized to study the properties of a two-component Fermi gas at unitarity. The problem is approximated by the lattice Hubbard Hamiltonian, and the continuum limit is realized by diluting the lattice. We have found that at zero temperature the predictions of this theory for the energy and the pairing gap agree remarkably well with the results of full numerical Monte-Carlo simulations. Investigating the evolution of the system with temperature we identify the existence of a second order phase transition associated with a jump in the heat capacity and the collapse of the pairing gap.Comment: 4 pages, 3 figure

State Dependent Effective Interaction for the Hyperspherical Formalism with Noncentral Forces

The recently developed effective interaction method for the hyperspherical harmonic formalism is extended to noncentral forces. Binding energies and radii of three- and four-body nuclei are calculated with AV6 and AV14 NN potentials. Excellent results for the convergence of the expansion are found, particularly for the three-nucleon system. Due to the higher density the convergence rate is a bit slower for the alpha particle. In comparison to central potential models there is only a very slight deterioration of the convergence due the tensor force, while other potential terms have no visible effect on the convergence. The obtained values for binding energy and radii also agree well with the results in the literature obtained with other few-body techniques.Comment: LaTeX, 12 pages, 6 ps figures, Figures in correct order in this replacemen

Role of final state interaction and of three-body force on the longitudinal response function of 4He

We present an ab-initio calculation of the longitudinal electron scattering response function off 4He with two- and three-nucleon forces and compare to experimental data. The full four-body continuum dynamics is considered via the Lorentz integral transform method. The importance of the final state interaction is shown at various energies and momentum transfers q. The three-nucleon force reduces the quasi-elastic peak by 10% for q between 300 and 500 MeV/c. Its effect increases significantly at lower q, up to about 40% at q=100 MeV/c. At very low q, however, data are missing.Comment: 4 pages, 3 figures, corrected typos, shorter versio

B-orbits in abelian nilradicals of types B, C and D: towards a conjecture of Panyushev

Let $B$ be a Borel subgroup of a semisimple algebraic group $G$ and let $\mathfrak m$ be an abelian nilradical in $\mathfrak b={\rm Lie} (B)$. Using subsets of strongly orthogonal roots in the subset of positive roots corresponding to $\mathfrak m$, D. Panyushev \cite{Pan} gives in particular classification of $B-$orbits in $\mathfrak m$ and ${\mathfrak m}^*$ and states general conjectures on the closure and dimensions of the $B-$orbits in both $\mathfrak m$ and ${\mathfrak m}^*$ in terms of involutions of the Weyl group. Using Pyasetskii correspondence between $B-$orbits in $\mathfrak m$ and ${\mathfrak m}^*$ he shows the equivalence of these two conjectures. In this Note we prove his conjecture in types $B_n, C_n$ and $D_n$ for adjoint case.Comment: 12 page

A microscopic calculation of neutrino neutral reaction on 4He

An ab-initio calculation of the inelastic neutral reaction of neutrino on 4He is presented, including realistic nuclear force and full final state interaction among the four nucleons. The calculation uses the powerful combintation of the Lorentz integral transform (LIT) method and the hyperspherical-harmonic effective interaction approach (EIHH). The neutrino - nucleus interaction is taken in the impulse approximation. With respect to previous calculations, the current work predicts an increased reaction cross-section by 10%-30% for neutrino temperature up to 15 MeV.Comment: 3 pages, talk presented at the "19th European Conference on Few-Body Systems (EFB2004)", Groningen, Netherlands, August 23 - August 27, 200

Low-Energy Inelastic Neutrino Reactions on 4He

The inelastic scattering of neutrino off 4He is calculated microscopically at energies typical for core collapse supernova environment. The calculation is carried out with the Argonne V18 nucleon--nucleon potential and the Urbana IX three nucleon force. Full final state interaction is included via the Lorentz integral transform (LIT) method. The contribution of axial meson exchange currents to the cross sections is taken into account from effective field theory of nucleons and pions to order O(Q^3).Comment: 5 pages, 1 figure, corrected typos and added reference, submitted to Phys. Rev. Let