Representative Democracy and Marginal Rate Progressive Income Taxation

This paper develops a political economy model that is consistent with the fact that democracies have a preference for increasing marginal tax rates on income. We present a model in which there is an exogenous set of political parties with preferences over the set of admissible tax schedules. This set contains virtually any increasing and piecewise linear continuous function. Each party decides whether or not to present a candidate for election. There is a fixed cost of running. The elected candidate implements one of her preferred tax policies. Our main results provide conditions under which a Strong Nash Equilibrium exists, and a tax schedule with increasing marginal tax rates is implemented in some Nash Equilibria and in any Strong Nash Equilibrium.REPRESENTATIVE DEMOCRACY; MARGINAL RATE PROGRESSIVE INCOME TAXATION.

Nuclear models on a lattice

We present the first results of a quantum field approach to nuclear models obtained by lattice techniques. Renormalization effects for fermion mass and coupling constant in case of scalar and pseudoscalar interaction lagrangian densities are discussed.Comment: 4 pages - 7 figures ; Invited talk to QCD 05: 12th International QCD Conference, 4-9 Jul 2005, Montpellier, France ; To appear in Nucl. Phys. B (Proc. Suppl.

Can realistic nuclear interactions tolerate a resonant tetraneutron ?

The possible existence of four-neutron resonances close to the physical energy region is explored. Faddeev-Yakubovsky equations have been solved in configuration space using realistic nucleon-nucleon interaction models. Complex Scaling and Analytical Continuation in the Coupling Constant methods were used to follow the resonance pole trajectories, which emerge out of artificially bound tetraneutron states. The final pole positions for four-neutron states lie in the third energy quadrant with negative real energy parts and should thus not be physically observable.Comment: 10 pages, 6 figs, 2 tables. To be published in Phys. Rev.

Testing Non-local Nucleon-Nucleon Interactions in the Four-Nucleon Systems

The Faddeev-Yakubovski equations are solved in configuration space for the $\alpha$-particle and n-$^3$H continuum states. We test the ability of nonlocal nucleon-nucleon interaction models to describe 3N and 4N systems.Comment: 16 pages, 6 figure

Description of 4^{4}He tetramer bound and scattering states

Faddeev-Yakubovski equations are solved numerically for 4He tetramer and trimer states using realistic helium-helium interaction models. We describe the properties of ground and excited states, and we discuss with a special emphasis the 4He-4He3 low energy scattering

Four-nucleon scattering: Ab initio calculations in momentum space

The four-body equations of Alt, Grassberger and Sandhas are solved for \nH scattering at energies below three-body breakup threshold using various realistic interactions including one derived from chiral perturbation theory. After partial wave decomposition the equations are three-variable integral equations that are solved numerically without any approximations beyond the usual discretization of continuum variables on a finite momentum mesh. Large number of two-, three- and four-nucleon partial waves are considered until the convergence of the observables is obtained. The total \nH cross section data in the resonance region is not described by the calculations which confirms previous findings by other groups. Nevertheless the numbers we get are slightly higher and closer to the data than previously found and depend on the choice of the two-nucleon potential. Correlations between the $A_y$ deficiency in \nd elastic scattering and the total \nH cross section are studied.Comment: Corrected Eq. (10

Yukawa model on a lattice: two body states

We present first results of the solutions of the Yukawa model as a Quantum Field Theory (QFT) solved non perturbatively with the help of lattice calculations. In particular we will focus on the possibility of binding two nucleons in the QFT, compared to the non relativistic result.Comment: 3 pages, talk at "IVth International Conference on Quarks and Nuclear Physics" (Madrid, June 2006

Damage analysis of masonry structures subjected to rockfalls

Masonry structures present substantial vulnerability to rockfalls. The methodologies for the damage quantification of masonry structures subjected to rockfalls are scarce. An analytical procedure for the damage assessment of masonry structures is presented. The procedure comprises three stages: (1) determination of the rockfall impact actions which are applied to a masonry structure, in terms of external forces, using the particle finite element method (PFEM), (2) evaluation of the mechanical properties, modelling of the masonry structure, and calculation of the internal stresses, using the finite element method (FEM), (3) assessment of the damage due to the rockfall actions, applying a failure criterion adapted to masonries, and calculation of the damage in terms of the percentage of the damaged wall surface. Three real rockfall events and their impact on buildings are analysed. A sensitivity analysis of the proposed procedure is then used to identify the variables that mostly affect the extent of the wall damage, which are the masonry width, the tensile strength, the block diameter and lastly, velocity

Low energy n-\nuc{3}{H} scattering : a novel testground for nuclear interaction

The low energy n-\nuc{3}{H} elastic cross sections near the resonance peak are calculated by solving the 4-nucleon problem with realistic NN interactions. Three different methods -- Alt, Grassberger and Shandas (AGS), Hyperspherical Harmonics and Faddeev-Yakubovsky -- have been used and their respective results are compared. We conclude on a failure of the existing NN forces to reproduce the n-\nuc{3}{H} total cross section.Comment: To be published in Phys. Rev.