Optimal Monetary Policy with Endogenous Entry and Product Variety

We show that deviations from long-run stability of product prices are optimal in the presence of endogenous producer entry and product variety in a sticky-price model with monopolistic competition in which price stability would be optimal in the absence of entry. Specifically, a long-run positive (negative) rate of inflation is optimal when the benefit of variety to consumers falls short of (exceeds) the market incentives for creating that variety under flexible prices, governed by the desired markup. Plausible preference specifications and parameter values justify a long-run inflation rate of two percent or higher. Price indexation implies even larger deviations from long-run price stability. However, price stability (around this non-zero trend) is close to optimal in the short run, even in the presence of time-varying flexible-price markups that distort the allocation of resources across time and states. The central bank uses its leverage over real activity in the long run, but not in the short run. Our results point to the need for continued empirical research on the determinants of markups and investigation of the benefit of product variety to consumers.

Triton binding energy calculated from the SU_6 quark-model nucleon-nucleon interaction

Properties of the three-nucleon bound state are examined in the Faddeev formalism, in which the quark-model nucleon-nucleon interaction is explicitly incorporated to calculate the off-shell T-matrix. The most recent version, fss2, of the Kyoto-Niigata quark-model potential yields the ground-state energy ^3H=-8.514 MeV in the 34 channel calculation, when the np interaction is used for the nucleon-nucleon interaction. The charge root mean square radii of the ^3H and ^3He are 1.72 fm and 1.90 fm, respectively, including the finite size correction of the nucleons. These values are the closest to the experiments among many results obtained by detailed Faddeev calculations employing modern realistic nucleon-nucleon interaction models.Comment: 10 pages, no figure

Magnetic phase diagram of a frustrated ferrimagnetic ladder: Relation to the one-dimensional boson Hubbard model

We study the magnetic phase diagram of two coupled mixed-spin $(1,{1/2})$ Heisenberg chains as a function of the frustration parameter related to diagonal exchange couplings. The analysis is performed by using spin-wave series and exact numerical diagonalization techniques. The obtained phase diagram--containing the Luttinger liquid phase, the plateau phase with a magnetization per rung $M=1/2$, and the fully polarized phase--is closely related to the generic $(J/U,\mu/U)$ phase diagram of the one-dimensional boson Hubbard model.Comment: 4 pages, 2 figure

Hybridization Mechanism for Cohesion of Cd-based Quasicrystals

Cohesion mechanism of cubic approximant crystals of newly discovered binary quasicrystals, Cd$_6$M (M=Yb and Ca), are studied theoretically. It is found that stabilization due to alloying is obtained if M is an element with low-lying unoccupied $d$ states. This leads to conclusion that the cohesion of the Cd-based compounds is due to the hybridization of the $d$ states of Yb and Ca with a wide $sp$ band. %unlike known stable quasicrystals without transition elements %such as Al-Li-Cu and Zn-Mg-RE (RE:rare earth). Although a diameter of the Fermi sphere coincides with the strong Bragg peaks for Cd-Yb and Cd-Ca, the Hume-Rothery mechanism does not play a principal role in the stability because neither distinct pseudogap nor stabilization due to alloying is obtained for isostructural Cd-Mg. In addition to the electronic origin, matching of the atomic size is very crucial for the quasicrystal formation of the Cd-based compounds. It is suggested that the glue atoms, which do not participate in the icosahedral cluster, play an important role in stabilization of the compound.Comment: 4 pages, 2 figure

Electronic structure and effects of dynamical electron correlation in ferromagnetic bcc-Fe, fcc-Ni and antiferromagnetic NiO

LDA+DMFT method in the framework of the iterative perturbation theory (IPT) with full LDA Hamiltonian without mapping onto the effective Wannier orbitals. We then apply this LDA+DMFT method to ferromagnetic bcc-Fe and fcc-Ni as a test of transition metal, and to antiferromagnetic NiO as an example of transition metal oxide. In Fe and Ni, the width of occupied 3d bands is narrower than those in LDA and Ni 6eV satellite appears. In NiO, the resultant electronic structure is of charge-transfer insulator type and the band gap is 4.3eV. These results are in good agreement with the experimental XPS. The configuration mixing and dynamical correlation effects play a crucial role in these results

A Realistic Description of Nucleon-Nucleon and Hyperon-Nucleon Interactions in the SU_6 Quark Model

We upgrade a SU_6 quark-model description for the nucleon-nucleon and hyperon-nucleon interactions by improving the effective meson-exchange potentials acting between quarks. For the scalar- and vector-meson exchanges, the momentum-dependent higher-order term is incorporated to reduce the attractive effect of the central interaction at higher energies. The single-particle potentials of the nucleon and Lambda, predicted by the G-matrix calculation, now have proper repulsive behavior in the momentum region q_1=5 - 20 fm^-1. A moderate contribution of the spin-orbit interaction from the scalar-meson exchange is also included. As to the vector mesons, a dominant contribution is the quadratic spin-orbit force generated from the rho-meson exchange. The nucleon-nucleon phase shifts at the non-relativistic energies up to T_lab=350 MeV are greatly improved especially for the 3E states. The low-energy observables of the nucleon-nucleon and the hyperon-nucleon interactions are also reexamined. The isospin symmetry breaking and the Coulomb effect are properly incorporated in the particle basis. The essential feature of the Lambda N - Sigma N coupling is qualitatively similar to that obtained from the previous models. The nuclear saturation properties and the single-particle potentials of the nucleon, Lambda and Sigma are reexamined through the G-matrix calculation. The single-particle potential of the Sigma hyperon is weakly repulsive in symmetric nuclear matter. The single-particle spin-orbit strength for the Lambda particle is very small, in comparison with that of the nucleons, due to the strong antisymmetric spin-orbit force generated from the Fermi-Breit interaction.Comment: Revtex v2.09, 69 pages with 25 figure

Differential Geometry of Group Lattices

In a series of publications we developed "differential geometry" on discrete sets based on concepts of noncommutative geometry. In particular, it turned out that first order differential calculi (over the algebra of functions) on a discrete set are in bijective correspondence with digraph structures where the vertices are given by the elements of the set. A particular class of digraphs are Cayley graphs, also known as group lattices. They are determined by a discrete group G and a finite subset S. There is a distinguished subclass of "bicovariant" Cayley graphs with the property that ad(S)S is contained in S. We explore the properties of differential calculi which arise from Cayley graphs via the above correspondence. The first order calculi extend to higher orders and then allow to introduce further differential geometric structures. Furthermore, we explore the properties of "discrete" vector fields which describe deterministic flows on group lattices. A Lie derivative with respect to a discrete vector field and an inner product with forms is defined. The Lie-Cartan identity then holds on all forms for a certain subclass of discrete vector fields. We develop elements of gauge theory and construct an analogue of the lattice gauge theory (Yang-Mills) action on an arbitrary group lattice. Also linear connections are considered and a simple geometric interpretation of the torsion is established. By taking a quotient with respect to some subgroup of the discrete group, generalized differential calculi associated with so-called Schreier diagrams are obtained.Comment: 51 pages, 11 figure

Optimal Monetary Policy with Endogenous Entry and Product Variety

We show that deviations from long-run stability of product prices are optimal in the presence of endogenous producer entry and product variety in a sticky-price model with monopolistic competition in which price stability would be optimal in the absence of entry. Specifically, a long-run positive (negative) rate of inflation is optimal when the benefit of variety to consumers falls short of (exceeds) the market incentives for creating that variety under flexible prices, governed by the desired markup. Plausible preference specifications and parameter values justify a long-run inflation rate of two percent or higher. Price indexation implies even larger deviations from long-run price stability. However, price stability (around this non-zero trend) is close to optimal in the short run, even in the presence of time-varying flexible-price markups that distort the allocation of resources across time and states. The central bank uses its leverage over real activity in the long run, but not in the short run. Our results point to the need for continued empirical research on the determinants of markups and investigation of the benefit of product variety to consumers.Entry, Optimal Inflation Rate, Price Stability, Product Variety, Ramsey-Optimal Monetary Policy