Effects of the Λ\Lambda(1405) on the Structure of Multi-Antikaonic Nuclei

The effects of the $\Lambda$(1405) ($\Lambda^\ast$) on the structure of the multi-antikaonic nucleus (MKN), in which several $K^-$ mesons are embedded to form deeply bound states, are considered based on chiral symmetry combined with a relativistic mean-field theory. It is shown that additional attraction resulting from the $\Lambda^\ast$ pole has a sizable contribution to not only the density profiles for the nucleons and $K^-$ mesons but also the ground state energy of the $K^-$ mesons and binding energy of the MKN as the number of the embedded $K^-$ mesons increases.Comment: 4 pages, 3 figures, Talk presented at the 10th International Conference on Hypernuclear and Strange Particle Physics (Hyp-X), Tokai, Japan, Sept. 14-18, 2009. To be published in Nucl. Phys.

Meson Condensations in High-Density Matter

Recent studies on meson condensations (pions and kaons) in high-density hadronic matter are reviewed. After summarizing onset mechanisms of pion and kaon condensations, we discuss implications for neutron star phenomena such as rapid cooling through neutrino emission, static and dynamic properties of neutron stars. Recent studies on coexistence problem of pion and kaon condensations are briefly introduced. Finally, relevance of meson condensations in hadronic matter to those in color superconductivity are briefly mentioned.Comment: 16 pages, 6 figures, proceedings of Finite Density QCD at Nara, July 10-12, 2003, Nara, Japa

D-branes on Three-dimensional Nonabelian Orbifolds

We study D-branes on a three complex dimensional nonabelian orbifold ${\bf C}^3/\Gamma$ with $\Gamma$ a finite subgroup of SU(3). We present general formulae necessary to obtain quiver diagrams which represent the gauge group and the spectrum of the D-brane worldvolume theory for dihedral-like subgroups $\Delta(3n^2)$ and $\Delta(6n^2)$. It is found that the quiver diagrams have a similar structure to webs of branes.Comment: 13 pages, LaTex, 2 figures, minor corrections, to appear in JHE

Monetary Policy and Learning from the Central Bank's Forecast

We examine the expectational stability (E-stability) of the rational expectations equilibrium (REE) in a simple New Keynesian model in which private agents engage in adaptive learning by referring to the central bank's forecast. In this environment, to satisfy the E-stability condition, the central bank must respond more strongly to the expected inflation rate than the so-called Taylor principle suggests. On the other hand, the central bank's strong reaction to the expected inflation rate raises the possibility of indeterminacy of the REE. In considering these problems, a robust policy is to respond to the current inflation rate to a certain degree.Adaptive Learning, E-stability, New Keynesian Model, Monetary Policy, Taylor principle

Productivity Growth, Transparency, and Monetary Policy

In this study, we investigate how central bank transparency about views on future productivity growth influences social welfare. To this end, we use a New Keynesian framework in which both the central bank and private agents are engaged in filtering problems regarding the persistence of productivity growth. Since the central bank and private agents do not know the true value of the signal-to-noise ratio, the gain parameters used in the filtering problems can be heterogeneous. If the central bank is not transparent, private agents must conjecture the central bank's estimate of the efficient level of the real interest rate. Under this setup, we show that central bank transparency does not necessarily improve social welfare. It can potentially yield a welfare loss, depending on (i) the gain parameters used by the central bank and private agents and (ii) private agents' conjecture on the gain parameter used by the central bank. If the central bank is uncertain about the combination of these gain parameters, it is sensible for the central bank to respond strongly to the variations of the inflation rate, because the misperceptions about these parameters become the source of demand shock.New Keynesian Model, Monetary Policy, Transparency, Productivity Growth, Learning

Stability of Quiver Representations and Topology Change

We study phase structure of the moduli space of a D0-brane on the orbifold C^3/Z_2 \times Z_2 based on stability of quiver representations. It is known from an analysis using toric geometry that this model has multiple phases connected by flop transitions. By comparing the results of the two methods, we obtain a correspondence between quiver representations and geometry of toric resolutions of the orbifold. It is shown that a redundancy of coordinates arising in the toric description of the D-brane moduli space, which is a key ingredient of disappearance of non-geometric phases, is understood from the monodromy around the orbifold point. We also discuss why only geometric phases appear from the viewpoint of stability of D0-branes.Comment: 16 pages, 7 figures, minor corrections, references adde