Declining Rotation Curve and Brown Dwarf MACHOs

If the Galactic rotation speed at the Solar circle is $\sim 200$ km s$^{-1}$ or smaller, which is supported by several recent studies, the rotation curve of the Galaxy could be declining in the outermost region. Motivated by this, we investigate the effect of such declining rotation curve on the estimate of the MACHO mass and the fractional contribution of the MACHOs to the Galactic dark halo. Using Hernquist and Plummer halo models instead of the standard halo model, we find that the MACHO mass could be significantly smaller than that for the standard halo case. In particular, there exists a certain set of halo parameters for which the MACHO mass is 0.1$M_\odot$ or less and at the same time the MACHO contribution to the total mass of the halo is almost 100 %. This result indicates that a halo which consists solely of brown dwarfs can be consistent with both of the observed microlensing properties and the constraints from the rotation curve, provided the outer rotation curve is indeed declining.Comment: 8 pages and 4 figures, accepted for publication in ApJ Letter

J-Net Galactic Plane Survey of VLBI Radio Sources for VLBI Exploration of Radio Astrometry (VERA)

In order to search for new VLBI sources in the Galactic plane that can be used as phase reference sources in differential VLBI, we have conducted 22 GHz observations of radio sources in the Galactic plane using the Japanese VLBI Network (J-Net). We have observed 267 VLBI source candidates selected from existing radio surveys and have detected 93 sources at the signal-to-noise ratio larger than 5. While 42 of the 93 detected sources had already been detected with VLBI at relatively lower frequency (typically 2 to 8 GHz), the remaining 51 are found to be new VLBI sources detected for the first time. These VLBI sources are located within $|b|\le 5^\circ$, and have a large number of Galactic maser sources around them. Thus, they are potential candidates for phase reference sources for VLBI Exploration of Radio Astrometry (VERA), which is the first VLBI array dedicated to the phase referencing VLBI astrometry aiming at measuring the parallax and proper motion of maser sources in the whole Galaxy.Comment: to be published in PASJ (2000, Vol.52, No.5), 13 pages and 2 figure

Hot isostatic pressing of ceramics

A mixture containing glass 70 to 95 and BN or B4C powder (0.1-10 microns) 5 to 30 vol. % is used as a secondary pressure medium in hot isostatic pressing of ceramics. Thus, Pyrex beads were mixed with 15% vol. BN powder (average diameter 2 microns), fused at 1400 deg for 2 h, cooled, crushed, and put into a graphite crucible. A Si3N4 sintered body was embedded in the powder, heated in vacuum at 1200 deg for 2 h, treated in a hot isostatic press furnace at 1700 deg and 1000 atm. for 1 h, and cooled to give a Si3N4 ceramic. It was easily separated from the crucible

Pollution Tax under Lobbying Duopolists

We study a model which explains a politically determined pollution tax outcome under asymmetric duopoly. We assume an asymmetry of firms in the pollution emissions per unit of output. The polluting duopoly and three-stage political game are considered. We derive the equilibrium tax rate and show that it might excess the marginal external damages, even without an environmental group. The politically determined tax rate is decomposed to the marginal external damages, the imperfect competition effect, and the lobbying effect. Under linear demand and cost functions, we derive the condition that Pigouvian taxation is politically determined. The effect on the equilibrium tax of firm heterogeneity is discussed.Cournot duopoly, firm heterogeneity, lobbying activity, political economy, pollution tax

Local B-model Yukawa couplings from A-twisted correlators

Using the exact formula for the A-twisted correlation functions of the two dimensional $\mathcal{N}=(2,2)$ gauged linear sigma model, we reconsider the computation of the B-model Yukawa couplings of the local toric Calabi-Yau varieties. Our analysis is based on an exact result that has been evaluated from the supersymmetric localization technique and careful treatment of its application. We provide a detailed description of a procedure to investigate the local B-model Yukawa couplings and also test our prescription by comparing the results with known expressions evaluated from the local mirror symmetry approach. In particular, we find that the ambiguities of classical intersection numbers of a certain class of local toric Calabi-Yau varieties discovered previously can be interpreted as degrees of freedom of the twisted mass deformations.Comment: 29 pages, 7 figures. v2: minor changes. v3: minor changes, published versio

On the Flux Vacua in F-theory Compactifications

We study moduli stabilization of the F-theory compactified on an elliptically fibered Calabi-Yau fourfold. Our setup is based on the mirror symmetry framework including brane deformations. The complex structure moduli dependence of the resulting 4D N=1 effective theory is determined by the associated fourfold period integrals. By turning on appropriate G-fluxes, we explicitly demonstrate that all the complex structure moduli fields can be stabilized around the large complex structure point of the F-theory fourfold.Comment: 5 pages, v2: published versio

Determinantal Calabi-Yau varieties in Grassmannians and the Givental II-functions

We examine a class of Calabi-Yau varieties of the determinantal type in Grassmannians and clarify what kind of examples can be constructed explicitly. We also demonstrate how to compute their genus-0 Gromov-Witten invariants from the analysis of the Givental $I$-functions. By constructing $I$-functions from the supersymmetric localization formula for the two dimensional gauged linear sigma models, we describe an algorithm to evaluate the genus-0 A-model correlation functions appropriately. We also check that our results for the Gromov-Witten invariants are consistent with previous results for known examples included in our construction.Comment: 50 page