Spontaneous Breakdown of Lorentz Invariance in IIB Matrix Model

We study the IIB matrix model, which is conjectured to be a nonperturbative definition of superstring theory, by introducing an integer deformation parameter `nu' which couples to the imaginary part of the effective action induced by fermions. The deformed IIB matrix model continues to be well-defined for arbitrary `nu', and it preserves gauge invariance, Lorentz invariance, and the cluster property. We study the model at `nu' = infinity using a saddle-point analysis, and show that ten-dimensional Lorentz invariance is spontaneously broken at least down to an eight-dimensional one. We argue that it is likely that the remaining eight-dimensional Lorentz invariance is further broken, which can be checked by integrating over the saddle-point configurations using standard Monte Carlo simulation.Comment: 12 pages, latex, no figures, references added, version to appear in JHE

Feasibility of a storage ring for polar molecules in strong-field-seeking states

We show, through modeling and simulation, that it is feasible to construct a storage ring that will store dense bunches of strong-field-seeking polar molecules at 30 m/s (kinetic energy of 2K) and hold them, for several minutes, against losses due to defocusing, oscillations, and diffusion. The ring, 3 m in diameter, has straight sections that afford access to the stored molecules and a lattice structure that may be adapted for evaporative cooling. Simulation is done using a newly-developed code that tracks the particles, in time, through 400 turns; it accounts for longitudinal velocity changes as a function of external electric field, focusing and deflection nonlinearities, and the effects of gravity. An injector, decelerator, and source are included and intensities are calculated.Comment: 6 pages 5 figures, 3 table

"Liquidity Motives of Holding Money under Investment Risk: A Dynamic Analysis"

Jones and Ostroy (1984) argue that money,as an asset of the least transaction cost, offers exibility to its holder, which other assets cannot provide. We extend the idea of Jones and Ostroy into a truely dynamic framework of infinite horizon with a risk-neutral decision-maker. We then investigate the effect of an increase in investment risk on the demand for liquidity a la Jones and Ostroy. In particular, we prove that the opitmal strategy exists, that it has a reservation property, and that the reservation value increases when investment risk increases in the sense of a mean-preserving spread. While the effect of a mean-preserving spread on the reservation value is unambiguous, its e ect on money demand is ambiguous. We then provide conditions on increasing investment risk under which money demand unambiguously increases.

"Search under the Knightian Uncertainty"

Suppose that "uncertainty" about labor market conditions has increased. Does this change induce an unemployed worker to search longer, or shorter? This paper shows that the answer is drastically different depending on whether an increase in "uncertainty" is an increase in risk or that in true uncertainty in the sense of Frank Knight. We show in a general framework that, while an increase in risk (the mean-preserving spread of the wage distribution that the worker thinks she faces) increases the reservation wage, an increase in the Knightian uncertainty (a decrease in her confidence about the wage distribution) reduces it.

"Economics of Self-Feeding Fear"

A model of self-feeding fear is presented. Suppose that an economic agent is (1-ƒÃ)~100% certain that uncertainty she faces is characterized by a particular probability measure, but that she has a fear that, with ƒÃ~100% chance, her conviction is completely wrong and she is left perfectly ignorant about the true measure in the present as well as in the future. We call this situation ƒÃ-contamination of confidence. In this situation, if the economic agent follows Bayesian procedure or its variant, which is considered as rational in the theory of economics, her confidence erodes after having new observation.

"A Simple Axiomatization of Iterated Choquet Objectives"

A set of axioms which characterizes a preference representable by the iterated Choquet expected utility is presented. This objective function is attractive since it possesses a feature of dynamical consistency. Furthermore,we show that under the same axioms the conditional preference is represented by the Choquet expected utility with respect to the capacity which is updated according to the Dempster-Shafer rule. We do this by weakening Schmeidler's axiom of comonotonic independence to our axiom of constrained comonotonic independence and by adding the axiom of dynamical consistency.

"Distortion in Land Price Information---Mechanism in Sales Comparables and Appraisal Value Relation---"

This paper investigates the nature and magnitude of distortion in land price information publicly available in Japan, especially in the Published Land Price of the Japanese Government. After examining characteristics of various land price information in Japan, we construct hedonic price indexes based on both actual transaction prices and Published Land Prices, and compare them to find possible distortion in the governmental price information. We find a large and systematic discrepancy between actual transaction prices and Published Land Prices, suggesting serious problems in the governmental information system. We also consider possibility of structural change in the Japanese real estate markets, and examine its effect on price indexes.

"Does e-Commerce Always Increase Social Welfare in the Long Run?"

We examine the effect of electronic commerce ("e-commerce") on social welfare, in the framework of conventional spatial competition models. We consider the case where both conventional and electronic retailers coexist in equilibrium. We show that e-commerce does not necessarily increase social welfare in the long run. In particular, when electronic retailers have clear cost advantage over conventional retailers, then the advent of e-commerce is shown to reduce social welfare.

"An Axiomatic Approach to ƒÃ-contamination"

Suppose that an economic agent is (1|ƒÃ)~100% certain that uncertainty she faces is characterized by a particular probability measure, but that she has a fear that, with ƒÃ~100% chance, her conviction is completely wrong and she is left perfectly ignorant about the true measure in the present as well as in the future.This situation is often called "ƒÃ-contamination of con dence." The purpose of this paper is to provide a simple set of behavioral axioms under which the decision-maker's preference is represented by the Choquet expected utility with the ƒÃ-contamination of con dence.

"Irreversible Investment and Knightian Uncertainty"

When firms decide about irreversible investment, they may not have perfect confidence about their perceived probability measure describing future uncertainty. They may think other probability measures perturbed from the original one are also probable. Uncertainty characterized by not a single probability measure but a set of probability measures is called Knightian uncertainty. The effect of Knightian uncertainty on the value of irreversible investment opportunity is shown to be drastically different from that of the traditional uncertainty in the form of risk. Specifically, an increase in Knightian uncertainty decreases the value of investment opportunity while an increase in risk increases it.