Supersymmetric Particle Production at HERA

In the framework of the minimal supersymmetric standard model and the $R$-parity breaking model, we investigate various production processes of the supersymmetric partner at HERA energies. Our emphasis is paid upon the scalar top quark, the partner of top quark, characterized by its lighter mass than the top quark and other scalar quarks in a model. We propose experimentally feasible approaches to search for clean signals of the stop from either its production or decay processes.Comment: 30 pages, LaTeX, 21 figures available upon reques

Nominal Exchange Rate Flexibility and Real Exchange Rate Adjustment: Evidence from Dual Exchange Rates in Developing Countries

This study investigates whether exchange rate flexibility aids real exchange rate adjustment based on intra-period data on dual exchange rates from developing countries. Specifically, it analyzes whether the flexible parallel market rate produces faster or slower real exchange rate adjustment than the much less flexible official rate does. Half-life estimates of adjustment speeds are obtained using fractional time series analysis. We find no systematic evidence that greater exchange rate flexibility tends to produce faster or slower real exchange rate adjustment, albeit there is substantial heterogeneity in speed estimates across countries. With officially pegged exchange rates, developing countries often use parallel exchange markets as a back-door channel to facilitate real exchange rate adjustment, but the empirical evidence suggests that these parallel markets in most cases fail to help promote real rate adjustment.real exchange rate, fractional time series, half life

On Cross-Country Differences in the Persistence of Real Exchange Rates

Previous findings of long-run purchasing power parity come mainly from data for industrial countries, raising the issue of whether the results suffer sample-selection bias and exaggerate the general relevance of parity reversion. This study uncovers substantial cross-country heterogeneity in the persistence of deviations from parity. The results show that it is more likely, rather than less likely, to find parity reversion for developing countries than industrial countries. Although some persistence variations may partly reflect country differences in structural characteristics such as inflation experience and government spending, a considerable portion of those variations seems unaccounted for.Parity deviations, cross-country persistence differences, structural deterterminants

A Reappraisal of the Border Effect on Relative Price Volatility

Engel and Rogers (1996) find that crossing the US-Canada border can considerably raise relative price volatility and that exchange rate fluctuations explain about one-third of the volatility increase. In re-evaluating the border effect, this study shows that cross-country heterogeneity in price volatility can lead to significant bias in measuring the border effect unless proper adjustment is made to correct it. The analysis explores the implication of symmetric sampling for border effect estimation. Moreover, using a direct decomposition method, two conditions governing the strength of the border effect are identified. In particular, the more dissimilar the price shocks are across countries, the greater the border effect will be. Decomposition estimates also suggest that exchange rate fluctuations actually account for a large majority of the border effect.price volatility, exchange rate volatility, national border, distance, dissimilar shocks

Possible Excess in Charged Current Events with High-Q^2 at HERA from Stop and Sbottom Production

We investigate a production process e^+p \to \st X \to \sb W^+ X at HERA, where we consider a decay mode \sb \to \bar{\nu}_e d of the sbottom in the framework of an R-parity breaking supersymmetric standard model. Both processes of the stop production e^+ d \to \st and the sbottom decay \sb \to \bar{\nu}_e d are originated from an R-parity breaking superpotential $\lambda'_{131} \hat{L}_1 \hat{Q}_3 \hat{D^c}_1$. One of signatures of the process should be a large missing transverse momentum plus multijet events corresponding to hadronic decays of the $W$. It is shown that the signal could appear as an event excess in the charged current (CC) processes $e^+p \to \nu X$ with the high $Q^2$ at HERA. We compare expected event distributions with the CC data recently reported by the H1 and ZEUS groups at HERA. Methods for extracting the signal from the standard CC processes are also discussed.Comment: 13 pages, LaTeX, 3 figure

Single scalar top production with polarized beams in ep collisions at HERA

From the point of view of the R-parity breaking supersymmetric model, we propose a scalar top (stop) search with longitudinally polarized electron (e-) and positron(e+) beams which will soon be available at the upgraded HERA. Fully polarized e- or e+ beams could produce the stop two times as much as unpolarized beams, while they increase background events due to the process of the standard model by about 30% in comparison with unpolarized ones. We show that right-handed e+ beams at HERA is efficient to produce the stop in the model. With 1 fb**(-1) of integrated luminosity we estimate reach in the coupling constant lambda'(131) for masses of the stop in the range 160-400 GeV. We can set a 95% confidence-level exclusion limit for lambda'(131) > 0.01-0.05 in the stop mass range of 240-280 GeV if no singal of the stop is observed. We also point out that y(=Q**2/sx) distributions of e+ coming from the stop shows the different behavior from those of the standard model.Comment: 12 pages, 6 eps figure

Trade Openness, Market Competition, and Inflation: Some Sectoral Evidence from OECD Countries

This study evaluates the role market competition plays in determining inflation based on sector-level data from OECD countries. In theory, trade openness can affect inflation through changes in market competitiveness and productivity. Nonetheless, previous empirical studies often fail to account for productivity effects, and their results may overstate the role of market competition. This study shows that inflation decreases with greater market competitiveness even after controlling for productivity effects. Indeed, when market competition and productivity effects are both accounted for, trade openness becomes insignificant in explaining inflation. The results support that changes in market competitiveness and productivity are the main channels through which trade openness affects inflation.trade openness, inflation, market structure, static panel, dynamic panel

Dissecting the PPP Puzzle: The Unconventional Roles of Nominal Exchange Rate and Price Adjustment

The conventional view, as expounded by sticky-price models, is that price adjustment determines the PPP reversion rate. This study examines the mechanism by which PPP deviations are corrected. Nominal exchange rate adjustment, not price adjustment, is shown to be the key engine governing the speed of PPP convergence. Moreover, nominal exchange rates are found to converge much more slowly than prices. With the reversion being driven primarily by nominal exchange rates, real exchange rates also revert at a slower rate than prices, as identified by the PPP puzzle (Rogoff, 1996).

Robust and real-time control of magnetic bearings for space engines

Currently, NASA Lewis Research Center is developing magnetic bearings for Space Shuttle Main Engine (SSME) turbopumps. The control algorithms which have been used are based on either the proportional-intergral-derivative control (PID) approach or the linear quadratic (LQ) state space approach. These approaches lead to an acceptable performance only when the system model is accurately known, which is seldom true in practice. For example, the rotor eccentricity, which is a major source of vibration at high speeds, cannot be predicted accurately. Furthermore, the dynamics of a rotor shaft, which must be treated as a flexible system to model the elastic rotor shaft, is infinite dimensional in theory and the controller can only be developed on the basis of a finite number of modes. Therefore, the development of the control system is further complicated by the possibility of closed loop system instability because of residual or uncontrolled modes, the so called spillover problem. Consequently, novel control algorithms for magnetic bearings are being developed to be robust to inevitable parametric uncertainties, external disturbances, spillover phenomenon and noise. Also, as pointed out earlier, magnetic bearings must exhibit good performance at a speed over 30,000 rpm. This implies that the sampling period available for the design of a digital control system has to be of the order of 0.5 milli-seconds. Therefore, feedback coefficients and other required controller parameters have to be computed off-line so that the on-line computational burden is extremely small. The development of the robust and real-time control algorithms is based on the sliding mode control theory. In this method, a dynamic system is made to move along a manifold of sliding hyperplanes to the origin of the state space. The number of sliding hyperplanes equals that of actuators. The sliding mode controller has two parts; linear state feedback and nonlinear terms. The nonlinear terms guarantee that the systems would reach the intersection of all sliding hyperplanes and remain on it when bounds on the errors in the system parameters and external disturbances are known. The linear part of the control drives the system to the origin of state space. Another important feature is that the controller parameter can be computed off-line. Consequently, on-line computational burden is small