Dressing the Quark with QCD Condensates

A condensate of \pvec = 0 partons in the perturbative vacuum gives rise to a term $\propto\delta^4(p)$ in the free PQCD propagators. The leading condensate contribution to the quark propagator can be exactly summed since there is a factor $\delta^4(p)$ associated to each loop. We calculate the dressed quark propagator in the presence of either a gluon or a quark condensate, for a number of colors $N \to \infty$. The dressed quark propagator satisfies a Dyson-Schwinger type equation which can be exactly solved within our framework. In the case of a gluon condensate the dressed quark propagator has no pole, hence quarks cannot appear in asymptotic states, and moreover the DS equation has a solution which spontaneously breaks chiral symmetry. We also calculate the dressed quark-photon vertex and verify that the corresponding Ward-Takahashi identity is satisfied, and that the dressed self-energy correction to the photon propagator does not shift the physical photon pole.Comment: 17 pages, latex, 10 eps figure

Nominal Rigidities, Monetary Policy and Pigou Cycles

Based on a two sector dynamic new Keynesian model with sticky prices, this paper makes two contributions to the Pigou cycle literature. First, the paper quantifies the contribution of `news shocks' -- signals of future productivity changes. Maximum likelihood estimates indicate that nondurable sector news shocks are roughly as volatile as contemporary shocks; in the durable good sector, the standard deviation of news shocks is 1/4 that of contemporaneous shocks. Second, and perhaps more importantly, the paper shows that the estimated interest rule contributes to Pigou cycles arising from nondurable sector news shocks. In particular, the Ramsey-optimal policy does not exhibit Pigou cycles while the estimated policy rule does. With sticky prices, intermediate good producers set current prices based on expected future marginal cost. The news shock implies a lower future marginal cost, and so nondurable goods prices start falling immediately. The estimated interest rate rule then prescribes a lower nominal interest rate, and so a fall in both the real interest rate and user cost of durables. As a result, purchases of durables also rise. In contrast, the Ramsey-optimal policy requires a higher nominal interest rate because the Ramsey policy attempts to minimize the distortions associated with within-sector price dispersion. The resulting dynamics under the Ramsey policy are, then, essentially the opposite of those under the estimated policy. Put simply, Pigou cycles arise in the model precisely because the central bank accommodates them.Pigou cycles; monetary policy

Super-resolution imaging within reach

Although several optical techniques have been recently developed in order to overcome the resolution limit in microscopy, the imaging of sub-wavelength features is still a real challenge. In practise, super-resolution techniques remain difficult to build or are photo-toxic for the biological samples. However, microsphere-assisted microscopy has recently made super-resolution imaging accessible to scientists (e.g. optical metrologists, engineers and biologists). This paper presents an easy-to-implement optical setup to perform full-field and contactless super-resolution measurements of nanostructured media or biological elements. For this purpose, a classical microscope was enhanced by introducing a transparent microsphere. We show that this rather simple approach makes it possible to achieve a lateral resolution of 200 nm in air, i.e. the visualization of feature sizes of 100 nm

A Tale of Tax Policies in Open Economies

Recent financial crises in Europe as well as the periodic battles in the U.S. over the debt ceiling point to the importance of fiscal discipline among developed countries. This paper develops an open economy model, calibrated to the U.S. and a subset of the EMU, to evaluate the impact of various permanent tax changes. The first set of experiments considers a targeted one percentage point reduction in the government deficit-to-GDP ratio through raising one of: the consumption tax, the labor income tax, or the capital income tax. In terms of welfare, the consumption tax is found to be the least costly of the tax increases. A second set of experiments looks at deficit-neutral tax changes: partially replacing the capital income tax with either a higher labor income tax or higher consumption tax; and partially replacing the labor income tax with an increased consumption tax. Reducing reliance on capital income taxation is welfare-enhancing, although it leads to short term losses. Reducing labor income taxation improves international competitiveness and is welfare-improving.Fiscal policies, open economies, public deficits, tax reforms

Hypernovae as possible sources of Galactic positrons

INTEGRAL/SPI has recently observed a strong and extended emission resulting from electron-positron annihilation located in the Galactic center region, consistent with the Galactic bulge geometry, without any counterpart at high gamma-ray energies, nor in the 1809 keV $^{26}$Al decay line. In order to explain the rate of positron injection in the Galactic bulge, estimated to more than 10$^{43}$ s$^{-1}$, the most commonly considered positron injection sources are type Ia supernovae. However, SN Ia rate estimations show that those sources fall short to explain the observed positron production rate, raising a challenging question about the nature of the Galactic positron source. In this context, a possible source of Galactic positrons could be supernova events of a new type, as the recently observed SN2003dh/GRB030329, an exploding Wolf-Rayet star (type Ic supernova) associated with a hypernova/gamma-ray burst; the question about the rate of this kind of events remains open, but could be problematically low. In this paper, we explore the possibility of positron production and escape by such an event in the framework of an asymmetric model, in which a huge amount of $^{56}$Ni is ejected in a cone with a very high velocity; the ejected material becomes quickly transparent to positrons, which spread out in the interstellar medium.Comment: 8 pages, 2 figures. To appear in the Proceedings of the 5th INTEGRAL Workshop: "The INTEGRAL Universe", February 16-20, 2004, Munich, German

Infrastructure and economic growth in the Middle East and North Africa

This paper analyzes the impact of infrastructure on growth of total factor productivity and per capita income, using both growth accounting techniques and cross-country growth regressions. The two econometric techniques yield some consistent and some different results. Regressions based in the growth accounting framework suggest that electricity production helps explain cross-country differences in total factor productivity growth in the Middle East and North Africa region. Growth regressions support that conclusion, while also stressing an effect of telecommunications infrastructure. Finally, growth regressions also indicate quite consistently that the returns to infrastructure have been lower in the Middle East and North Africa region than in developing countries as a whole.Transport Economics Policy&Planning,Achieving Shared Growth,Economic Growth,E-Business,Energy Production and Transportation

Contingent Valuation of Competing Public Sector Programmes: An Experiment of Single versus Joint Evaluation

In this paper, we compare single and joint evaluation (JE) of competing public sector programmes in a contingent valuation exercise. Using survey data aimed at evaluating WTP for cancer interventions (n = 2628), we disantangle two types of effects of JE: informational effects and sequence effects. By the former, wemean: by presenting different programmes to respondents, they will acquire more information on each programme than they would if each programme was valued in isolation. Sequence effects are underisable and induced by the JE exercise itself: changing the order of the valuation sequence induces different WTP values.Our results show that there are informational effects but no sequence effects. We therefore argue that JE approaches can be added to the armoury of techniques aimed at designing better survey instruments in a way that induces informational effects without incurring problems of sequencing.Single Evaluation; Joint Evaluation Willingness to Pay; Contingent Valuation; Priorities Setting

Evidence That Obesity Risk Factor Potencies Are Weight Dependent, a Phenomenon That May Explain Accelerated Weight Gain in Western Societies

We have shown that individuals at the highest percentiles of the body mass index (BMI) distribution (i.e., most overweight) experience greater increases in body weight from sedentary lifestyle than those from the lowest percentiles. The purpose of the current analyses was to assess whether recent, accelerated increases in obesity could potentially be due to increased vulnerability to obesity risk factors as the population has become more overweight.Quantile regression was used to compare BMI population percentiles to obesity risk factors (lower education, diets characterized by high-meat/low-fruit content, parental adiposity) in two independent samples of men (N(1) = 3,513, N(2) = 11,365) and women (N(1) = 15,809, N(2) = 10,159). The samples were subsets of the National Walkers' (Study 1) and Runners' (Study 2) Health Studies whose physical activities fell short of nationally recommended activity levels. The data were adjusted for age, race, and any residual effects of physical activity. The regression slopes for BMI vs. education, diet, and family history became progressively stronger from the lowest (e.g., 5(th), 6(th)…) to the highest (e.g., …, 94(th), 95(th)) BMI percentiles. Compared to the 10(th) BMI percentile, their effects on the 90(th) BMI percentile were: 1) 2.7- to 8.6-fold greater in women and 2.0- to 2.4-fold greater in men for education; 2) 3.6- to 4.8-fold greater in women and 1.7- to 2.7-fold greater in men for diet; and 3) 2.0- to 2.6-fold greater in women and 1.7-fold greater in men for family history.Thus we propose risk factors that produce little weight gain in lean individuals may become more potent with increasing adiposity. This leads us to hypothesize that an individual's obesity is itself a major component of their obesogenic environment, and that, the cycle of weight gain and increased sensitivity to obesity risk factors may partly explain recent increases in obesity in western societies