Eikonalized mini-jet cross-sections in γγ\gamma \gamma collisions

In this note we assess the validity and uncertainties in the predictions of the eikonalised mini-jet model for $\sigma^{inel}_{\gamma \gamma}$. We are able to find a choice of parameters where the predictions are compatible with the current data. Even for this restricted range of parameters the predictions at the high c.m. energies, which can be reached at the TeV energy $e^+e^-$ colliders, differ by about $\pm 25\%$. LEP 2 data can help pinpoint these parameters and hence reduce the uncertainties in the predictions.Comment: 5 pages, latex, requires epsfig.sty, a4wide.sty, full ps file available at http://hpteor.lnf.infn.it/pancheri/lc2000.p

Photon-Photon total inelastic cross-section

We discuss predictions for the total inelastic gamma-gamma cross-section and their model dependence on the input parameters. We compare results from a simple extension of the Regge Pomeron exchange model as well as predictions from the eikonalized mini-jet model with recent LEP data.Comment: 7 pages, LateX, 2 eps figures. Talk presented at Photon'97, Egmond aan Zee, May 199

Interpreting the ERM Crisis: Country-Specific and Systemic Issues

Most interpretations of the Exchange Rate Mechanism crisis in 1992-93 ignore the key role played by structural policy spillovers among European countries, and overlook the effects of coordination (or lack thereof) of monetary and exchange rate policies among the countries making up the periphery of the system. This paper provides a simple analytical framework, able to encompass the recent literature on currency crises, while developing it by bringing out the decisive role of the strategic interactions among national policy makers in a multi-country monetary and exchange rate game. In contrast to an approach that focuses exclusively on country-specific issues, a systemic view is ultimately able to unravel more coherently, and more convincingly, the "puzzles" of the ERM crisis.

System-size convergence of point defect properties: The case of the silicon vacancy

We present a comprehensive study of the vacancy in bulk silicon in all its charge states from 2+ to 2-, using a supercell approach within plane-wave density-functional theory, and systematically quantify the various contributions to the well-known finite size errors associated with calculating formation energies and stable charge state transition levels of isolated defects with periodic boundary conditions. Furthermore, we find that transition levels converge faster with respect to supercell size when only the Gamma-point is sampled in the Brillouin zone, as opposed to a dense k-point sampling. This arises from the fact that defect level at the Gamma-point quickly converges to a fixed value which correctly describes the bonding at the defect centre. Our calculated transition levels with 1000-atom supercells and Gamma-point only sampling are in good agreement with available experimental results. We also demonstrate two simple and accurate approaches for calculating the valence band offsets that are required for computing formation energies of charged defects, one based on a potential averaging scheme and the other using maximally-localized Wannier functions (MLWFs). Finally, we show that MLWFs provide a clear description of the nature of the electronic bonding at the defect centre that verifies the canonical Watkins model.Comment: 10 pages, 6 figure

The "Mystery of the Printing Press" Monetary Policy and Self-fulfilling Debt Crises

Sovereign debt crises may be driven by either self-fulfilling expectations of default or fundamental fiscal stress. This paper studies the mechanisms by which either conventional or unconventional monetary policy can rule out the former. Conventional monetary policy is modelled as a standard choice of inflation, while unconventional policy as outright purchases in the debt market. By intervening in the sovereign debt market, the central bank effectively swaps risky government paper for monetary liabilities only exposed to inflation risk and thus yielding a lower interest rate. We show that, provided fiscal and monetary authorities share the same objective function, there is a minimum threshold for the size of interventions at which a backstop rules out self-fulfilling default without eliminating the possibility of fundamental default under fiscal stress. Fundamental default risk does not generally undermine the credibility of a backstop, nor does it foreshadow runaway inflation, even when the central bank is held responsible for its own losses

Debt Sustainability and the Terms of Official Support

We study theoretically and quantitatively how official lending regimes affect a government's decision to raise saving as opposed to defaulting, and its implication for sovereign bond pricing by investors. We reconsider debt sustainability in the face of both output and rollover risk under two types of institutional bailouts: one based on long-maturity, low-spread loans similar to the ones offered by the euro area official lenders; the other, on shorter maturity and high-spread loans, close to the International Monetary Fund standards. We show that official lending regimes raise the stock of safe debt and facilitate consumption smoothing through debt reduction. However, to the extent that bailouts translates into higher future debt stocks and countercyclical deficits in persistent recessions, they also have countervailing effects on sustainability. Quantitatively, the model is able to replicate Portuguese debt and spread dynamics in the years of the bailout after 2011. We show that, depending on the composition of debt by maturity and official lending, sustainable debt levels can vary between 50% of GDP and 180% of GDP depending on the state of the economy and the conditions for market access. Longer maturities have a stronger effect on sustainability than lower spreads

Mini-jet Total Cross-sections and Overlap Functions through Bloch-Nordsieck Summation

Predictions for total inelastic cross-sections for photon induced processes are discussed in the context of the QCD-inspired minijet model. Large theoretical uncertainties exist, some of them related to the parton distributions of hadrons in impact parameter space. A model for such distribution is presented, based on soft gluon summation. This model incorporates (the salient features of distributions obtained from) the intrinsic transverse momentum behaviour of hadrons. Under the assumption that the intrinsic behaviour is dominated by soft gluon emission stimulated by the scattering process, the b-spectrum becomes softer and softer as the scattering energy increases. In minijet models for the inclusive cross-sections, this will counter the increase from $\sigma_{jet}$ .Comment: 11 pages, two postscript figures, latex, uses epsfig.sty, a4wide.sty full postscript file of the paper is available at http://hpteor.lnf.infn.it/pancheri/starelesna.p

THE MYSTERY OF THE PRINTING PRESS: MONETARY POLICY AND SELF-FULFILLING DEBT CRISES

We study the mechanism by which unconventional (balance-sheet) monetary policy can rule out self-fulfilling sovereign default in a model with optimizing but discretionary fiscal and monetary policymakers. By purchasing sovereign debt, the central bank effectively swaps risky government paper for monetary liabilities only exposed to inflation risk, thus yielding a lower interest rate. We characterize a critical threshold for central bank purchases beyond which, absent fundamental fiscal stress, the government strictly prefers primary surplus adjustment to default. Since default may still occur for fundamental reasons, however, the central bank faces the risk of losses on sovereign debt holdings, which may generate inefficient inflation. This risk does not undermine the credibility of a backstop, nor the ability of a central bank to pursue its inflation objectives when the latter enjoys fiscal backing or fiscal authorities are sufficiently averse to inflation.Giancarlo Corsetti acknowledges the generous support of the Keynes Fellowship at Cambridge University,the Cambridge-Inet Institute at Cambridge, and the Centre For Macroeconomics.This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by Wiley

Evaluation of Ingenol mebutate efficacy for the treatment of actinic keratosis with Antera 3D camera

OBJECTIVE: Cumulative exposure of the skin to ultraviolet radiation promotes mutation in keratinocytes and their abnormal growth led to the formation of scaly lesions, called actinic keratoses (AKs). Its incidence is growing at an emerging rate, becoming a worldwide problem especially for occupational ultraviolet (UV) rays exposure. Detectable lesions are often associated with field changes, where the surrounding skin is altered and subclinical lesions may be present. Thus, a field-directed therapy, such as topical treatment, should be preferred for the prevention of invasive cancer development. A retrospective analysis was made, evaluating the efficacy of ingenol-mebutate gel, using a novel device the 3D in vivo optical skin Imaging (Antera 3D, Miravex, Ireland). PATIENTS AND METHODS: We included all patients with multiple non-hypertrophic Aks, to whom it was prescribed ingenol-mebutate gel, applied at the dosages of 0.015 for lesions in the scalp/face (for 3 consecutive days) and at the dosage of 0.05% for lesions in the trunk and/or extremities (for 2 consecutive days). RESULTS: A reduction of the lesions and of median hemoglobin levels, after a follow-up of 60 days, was observed in 100% of patients. CONCLUSIONS: Ingenol mebutate gel, the last topical molecule appeared in the Italian market showed its efficacy using Antera 3D also in terms of hemoglobin reduction. Therefore, this camera could be considered an useful tool for the identification of the area to be treated and for therapeutic follow-up

Beyond Competitive Devaluations: The Monetary Dimensions of Comparative Advantage

Motivated by the long-standing debate on the pros and cons of competitive devaluation, we propose a new perspective on how monetary and exchange rate policies can contribute to a country's international competitiveness. We refocus the analysis on the implications of monetary stabilization for a country's comparative advantage. We develop a two-country New-Keynesian model allowing for two tradable sectors in each country: while one sector is perfectly competitive,firms in the other sector produce differentiated goods under monopolistic competition subject to sunk entry costs and nominal rigidities, hence their performance is more sensitive to macroeconomic uncertainty. We show that, by stabilizing markups, monetary policy can foster the competitiveness of these firms, encouraging investment and entry in the differentiated goods sector, and ultimately affecting the composition of domestic output and exports. Panel regressions based on worldwide exports to the U.S. by sector lend empirical support to the theory.Constraining monetary policy with an exchange rate peg lowers a country's share of differentiated goods in exports between 4 and 12 percent