Supersymmetric Models for Fermions on a Lattice

We investigate the large-N behaviour of simple examples of supersymmetric interactions for fermions on a lattice. Witten's supersymmetric quantum mechanics and the BCS model appear just as two different aspects of one and the same model. For the BCS model, supersymmetry is only respected in a coherent superposition of Bogoliubov states. In this coherent superposition mesoscopic observables show better stability properties than in a Bogoliubov state.Comment: 17 pages, LATeX, no figure

Central limit theorems for the large-spin asymptotics of quantum spins

We use a generalized form of Dyson's spin wave formalism to prove several central limit theorems for the large-spin asymptotics of quantum spins in a coherent state.Comment: 28 pages, uses package amsref

Human Rights Violations After 9/11 and the Role of Constitutional Constraints

human rights, terrorism, 9/11, checks and balances, constitutions, constitutional courts

Does Aid Mitigate External Shocks?

This paper investigates the role of aid in mitigating the adverse effects of commodity export price shocks on growth in commodity-dependent countries. Using a large cross-country dataset, we find that negative shocks matter for short-term growth, while the ex ante risk of shocks does not seem to matter. We also find that both the level of aid and the flexibility of the exchange rate substantially lower the adverse growth effect of shocks. While the mitigating effect of aid is significant in both countries with pegs and countries with floats, the effect seems to be smaller for the latter, suggesting that aid and exchange rate flexibility are partly substitutes. We investigate whether aid has historically been targeted at shock-prone countries, but find no evidence that this is the case. This suggests that donors could increase aid effectiveness by redirecting aid towards countries with a high incidence of commodity export price shocks.aid, commodities, export, price shocks

Does aid mitigate external shocks?

This paper investigates the role of aid in mitigating the adverse effects of commodity export price shocks on growth in commodity-dependent countries. Using a large cross-country dataset, we find that negative shocks matter for short-term growth, while the ex ante risk of shocks does not seem to matter. We also find that both the level of aid and the flexibility of the exchange rate substantially lower the adverse growth effect of shocks. While the mitigating effect of aid is significant in both countries with pegs and countries with floats, the effect seems to be smaller for the latter, suggesting that aid and exchange rate flexibility are partly substitutes. We investigate whether aid has historically been targeted at shock-prone countries, but find no evidence that this is the case. This suggests that donors could increase aid effectiveness by redirecting aid towards countries with a high incidence of commodity export price shocks.commodity prices; aid; growth; external shocks

Structural Policies for Shock-Prone Developing Countries

Many developing countries periodically face large adverse shocks to their economies. We study two distinct types of such shocks - large declines in the price of a country’s commodity exports and severe natural disasters - , both of which have occurred frequently in the recent past. Unsurprisingly, adverse shocks reduce the short-term growth of constant-price GDP and we analyze which structural policies help to minimize these losses. Structural policies are incentives and regulations that are maintained for long periods, contrasting with policy responses to shocks, the analysis of which has dominated the literature. We show that some previously neglected structural policies have large effects that are specific to particular types of shock. In particular, regulations which reduce the speed of firm exit substantially increase the short-term growth loss from adverse non-agricultural export price shocks and so are particularly ill-suited to mineral exporting economies. Natural disasters appear to be better accommodated by labour market policies, perhaps because such shocks directly dislocate the population.commodity price shocks; natural disasters; growth, policies

Commodity Prices, Growth, and the Natural Resource Curse: Reconciling a Conundrum

Currently, evidence on the ‘resource curse’ yields a conundrum. While there is much crosssection evidence to support the curse hypothesis, time series analyses using vector autoregressive (VAR) models have found that commodity booms raise the growth of commodity exporters. This paper adopts panel cointegration methodology to explore longer term effects than permitted using VARs. We find strong evidence of a resource curse. Commodity booms have positive short-term effects on output, but adverse long-term effects. The long-term effects are confined to “high-rent”, non-agricultural commodities. We also find that the resource curse is avoided by countries with sufficiently good institutions. We test the channels of the resource curse proposed in the literature and find that a substantial part of it is explained by high public and private consumption, low or inefficient total investment, and an overvalued exchange rate. Our results fully account for the cross-section results in the seminal paper by Sachs and Warner (1995).commodity prices; natural resource curse; growth

Structural Policies for Shock-Prone Developing Countries..

Many developing countries periodically face large adverse shocks to their economies. We study two distinct types of such shocks - large declines in the price of a country’s commodity exports and severe natural disasters - , both of which have occurred frequently in the recent past. Unsurprisingly, adverse shocks reduce the short-term growth of constant-price GDP and we analyze which structural policies help to minimize these losses. Structural policies are incentives and regulations that are maintained for long periods, contrasting with policy responses to shocks, the analysis of which has dominated the literature. We show that some previously neglected structural policies have large effects that are specific to particular types of shock. In particular, regulations which reduce the speed of firm exit substantially increase the short-term growth loss from adverse non-agricultural export price shocks and so are particularly ill-suited to mineral exporting economies. Natural disasters appear to be better accommodated by labour market policies, perhaps because such shocks directly dislocate the population.