On Coherent States and q-Deformed Algebras

We review some aspects of the relation between ordinary coherent states and q-deformed generalized coherent states with some of the simplest cases of quantum Lie algebras. In particular, new properties of (q-)coherent states are utilized to provide a path integral formalism allowing to study a modified form of q-classical mechanics, to probe some geometrical consequences of the q-deformation and finally to construct Bargmann complex analytic realizations for some quantum algebras.Comment: Presented at the 'International Symposium on Coherent States' June 1993, USA 14 pages, plain LATEX, FTUV/93-37, IFIC/93-2

Depreciation bias, financial-sector fragility and currency risk

Do expected future exchange rate fluctuations affect current social welfare? In the third-generation approach to currency crises, financial fragility can trigger devaluation and default. Expected future depreciation is costly if it raises ex ante real interest rates. Given the strong violation of uncovered interest parity, expected future outcomes' current cost/benefit depends on the currency risk premium. I extend the static one-period Barro-Gordon welfare loss function to include expected future depreciation and show that, when foreign investors are risk-averse, depreciation bias is higher than the static case if aggregate demand is a function of ex ante real rates. If demand depends on the ex post real interest rate, average depreciation can be zero if current welfare is sufficiently sensitive to the state of the financial sector. In this stylised framework, depreciation bias can be mitigated even in the presence of time-inconsistency, and expected welfare may be higher

Endogenous Market Turbulence

In this paper I study a nonlinear feedback trading model which can generate stable, unstable, turbulent or chaotic asset returns depending on market conditions. The dynamics are driven by the stochastic price impact of net order flow (inverse market liquidity). If price impact grows beyond exogenous threshold values, liquidity dries up and asset returns become turbulent. In the absence of fundamental factors, the occurrence of turbulence and chaos is entirely endogenous. The results highlight the critical role of maintaining stable market-making conditions for averting “liquidity black holes”

Can Feedback Traders Rock the Markets? A Logistic Tale of Persistence and Chaos

This paper introduces a nonlinear feedback trading model at high frequency. All price adjustment is endogenous, driven by asset return and volatility in the previous trading period. There is no stochastic uncertainty or asymmetric information. The dynamics of expected returns display stable or unstable behavior–including the possibility of turbulence and chaos–as a function of market liquidity (inverse price impact) and the concentration of investor beliefs, which is proportional to the intensity of positive feedback. The results highlight the complementary role of investor diversity and market liquidity in maintaining financial stability

Fear of Floating and Social Welfare

This paper studies the welfare implications of financial stability and inflation stabilization as distinct monetary policy objectives. Introducing asymmetric aversion to exchange rate depreciation in the Barro-Gordon model mitigates inflation bias due to credibility problems. The net welfare impact of fear of floating depends on the economy’s recent track record, the credibility of monetary policy, and the central bank’s discount factor. It is shown that fear of floating is more appropriate for financially fragile developing countries with imperfectly credible monetary policy than for advanced economies