Renormalisation and fixed points in Hilbert Space

The energies of low-lying bound states of a microscopic quantum many-body system of particles can be worked out in a reduced Hilbert space. We present here and test a specific non-perturbative truncation procedure. We also show that real exceptional points which may be present in the spectrum can be identified as fixed points of coupling constants in the truncation procedure.Comment: 4 pages, 1 tabl

Being on the field when the game is still under way. The financial press and stock markets in times of crisis

This paper looks at the relationship between negative news and stock markets in times of global crisis, such as the 2008/2009 period. We analysed one year of front page banner headlines of three financial newspapers, the Wall Street Journal, Financial Times, and Il Sole24ore to examine the influence of bad news both on stock market volatility and dynamic correlation. Our results show that the press and markets influenced each other in generating market volatility and in particular, that the Wall Street Journal had a crucial effect both on the volatility and correlation between the US and foreign markets. We also found significant differences between newspapers in their interpretation of the crisis, with the Financial Times being significantly pessimistic even in phases of low market volatility. Our results confirm the reflexive nature of stock markets. When the situation is uncertain and unpredictable, market behaviour may even reflect qualitative, big picture, and subjective information such as streamers in a newspaper, whose economic and informative value is questionable

Calcul de l'énergie de liaison de la matière nucléaire avec des interactions séparables

Infinite nuclear matter calculations using the reaction matrix G of the Brueckner-Goldstone theory are simple in the case of a separable two-nucleon interaction. The latter is taken here to be Tabakin's potential and Hamman's separable potential, both of which reproduce the free two-nucleon scattering data up to 320 MeV. The results obtained for the computed average energy per particle and saturation density are discussed and compared.Le calcul, dans la matière nucléaire, de la matrice de réaction G de Brueckner-Goldstone, est simple si l'interaction nucléon-nucléon est séparable. L'application est faite à l'interaction de Tabakin et à celle de Hammann, toutes deux sommes de potentiels séparables qui reproduisent les déphasages nucléon-nucléon jusqu'à 320 MeV. Les résultats obtenus pour l'énergie de liaison par particule et la densité de saturation sont discutés et comparés

Un potentiel séparable pour l'interaction nucléon-nucléon

A non-local séparable potential is presented, which reproduces S, P and D wave phase shifts for nucleon-nucleon scattering up to 350 MeV. This potential contains very strong and short-ranged terms. As a preliminary theoretical test, the binding energy of nuclear matter is calculated using the reaction matrix G of the Brueckner-Goldstone theory. Saturation is found at a density corresponding to a Fermi momentum kF = 1.65 fm-1, with an average binding energy per particle of - 18 MeV.Un potentiel non local séparable est présenté, qui reproduit les déphasages S, P et D de la diffusion nucléon-nucléon jusqu'à 350 MeV. Ce potentiel contient des termes fortement répulsifs et de courte portée. L'énergie de liaison de la matière nucléaire infinie est calculée à l'aide de la matrice de réaction G de Brueckner-Goldstone. La saturation est obtenue pour une densité correspondant au moment de Fermi kF = 1,65 fm-1, avec une énergie de liaison moyenne par particule de -18 MeV

Adaptive Learning in an Expectational Difference Equation with Several Lags: Selecting among Learnable REE

"It is demonstrated that adaptive learning in the least squares sense may be incapable of satisfactorily reducing the number of attainable equilibria in a rational expectations model when focusing on the forward-solutions to the model. The model examined, as an illustration, is a basic asset pricing model for exchange rate determination that is augmented with technical trading in the currency market in the form of moving averages since it is the most commonly used technique according to questionnaire surveys. The forward-solutions to such a model are preferable to the backward-solutions that are normally utilized since announcement effects is an important feature in currency trade. Because of technical trading in foreign exchange, the current exchange rate depends on" "j" max "lags of the exchange rate, meaning that the model has" "j" max + 1"rational expectations equilibria, where several of them are adaptively learnable in the least squares sense. However, since past exchange rates should not affect the current exchange rate when technical trading is absent, it is possible to single out a unique equilibrium among the adaptively learnable equilibria that is economically meaningful. It is worth noting that the model examined can also be viewed as a model for stock price determination in which the forward-solutions to the model are preferable to the backward-solutions since the importance of announcement effects is a common characteristic for currency and stock markets." Copyright 2007 The Author Journal compilation (c) Blackwell Publishing Ltd.