Momentum distribution in nuclear matter and finite nuclei

A simple method is presented to evaluate the effects of short-range correlations on the momentum distribution of nucleons in nuclear matter within the framework of the Greens function approach. The method provides a very efficient representation of the single-particle Greens function for a correlated system. The reliability of this method is established by comparing its results to those obtained in more elaborate calculations. The sensitivity of the momentum distribution on the nucleon-nucleon interaction and the nuclear density is studied. The momentum distributions of nucleons in finite nuclei are derived from those in nuclear matter using a local-density approximation. These results are compared to those obtained directly for light nuclei like 16O.

Liquid-gas phase transition in nuclear matter from realistic many-body approaches

The existence of a liquid-gas phase transition for hot nuclear systems at subsaturation densities is a well-established prediction of finite-temperature nuclear many-body theory. In this paper, we discuss for the first time the properties of such a phase transition for homogeneous nuclear matter within the self-consistent Green's function approach. We find a substantial decrease of the critical temperature with respect to the Brueckner-Hartree-Fock approximation. Even within the same approximation, the use of two different realistic nucleon-nucleon interactions gives rise to large differences in the properties of the critical point.

Binding energy and momentum distribution of nuclear matter using Green's functions methods

The influence of hole-hole (h-h) propagation in addition to the conventional particle-particle (p-p) propagation, on the energy per particle and the momentum distribution is investigated for the v2 central interaction which is derived from Reid¿s soft-core potential. The results are compared to Brueckner-Hartree-Fock calculations with a continuous choice for the single-particle (SP) spectrum. Calculation of the energy from a self-consistently determined SP spectrum leads to a lower saturation density. This result is not corroborated by calculating the energy from the hole spectral function, which is, however, not self-consistent. A generalization of previous calculations of the momentum distribution, based on a Goldstone diagram expansion, is introduced that allows the inclusion of h-h contributions to all orders. From this result an alternative calculation of the kinetic energy is obtained. In addition, a direct calculation of the potential energy is presented which is obtained from a solution of the ladder equation containing p-p and h-h propagation to all orders. These results can be considered as the contributions of selected Goldstone diagrams (including p-p and h-h terms on the same footing) to the kinetic and potential energy in which the SP energy is given by the quasiparticle energy. The results for the summation of Goldstone diagrams leads to a different momentum distribution than the one obtained from integrating the hole spectral function which in general gives less depletion of the Fermi sea. Various arguments, based partly on the results that are obtained, are put forward that a self-consistent determination of the spectral functions including the p-p and h-h ladder contributions (using a realistic interaction) will shed light on the question of nuclear saturation at a nonrelativistic level that is consistent with the observed depletion of SP orbitals in finite nuclei.

Bargmann-Wigner method and (6S + 1)-component wave equations

A modified Bargmann-Wigner method is used to derive (6s + 1)-component wave equations. The relation between different forms of these equations is shown.

Newton-Hooke algebras, nonrelativistic branes, and generalized pp-wave metrics

The Newton-Hooke algebras in d dimensions are constructed as contractions of dS(AdS) algebras. Nonrelativistic brane actions are WZ terms of these Newton-Hooke algebras. The NH algebras appear also as subalgebras of multitemporal relativistic conformal algebras, SO(d+1,p+2). We construct generalizations of pp-wave metrics from these algebras.

On the zeta-function regularization of a two-dimensional series of epsten-Hurwitz type

For a few years now, the study of quantum field theories in partially compactified space-time manifolds has acquired increasing importance in several domains of quantum physics. Let me just mention the issues of dimensional reduction and spontaneous compactification, and the multiple questions associated with the study of quantum field theories in the presence of boundaries (like the Casimir effect) and on curved space-time (manifolds with curvature and nontrivial topology), a step towards quantum gravity.

Perturbation theory for classical thermodynamic Green's functions

A systematic time-dependent perturbation scheme for classical canonical systems is developed based on a Wick's theorem for thermal averages of time-ordered products. The occurrence of the derivatives with respect to the canonical variables noted by Martin, Siggia, and Rose implies that two types of Green's functions have to be considered, the propagator and the response function. The diagrams resulting from Wick's theorem are "double graphs" analogous to those introduced by Dyson and also by Kawasaki, in which the response-function lines form a "tree structure" completed by propagator lines. The implication of a fluctuation-dissipation theorem on the self-energies is analyzed and compared with recent results by Deker and Haake.

In defense of the "tunneling" wave function of the universe

The tunneling approach to the wave function of the Universe has been recently criticized by Bousso and Hawking who claim that it predicts a catastrophic instability of de Sitter space with respect to pair production of black holes. We show that this claim is unfounded. First, we argue that different horizon size regions in de Sitter space cannot be treated as independently created, as they contend. And second, the WKB tunneling wave function is not simply the inverse of the Hartle-Hawking one, except in very special cases. Applied to the related problem of pair production of massive particles, we argue that the tunneling wave function leads to a small constant production rate, and not to a catastrophe as the argument of Bousso and Hawking would suggest.

The determinants of industrial location in Spain, 1856-1929

Durant el segle XIX, l'economia espanyola va transitar per les primeres etapes de la industrialització. Aquest procés es va donar en paral·lel a la integració del mercat domèstic de béns i factors, en un moment en què les reformes liberals i la construcció de la xarxa ferroviària, entre d'altres, van generar una important caiguda en els costos detransport. Al mateix temps que es donava aquesta progressiva integració del mercat domèstic espanyol, es van produir canvis significatius en la pauta de localització industrial. D'una banda, hi hagué un augment considerable de la concentració espacial de la indústria des de mitjans de segle XIX i fins a la Guerra Civil, i d¿altra, un increment de l'especialització regional. Ara bé, quines van ser les forces que van generar aquests canvis? Des d¿un punt de vista teòric, el model de Heckscher-Ohlin suggereix que la distribució a l'espai de l¿activitat econòmica ve determinada per l'avantatge comparativa dels territoris en funció de la dotació relativa de factors. Al seu torn, els models de Nova Geografia Econòmica (NEG) mostren l'existència d'una relació en forma de campana entre el procés d'integració econòmica i el grau de concentració geogràfica de l'activitat industrial. Aquest article examina empíricament els determinants de la localització industrial a Espanya entre 1856 i 1929, mitjançant l'estimació d¿un model que combina els elements de tipus Heckscher-Ohlin i els factors apuntats des de la NEG, amb l'objectiu de contrastar la força relativa dels arguments vinculats a aquestes dues interpretacions a l'hora de modular la localització de la indústria a Espanya. L'anàlisi dels resultats obtinguts mostra que tant la dotació de factors com els mecanismes de tipus NEG van ser elements determinants que expliquen la distribució geogràfica de la indústria des del segle XIX, tot i que la seva força relativa va anar variant amb el temps.

Integración económica y localización industrial. Cataluña, la fábrica de España: ¿cuándo y por qué?

En este artículo se analizan los determinantes de la localización de la actividad industrial en España durante la segunda mitad del siglo XIX. El objetivo es estudiar la existencia de cambios en los factores explicativos de la localización, con el fin de identificar los efectos de la integración económica sobre la geografía industrial española. Para hacerlo, en primer lugar se analiza la literatura histórica existente. En segundo lugar, se describen las teorías que explican la localización de l'actividad. En tercer lugar, se realiza un análisis empírico de la localización y la concentración de la industria española al siglo XIX. A continuación, se propone un estudio econométrico de los determinantes de la localización industrial en dos cortes temporales, 1856 y 1893. Los resultados son consistentes con las teorías del comercio. Durante el decurso de la segunda mitad del siglo XIX, España paso a ser una economía integrada, la movilidad del trabajo y del capital se vio favorecida y como resultado, las diferencias relativas en las dotaciones de factores perdieron importancia en la explicación de las pautas de especialización industrial. Por el contrario, la integración económica favoreció la significación relativa de las economías de escala o de la proximidad a los mercados como elementos explicativos de la localización de la industria, favoreciendo, de esta manera, la aglomeración de la actividad industrial

Regional integration and specialisation patterns in Spain

The aim of this paper is to analyse how economic integration in Europe has affected industrial geographical concentration in Spain and explain what the driving forces behind industry location are. Firstly, we construct regional specialisation and geographical concentration indices for Spanish 50 provinces and 30 industrial sectors in 1979, 1986 and 1992. Secondly, we carry out an econometric analysis of the determinants of geographical concentration of industries. Our main conclusion is that there is no evidence of increasing specialisation in Spain between 1979 and 1992 and that the most important determinant of Spain¿s economic geography is scale economies. Furthermore, traditional trade theory has no effects in explaining the pattern of industrial concentration

Industrial agglomerations and wage gradients: the Spanish economy in the interwar period

This paper gives new evidence on the relationship between integration and industrial agglomeration in the presence of scale economies, by testing directly one of the predictions that can be derived from Krugman (1991), that is, the existence of regional nominal wage gradients and its transformation following changes in trade regimes. Our case study analyzes the effects of the substitution of an open economy by a closed economy regime, exactly the opposite process studied by Hanson (1996, 1997). In Spain, during the interwar period, protectionist policies would have favored the loss of centrality of the coastal location (Barcelona) and the relative rise of central locations (such as Madrid). Our results indicate the existence of a wage gradient centered in Barcelona during the interwar period (1914-1930) and its weakening after 1925.

The geographical concentration of industry across Spanish Regions, 1856-1995

New economic geography models show that there may be a strong relationship between economic integration and the geographical concentration of industries. Nevertheless, this relationship is neither unique nor stable, and may follow a ?-shaped pattern in the long term. The aim of the present paper is to analyze the evolution of the geographical concentration of manufacturing across Spanish regions during the period 1856-1995. We construct several geographical concentration indices for different points in time over these 140 years. The analysis is carried out at two levels of aggregation, in regions corresponding to the NUTS-II and NUTS-III classifications. We confirm that the process of economic integration stimulated the geographical concentration of industrial activity. Nevertheless, the localization coefficients only started to fall after the beginning of the integration of the Spanish Economy into the international markets in the mid-70s, and this new path was not interrupted by Spain¿s entry in the European Union some years later