Parametric Resonance in an Expanding Universe

Parametric resonance has been discussed as a mechanism for copious particle production following inflation. Here we present a simple and intuitive calculational method for estimating the efficiency of parametric amplification as a function of parameters. This is important for determining whether resonant amplification plays an important role in the reheating process. We find that significant amplification occurs only for a limited range of couplings and interactions.Comment: 18 pages, Latex, 4 figure

Agricultural development in Russia, 1906-1917: Land reform, social agronomy and cooperation.

This thesis describes the efforts of Russia's central government, local governments (zemstvos) and various social institutions to modernize peasant agriculture during the period 1906-17. The focus is on the micro-economic dynamics of the development program, on the interaction between various types of extension workers and peasant farmers. After a short discussion of Russia's economic backwardness at the beginning of the 20th century, the thesis examines the nature of rural society and the technological characteristics of peasant agriculture. The agricultural development program which evolved after 1906 is divided into three inter-related branches: land reform, social agronomy and cooperation. The land reform (consisting of resettlement, increased gentry land sales to the peasantry, privatization of peasant allotments and consolidation of strips into consolidated farmsteads) is examined in terms of quantitative results and social dynamics. We look at the strategies of the cadres pushing through the reform, the reaction of the peasantry and the effects of the reform on peasant farming. Social agronomy (mass agronomic education) was an innovative program administered jointly by the Ministry of Agriculture and the zemstvos; We examine in detail the work of local agronomists, their lifestyle and their effect on peasant society. Agricultural cooperation (agricultural societies, credit cooperatives, dairy cooperatives, etc.) experienced rapid growth during this time; we examine the role of cooperatives in providing farm credit, marketing services, farm supplies and agronomic advice to peasant farmers. Finally, the thesis describes the significant impact of the agricultural development program on agricultural technology and Russia's agricultural progress. The expansion of the farming sector in turn affected Russia's economy as a whole. In order to reinforce the hypothesis that the agricultural development program was directly responsible for a large part of Russia's agricultural expansion, we employ regression analysis on a database consisting of variables such as crop yields, land tenure, urbanization, etc. across 42 provinces of European Russia. The conclusion is that, in spite of its short life, the agricultural development program of 1906-17 succeeded in considerably improving the state of Russian agriculture

An Example of Semiclassical Instanton-Like Scattering: (1+1) Dimensional Sigma Model

A solution to the classical field equations in the massless (1+1)-dimensional O(3) sigma model is found, which describes a multi-particle instanton-like transition at high energy. In the limit of small number of initial particles, the number of final particles is shown to be also small, and the probability of the transition is suppressed by $\exp(-2S_0)$, where $S_0$ is the instanton action. This solution, however, does not correspond to the maximum transition probability among all states with given number of incoming particles and energy. Unless the limit $g^2 n_{initial}\to0$ is exponentially sensitive to the structure of the initial state, our results imply that well above the sphaleron energy, the instanton-induced cross section becomes again suppressed by the instanton exponent, and the number of final paricles is again small.Comment: 28 pages, LaTeX preprint TPI-MINN-92/66-