Can we make a Finsler metric complete by a trivial projective change?

A trivial projective change of a Finsler metric $F$ is the Finsler metric $F + df$. I explain when it is possible to make a given Finsler metric both forward and backward complete by a trivial projective change. The problem actually came from lorentz geometry and mathematical relativity: it was observed that it is possible to understand the light-line geodesics of a (normalized, standard) stationary 4-dimensional space-time as geodesics of a certain Finsler Randers metric on a 3-dimensional manifold. The trivial projective change of the Finsler metric corresponds to the choice of another 3-dimensional slice, and the existence of a trivial projective change that is forward and backward complete is equivalent to the global hyperbolicity of the space-time.Comment: 11 pages, one figure, submitted to the proceedings of VI International Meeting on Lorentzian Geometry (Granada

Translog Cost Functions: An Application for Mexican Manufacturing.

We use translog cost functions to estimate own-price and substitution elasticities of input demands, economies of scale and average costs in Mexican manufacturing. Data from the Mexican Annual Industrial Survey is used for 1996, 2000 and 2003. We show that a model that allows for nonhomotheticity and nonunitary elasticities of substitution is appropriate to represent the production structure. Allen-Uzawa elasticities indicate the existence of substitution possibilities amongst inputs. The demand for electricity is essentially unitary elastic. All cross-price elasticities are less than one. Both scale economies and average costs diminish as the size of activity class increases. Economies of scale increased for any level of output. The differences in average costs between small and large activity classes were reduced and some disparities prevail in a number of manufacturing groups.Simultaneous equation models, Translog cost function, Manufacturing

MEXICAN-U.S. FRESH TOMATO TRADE: AN ANALYSIS OF VOLUME, PRICES AND TRANSACTION COSTS

Tomato trade between the U.S. and Mexico has grown significantly during the past decade. Although the tariff reductions accorded under NAFTA may explain part of his increase, there are other supply and demand factors that affect trade flows. This study develops a U.S.-Mexico tomato trade model, with special focus on the interdependence between trading costs and the volume of Mexican imports. As expected, the exchange rate is a significant determinant of trading costs, but the level of tariffs was insignificant in both the trading and tomato supply equations. The shipping point price level and volume of imports also appear to affect these costs. For the import supply and demand models, there appears to be a significant share of imports that rely on previous levels of imports, rather than the expected economic factors (prices, income, and producer price index). We conclude that the structure and performance of the tomato trading market is changing, and may be more influential than tariff reductions in explaining increased trade flows.Crop Production/Industries, International Relations/Trade,

Multifactor Productivity and its Determinants: Al Empirical Analysis for Mexican Manufacturing.

We use data from the Annual Industrial Survey for 1996-2003. First, we estimate production functions by means of growth accounting exercises and panel data econometrics for the whole sector and for 14 comprehensive groups. Various measures of Multifactor Productivity (MFP) are constructed, as we consider diverse combinations of inputs with capital, labour, electricity and transport. This allows us to compare MFP growth rates between groups. Second, we analyse econometrically some of the determinants of MFP and Labour Productivity (LP) growth. We find that, on the one hand, there is some evidence of a positive relationship between market concentration and technology adoption; on the other hand, both technology adoption and human capital seem to be promoting productivity, whilst market concentration is exerting a negative influence on it. In sum, our results suggest that, once controlling for the effect on technology adoption, more concentration (conversely, less competition) has a negative impact on productivity.Panel data, Productivity, Manufacturing, Competition

PRICE RELATIONSHIPS AMONG NORTH AMERICAN FRESH TOMATO MARKETS: A COMPARISON BETWEEN MEXICAN AND U.S. MARKETS

Tomato trade between the U.S. and Mexican has grown significantly during the past decade, and market structure suggests increased market integration. This study examines fresh tomato price relationships between two major North American shipping points (Sinaloa, and Florida) and several major terminal markets in the U.S. and Mexico to infer whether business strategies vary by supply region or the geography of consumer markets. The results show some evidence of inefficient pricing behavior among some markets, and suggest that Mexican shipping point prices are less integrated with Mexico's own terminal markets than the closest U.S. market, Los Angeles. Moreover, perfectly competitive price behavior is less likely in a terminal market (Chicago) where Sinaloa and Florida compete during winter months. These results are the basis of discussion on the role of strategic behavior and trade policy influence in these markets.International Relations/Trade,

Systematic uncertainties from halo asphericity in dark matter searches

Although commonly assumed to be spherical, dark matter halos are predicted to be non-spherical by N-body simulations and their asphericity has a potential impact on the systematic uncertainties in dark matter searches. The evaluation of these uncertainties is the main aim of this work, where we study the impact of aspherical dark matter density distributions in Milky-Way-like halos on direct and indirect searches. Using data from the large N-body cosmological simulation Bolshoi, we perform a statistical analysis and quantify the systematic uncertainties on the determination of local dark matter density and the so-called $J$ factors for dark matter annihilations and decays from the galactic center. We find that, due to our ignorance about the extent of the non-sphericity of the Milky Way dark matter halo, systematic uncertainties can be as large as 35%, within the 95% most probable region, for a spherically averaged value for the local density of 0.3-0.4 GeV/cm$^3$. Similarly, systematic uncertainties on the $J$ factors evaluated around the galactic center can be as large as 10% and 15%, within the 95% most probable region, for dark matter annihilations and decays, respectively.Comment: 29 pages, 6 artistic figures, version accepted for publication in JCA

Application of the coherent state formalism to multiply excited states

A general expression is obtained for the matrix element of an m-body operator between coherent states constructed from multiple orthogonal coherent boson species. This allows the coherent state formalism to be applied to states possessing an arbitrarily large number of intrinsic excitation quanta. For illustration, the formalism is applied to the two-dimensional vibron model [U(3) model], to calculate the energies of all excited states in the large-N limit.Comment: LaTeX (iopart); 10 pages; to be published in J. Phys.