Local points on Shimura coverings of Shimura curves at bad reduction primes

Let XD be the Shimura curve associated with an indefinite rational quaternion algebra of reduced discriminant D>1. For each prime l|D, there is a natural cyclic Galois covering of Shimura curves XD,l → XD constructed by adding certain level structure at l. The main goal of this note is to study the existence of local points at primes p≠l of bad reduction on the intermediate curves of these coverings and their Atkin–Lehner quotients.Peer ReviewedPostprint (author's final draft

Análisis y diseño de materiales didácticos

El objetivo fundamental de este capítulo es establecer unas pautas generales que permiten a los profesores de español desarrollar una actitud crítica con respecto a los materiales que se emplean en la enseñanza de español como lengua extranjera. Como consecuencia, ellos mismos serán capaces de seleccionar el material adecuado para el grupo meta de estudiantes y, si es necesario, adaptar los materiales ya existentes o crear sus propios materiales. Al comienzo de este capítulo se presenta un panorama de los estudios e investigaciones que se han dedicado, por una parte, al análisis y a la evaluación de materiales didácticos para la enseñanza de español como lengua extranjera de forma general (Fernández López, 2004; Lozano y Ruiz-Campillo, 2009 y Sans, 2000) y, por otra, a las investigaciones que se han ocupado de analizar los materiales teniendo en cuenta elementos específicos (Baralo, 2013; Ezeiza, 2009; Gil y León, 1998). A continuación, se incluyen las diferentes propuestas de diversos autores sobre el análisis, la evaluación de materiales y unidades didácticas y el diseño de los materiales. Finalmente, se desarrolla una plantilla general que comprende los elementos necesarios para analizar y evaluar los materiales didácticos y, consecuentemente, para guiar al docente en el diseño de materiales o en la adaptación de los materiales ya publicados

Moduli as Inflatons in Heterotic M-theory

We consider different cosmological aspects of Heterotic M-theory. In particular we look at the dynamical behaviour of the two relevant moduli in the theory, namely the length of the eleventh segment (pi rho) and the volume of the internal six manifold (V) in models where supersymmetry is broken by multiple gaugino condensation. We look at different ways to stabilise these moduli, namely racetrack scenarios with or without non-perturbative corrections to the Kahler potential. The existence of different flat directions in the scalar potential, and the way in which they can be partially lifted, is discussed as well as their possible role in constructing a viable model of inflation. Some other implications such as the status of the moduli problem within these models are also studied.Comment: 16 pages, 8 Postscript figures. Final version to appear in JHE

Endogenous Borrowing Constraints and Consumption Volatility in a Small Open Economy

Consumption volatility relative to output volatility is consistently higher in emerging economies than in developed economies. One natural explanation is that emerging economies are more likely to face borrowing constraints and, as a consequence, find it more difficult to use international capital markets to smooth consumption. The author investigates how much this mechanism alone can account for the relative consumption volatility differential between emerging and developed economies. His theoretical approach relies on a standard dynamic general-equilibrium model of a small open endowment economy that is subject to an endogenous borrowing constraint. The borrowing constraint makes the small economy exactly indifferent between two options: (i) repaying its external debt, or (ii) defaulting and having to live in financial autarky in the future. The model for the constrained economy is calibrated to match Brazilian data during the period 1980-2001. The author's findings suggest that the model is capable of accounting for more than half of the observed relative consumption volatility differential.International topics

IMF-Supported Adjustment Programs: Welfare Implications and the Catalytic Effect

The author studies the welfare implications of adjustment programs supported by the International Monetary Fund (IMF). He uses a model where an endogenous borrowing constraint, set up by international lenders who will never lend more than a debt ceiling, forces the borrowing economy to always choose repayment over default. The immediate potential welfare cost of joining a program is driven by IMF conditionality: to be able to borrow from the IMF, the country has to submit to limits on the consumption of public goods. The benefits derive from the additional borrowing from the IMF (at a lower interest rate) and/or through a "catalytic effect" on private loans, which facilitates consumption smoothing over time. Simulations of the dynamic model in two institutional environments -- with and without the IMF -- are compared. Results indicate that when conditionality forces the country to save more, at a cost that does not prevent it from joining an IMF program, the resulting lower probability of default can induce private lenders to relax their borrowing constraints. Based on a calibration of the model for the Brazilian economy, the overall welfare gains associated with IMF programs are relatively small.International topics

The Generalized Dilaton Supersymmetry Breaking Scenario

We show that the usual dilaton dominance scenario, derived from the tree level K\"ahler potential, can never correspond to a global minimum of the potential at $V=0$. Similarly, it cannot correspond to a local minimum either, unless a really big conspiracy of different contributions to the superpotential $W(S)$ takes place. These results, plus the fact that the K\"ahler potential is likely to receive sizeable string non-perturbative contributions, strongly suggest to consider a more general scenario, leaving the K\"ahler potential arbitrary. In this way we obtain generalized expressions for the soft breaking terms but a predictive scenario still arises. Finally, we explore the phenomenological capability of some theoretically motivated forms for non-perturbative K\"ahler potentials, showing that it is easy to stabilize the dilaton at the realistic value $S\sim 2$ with just one condensate and no fine-tuning.Comment: 10 pages, plain LaTeX. Some references added and eq.(35) simplifie