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ABSTRAeTThis papel' analyzes the equilibrium dynamics of an AK-type endogenous growth model with vintage capital. The inclusion of vintage capital leads to oscillatory dynamics governed by replacement echoes, which additionally influence the intercept of the balanced growth path. These features, which are in sharp contrast to those from the standard AK model, can contribute to explaining the short-run deviations observed bctween investment and growth rates time series. To characterize the convergence properties and the dynamics of the model we develop analytical and numencaJ rnethods that should be of ¡nterest fOl the general resolution of endogenous growth models with vintage capital. RESUMENEn este artículo se analiza la dinámica de uu modelo de crecimiento endógeno de la clase AK en presencia de cosechas de capital (vintage capital). La inclusión en el modelo de una estructura vintage da lugar a una dinámica oscilatoria, vinculada a lo que se conoce como ecos de reemplazo, los cuales a su vez tienen efectos sobre el nivel de la senda de crecimiento equilibrado. Esta propiedad contrasta marcadamente con el comportamiento del modelo AK estándar, y puede contribuir a explicar las desviaciones a corto plazo, que se observan en los datos, ent.re las tasas de inversión y las tasas de crecimiento. Para caracterizar las propiedades de convergencia y la dinámica del modelo se desarrollan métodos analíticos y numéricos que son de interés para la resolución de modelos de crecimiento endógeno con cosechas de capital.

We consider an overlapping generations model with uncertain lifetime and endogenous growth. Individuals have t o c hoose the length of time devoted to schooling before starting to work. We show that it depends positively on life expectancy but that the positive e ect of a longer life on growth could beo set by a decrease in the participation rate. Dynamics are characterized by a delay di erential equation and human capital converges with oscillations to a balanced growth path.

We study the welfare gains from trade in an economy with heterogeneous firms, variable markups and endogenous growth. Variable markups arise from oligopolistic competition, and cost-reducing innovation is the engine of long-run growth. Trade liberalisation stiffens competition by reducing markups, generating tougher firm selection and increasing the aggregate productivity level. Selection increases firms' incentives to innovate, thereby leading to a higher aggregate productivity growth rate. Endogenous productivity growth boosts the selection gains from trade, leading to substantial welfare improvements. A calibrated version of the model shows that growth doubles the welfare gains obtainable in models with static firm-level productivity.If the gains from trade are small, is it worth facing the potentially disruptive distributional consequences of globalisation?1 Assessing the size and identifying the sources of gains from trade is a long-standing challenge for economists. In recent decades, a new line of research introducing firm heterogeneity in trade models has uncovered a new source of welfare gains. Trade-induced reallocations of market shares from low to highly productive firms within the same industries increase sectorial efficiency, leading to improvements in aggregate productivity and to potentially large welfare gains. However, selection also carries welfare losses that can possibly outweigh the gains: firms' exit has a negative effect on welfare by reducing the variety of goods available in the economy.Theoretical and quantitative analyses assessing the contribution of the selection margin have mainly featured market structures with perfect or monopolistic competition, focused on static models or on dynamic economies without long-run productivity growth. The goal of this article is to fill these gaps by providing a theory of trade with heterogeneous firms under oligopolistic competition and innovationdriven productivity growth. On the one hand, because of 'cross-hauling' of identical goods, oligopoly trade is potentially wasteful, therefore representing a more difficult environment in which to obtain welfare gains. On the other hand, trade reduces markups thereby generating pro-competitive effects which are absent in environments where firms' market power is constant. Moreover, innovation-driven growth can potentially magnify the gains from selection, as market share reallocations can affect not only the productivity level but also its growth rate. We show that the new gains due