Forecasting cosmic doomsday from CMB-LSS cross-correlations.

A broad class of dark energy models, which have been proposed in attempts at solving the cosmological constant problems, predict a late time variation of the equation of state with redshift. The variation occurs as a scalar field picks up speed on its way to negative values of the potential. The negative potential energy eventually turns the expansion into contraction and the local universe undergoes a big crunch. In this paper we show that cross-correlations of the cosmic microwave background anisotropy and matter distribution, in combination with other cosmological data, can be used to forecast the imminence of such cosmic doomsday.

The effect of tax enforcement on tax elasticities: Evidence from charitable contributions in France

Optimal tax formulas expressed in "sufficient statistics" are usually calibrated under the assumptionthat the relevant tax elasticities are unaffected by other available policy instruments.In practice though, tax authorities have many more instruments than the mere tax rates andtax elasticities are functions of all these policy instruments. In this paper we provide evidencethat tax elasticities are extremely sensitive to a particular policy instrument: the level of taxenforcement. We exploit a natural experiment that took place in France in 1983, when the taxadministration tightened the requirements to claim charitable deductions. The reform led to asubstantial drop in the amount of contributions reported to the administration, which can becredibly attributed to overreporting of charitable contributions before the reform, rather thanto a real change in giving behaviours. We show that the reform was also associated with asubstantial decline in the absolute value of the elasticity of reported contributions. This findingallows us to partially identify the elasticity of overreporting contributions, which is shown tobe large and inferior to -2 in the lax enforcement regime. We further show using bunching oftaxpayers at kink-points of the tax schedule that the elasticity of taxable income also experienceda significant decline after the reform. Our results suggest that optimizing the tax rate fora given tax elasticity when other policy instruments are not optimized can lead to misleadingconclusions when tax authorities have another instrument that could set the tax elasticity itselfat its optimal level as in Kopczuk and Slemrod [2002].

The Conservativeness of the Central Bank when Institutional Quality is Poor

We propose an extension of Alesina and Tabellini 's model (1987) to include corruption, which is understood as the presence of weak institutions collecting revenue through formal tax channels. This paper analyses how conservative should an independent central bank be when the institutional quality is poor. When there are no political distortions, we show that the central bank has to be more conservative than the government, except with complete corruption. In this particular case, the central bank should be as conservative as the government. Further, we obtain that the relationship between the optimal relative degree of conservativeness of the central bank and the degree of corruption is affected by supply shocks. Concretely, when these shocks are not important, the central bank should be less conservative if the degree of corruption increases. However, this result may not hold when the shocks are relevant. JEL classi fication: D6, D73, E52, E58, E62, E63. Keywords: Central Bank Conservativeness; Corruption; Fiscal Policy; Monetary Policy; Seigniorage.

On the tractability of the piecewise-linear approximation for general discrete-choice network revenue management

The choice network revenue management (RM) model incorporates customer purchase behavioras customers purchasing products with certain probabilities that are a function of the offeredassortment of products, and is the appropriate model for airline and hotel network revenuemanagement, dynamic sales of bundles, and dynamic assortment optimization. The underlyingstochastic dynamic program is intractable and even its certainty-equivalence approximation, inthe form of a linear program called Choice Deterministic Linear Program (CDLP) is difficultto solve in most cases. The separation problem for CDLP is NP-complete for MNL with justtwo segments when their consideration sets overlap; the affine approximation of the dynamicprogram is NP-complete for even a single-segment MNL. This is in contrast to the independentclass(perfect-segmentation) case where even the piecewise-linear approximation has been shownto be tractable. In this paper we investigate the piecewise-linear approximation for network RMunder a general discrete-choice model of demand. We show that the gap between the CDLP andthe piecewise-linear bounds is within a factor of at most 2. We then show that the piecewiselinearapproximation is polynomially-time solvable for a fixed consideration set size, bringing itinto the realm of tractability for small consideration sets; small consideration sets are a reasonablemodeling tradeoff in many practical applications. Our solution relies on showing that forany discrete-choice model the separation problem for the linear program of the piecewise-linearapproximation can be solved exactly by a Lagrangian relaxation. We give modeling extensionsand show by numerical experiments the improvements from using piecewise-linear approximationfunctions.