A dynamical characterization of acylindrically hyperbolic groups

We give a dynamical characterization of acylindrically hyperbolic groups. As an application, we prove that non-elementary convergence groups are acylindrically hyperbolic

Note on DBI dynamics of Dbrane Near NS5-branes

In this note, we investigate the homogeneous radial dynamics of (Dp, NS5)-systems without and with one compactified transverse direction, in the framework of DBI effective action. During the homogeneous evolution, the electric field on the D-brane is always conserved and the radial motion could be reduced to an one-dimension dynamical system with an effective potential. When the Dp-brane energy is not high, the brane moves in a restricted region, with the orbits depending on the conserved energy, angular momentum through the form of the effective potential. When the Dp-brane energy is high enough, it can escape to the infinity. It turns out that the conserved angular momentum plays an interesting role in the dynamics. Moreover, we discuss the gauge dynamics around the tachyon vacuum and find that the dynamics is very reminiscent of the string fluid in the rolling tachyon case.Comment: 13 pages, 2 figures; typos corrected, discussions improved; gauge dynamics has been include

The Price of Egalitarianism

We compute the welfare cost of egalitarianism - a tax policy that equalizes wages for all. The benchmark "laissez-faire" economy has features a la Aiyagari (1994) with endogenous labor supply. A progressive income tax provides insurance against income risks but at the cost of efficiency: it undermines highly productive workers' incentives to work. We find that in an economy with the labor-supply elasticity of 1, the welfare cost of egalitarianism, measured in consumption-equivalence units, is only 1% as the welfare gain from insurance against income risks nearly offsets the efficiency loss from distorting labor effort. However, with an elastic labor supply, the welfare cost of egalitarianism is as large as 7.5% of steady state consumption.Egalitarianism; Welfare Cost; Equal-Wage Policy; Income Risks.

Taxes and Unmarried Fathers’ Participation in the Underground Economy

In this paper we employ data from the Fragile Families and Child Well-Being Study in order to estimate a model of underground labor supply developed by Lemieux et al. (1994). We focus specifically on the underground labor supply of unmarried fathers, a group that is likely to have significant involvement in the underground economy. We also extend the empirical analysis of Lemieux et al. by taking into account exogenous state and local variation in marginal tax rates, as well as sociodemographic variables related to the likelihood of participation in the underground. In accordance with expectations, we find that a significant proportion of unmarried fathers report participation in the underground. However, although the theoretical model predicts a positive relationship between the tax rate and underground hours of work (under certain conditions), we find that the effect of the tax rate on hours is statistically indistinguishable from zero, even after including exogenous variation in tax rates. We also fail to find a positive and statistically significant effect of the tax rate on participation in the underground. Within the context of the model, these results have specific implications for the magnitudes of the probability of detection and the penalty on evaded tax. Therefore, we conclude that additional empirical information is needed regarding these parameters. Future research might also employ other datasets in the estimation of the theoretical model outlined by Lemieux et al., as well as investigate the applicability of other models of underground labor supply.