THz radiation induced circular Hall effect in graphene

We report on the observation of the circular transversal terahertz photoconductivity in monolayer graphene supplied by a back gate. The photoconductivity response is caused by the free carrier absorption and reverses its sign upon switching the radiation helicity. The observed dc Hall effect manifests the time inversion symmetry breaking induced by circularly polarized terahertz radiation in the absence of a magnetic field. For low gate voltages, the photosignal is found to be proportional to the radiation intensity and can be ascribed to the alignment of electron momenta by the combined action of THz and static electric fields as well as by the dynamic heating and cooling of the electron gas. Strikingly, at high gate voltages, we observe that the linear-in-intensity Hall photoconductivity vanishes; the photoresponse at low intensities becomes superlinear and varies with the square of the radiation intensity. We attribute this behavior to the interplay of the second- and fourth-order effects in the radiation electric field which has not been addressed theoretically so far and requires additional studies

Violating United Nations Global Compact Principles: An Event Study

The Volkswagen diesel scandal of September 2015 demonstrated that financial metrics are insufficient to capture Corporate Socially Responsible risks. In this paper we conduct an event study of corporate news with violations of CSR principles as formulated in the UN Global Compact, using daily data and quoted companies between 2009 and 2015. We find that companies behaving irresponsibly face a significant stock price decrease on the announcement day. We analyze the impact of each principle and demonstrate that those components associated with stronger economic and legal consequences such as pollution, complicity, and bribery have a significant permanent impact while violations linked to freedom of association, human rights, child labour, forced labour, and discrimination do not reveal a pronounced persistent effect on stock prices. Another consequence is a large reputation cost

Predicting tail-related risk measures: The consequences of using GARCH filters for non GARCH data

We investigate the consequences for Value-at-Risk and expected shortfall purposes of using a GARCH filter on various mis-specified processes. In general. we find that the McNeil and Frey (McNeil, A.J. and R. Frey, 2000, Estimation of Tail-Related Risk Measures for Heteroscedastic Financial Time Series: An Extreme Value Approach, journal of Empirical Finance 7, 271-300.) two step procedure has very good forecasting properties. Using an unconditional non-filtered tail estimate also appears to perform satisfactorily for expected shortfall measurements but less so for VaR computations. Methods assuming specific densities such as the Gaussian or Student-t may yield wrong predictions. Thus, the use of an adequacy test for filtered data to given densities appears relevant. The paper builds on recent techniques to obtain thresholds for extreme value computations. Statistical tests for the expected shortfall, based on the circular bootstrap, are developed