Characterization of arbitrage-free markets

The present paper deals with the characterization of no-arbitrage properties of a continuous semimartingale. The first main result, Theorem \refMainTheoremCharNA, extends the no-arbitrage criterion by Levental and Skorohod [Ann. Appl. Probab. 5 (1995) 906-925] from diffusion processes to arbitrary continuous semimartingales. The second main result, Theorem 2.4, is a characterization of a weaker notion of no-arbitrage in terms of the existence of supermartingale densities. The pertaining weaker notion of no-arbitrage is equivalent to the absence of immediate arbitrage opportunities, a concept introduced by Delbaen and Schachermayer [Ann. Appl. Probab. 5 (1995) 926-945]. Both results are stated in terms of conditions for any semimartingales starting at arbitrary stopping times \sigma. The necessity parts of both results are known for the stopping time \sigma=0 from Delbaen and Schachermayer [Ann. Appl. Probab. 5 (1995) 926-945]. The contribution of the present paper is the proofs of the corresponding sufficiency parts.Comment: Published at http://dx.doi.org/10.1214/105051604000000558 in the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org

Incitement, Threats, and Constitutional Guarantees: First Amendment Protections pre- and post-Elonis

[Excerpt] While the First Amendment to the United States Constitution protects the freedom of expression, individuals issuing threats or advocating illegal conduct may be subject to punishment. What constitutes proscribable speech has long been evolving, and the recent jurisprudence suggests that First Amendment protections are more robust for advocacy of illegal conduct than for threats. Elonis v. United States provided the Court with a golden opportunity to clarify First Amendment threat jurisprudence; however, those hoping for an illuminating analysis cannot help but be disappointed. Part I of this Article discusses the developing First Amendment jurisprudence regarding the regulation of incitement, focusing on how constitutional protections for such speech have increased over time. Part II discusses the constitutional limitations on the regulation of threats, noting the Court\u27s consistent refusal to address what kind of subjective intent is necessary in order for an individual to be convicted of having made a threat. Part III focuses on Elonis in particular, explaining how the case wasted the opportunity to clarify a number of First Amendment issues. The article concludes by pointing to several areas the Court may be forced to address in the not-too-distant future, including some of the confusions created by the Elonis opinion itself

On the correlation structure of microstructure noise in theory and practice

We argue for incorporating the financial economics of market microstructure into the financial econometrics of asset return volatility estimation. In particular, we use market microstructure theory to derive the cross-correlation function between latent returns and market microstructure noise, which feature prominently in the recent volatility literature. The cross-correlation at zero displacement is typically negative, and cross-correlations at nonzero displacements are positive and decay geometrically. If market makers are sufficiently risk averse, however, the cross-correlation pattern is inverted. Our results are useful for assessing the validity of the frequently-assumed independence of latent price and microstructure noise, for explaining observed cross-correlation patterns, for predicting as-yet undiscovered patterns, and for making informed conjectures as to improved volatility estimation methods

Responsibility Effects in Decision Making under Risk

We systematically explore decision situations in which a decision maker bears responsibility for somebody else's outcomes as well as for her own in situations of payoff equality. In the gain domain we confirm the intuition that being responsible for somebody else's payoffs increases risk aversion. This is however not attributable to a 'cautious shift' as often thought. Indeed, looking at risk attitudes in the loss domain, we find an increase in risk seeking under responsibility. This raises issues about the nature of various decision biases under risk, and to what extent changed behavior under responsibility may depend on a social norm of caution in situations of responsibility versus naive corrections from perceived biases. To further explore this issue, we designed a second experiment to explore risk-taking behavior for gain prospects offering very small or very large probabilities of winning. For large probabilities, we find increased risk aversion, thus confirming our earlier finding. For small probabilities however, we find an increase of risk seeking under conditions of responsibility. The latter finding thus discredits hypotheses of a social rule dictating caution under responsibility, and can be explained through flexible self-correction models predicting an accentuation of the fourfold pattern of risk attitudes predicted by prospect theory. An additional accountability mechanism does not change risk behavior, except for mixed prospects, in which it reduces loss aversion. This indicates that loss aversion is of a fundamentally different nature than probability weighting or utility curvature. Implications for debiasing are discussed