Arguing against obligatory feature inheritance: Evidence from French transitive participle agreement

In this article, we accept the view that the relevant type of case/agreement features originate on phase heads, but argue against a strong view of the Percolation Hypothesis on which uninterpretable features obligatorily percolate down from a phase head onto a selected head: on the contrary, we maintain that there are structures in which uninterpretable case/agreement features remain on the phase head throughout the derivation. The main empirical evidence we adduce in support of our claim comes from a novel analysis of French past participle agreement which builds on earlier work by Radford and Vincent (2007) and Vincent (2007). In section 2, we briefly characterise French past participle agreement, and outline the key assumptions which our analysis makes. We show how our analysis handles past participle agreement with a local direct object in section 3, and go on to show how it correctly specifies when (and why) agreement can take place with the subject of an embedded infinitive complement in section 4. In section 5, we present further empirical evidence against the Percolation Hypothesis from a range of independent phenomena, and highlight some theoretical inadequacies of the hypothesis, as well as reconsidering the motivation for feature percolation. Finally, in section 6 we summarize our overall conclusions

Curvature Spectra and Nongaussianities in the Roulette Inflation Model

Using the gradient expansion method of Rigopoulos, Shellard and van Tent which treats cosmological perturbations as gradients on top of a homogeneous and isotropic FRW background, we study the production of nongaussianities in the roulette model of inflation. Investigating a number of trajectories within this two-field model of inflation, we find that while the superhorizon influence of the isocurvature modes on the curvature bispectrum produces nonzero contribution to f_NL, the effect is negligible next to the standard inflationary prediction |f_NL| ~ n_s - 1. This is the case in both the squeezed and equilateral configurations of the bispectrum, although the former is slightly larger in the trajectories under consideration.Comment: 23 pages, 6 figures, 3 tables, 1 appendix; Added references, slightly extended section

Observable Graphs

An edge-colored directed graph is \emph{observable} if an agent that moves along its edges is able to determine his position in the graph after a sufficiently long observation of the edge colors. When the agent is able to determine his position only from time to time, the graph is said to be \emph{partly observable}. Observability in graphs is desirable in situations where autonomous agents are moving on a network and one wants to localize them (or the agent wants to localize himself) with limited information. In this paper, we completely characterize observable and partly observable graphs and show how these concepts relate to observable discrete event systems and to local automata. Based on these characterizations, we provide polynomial time algorithms to decide observability, to decide partial observability, and to compute the minimal number of observations necessary for finding the position of an agent. In particular we prove that in the worst case this minimal number of observations increases quadratically with the number of nodes in the graph. From this it follows that it may be necessary for an agent to pass through the same node several times before he is finally able to determine his position in the graph. We then consider the more difficult question of assigning colors to a graph so as to make it observable and we prove that two different versions of this problem are NP-complete.Comment: 15 pages, 8 figure