Signature, positive Hopf plumbing and the Coxeter transformation

By a theorem of A'Campo, the eigenvalues of certain Coxeter transformations are positive real or lie on the unit circle. By optimally bounding the signature of tree-like positive Hopf plumbings from below by the genus, we prove that at least two thirds of them lie on the unit circle. In contrast, we show that for divide links, the signature cannot be linearly bounded from below by the genus.Comment: 16 pages, 5 figures, with appendix by Peter Feller and Livio Liecht

Strangeness production as a function of charged particle multiplicity in proton-proton collisions

Recent measurements performed in high-multiplicity proton-proton (pp) and proton-lead (p-Pb) collisions have shown features that are reminiscent of those observed in lead-lead (Pb-Pb) collisions. These observations warrant a comprehensive measurement of the production of identified particles. We report on the production of \allparts at mid-rapidity measured as a function of multiplicity in pp collisions at $\sqrt{s}$ = 7 TeV with the ALICE experiment. Spectral shapes studied both for individual particles and via particle ratios such as ($\Lambda/K^{0}_{S}$) as a function of $p_{T}$ exhibit an evolution with event multiplicity and the production rates of hyperons are observed to increase more strongly than those of non-strange hadrons. These phenomena are qualitatively similar to the ones observed in p-Pb and Pb-Pb collisions

Minimal dilatation in Penner's construction

For all orientable closed surfaces, we determine the minimal dilatation among mapping classes arising from Penner's construction. We also discuss generalisations to surfaces with punctures.Comment: 11 pages, 6 figure

The functional form of the demand for euro area M1

A remarkable development seen in recent years is the pronounced decline in euro area M1 velocity vis--vis a moderate decline in short-term interest rates, which represent the most natural opportunity cost for M1, suggesting an increase in the interest rate elasticity of M1 demand. In fact, estimating a theoretically plausible and stable demand function for M1 in the euro area is possible, if a functional form of money demand allowing for an interest rate elasticity decreasing in size with the level of the interest rate is imposed. This finding would apparently suggest that the decline in inflation and nominal interest rates in Europe experienced in the run-up to the euro should have 'naturally' brought about an increased degree of preference for liquidity without any fundamental change in agents' preferences. To test the validity of this conclusion, a time-varying parameters model is estimated through Kalman filter on the level of real M1, which is able to test simultaneously the stability of the parameters and the functional form of the demand for euro area M1. In this case, results clearly suggest the double log function to be very close to the true 'deep' functional form of M1 demand in the euro area, consistent with the findings of Chadha, Haldane and Janssen (1998) for the United Kingdom and of Lucas (2000) for the United States. At the same time, there is evidence of an increased interest rate elasticity in M1 demand in the most recent years, presumably associated with the transition to the new environment prevailing from the start of Stage Three of EMU JEL Classification: E41, E52

A speed limit monetary policy rule for the euro area

This paper estimates a hybrid New Keynesian model on euro area data and evaluates the performance of different simple policy rules and of the optimal unconstrained rule under commitment. The study reaches two main conclusions. First, inflation is found to be mainly forward-looking in the euro area, which implies the optimal policy reaction to cost push shocks is a muted one. Second, a "speed limit" rule of the type recently proposed by Walsh (2003) is able to closely approximate the performance of the optimal rule under commitment. The optimal speed limit rule is also characterised by super-inertia, making it a first difference rule similar to those recently proposed as a possible solution to measurement problems in the level of the natural interest rate and of potential output. JEL Classification: E52, E58commitment, euro area, hybrid New Keynesian model, monetary policy rules, speed limit policies