Conditions for Equality between Lyapunov and Morse Decompositions

Let $Q\rightarrow X$ be a continuous principal bundle whose group $G$ is reductive. A flow $\phi$ of automorphisms of $Q$ endowed with an ergodic probability measure on the compact base space $X$ induces two decompositions of the flag bundles associated to $Q$. A continuous one given by the finest Morse decomposition and a measurable one furnished by the Multiplicative Ergodic Theorem. The second is contained in the first. In this paper we find necessary and sufficient conditions so that they coincide. The equality between the two decompositions implies continuity of the Lyapunov spectra under pertubations leaving unchanged the flow on the base space

Simulated Tempering: A New Monte Carlo Scheme

We propose a new global optimization method ({\em Simulated Tempering}) for simulating effectively a system with a rough free energy landscape (i.e. many coexisting states) at finite non-zero temperature. This method is related to simulated annealing, but here the temperature becomes a dynamic variable, and the system is always kept at equilibrium. We analyze the method on the Random Field Ising Model, and we find a dramatic improvement over conventional Metropolis and cluster methods. We analyze and discuss the conditions under which the method has optimal performances.Comment: 12 pages, very simple LaTeX file, figures are not included, sorr

Geometric scaling of purely-elastic flow instabilities

We present a combined experimental, numerical and theoretical investigation of the geometric scaling of the onset of a purely-elastic flow instability in a serpentine channel. Good qualitative agreement is obtained between experiments, using dilute solutions of flexible polymers in microfluidic devices, and two-dimensional numerical simulations using the UCM model. The results are confirmed by a simple theoretical analysis, based on the dimensionless criterion proposed by Pakdel-McKinley for onset of a purely-elastic instability

Charged Higgs Boson Pairs at the LHC

We compute the cross section for pair production of charged Higgs bosons at the LHC and compare the three production mechanisms. The bottom-parton scattering process is computed to NLO, and the validity of the bottom-parton approach is established in detail. The light-flavor Drell-Yan cross section is evaluated at NLO as well. The gluon fusion process through a one-loop amplitude is then compared with these two results. We show how a complete sample of events could look, in terms of total cross sections and distributions of the heavy final states.Comment: 15 pages with 8 figure

Stripe-tetragonal phase transition in the 2D Ising model with dipole interactions: Partition-function zeros approach

We have performed multicanonical simulations to study the critical behavior of the two-dimensional Ising model with dipole interactions. This study concerns the thermodynamic phase transitions in the range of the interaction \delta where the phase characterized by striped configurations of width h=1 is observed. Controversial results obtained from local update algorithms have been reported for this region, including the claimed existence of a second-order phase transition line that becomes first order above a tricritical point located somewhere between \delta=0.85 and 1. Our analysis relies on the complex partition function zeros obtained with high statistics from multicanonical simulations. Finite size scaling relations for the leading partition function zeros yield critical exponents \nu that are clearly consistent with a single second-order phase transition line, thus excluding such tricritical point in that region of the phase diagram. This conclusion is further supported by analysis of the specific heat and susceptibility of the orientational order parameter.Comment: to appear in Phys. Rev.