Critical fluctuations and slowing down of chaos

Fluids cooled to the liquid-vapor critical point develop system-spanning fluctuations in density that transform their visual appearance. Despite a rich phenomenology, however, there is not currently an explanation of the mechanical instability in the molecular motion at this critical point. Here, we couple techniques from nonlinear dynamics and statistical physics to analyze the emergence of this singular state. Numerical simulations and analytical models show how the ordering mechanisms of critical dynamics are measurable through the hierarchy of spatiotemporal Lyapunov vectors. A subset of unstable vectors soften near the critical point, with a marked suppression in their characteristic exponents that reflects a weakened sensitivity to initial conditions. Finite-time fluctuations in these exponents exhibit sharply peaked dynamical timescales and power law signatures of the critical dynamics. Collectively, these results are symptomatic of a critical slowing down of chaos that sits at the root of our statistical understanding of the liquid-vapor critical point

Mesoscopic Noise Theory: Microscopics, or Phenomenology?

We argue, physically and formally, that existing diffusive models of noise yield inaccurate microscopic descriptions of nonequilibrium current fluctuations. The theoretical shortfall becomes pronounced in quantum-confined metallic systems, such as the two-dimensional electron gas. In such systems we propose a simple experimental test of mesoscopic validity for diffusive theory's central claim: the smooth crossover between Johnson-Nyquist and shot noise.Comment: Invited paper, UPoN'99 Conference, Adelaide. 13 pp, no figs. Minor revisions to text and reference

Comparison of Canonical and Grand Canonical Models for selected multifragmentation data

Calculations for a set of nuclear multifragmentation data are made using a Canonical and a Grand Canonical Model. The physics assumptions are identical but the Canonical Model has an exact number of particles, whereas, the Grand Canonical Model has a varying number of particles, hence, is less exact. Interesting differences are found.Comment: 12 pages, Revtex, and 3 postscript figure

Effective Actions for 0+1 Dimensional Scalar QED and its SUSY Generalization at T≠0T\neq 0

We compute the effective actions for the 0+1 dimensional scalar field interacting with an Abelian gauge background, as well as for its supersymmetric generalization at finite temperature.Comment: 5 pages, Latex fil

Tunneling transport in NSN junctions made of Majorana nanowires across the topological quantum phase transition

We theoretically consider transport properties of a normal metal (N)- superconducting semiconductor nanowire (S)-normal metal (N) structure (NSN) in the context of the possible existence of Majorana bound states in disordered semiconductor-superconductor hybrid systems in the presence of spin-orbit coupling and Zeeman splitting induced by an external magnetic field. We study in details the transport signatures of the topological quantum phase transition as well as the existence of the Majorana bound states in the electrical transport properties of the NSN structure. Our theory includes the realistic nonperturbative effects of disorder, which is detrimental to the topological phase (eventually suppressing the superconducting gap completely), and the effects of the tunneling barriers (or the transparency at the tunneling NS contacts), which affect (and suppress) the zero bias conductance peak associated with the zero energy Majorana bound states. We show that in the presence of generic disorder and barrier transparency the interpretation of the zero bias peak as being associated with the Majorana bound state is problematic since the nonlocal correlations between the two NS contacts at two ends may not manifest themselves in the tunneling conductance through the whole NSN structure. We establish that a simple modification of the standard transport measurements using conductance differences (rather than the conductance itself as in a single NS junction) as the measured quantity can allow direct observation of the nonlocal correlations inherent in the Majorana bound states and enables the mapping out of the topological phase diagram (even in the presence of considerable disorder) by precisely detecting the topological quantum phase transition point.Comment: 34 pages, 7 figures, 1 table. New version with minor modifications and more physical discussion