Thermal Transport in Chiral Conformal Theories and Hierarchical Quantum Hall States

Chiral conformal field theories are characterized by a ground-state current at finite temperature, that could be observed, e.g. in the edge excitations of the quantum Hall effect. We show that the corresponding thermal conductance is directly proportional to the gravitational anomaly of the conformal theory, upon extending the well-known relation between specific heat and conformal anomaly. The thermal current could signal the elusive neutral edge modes that are expected in the hierarchical Hall states. We then compute the thermal conductance for the Abelian multi-component theory and the W-infinity minimal model, two conformal theories that are good candidates for describing the hierarchical states. Their conductances agree to leading order but differ in the first, universal finite-size correction, that could be used as a selective experimental signature.Comment: Latex, 17 pages, 2 figure

2D Superconductivity: Classification of Universality Classes by Infinite Symmetry

I consider superconducting condensates which become incompressible in the infinite gap limit. Classical 2D incompressible fluids possess the dynamical symmetry of area-preserving diffeomorphisms. I show that the corresponding infinite dynamical symmetry of 2D superconducting fluids is the coset ${{W_{1+\infty} \otimes \bar W_{1+\infty}} \over U(1)_{\rm diagonal}}$, with $W_{1+\infty}$ the chiral algebra of quantum area-preserving diffeomorphisms and I derive its minimal models. These define a discrete set of 2D superconductivity universality classes which fall into two main categories: conventional superconductors with their vortex excitations and unconventional superconductors. These are characterized by a broken $U(1)_{\rm vector} \otimes U(1)_{\rm axial}$ symmetry and are labeled by an integer level $m$. They possess neutral spinon excitations of fractional spin and statistics $S = {\theta \over 2\pi} = {{m-1} \over 2m}$ which carry also an $SU(m)$ isospin quantum number; this hidden $SU(m)$ symmetry implies that these anyon excitations are non-Abelian. The simplest unconventional superconductor is realized for $m=2$: in this case the spinon excitations are semions (half-fermions). My results show that spin-charge separation in 2D superconductivity is a universal consequence of the infinite symmetry of the ground state. This infinite symmetry and its superselection rules realize a quantum protectorate in which the neutral spinons can survive even as soft modes on a rigid, spinless charge condensate.Comment: Revised version to appear in Nuclear Physics

Modular Invariant Partition Functions in the Quantum Hall Effect

We study the partition function for the low-energy edge excitations of the incompressible electron fluid. On an annular geometry, these excitations have opposite chiralities on the two edges; thus, the partition function takes the standard form of rational conformal field theories. In particular, it is invariant under modular transformations of the toroidal geometry made by the angular variable and the compact Euclidean time. The Jain series of plateaus have been described by two types of edge theories: the minimal models of the W-infinity algebra of quantum area-preserving diffeomorphisms, and their non-minimal version, the theories with U(1)xSU(m) affine algebra. We find modular invariant partition functions for the latter models. Moreover, we relate the Wen topological order to the modular transformations and the Verlinde fusion algebra. We find new, non-diagonal modular invariants which describe edge theories with extended symmetry algebra; their Hall conductivities match the experimental values beyond the Jain series.Comment: Latex, 38 pages, 1 table (one minor error has been corrected

Investigating the structure of expansions and recessions in US business cycle: a modified recursive partitioning approach

In this paper the problem of identifying the structure of expansions and recessions in the US economy is placed in the framework of recursive partitioning and discriminant analysis. The classification provided by the National Bureau ofEconomic Research (NBER) is considered. Using as covariates themain variables and indicators deemed useful to predict the business cycle, a modified recursive partitioning approach isproposed at each step (tree node) the method identifies the linear combination of the covariates that discriminates the mostbetween being in and out of a recession this new covariate is then used to split the data. The application to the case of the US business cycle and the comparison with classical logisticregression shows the merits of the proposed approach that represents a useful to tool to identify and to interpret thestructure of expansionsand recessions.Business-cycle indicators

Public policy and downsizing decisions

Public policy ; Labor market ; Labor productivity

Examining the Incidence of Downsizing and Its Effect on Establishment Performance

The interest in examining job security and job stability has been driven in part by the phenomenon of downsizing. The distinctiveness of downsizing, as opposed to more traditional layoffs, is that the job cuts do not necessarily appear to be driven by shortfalls in demand but instead appear to be driven by the search for operating efficiencies. Despite the interest in downsizing, there has been essentially no serious investigation into its causes. I distinguish downsizing from job cuts associated with shortfalls in demand and find that employment and management practices over which employers have control, such as severance pay and profit sharing, are important predictors of subsequent downsizing and more general job losses. Surprisingly, excess operating capacity is not necessarily related to more general job losses at the establishment level. I also examine the relationship between both job losses associated with shortfalls in demand and downsizing and subsequent financial performance. The results suggest, among other things, that downsizing reduces labor costs per employee but also sales per employee. Job cuts associated with excess capacity appear to be somewhat more successful at improving sales per employee than is downsizing.

Technology and skill requirements: implications for establishment wage structures

Wages ; Human capital ; Technology ; Income distribution ; Labor market ; Regression analysis

Multipole Expansion in the Quantum Hall Effect

The effective action for low-energy excitations of Laughlin's states is obtained by systematic expansion in inverse powers of the magnetic field. It is based on the W-infinity symmetry of quantum incompressible fluids and the associated higher-spin fields. Besides reproducing the Wen and Wen-Zee actions and the Hall viscosity, this approach further indicates that the low-energy excitations are extended objects with dipolar and multipolar moments.Comment: 29 pages, 5 figures; v2: comments and references adde