On the c-theorem in more than two dimensions

Several pieces of evidence have been recently brought up in favour of the c-theorem in four and higher dimensions, but a solid proof is still lacking. We present two basic results which could be useful for this search: i) the values of the putative c-number for free field theories in any even dimension, which illustrate some properties of this number; ii) the general form of three-point function of the stress tensor in four dimensions, which shows some physical consequences of the c-number and of the other trace-anomaly numbers.Comment: Latex, 7 pages, 1 tabl

Classification of Quantum Hall Universality Classes by $\ W_{1+\infty}\ $ symmetry

We show how two-dimensional incompressible quantum fluids and their excitations can be viewed as $\ W_{1+\infty}\$ edge conformal field theories, thereby providing an algebraic characterization of incompressibility. The Kac-Radul representation theory of the $\ W_{1+\infty}\$ algebra leads then to a purely algebraic complete classification of hierarchical quantum Hall states, which encompasses all measured fractions. Spin-polarized electrons in single-layer devices can only have Abelian anyon excitations.Comment: 11 pages, RevTeX 3.0, MPI-Ph/93-75 DFTT 65/9

Symmetry Aspects and Finite-Size Scaling of Quantum Hall Fluids

The exactness and universality observed in the quantum Hall effect suggests the existence of a symmetry principle underlying Laughlin's theory. We review the role played by the infinite $W_{\infty }$ and conformal algebras as dynamical symmetries of incompressible quantum fluids and show how they predict universal finite-size effects in the excitation spectrum.Comment: 15 pages, CERN-TH-6784/93, LateX fil

Infrared Behaviour of Massless Integrable Flows entering the Minimal Models from phi_31

It is known that any minimal model M_p receives along its phi_31 irrelevant direction *two* massless integrable flows: one from M_{p+1} perturbed by phi_{13}, the other from Z_{p-1} parafermionic model perturbed by its generating parafermion field. By comparing Thermodynamic Bethe Ansatz data and ``predictions'' of infrared Conformal Perturbation Theory we show that these two flows are received by M_p with opposite coupling constants of the phi_31 irrelevant perturbation. Some comments on the massless S matrices of these two flows are added.Comment: 12 pages, Latex - One misprinted (uninfluent) coefficient corrected in Tab.

Chiral Partition Functions of Quantum Hall Droplets

Chiral partition functions of conformal field theory describe the edge excitations of isolated Hall droplets. They are characterized by an index specifying the quasiparticle sector and transform among themselves by a finite-dimensional representation of the modular group. The partition functions are derived and used to describe electron transitions leading to Coulomb blockade conductance peaks. We find the peak patterns for Abelian hierarchical states and non-Abelian Read-Rezayi states, and compare them. Experimental observation of these features can check the qualitative properties of the conformal field theory description, such as the decomposition of the Hilbert space into sectors, involving charged and neutral parts, and the fusion rules.Comment: 37 pages, 8 figure

A note on the topological order of noncommutative Hall fluids

We evaluate the ground state degeneracy of noncommutative Chern-Simons models on the two-torus, a quantity that is interpreted as the "topological order" of associated phases of Hall fluids. We define the noncommutative theory via T-duality from an ordinary Chern-Simons model with non-abelian 't Hooft magnetic fluxes. Motivated by this T-duality, we propose a discrete family of noncommutative, non-abelian fluid models, arising as a natural generalization of the standard noncommutative Chern-Simons effective models. We compute the topological order for these universality classes, and comment on their possible microscopic interpretation.Comment: 14 page

Area Preserving Transformations in Non-commutative Space and NCCS Theory

We propose an heuristic rule for the area transformation on the non-commutative plane. The non-commutative area preserving transformations are quantum deformation of the classical symplectic diffeomorphisms. Area preservation condition is formulated as a field equation in the non-commutative Chern-Simons gauge theory. The higher dimensional generalization is suggested and the corresponding algebraic structure - the infinite dimensional $\sin$-Lie algebra is extracted. As an illustrative example the second-quantized formulation for electrons in the lowest Landau level is considered.Comment: revtex, 9 pages, corrected typo

Neutral modes edge state dynamics through quantum point contacts

Dynamics of neutral modes for fractional quantum Hall states is investigated for a quantum point contact geometry in the weak-backscattering regime. The effective field theory introduced by Fradkin-Lopez for edge states in the Jain sequence is generalized to the case of propagating neutral modes. The dominant tunnelling processes are identified also in the presence of non-universal phenomena induced by interactions. The crossover regime in the backscattering current between tunnelling of single-quasiparticles and of agglomerates of p-quasiparticles is analysed. We demonstrate that higher order cumulants of the backscattering current fluctuations are a unique resource to study quantitatively the competition between different carrier charges. We find that propagating neutral modes are a necessary ingredient in order to explain this crossover phenomena.Comment: 28 pages, 5 figure