Yong-Shi Wu

Stable Nontrivial Z2 Topology in Ultrathin Bi (111) Films: A First-Principles Study

Recently, there have been intense efforts in searching for new topological insulator materials. Based on first-principles calculations, we find that all the ultrathin Bi (111) films are characterized by a nontrivial Z(2) number independent of the film thickness, without the odd-even oscillation of topological triviality as commonly perceived. The stable nontrivial Z(2) topology is retained by the concurrent band gap inversions at multiple time-reversal-invariant k points with the increasing film thickness and associated with the intermediate interbilayer coupling of the Bi film. Our calculations further indicate that the presence of metallic surface states in thick Bi (111) films can be effectively removed by surface adsorption.

Two-loop analysis of non-Abelian Chern-Simons theory.

Perturbative renormalization of a non-Abelian Chern-Simons gauge theory is examined. It is demonstrated by explicit calculation that, in the pure Chern-Simons theory, the [beta] function for the coefficient of the Chern-Simons term vanishes to three-loop order. Both dimensional regularization and regularization by introducing a conventional Yang-Mills term in the action are used. It is shown that dimensional regularization is not gauge invariant at two loops. A variant of this procedure, similar to regularization by dimensional reduction used in supersymmetric field theories, is shown to obey the Slavnov-Taylor identity to two loops and gives no renormalization of the Chern-Simons term. Regularization with the Yang-Mills term yields a finite integer-valued renormalization of the coefficient of the Chern-Simons term at one loop, and we conjecture no renormalization at higher order. We also examine the renormalization of Chern-Simons theory coupled to matter. We show that in the non-Abelian case the Chern-Simons gauge field as well as the matter fields require infinite renormalization at two loops and therefore obtain nontrivial anomalous dimensions. We show that the [beta] function for the gauge coupling constant is zero to two-loop order, consistent with the topological quantization condition for this constant.

Comments on the Hopf lagrangian and fractional statistics of solitons

Abstract We show that the nonlocal Hopf lagrangian in a model for solitons obeying fractional statistics, namely the (2 + 1)-dimensional O(3) nonlinear σ-model, can be written in a local form and is locally a total divergence. With these properties the effects of this lagrangian are converted to a multi-valued phase of the wave functional. In doing so we make it clear why an arbitrary nontopological or nonlocal lagrangian does not determine statistics at all.

Integrable open spin chain in super Yang-Mills and the plane-wave/SYM duality

We investigate the integrable structures in an = 2 superconformal Sp(N) Yang-Mills theory with matter, which is dual to an open+closed string system. We restrict ourselves to the BMN operators that correspond to free string states. In the closed string sector, an integrable structure is inherited from its parent theory, = 4 SYM. For the open string sector, the planar one-loop mixing matrix for gauge invariant holomorphic scalar operators is identified with the hamiltonian of an integrable SU(3) open spin chain. Using the K-matrix formalism we identify the integrable open-chain boundary conditions that correspond to string boundary conditions. The solutions to the algebraic Bethe ansatz equations (ABAE) with a few impurities are shown to recover the anomalous dimensions that exactly match the spectrum of free open string in the plane-wave background. We also discuss the properties of the solutions of ABAE beyond the BMN regime.

Noncommutative gauge theories in matrix theory

We present a general framework for matrix theory compactified on a quotient space

Covariant quantization of chiral bosons and OSp(1, 1|2) symmetry

{\mathbf{R}}^{n}/\ensuremath{\Gamma},

Towards a noncommutative geometric approach to matrix compactification

with \ensuremath{\Gamma} a discrete group of Euclidean motions in

Open spin chain and open spinning string

{\mathbf{R}}^{n}.

Integrable spin chain and operator mixing in N=1,2 supersymmetric theories

The general solution to the quotient conditions gives a gauge theory on a noncommutative space. We characterize the resulting noncommutative gauge theory in terms of the twisted group algebra of \ensuremath{\Gamma} associated with a projective regular representation. Also we show how to extend our treatments to incorporate orientifolds.

Near-Horizon Virasoro Symmetry and the Entropy of de Sitter Space in Any Dimension

The covariant quantization of a chiral boson is carried out on an extended phase space. To convert the second-class constraint ∂+φ(σ, τ) = 0 into first-class ones, a la Faddeev and Shatashvili, infinitely many auxiliary scalars are introduced. We have explored the OSp(1, 1|2) symmetry, which is a group theoretical extension of the BRST symmetry, to prove the no-ghost theorem and the chirality of the physical subspace. The infinite product of determinants from the ghosts and auxiliary scalars in path integral are regularized in an OSp invariant way, leading to the desired partition function. The formulation holds good in the presence of static background gauge fields.