arXiv subjects

Kuo-Wei Huang

Publications and source records attributed to Kuo-Wei Huang.

32 records · Page 2Linked to original sources

arXiv2017

Displacement Operators and Constraints on Boundary Central Charges

Boundary conformal field theories have several additional terms in the trace anomaly of the stress tensor associated purely with the boundary. We constrain the corresponding boundary central charges in three- and four-dimensional conformal field theories in terms of two- and three-point correlation functions of the displacement operator. We provide a general derivation by comparing the trace anomaly with scale dependent contact terms in the correlation functions. We conjecture a relation between the a-type boundary charge in three dimensions and the stress tensor two-point function near the boundary. We check our results for several free theories.

hep-th↗

arXiv2017

Synthesis of Single-crystal-like Nanoporous Carbon Membranes and Their Applications in Overall Water Splitting

Nanoporous graphitic carbon membranes with defined chemical composition and pore architecture are novel nanomaterials that are actively pursued. Compared to easy-to-make porous carbon powders that dominate the porous carbon research and applications in energy generation/conversion and environmental remediation, porous carbon membranes are synthetically more challenging though rather appealing from an application perspective due to their structural integrity, interconnectivity and purity. Here we report a simple bottom-up approach to fabricate large-size, freestanding, porous carbon membranes that feature an unusual single-crystal-like graphitic order and hierarchical pore architecture plus favorable nitrogen doping. When loaded with cobalt nanoparticles, such carbon membranes serve as high-performance carbon-based non-noble metal electrocatalyst for overall water splitting.

cond-mat.mtrl-sci↗

arXiv2016

Boundary Fluctuations and A Reduction Entropy

The boundary Weyl anomalies live on a codimension-1 boundary, $\partial {\cal M}$. The entanglement entropy originates from infinite correlations on both sides of a codimension-2 surface, $Σ$. Motivated to have a further understanding of the boundary effects, we introduce a notion of reduction entropy, which, guided by thermodynamics, is a combination of the boundary effective action and the boundary stress tensor defined by allowing the metric on $\partial {\cal M}$ to fluctuate. We discuss how a reduction might be performed so that the reduction entropy reproduces the entanglement structure.

hep-th↗

arXiv2016

High-flux water desalination with interfacial salt sieving effect in nanoporous carbon composite membranes

Nanoporous carbon composite membranes, comprising a layer of porous carbon fiber structures with an average channel width of 30-60 nm grown on a porous ceramic substrate, are found to exhibit robust desalination effect with high freshwater flux. In three different membrane processes of vacuum membrane distillation, reverse osmosis and forward osmosis, the carbon composite membrane showed 100% salt rejection with 3.5 to 20 times higher freshwater flux compared to existing polymeric membranes. Thermal accounting experiments found that at least 80% of the freshwater pass through the carbon composite membrane with no phase change. Molecular dynamics simulations revealed a unique salt rejection mechanism. When seawater is interfaced with either vapor or the surface of carbon, one to three interfacial atomic layers contain no salt ions. Below the liquid entry pressure, the salt solution is stopped at the openings to the porous channels and forms a meniscus, while the surface layer of freshwater can feed the surface diffusion flux that is fast-transported on the surfaces of the carbon fibers, driven by the chemical potential gradient. As the surface-transported water does not involve a phase change, hence that component involves no energy expenditure in the form of latent heat.

cond-mat.mtrl-sci↗

arXiv2016

Boundary Anomalies and Correlation Functions

It was shown recently that boundary terms of conformal anomalies recover the universal contribution to the entanglement entropy and also play an important role in the boundary monotonicity theorem of odd-dimensional quantum field theories. Motivated by these results, we investigate relationships between boundary anomalies and the stress tensor correlation functions in conformal field theories. In particular, we focus on how the conformal Ward identity and the renormalization group equation are modified by boundary central charges. Renormalized stress tensors induced by boundary Weyl invariants are also discussed, with examples in spherical and cylindrical geometries.

hep-th↗

arXiv2016

Central Charge and Entangled Gauge Fields

Entanglement entropy of gauge fields is calculated using the partition function in curved spacetime with a boundary. We derive a Gibbons-Hawking-like term from a Becchi-Rouet-Stora-Tyutin (BRST) action and a Wald-entropy-like codimension-2 surface term is produced. It is further suggested that boundary degrees of freedom localized on the entanglement surface generated from the gauge redundancy could be used to resolve a subtle mismatch in a universal conformal anomaly- entanglement entropy relation.

hep-th↗

arXiv2015

Universal Entanglement and Boundary Geometry in Conformal Field Theory

Employing a conformal map to hyperbolic space cross a circle, we compute the universal contribution to the vacuum entanglement entropy (EE) across a sphere in even-dimensional conformal field theory. Previous attempts to derive the EE in this way were hindered by a lack of knowledge of the appropriate boundary terms in the trace anomaly. In this paper we show that the universal part of the EE can be treated as a purely boundary effect. As a byproduct of our computation, we derive an explicit form for the A-type anomaly contribution to the Wess-Zumino term for the trace anomaly, now including boundary terms. In d=4 and 6, these boundary terms generalize earlier bulk actions derived in the literature.

hep-th↗

arXiv2014

Linear Resistivity from Non-Abelian Black Holes

Starting with the holographic p-wave superconductor, we show how to obtain a finite DC conductivity through a non-abelian gauge transformation. The translational symmetry is preserved. We obtain phenomenological similarities with high temperature cuprate superconductors. Our results suggest that a lattice or impurities are not essential to produce a finite DC resistivity with a linear temperature dependence. An analogous field theory calculation for free fermions, presented in the appendix, indicates our results may be a special feature of strong interactions.

hep-th↗

arXiv2014

Non-Abelian Chiral 2-Form and M5-Branes

We first review self-dual (chiral) gauge field theories by studying their Lorentz non-covariant and Lorentz covariant formulations. We next construct a non-Abelian self-dual two-form gauge theory in six dimensions with a spatial direction compactified on a circle. This model reduces to the Yang-Mills theory in five dimensions for a small compactified radius R. The model also reduces to the Lorentz-invariant Abelian self-dual two-form theory when the gauge group is Abelian. The model is expected to describe multiple 5-branes in M-theory. We also discuss its decompactified limit, covariant formulation, BRST-antifield quantization and other generalizations.

hep-th↗

arXiv2013

Weyl Anomaly Induced Stress Tensors in General Manifolds

Considering arbitrary conformal field theories in general (non-conformally flat) backgrounds, we adopt a dimensional regularization approach to obtain stress tensors from Weyl anomalies. The results of type A anomaly-induced stress tensors in four and six-dimensions generalize the previous results calculated in a conformally flat background. On the other hand, regulators are needed to have well-defined type B anomaly-induced stress tensors. We also discuss ambiguities related to type D anomalies, Weyl invariants and order of limit issues.

hep-th↗

arXiv2013

Stress Tensors from Trace Anomalies in Conformal Field Theories

Using trace anomalies, we determine the vacuum stress tensors of arbitrary even dimensional conformal field theories in Weyl flat backgrounds. We demonstrate a simple relation between the Casimir energy on the real line times a sphere and the type A anomaly coefficient. This relation generalizes earlier results in two and four dimensions. These field theory results for the Casimir are shown to be consistent with holographic predictions in two, four, and six dimensions.

hep-th↗

arXiv2011

A Non-Abelian Self-Dual Gauge Theory in 5+1 Dimensions

We construct a non-Abelian gauge theory of chiral 2-forms (self-dual gauge fields) in 6 dimensions with a spatial direction compactified on a circle of radius R. It has the following two properties. (1) It reduces to the Yang-Mills theory in 5 dimensions for small R. (2) It is equivalent to the Lorentz-invariant theory of Abelian chiral 2-forms when the gauge group is Abelian. Previous no-go theorems prohibiting non-Abelian deformations of the chiral 2-form gauge theory are circumvented by introducing nonlocality along the compactified dimension.

hep-th↗

arXiv2010

Lie 3-Algebra Non-Abelian (2,0) Theory in Loop Space

It is believed that the multiple M5-branes are described by the non-abelian (2,0) theory and have the non-local structure. In this note we investigate the non-abelian (2,0) theory in loop space which incorporates the non-local property. All fields will be formulated as loop fields and the two-form potential becomes a part of connection. We make an ansatz for field supersymmetry transformation with a help of Lie 3-algebra and examine the closure condition of the transformation to find the field equations. However, the closure conditions lead to several complex terms and we have not yet found a simple form for some constrain field equations. In particular, we present the clear scheme and several detailed calculations in each step. Many useful $Γ$ matrix algebras are derived in the appendix.

hep-th↗

arXiv2008

Thermodynamics on Noncommutative Geometry in Coherent State Formalism

The thermodynamics of ideal gas on the noncommutative geometry in the coherent state formalism is investigated. We first evaluate the statistical interparticle potential and see that there are residual "attraction (repulsion) potential" between boson (fermion) in the high temperature limit. The characters could be traced to the fact that, the particle with mass $m$ in noncommutative thermal geometry with noncommutativity $θ$ and temperature $T$ will correspond to that in the commutative background with temperature $T(1+kTmθ)^{-1}$. Such a correspondence implies that the ideal gas energy will asymptotically approach to a finite limiting value as that on commutative geometry at $T_θ= (kmθ)^{-1}$. We also investigate the squeezed coherent states and see that they could have arbitrary mean energy. The thermal properties of those systems are calculated and compared to each other. We find that the heat capacity of the squeezed coherent states of boson and fermion on the noncommutative geometry have different values, contrast to that on the commutative geometry.

hep-th↗