Three-point Green function of massless QED in position space to lowest order

The transverse part of the three-point Green function of massless QED is determined to the lowest order in position space. Taken together with the evaluation of the longitudinal part in arXiv:0803.2630, this gives a relation for QED which is analogous to the star-triangle relation. We relate our result to conformal-invariant three-point functions.Comment: 8 page

Symmetric-Gapped Surface States of Fractional Topological Insulators

We construct the symmetric-gapped surface states of a fractional topological insulator with electromagnetic $\theta$-angle $\theta_{em} = \frac{\pi}{3}$ and a discrete $\mathbb{Z}_3$ gauge field. They are the proper generalizations of the T-pfaffian state and pfaffian/anti-semion state and feature an extended periodicity compared with their of "integer" topological band insulators counterparts. We demonstrate that the surface states have the correct anomalies associated with time-reversal symmetry and charge conservation.Comment: 5 pages, 33 references and 2 pages of supplemental materia

3-point off-shell vertex in scalar QED in arbitrary gauge and dimension

We calculate the complete one-loop off-shell three-point scalar-photon vertex in arbitrary gauge and dimension for Scalar Quantum Electrodynamics. Explicit results are presented for the particular cases of dimensions 3 and 4 both for massive and massless scalars. We then propose non-perturbative forms of this vertex that coincide with the perturbative answer to order $e^2$.Comment: Uses axodra

Mapping the magneto-structural quantum phases of Mn3O4

We present temperature-dependent x-ray diffraction and temperature- and field-dependent Raman scattering studies of single crystal Mn3O4, which reveal the novel magnetostructural phases that evolve in the spinels due to the interplay between strong spin-orbital coupling, geometric frustration, and applied magnetic field. We observe a structural transition from tetragonal to monoclinic structures at the commensurate magnetic transition at T2=33K, show that the onset and nature of this structural transition can be controlled with an applied magnetic field, and find evidence for a field-tuned quantum phase transition to a tetragonal incommensurate or spin glass phase.Comment: 5 pages, 3 figures, submitted to Phys. Rev. Lett; typos correcte

On the Summation of Feynman Graphs

A functional method to achieve the summation of all Feynman graphs relevant to a particular Field Theory process is suggested, and applied to QED, demonstrating manifestly gauge invariant calculations of the dressed photon propagator in approximations of increas- ing complexity. These lead in a natural way to the extraction of the leading logarithmic divergences of every perturbative order, and to a demonstration of the possible cancellation of all such divergences in the calculation of the (inverse of the) photon's wavefunction renormalization constant Z3. This analysis provides a qualitative understanding of why the measured value of the renormalized fine structure constant is, approximately, 1/137

A nontrivial bosonic representation of large spin systems at high temperatures

We report on a nontrivial bosonization scheme for spin operators. It is shown that in the large $N$ limit, at infinite temperature, the operators $\sum_{k=1}^N \hat s_{k\pm}/\sqrt{N}$ behave like the creation and annihilation operators, $a^\dag$ and $a$, corresponding to a harmonic oscillator in thermal equilibrium, whose temperature and frequency are related by $\hbar\omega/k_B T=\ln 3$. The $z$ component is found to be equivalent to the position variable of another harmonic oscillator occupying its ground Gaussian state at zero temperature. The obtained results are applied to the Heisenberg XY Hamiltonian at finite temperature.Comment: 12 pages, preprint, we have included a brief discussion of the antiferromagnetic cas

Tuning the effects of Landau-level mixing on anisotropic transport in quantum Hall systems

Electron-electron interactions in half-filled high Landau levels in two-dimensional electron gases in a strong perpendicular magnetic field can lead to states with anisotropic longitudinal resistance. This longitudinal resitance is generally believed to arise from broken rotational invariance, which is indicated by charge density wave (CDW) order in Hartree-Fock calculations. We use the Hartree-Fock approximation to study the influence of externally tuned Landau level mixing on the formation of interaction induced states that break rotational invariance in two-dimensional electron and hole systems. We focus on the situation when there are two non-interacting states in the vicinity of the Fermi level and construct a Landau theory to study coupled charge density wave order that can occur as interactions are tuned and the filling or mixing are varied. We examine in detail a specific example where mixing is tuned externally through Rashba spin-orbit coupling. We calculate the phase diagram and find the possibility of ordering involving coupled striped or triangular charge density waves in the two levels. Our results may be relevant to recent transport experiments on quantum Hall nematics in which Landau-level mixing plays an important role.Comment: 25 pages, 6 figure

Fusion rules and vortices in px+ipyp_x+ip_y superconductors

The "half-quantum" vortices ($\sigma$) and quasiparticles ($\psi$) in a two-dimensional $p_x+ip_y$ superconductor obey the Ising-like fusion rules $\psi\times \psi=1$, $\sigma\times \psi=\sigma$, and $\sigma\times \sigma= 1+\psi$. We explain how the physical fusion of vortex-antivortex pairs allows us to use these rules to read out the information encoded in the topologically protected space of degenerate ground states. We comment on the potential applicability of this fact to quantum computation. Modified 11/30/05 to reflect manuscript as accepted for publication. Includes corrected last section.Comment: 23 pages, REVTEX

Conformal Higher Spin Theory

We construct gauge theory of interacting symmetric traceless tensor fields of all ranks s=0,1,2,3, ... which generalizes Weyl-invariant dilaton gravity to the higher spin case, in any dimension d>2. The action is given by the trace of the projector to the subspace with positive eigenvalues of an arbitrary hermitian differential operator H, the symmetric tensor fields emerge after expansion of the latter in power series in derivatives. After decomposition in perturbative series around a conformally flat point H=\Box, the quadratic part of the action breaks up as a sum of free gauge theories of symmetric traceless tensors of rank s with actions of d-4+2s order in derivatives introduced in 4d case by Fradkin and Tseytlin and studied at the cubic order level by Fradkin and Linetsky. Higher orders in interaction are well-defined. We discuss in detail global symmetries of the model which give rise to infinite dimensional conformal higher spin algebras for any d. We stress geometric origin of conformal higher spin fields as background fields of a quantum point particle, and make the conjecture generalizing this geometry to the system "tensionless d-1 brane + Fronsdal higher spin massless fields in d+1 dimensions". We propose a candidate on the role of Higgs-like higher spin compensator able to spontaneously break higher spin symmetries. At last, we make the conjecture that, in even dimensions d, the action of conformal higher spin theory equals the logarithmically divergent term of the action of massless higher spin fields on AdS_{d+1} evaluated on the solutions of Dirichlet-like problem, where conformal higher spin fields are boundary values of massless higher spin fields on AdS_{d+1}, the latter conjecture provides information on the full higher spin action in AdS_{d+1}.Comment: 142 page