On the geometry of regular maps from a quasi-projective surface to a curve

By exploring the consequences of the triviality of the monodromy group for a class of surfaces of which the mixed Hodge structure is pure, we extend results of Miyanishi and Sugie, Dimca, Zaidenberg and Kaliman.Comment: 19 pages. Some corrections and more references. European Journal of Mathematics, to appea

The Weakly Coupled Pfaffian as a Type I Quantum Hall Liquid

The Pfaffian phase of electrons in the proximity of a half-filled Landau level is understood to be a p+ip superconductor of composite fermions. We consider the properties of this paired quantum Hall phase when the pairing scale is small, i.e. in the weak-coupling, BCS, limit, where the coherence length is much larger than the charge screening length. We find that, as in a Type I superconductor, the vortices attract so that, upon varying the magnetic field from its magic value at \nu=5/2, the system exhibits Coulomb frustrated phase separation. We propose that the weakly and strongly coupled Pfaffian states exemplify a general dichotomy between Type I and Type II quantum Hall fluids.Comment: 4 pages, 1 figur

Accidental SUSY: Enhanced Bulk Supersymmetry from Brane Back-reaction

We compute how bulk loops renormalize both bulk and brane effective interactions for codimension-two branes in 6D gauged chiral supergravity, as functions of the brane tension and brane-localized flux. We do so by explicitly integrating out hyper- and gauge-multiplets in 6D gauged chiral supergravity compactified to 4D on a flux-stabilized 2D rugby-ball geometry, specializing the results of a companion paper, arXiv:1210.3753, to the supersymmetric case. While the brane back-reaction generically breaks supersymmetry, we show that the bulk supersymmetry can be preserved if the amount of brane-localized flux is related in a specific BPS-like way to the brane tension, and verify that the loop corrections to the brane curvature vanish in this special case. In these systems it is the brane-bulk couplings that fix the size of the extra dimensions, and we show that in some circumstances the bulk geometry dynamically adjusts to ensure the supersymmetric BPS-like condition is automatically satisfied. We investigate the robustness of this residual supersymmetry to loops of non-supersymmetric matter on the branes, and show that supersymmetry-breaking effects can enter only through effective brane-bulk interactions involving at least two derivatives. We comment on the relevance of this calculation to proposed applications of codimension-two 6D models to solutions of the hierarchy and cosmological constant problems.Comment: 49 pages + appendices. This is the final version to appear in JHE

AKLT Models with Quantum Spin Glass Ground States

We study AKLT models on locally tree-like lattices of fixed connectivity and find that they exhibit a variety of ground states depending upon the spin, coordination and global (graph) topology. We find a) quantum paramagnetic or valence bond solid ground states, b) critical and ordered N\'eel states on bipartite infinite Cayley trees and c) critical and ordered quantum vector spin glass states on random graphs of fixed connectivity. We argue, in consonance with a previous analysis, that all phases are characterized by gaps to local excitations. The spin glass states we report arise from random long ranged loops which frustrate N\'eel ordering despite the lack of randomness in the coupling strengths.Comment: 10 pages, 1 figur

Low Temperature metamagnetism and Hall effect anomaly in Kondo compound CeAgBi2

Heavy fermion (HF) materials exhibit a rich array of phenomena due to the strong Kondo coupling between their localized moments and itinerant electrons. A central question in their study is to understand the interplay between magnetic order and charge transport, and its role in stabilizing new quantum phases of matter. Particularly promising in this regard is a family of tetragonal intermetallic compounds Ce{$TX$}$_2$ ($T=$ transition metal, $X=$ pnictogen), that includes a variety of HF compounds showing $T$-linear electronic specific heat $\bf{C_e \sim \gamma T}$, with $\gamma\sim$ 20-500 mJ$\cdot$mol$^{-1}$~K$^{-2}$, reflecting an effective mass enhancement ranging from small to modest. Here, we study the low-temperature field-tuned phase diagram of high-quality CeAgBi$_2$ using magnetometry and transport measurements. We find an antiferromagnetic transition at ${T_{N} = 6.4}$~K with weak magnetic anisotropy and the easy axis along the $c$-axis, similar to previous reports (${T_{N} = 6.1}$~K). This scenario, along with the presence of two anisotropic Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions, leads to a rich field-tuned magnetic phase diagram, consisting of five metamagnetic transitions of both first and second order. In addition, we unveil an anomalous Hall contribution for fields $H<54$ kOe which is drastically altered when $H$ is tuned through a trio of transitions at 57, 78, and 84~kOe, suggesting that the Fermi surface is reconstructed in a subset of the metamagnetic transitions.Comment: (*equal contribution

Pulmonary tuberculosis in outpatients in Sabah, Malaysia: Advanced disease but low incidence of HIV co-infection

BackgroundTuberculosis (TB) is generally well controlled in Malaysia, but remains an important problem in the nation&rsquo;s eastern states. In order to better understand factors contributing to high TB rates in the eastern state of Sabah, our aims were to describe characteristics of patients with TB at a large outpatient clinic, and determine the prevalence of HIV co-infection. Additionally, we sought to test sensitivity and specificity of the locally-available point-of-care HIV test kits.MethodsWe enrolled consenting adults with smear-positive pulmonary TB for a 2-year period at Luyang Clinic, Kota Kinabalu, Malaysia. Participants were questioned about ethnicity, smoking, prior TB, disease duration, symptoms and comorbidities. Chest radiographs were scored using a previously devised tool. HIV was tested after counselling using 2 point-of-care tests for each patient: the test routinely in use at the TB clinic (either Advanced Quality&trade; Rapid Anti-HIV 1&amp;2, FACTS anti-HIV 1/2 RAPID or HIV (1 + 2) Antibody Colloidal Gold), and a comparator test (Abbott Determine&trade; HIV-1/2, Inverness Medical). Positive tests were confirmed by enzyme immunoassay (EIA), particle agglutination and line immunoassay.Results176 participants were enrolled; 59 (33.5%) were non-Malaysians and 104 (59.1%) were male. Smoking rates were high (81/104 males, 77.9%), most had cavitary disease (51/145, 64.8%), and 81/176 (46.0%) had haemoptysis. The median period of symptoms prior to treatment onset was 8 weeks. Diabetes was present in 12. People with diabetes or other comorbidities had less severe TB, suggesting different healthcare seeking behaviours in this group. All participants consented to HIV testing: three (1.7%) were positive according to Determine&trade; and EIA, but one of these tested negative on the point-of-care test available at the clinic (Advanced Quality&trade; Rapid Anti-HIV 1&amp;2). The low number of positive tests and changes in locally-available test type meant that accurate estimates of sensitivity and specificity were not possible.ConclusionPatients had advanced disease at diagnosis, long diagnostic delays, low HIV co-infection rates, high smoking rates among males, and migrants may be over-represented. These findings provide important insights to guide local TB control efforts. Caution is required in using some point-of-care HIV tests, and ongoing quality control measures are of major importance