Detection of transit timing variations in excess of one hour in the Kepler multi-planet candidate system KOI 806 with the GTC

We report the detection of transit timing variations (TTVs) well in excess of one hour in the Kepler multi-planet candidate system KOI 806. This system exhibits transits consistent with three separate planets -- a Super-Earth, a Jupiter, and a Saturn -- lying very nearly in a 1:2:5 resonance, respectively. We used the Kepler public data archive and observations with the Gran Telescopio de Canarias to compile the necessary photometry. For the largest candidate planet (KOI 806.02) in this system, we detected a large transit timing variation of -103.5$\pm$6.9 minutes against previously published ephemeris. We did not obtain a strong detection of a transit color signature consistent with a planet-sized object; however, we did not detect a color difference in transit depth, either. The large TTV is consistent with theoretical predictions that exoplanets in resonance can produce large transit timing variations, particularly if the orbits are eccentric. The presence of large TTVs among the bodies in this systems indicates that KOI806 is very likely to be a planetary system. This is supported by the lack of a strong color dependence in the transit depth, which would suggest a blended eclipsing binary.Comment: 9 pages, 4 figures, accepted into A&A Letter

Fermi-Liquid Interactions in d-Wave Superconductor

This article develops a quantitative quasiparticle model of the low-temperature properties of d-wave superconductors which incorporates both Fermi-liquid effects and band-structure effects. The Fermi-liquid interaction effects are found to be classifiable into strong and negligible renormalizaton effects, for symmetric and antisymmetric combinations of the energies of $k\uparrow$ and $-k\downarrow$ quasiparticles, respectively. A particularly important conclusion is that the leading clean-limit temperature-dependent correction to the superfluid density is not renormalized by Fermi-liquid interactions, but is subject to a Fermi velocity (or mass) renormalization effect. This leads to difficulties in accounting for the penetration depth measurements with physically acceptable parameters, and hence reopens the question of the quantitative validity of the quasiparticle picture.Comment: 4 page

The Challenge of Wide-Field Transit Surveys: The Case of GSC 01944-02289

Wide-field searches for transiting extra-solar giant planets face the difficult challenge of separating true transit events from the numerous false positives caused by isolated or blended eclipsing binary systems. We describe here the investigation of GSC 01944-02289, a very promising candidate for a transiting brown dwarf detected by the Transatlantic Exoplanet Survey (TrES) network. The photometry and radial velocity observations suggested that the candidate was an object of substellar mass in orbit around an F star. However, careful analysis of the spectral line shapes revealed a pattern of variations consistent with the presence of another star whose motion produced the asymmetries observed in the spectral lines of the brightest star. Detailed simulations of blend models composed of an eclipsing binary plus a third star diluting the eclipses were compared with the observed light curve and used to derive the properties of the three components. Our photometric and spectroscopic observations are fully consistent with a blend model of a hierarchical triple system composed of an eclipsing binary with G0V and M3V components in orbit around a slightly evolved F5 dwarf. We believe that this investigation will be helpful to other groups pursuing wide-field transit searches as this type of false detection could be more common than true transiting planets, and difficult to identify.Comment: To appear in ApJ, v. 621, 2005 March 1

Optical properties of the pseudogap state in underdoped cuprates

Recent optical measurements of deeply underdoped cuprates have revealed that a coherent Drude response persists well below the end of the superconducting dome. In addition, no large increase in optical effective mass has been observed, even at dopings as low as 1%. We show that this behavior is consistent with the resonating valence bond spin-liquid model proposed by Yang, Rice, and Zhang. In this model, the overall reduction in optical conductivity in the approach to the Mott insulating state is caused not by an increase in effective mass, but by a Gutzwiller factor, which describes decreased coherence due to correlations, and by a shrinking of the Fermi surface, which decreases the number of available charge carriers. We also show that in this model, the pseudogap does not modify the low-temperature, low-frequency behavior, though the magnitude of the conductivity is greatly reduced by the Gutzwiller factor. Similarly, the profile of the temperature dependence of the microwave conductivity is largely unchanged in shape, but the Gutzwiller factor is essential in understanding the observed difference in magnitude between ortho-I and -II YBa$_2$Cu$_3$O$_y$.Comment: 9 pages, 6 figures, submitted to Eur. Phys. J.

Orthorhombicity mixing of s- and d- gap components in YBa2Cu3O7YBa_2Cu_3O_7 without involving the chains

Momentum decoupling develops when forward scattering dominates the pairing interaction and implies tendency for decorrelation between the physical behavior in the various regions of the Fermi surface. In this regime it is possible to obtain anisotropic s- or d-wave superconductivity even with isotropic pairing scattering. We show that in the momentum decoupling regime the distortion of the $CuO_2$ planes is enough to explain the experimental reports for s- mixing in the dominantly d-wave gap of $YBa_2Cu_3O_7$. In the case of spin fluctuations mediated pairing instead, a large part of the condensate must be located in the chains in order to understand the experiments.Comment: LATEX file and 3 Postscript figure

Twin boundaries in d-wave superconductors

Twin boundaries in orthorhombic d-wave superconductors are investigated numerically using the Bogoliubov-deGennes formalism within the context of an extended Hubbard model. The twin boundaries are represented by tetragonal regions of variable width, with a reduced chemical potential. For sufficiently large twin boundary width and change in chemical potential, an induced s-wave component may break time-reversal symmetry at a low temperature. This temperature, and the magnitude of the complex component, are found to depend strongly on electron density. The results are compared with recent tunneling measurements.Comment: ReVTeX, 4 pages, 4 postscript figure

Spontaneous Flux and Magnetic Interference Patterns in 0-pi Josephson Junctions

The spontaneous flux generation and magnetic field modulation of the critical current in a 0-pi Josephson junction are calculated for different ratios of the junction length to the Josephson penetration depth, and different ratios of the 0-junction length to the pi-junction length. These calculations apply to a Pb-YBCO c-axis oriented junction with one YBCO twin boundary, as well as other experimental systems. Measurements of such a junction can provide information on the nature of the c-axis Josephson coupling and the symmetry of the order parameter in YBCO. We find spontaneous flux even for very short symmetric 0-pi junctions, but asymmetric junctions have qualitatively different behavior.Comment: 13 pages, TEX,+ 7 figures, postscrip

Clinical Indicators of Symptom Dimensions and Cognitive Ability in Schizophrenia

INTRODUCTION: Schizophrenia is a heterogeneous disorder and it is unknown what causes individual variability in symptoms and cognitive ability. OBJECTIVES: To examine the association between nine clinical predictors measurable at the onset of schizophrenia and five phenotype dimensions: positive, negative (diminished expressivity), negative (motivation and pleasure), disorganised symptoms and cognitive ability. METHODS: 852 participants (mean age 49 years old) with a diagnosis of schizophrenia or schizoaffective depression were included from the CardiffCOGS cross-sectional sample. Phenotype dimensions were created using confirmatory factor analysis and a 5-factor model. Associations were tested using linear regression, adjusting for age and sex. A Bonferroni correction was applied for (p<1.1x10(-3)) for multiple testing. RESULTS: Age of onset of psychosis was significantly associated with positive symptoms (β=-0.18, p=4.0 x10(-6)). Lower premorbid IQ was associated with diminished expressivity (β=-0.25, p= 7.0x10(-13)), reduced motivation and pleasure (β=-0.23, p= 4.3x10(-11)), disorganised symptoms (β=-0.14, p= 7.6x10(-5)) and reduced cognition (β=0.54, p= 4.8x10(-77)). Poor premorbid social adjustment held associations with all except positive. Developmental delay was associated with reduced cognition (β=-0.35, p= 4.3x10(-5)). Cannabis use (year before onset), psychosocial stressors (within 6 months), childhood abuse and family history of schizophrenia held no associations. CONCLUSIONS: Clinical indicators measurable at schizophrenia onset are associated with lifetime symptom variability. A younger psychosis onset is associated with more severe positive symptoms, suggesting possible age-targeted management. Pre-established links of lower premorbid IQ with poor premorbid social adjustment and negative symptom severity with cognition are strengthened. Further investigation could potentially improve diagnosis and guide treatment choice for aspects of schizophrenia with poor outcomes. DISCLOSURE: No significant relationships