Type Ia supernova diversity: Standardizing the candles

Future use of type Ia supernovae for cosmology aims not only to determine the equation of state of dark energy, but also to constrain possible variations in its value. To achieve this goal, supernovae need to become better calibrated standard candles - not only to improve the precision of the measurement, but more importantly to gain better control over systematic uncertainties in order to ensure the accuracy of the result. Here we report on a project to quantify the diversity in type Ia supernovae, and to look for trends and/or sub-types that can be used to improve their calibration as standard candles. We implement a version of principal component analysis on type Ia supernova spectra. Although the quantity of data is not sufficient to draw any firm conclusions we show that this method holds promise for, at the very least, effectively separating peculiar supernovae. Whether it can be further used to improve the calibration of normal type Ia's remains a project for future study.Comment: Conference Proceedings. Cefalu 2006, The multicoloured landscape of compact objects and their explosive origins. Six pages, three figure

Electronic structure of the cuprate superconducting and pseudogap phases from spectroscopic imaging STM

We survey the use of spectroscopic imaging scanning tunneling microscopy (SI-STM) to probe the electronic structure of underdoped cuprates. Two distinct classes of electronic states are observed in both the d-wave superconducting (dSC) and the pseudogap (PG) phases. The first class consists of the dispersive Bogoliubov quasiparticle excitations of a homogeneous d-wave superconductor, existing below a lower energy scale E = Delta(0). We find that the Bogoliubov quasiparticle interference (QPI) signatures of delocalized Cooper pairing are restricted to a k-space arc, which terminates near the lines connecting k = +/-(pi/a(0), 0) to k = +/-(0, pi/a(0)). This arc shrinks continuously with decreasing hole density such that Luttinger's theorem could be satisfied if it represents the front side of a hole-pocket that is bounded behind by the lines between k = +/-(pi/a(0), 0) and k = +/-(0, pi/a(0)). In both phases, the only broken symmetries detected for the vertical bar E vertical bar < Delta(0) states are those of a d-wave superconductor. The second class of states occurs proximate to the PG energy scale E = Delta(1). Here the non-dispersive electronic structure breaks the expected 90 degrees-rotational symmetry of electronic structure within each unit cell, at least down to 180 degrees-rotational symmetry. This electronic symmetry breaking was first detected as an electronic inequivalence at the two oxygen sites within each unit cell by using a measure of nematic (C-2) symmetry. Incommensurate non-dispersive conductance modulations, locally breaking both rotational and translational symmetries, coexist with this intra-unit-cell electronic symmetry breaking at E = Delta(1). Their characteristic wavevector Q is determined by the k-space points where Bogoliubov QPI terminates and therefore changes continuously with doping. The distinct broken electronic symmetry states (intra-unit-cell and finite Q) coexisting at E similar to Delta(1) are found to be indistinguishable in the dSC and PG phases. The next challenge for SI-STM studies is to determine the relationship of the E similar to Delta(1) broken symmetry electronic states with the PG phase, and with the E < Delta(0) states associated with Cooper pairing.Publisher PDFPeer reviewe

Comparisons of commercial frozen yogurt with ksu formulation

Ten samples of vanilla frozen yogurt were purchased in Kansas and compared to a highprotein, KSU formulation. The KSU formulation had similar solids, fat, and sugar contents as the commercial samples. All commercial samples had lower protein (almost less than half) content and more lactose, and almost all samples had fewer lactic acid bacteria than the KSU formulation. All but one commercial sample had lower b-galactosidase activity than the KSU formulation. This may reflect the differing lactic acid bacterial populations in the frozen yogurts

Phase-coherent detection of an optical dipole force by Doppler velocimetry

We report phase-coherent Doppler detection of optical dipole forces using large ion crystals in a Penning trap. The technique is based on laser Doppler velocimetry using a cycling transition in $^{9}$Be$^{+}$ near 313 nm and the center-of-mass (COM) ion motional mode. The optical dipole force is tuned to excite the COM mode, and measurements of photon arrival times synchronized with the excitation potential show oscillations with a period commensurate with the COM motional frequency. Experimental results compare well with a quantitative model for a driven harmonic oscillator. This technique permits characterization of motional modes in ion crystals; the measurement of both frequency and phase information relative to the driving force is a key enabling capability -- comparable to lockin detection -- providing access to a parameter that is typically not available in time-averaged measurements. This additional information facilitates discrimination of nearly degenerate motional modes.Comment: Related manuscripts at http://www.physics.usyd.edu.au/~mbiercuk

Coulomb's law modification in nonlinear and in noncommutative electrodynamics

We study the lowest-order modifications of the static potential for Born-Infeld electrodynamics and for the $\theta$-expanded version of the noncommutative U(1) gauge theory, within the framework of the gauge-invariant but path-dependent variables formalism. The calculation shows a long-range correction ($1/r^5$-type) to the Coulomb potential in Born-Infeld electrodynamics. However, the Coulomb nature of the potential (to order $e^2$) is preserved in noncommutative electrodynamics.Comment: 14 pages, 1 figur

Simple Impurity Embedded in a Spherical Jellium: Approximations of Density Functional Theory compared to Quantum Monte Carlo Benchmarks

We study the electronic structure of a spherical jellium in the presence of a central Gaussian impurity. We test how well the resulting inhomogeneity effects beyond spherical jellium are reproduced by several approximations of density functional theory (DFT). Four rungs of Perdew's ladder of DFT functionals, namely local density approximation (LDA), generalized gradient approximation (GGA), meta-GGA and orbital-dependent hybrid functionals are compared against our quantum Monte Carlo (QMC) benchmarks. We identify several distinct transitions in the ground state of the system as the electronic occupation changes between delocalized and localized states. We examine the parameter space of realistic densities ($1 \le r_s\le 5$) and moderate depths of the Gaussian impurity ($Z<7$). The selected 18 electron system (with closed-shell ground state) presents $1d \to 2s$ transitions while the 30 electron system (with open-shell ground state) exhibits $1f \to 2p$ transitions. For the former system, the accuracy for the transitions is clearly improving with increasing sophistication of functionals with meta-GGA and hybrid functionals having only small deviations from QMC. However, for the latter system, we find much larger differences for the underlying transitions between our pool of DFT functionals and QMC. We attribute this failure to treatment of the exact exchange within these functionals. Additionally, we amplify the inhomogeneity effects by creating the system with spherical shell which leads to even larger errors in DFT approximations.Comment: 8 pages, 4 figures, submitted to PRB as a regular article revisited version after revie

Multiorbital tunneling ionization of the CO molecule

We coincidently measure the molecular frame photoelectron angular distribution and the ion sum-momentum distribution of single and double ionization of CO molecules by using circularly and elliptically polarized femtosecond laser pulses, respectively. The orientation dependent ionization rates for various kinetic energy releases allow us to individually identify the ionizations of multiple orbitals, ranging from the highest occupied to the next two lower-lying molecular orbitals for various channels observed in our experiments. Not only the emission of a single electron, but also the sequential tunneling dynamics of two electrons from multiple orbitals are traced step by step. Our results confirm that the shape of the ionizing orbitals determine the strong laser field tunneling ionization in the CO molecule, whereas the linear Stark effect plays a minor role.Comment: This paper has been accepted for publication by Physical Review Letter