Photometric Calibration of the Supernova Legacy Survey Fields

The 5-year project Supernova Legacy Survey (SNLS) delivers $\sim 100$ Type-Ia supernovae (SNe Ia) per year, in the redshift range $0.3 < z < 1.0$, with well-sampled $g'r'i'z'$ lightcurves. The SNLS Collaboration uses the 1 deg$^2$ Megacam imager (36 $2048 \times 4612$ thinned CCDs) mounted on the 3.6-m Canada-France-Hawaii Telescope (CFHT) to observe four fields around the sky, in four filters. The primary goal of the project is to measure the dark energy equation of state with a final statistical precision of $\pm 0.05$. We have shown, using the first year dataset that the calibration uncertainties are currently the dominant contribution to the systematic error budget. The calibration of the SNLS dataset is challenging in several aspects. First, Megacam is a wide-field imager, and only a handful of its 36 CCDs can be directly calibrated using standard star observations. Second, measuring the rest-frame $B$-band luminosity of SNe Ia over the $0.3<z<1.0$ redshift range requires an excellent flux intercalibration of the Megacam bands. Finally, the SN Ia SED differs significantly from that of stars and transfering the stellar calibration to the SNLS data requires a precise knowledge of the SN Ia spectra and the instrument transmissions. We present and discuss the SNLS calibration strategy used to analyze the first year data set. We present the calibration aspects which impact most the cosmological measurements. We also discuss the intercalibration of the SNLS with other surveys, such as the CFHTLS-Wide and the SDSS.Comment: To Appear in "The Future of Photometric, Spectrophotometric and Polarimetric Standardization" Conference Proceedings, C. Sterken e

A Nearby Supernovae Search: Eros2

Type Ia supernovae (SNIa) have been used as approximate standard candles to measure cosmological parameters such as the Hubble constant and the deceleration parameter. These measurements rely on empirical correlations between peak luminosities and other features that can be observed in the supernovae spectra and their light curves. Such correlations deserve further study since they have been established from small samples of nearby SNIa. Two years ago, the EROS2 collaboration launched an automated search for supernovae with the 1m Marly telescope operating at La Silla. In all, 57 SNe have been discovered in this EROS2 search and spectra have been obtained for 26 of them. We found that 75% were of type Ia and 25% of type II. Using this sample, a preliminary SN explosion rate has been obtained. Our most recent observation campaign took place in February and March 99. It was performed in the framework of a large consortium led by the {\em Supernova Cosmology Project}. The aim of this intensive campaign was to provide an independent set of high quality light curves and spectra to study systematic effects in the measurement of cosmological parameters. We will briefly describe our search procedure and present the status of our ongoing analysis.Comment: 5 page

Broadening effects due to alloy scattering in Quantum Cascade Lasers

We report on calculations of broadening effects in QCL due to alloy scattering. The output of numerical calculations of alloy broadened Landau levels compare favorably with calculations performed at the self-consistent Born approximation. Results for Landau level width and optical absorption are presented. A disorder activated forbidden transition becomes significant in the vicinity of crossings of Landau levels which belong to different subbands. A study of the time dependent survival probability in the lowest Landau level of the excited subband is performed. It is shown that at resonance the population relaxation occurs in a subpicosecond scale.Comment: 7 pages, 8 figure

Parafermionic states in rotating Bose-Einstein condensates

We investigate possible parafermionic states in rapidly rotating ultracold bosonic atomic gases at lowest Landau level filling factor nu=k/2. We study how the system size and interactions act upon the overlap between the true ground state and a candidate Read-Rezayi state. We also consider the quasihole states which are expected to display non-Abelian statistics. We numerically evaluate the degeneracy of these states and show agreement with a formula given by E. Ardonne. We compute the overlaps between low-lying exact eigenstates and quasihole candidate wavefunctions. We discuss the validity of the parafermion description as a function of the filling factor.Comment: 23 pages, 10 figure

Quantum Hall fractions in ultracold atomic vapors

Atomic vapors can be prepared and manipulated at very low densities and temperatures. When they are rotating, they can reach a quantum Hall regime in which there should be manifestations of the fractional quantum Hall effect. We discuss the appearance of the principal sequence of fractions nu =p/(p+- 1) for bosonic atoms. The termination point of this series is the paired Moore-Read Pfaffian state. Exotic states fill the gap between the paired state and the vortex lattice expected at high filling of the lowest Landau level. In fermionic vapors, the p-wave scattering typical of ultralow energy collisions leads to the hard-core model when restricted to the lowest Landau level.Comment: 7 pages, 2 figs, brief review submitted to Modern Physics Letters

Poisson algebra of 2d dimensionally reduced gravity

Using a Lax pair based on twisted affine $sl(2,R)$ Kac-Moody and Virasoro algebras, we deduce a r-matrix formulation of two dimensional reduced vacuum Einstein's equations. Whereas the fundamental Poisson brackets are non-ultralocal, they lead to pure c-number modified Yang-Baxter equations. We also describe how to obtain classical observables by imposing reasonable boundaries conditions.Comment: 16 pages, minor corrections. To appear in JHE