943 research outputs found

### 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

### 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

### Emergent Many-Body Translational Symmetries of Abelian and Non-Abelian Fractionally Filled Topological Insulators

The energy and entanglement spectrum of fractionally filled interacting
topological insulators exhibit a peculiar manifold of low energy states
separated by a gap from a high energy set of spurious states. In the current
manuscript, we show that in the case of fractionally filled Chern insulators,
the topological information of the many-body state developing in the system
resides in this low-energy manifold. We identify an emergent many-body
translational symmetry which allows us to separate the states in
quasi-degenerate center of mass momentum sectors. Within one center of mass
sector, the states can be further classified as eigenstates of an emergent (in
the thermodynamic limit) set of many-body relative translation operators. We
analytically establish a mapping between the two-dimensional Brillouin zone for
the Fractional Quantum Hall effect on the torus and the one for the fractional
Chern insulator. We show that the counting of quasi-degenerate levels below the
gap for the Fractional Chern Insulator should arise from a folding of the
states in the Fractional Quantum Hall system at identical filling factor. We
show how to count and separate the excitations of the Laughlin, Moore-Read and
Read-Rezayi series in the Fractional Quantum Hall effect into two-dimensional
Brillouin zone momentum sectors, and then how to map these into the momentum
sectors of the Fractional Chern Insulator. We numerically check our results by
showing the emergent symmetry at work for Laughlin, Moore-Read and Read-Rezayi
states on the checkerboard model of a Chern insulator, thereby also showing, as
a proof of principle, that non-Abelian Fractional Chern Insulators exist.Comment: 32 pages, 9 figure

### Analysis of a SU(4) generalization of Halperin's wave function as an approach towards a SU(4) fractional quantum Hall effect in graphene sheets

Inspired by the four-fold spin-valley symmetry of relativistic electrons in
graphene, we investigate a possible SU(4) fractional quantum Hall effect, which
may also arise in bilayer semiconductor quantum Hall systems with small Zeeman
gap. SU(4) generalizations of Halperin's wave functions [Helv. Phys. Acta 56,
75 (1983)], which may break differently the original SU(4) symmetry, are
studied analytically and compared, at nu=2/3, to exact-diagonalization studies.Comment: 4+epsilon pages, 4 figures; published version with minor correction

- …