33,338 research outputs found
Weak-Field Thermal Hall Conductivity in the Mixed State of d-Wave Superconductors
Thermal transport in the mixed state of a d-wave superconductor is considered
within the weak-field regime. We express the thermal conductivity,
, and the thermal Hall conductivity, , in terms of
the cross section for quasiparticle scattering from a single vortex. Solving
for the cross section (neglecting the Berry phase contribution and the
anisotropy of the gap nodes), we obtain and
in surprisingly good agreement with the qualitative features
of the experimental results for YBaCuO. In particular, we
show that the simple, yet previously unexpected, weak-field behavior,
, is that of thermally-excited nodal
quasiparticles, scattering primarily from impurities, with a small skew
component provided by vortex scattering.Comment: 5 pages, 2 figures; final version as published in Phys Rev Let
Diffuse Atomic and Molecular Gas in the Interstellar Medium of M82 toward SN 2014J
We present a comprehensive analysis of interstellar absorption lines seen in
moderately-high resolution, high signal-to-noise ratio optical spectra of SN
2014J in M82. Our observations were acquired over the course of six nights,
covering the period from ~6 days before to ~30 days after the supernova reached
its maximum B-band brightness. We examine complex absorption from Na I, Ca II,
K I, Ca I, CH+, CH, and CN, arising primarily from diffuse gas in the
interstellar medium (ISM) of M82. We detect Li I absorption over a range in
velocity consistent with that exhibited by the strongest Na I and K I
components associated with M82; this is the first detection of interstellar Li
in a galaxy outside of the Local Group. There are no significant temporal
variations in the absorption-line profiles over the 37 days sampled by our
observations. The relative abundances of the various interstellar species
detected reveal that the ISM of M82 probed by SN 2014J consists of a mixture of
diffuse atomic and molecular clouds characterized by a wide range of
physical/environmental conditions. Decreasing N(Na I)/N(Ca II) ratios and
increasing N(Ca I)/N(K I) ratios with increasing velocity are indicative of
reduced depletion in the higher-velocity material. Significant
component-to-component scatter in the N(Na I)/N(Ca II) and N(Ca I)/N(Ca II)
ratios may be due to variations in the local ionization conditions. An apparent
anti-correlation between the N(CH+)/N(CH) and N(Ca I)/N(Ca II) ratios can be
understood in terms of an opposite dependence on gas density and radiation
field strength, while the overall high CH+ abundance may be indicative of
enhanced turbulence in the ISM of M82. The Li abundance also seems to be
enhanced in M82, which supports the conclusions of recent gamma-ray emission
studies that the cosmic-ray acceleration processes are greatly enhanced in this
starburst galaxy.Comment: 32 pages, 6 figures, accepted to ApJ; added table giving single-epoch
equivalent widths; improved discussion regarding the lack of temporal
variations; improved analysis of the Li I regio
An Improved Red Spectrum of the Methane or T-dwarf SDSS 1624+0029: Role of the Alkali Metals
A Keck~II low resolution spectrum shortward of ome-micron is presented for
SDSS 1624+0029, the first field methane or T dwarf discovered in the Sloan
Digital Sky Survey. Significant flux is detected down to the spectrum's short
wavelength limit of 6200\AA. The spectrum exhibits a broad absorption feature
centered at 7700\AA, which we interpret as the K~I 7665/7699 resonance doublet.
The observed flux declines shortward of 7000\AA, due most likely to the red
wing of the Na~I doublet. Both Cs~I doublet lines are detected more strongly
than in an earlier red spectrum. Neither Li~I absorption nor H emission
are detected. An exploratory model fit to the spectrum suggests that the shape
of the red spectrum can be primarily accounted for by the broad wings of the
K~I and Na~I doublets. This behavior is consistent with the argument proffered
by Burrows, Marley and Sharp that strong alkali absorption is principally
responsible for depressing T dwarf spectra shortward of 1m. In particular,
there seems no compelling reason at this time to introduce dust or an
additional opacity source in the atmosphere of the SDSS object. The width of
the K~I and strengths of the Cs~I lines also indicate that the Sloan object is
warmer than Gl~229B.Comment: accepted March 3, 2000 for Ap.J. Letters, LaTeX, 2 figure
How many invariant polynomials are needed to decide local unitary equivalence of qubit states?
Given L-qubit states with the fixed spectra of reduced one-qubit density
matrices, we find a formula for the minimal number of invariant polynomials
needed for solving local unitary (LU) equivalence problem, that is, problem of
deciding if two states can be connected by local unitary operations.
Interestingly, this number is not the same for every collection of the spectra.
Some spectra require less polynomials to solve LU equivalence problem than
others. The result is obtained using geometric methods, i.e. by calculating the
dimensions of reduced spaces, stemming from the symplectic reduction procedure.Comment: 22 page
A Preliminary Indication of Evolution of Type Ia Supernovae from their Risetimes
We have compared the risetime for samples of nearby and high-redshift type Ia
supernovae (SNe Ia).
The fiducial risetime of the nearby SNe Ia is 2.5+/-0.4 days longer than the
proemial risetime determined by Goldhaber (1998a,b) for high-redshift SNe
Ia from the Supernova Cosmology Project.
The statistical likelihood that the two samples have different fiducial
risetimes is high (5.8 sigma) and indicates possible evolution between the
samples of SNe Ia. We consider the likely effects of several sources of
systematic error, but none of these resolves the difference in the risetimes.
Currently, we cannot directly determine the impact of the apparent evolution
on previous determinations of cosmological parameters.Comment: Accepted by the Astronomical Journal, 11 pages, 5 figure
The Deepest Supernova Search is Realized in the Hubble Ultra Deep Field Survey
The Hubble Ultra Deep Field Survey has not only provided the deepest optical
and near infrared views of universe, but has enabled a search for the most
distant supernovae to z~2.2. We have found four supernovae by searching spans
of integrations of the Ultra Deep Field and the Ultra Deep Field Parallels
taken with the Hubble Space Telescope paired with the Advanced Camera for
Surveys and the Near Infrared Multi Object Spectrometer. Interestingly, none of
these supernovae were at z>1.4, despite the substantially increased sensitivity
per unit area to such objects over the Great Observatories Origins Deep Survey.
We present the optical photometric data for the four supernovae. We also show
that the low frequency of Type Ia supernovae observed at z>1.4 is statistically
consistent with current estimates of the global star formation history combined
with the non-trivial assembly time of SN Ia progenitors.Comment: 24 pages (6 figures), submitted to the Astronomical Journa
Quantum phase transition for the BEC--BCS crossover in condensed matter physics and CPT violation in elementary particle physics
We discuss the quantum phase transition that separates a vacuum state with
fully-gapped fermion spectrum from a vacuum state with topologically-protected
Fermi points (gap nodes). In the context of condensed-matter physics, such a
quantum phase transition with Fermi point splitting may occur for a system of
ultracold fermionic atoms in the region of the BEC-BCS crossover, provided
Cooper pairing occurs in the non-s-wave channel. For elementary particle
physics, the splitting of Fermi points may lead to CPT violation, neutrino
oscillations, and other phenomena.Comment: 13 pages, 1 figure, v3: published versio
The Case for an Accelerating Universe from Supernovae
The unexpected faintness of high-redshift Type Ia supernovae (SNe Ia), as
measured by two teams, has been interpreted as evidence that the expansion of
the Universe is accelerating. We review the current challenges to this
interpretation and seek to answer whether the cosmological implications are
compelling. We discuss future observations of SNe Ia which could offer
extraordinary evidence to test acceleration.Comment: To appear as an Invited Review for PASP 20 pages, 13 figure
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