292,051 research outputs found
Testing Gravity Against Early Time Integrated Sachs-Wolfe Effect
A generic prediction of general relativity is that the cosmological linear
density growth factor is scale independent. But in general, modified
gravities do not preserve this signature. A scale dependent can cause time
variation in gravitational potential at high redshifts and provides a new
cosmological test of gravity, through early time integrated Sachs-Wolfe (ISW)
effect-large scale structure (LSS) cross correlation. We demonstrate the power
of this test for a class of gravity, with the form . Such gravity, even with degenerate
expansion history to CDM, can produce detectable ISW effect at z\ga
3 and l\ga 20. Null-detection of such effect would constrain to
be at confidence level. On the other hand, robust
detection of ISW-LSS cross correlation at high will severely challenge
general relativity.Comment: 5 pages, 2 figures. Accepted to PRD. v2: Revised to address to more
general audience. v3: added discussion
A note on the Lee-Yang singularity coupled to 2d quantum gravity
We show how to obtain the critical exponent of magnetization in the Lee-Yang
edge singularity model coupled to two-dimensional quantum gravity
Optical detection of a BCS phase transition in a trapped gas of fermionic atoms
Light scattering from a spin-polarized degenerate Fermi gas of trapped
ultracold Li-6 atoms is studied. We find that the scattered light contains
information which directly reflects the quantum pair correlation due to the
formation of atomic Cooper pairs resulting from a BCS phase transition to a
superfluid state. Evidence for pairing can be observed in both the space and
time domains.Comment: 8 pages, 4 figures, revte
Buried heterostructure vertical-cavity surface-emitting laser with semiconductor mirrors
We report a buried heterostructure vertical-cavity surface-emitting laser
fabricated by epitaxial regrowth over an InGaAs quantum well gain medium. The
regrowth technique enables microscale lateral confinement that preserves a high
cavity quality factor (loaded 4000) and eliminates parasitic
charging effects found in existing approaches. Under optimal spectral overlap
between gain medium and cavity mode (achieved here at = 40 K) lasing was
obtained with an incident optical power as low as = 10 mW
( = 808 nm). The laser linewidth was found to be 3
GHz at 5
Tolerance and Sensitivity in the Fuse Network
We show that depending on the disorder, a small noise added to the threshold
distribution of the fuse network may or may not completely change the
subsequent breakdown process. When the threshold distribution has a lower
cutoff at a finite value and a power law dependence towards large thresholds
with an exponent which is less than , the network is not sensitive
to the added noise, otherwise it is. The transition between sensitivity or not
appears to be second order, and is related to a localization-delocalization
transition earlier observed in such systems.Comment: 12 pages, 3 figures available upon request, plain Te
Cross-spectral analysis of the X-ray variability of Mrk 421
Using the cross-spectral method, we confirm the existence of the X-ray hard
lags discovered with cross-correlation function technique during a large flare
of Mrk 421 observed with BeppoSAX . For the 0.1--2 versus 2--10keV light
curves, both methods suggest sub-hour hard lags. In the time domain, the degree
of hard lag, i.e., the amplitude of the 3.2--10 keV photons lagging the lower
energy ones, tends to increase with the decreasing energy. In the Fourier
frequency domain, by investigating the cross-spectra of the 0.1--2/2--10 keV
and the 2--3.2/3.2--10 keV pairs of light curves, the flare also shows hard
lags at the lowest frequencies. However, with the present data, it is
impossible to constrain the dependence of the lags on frequencies even though
the detailed simulations demonstrate that the hard lags at the lowest
frequencies probed by the flare are not an artifact of sparse sampling, Poisson
and red noise. As a possible interpretation, the implication of the hard lags
is discussed in the context of the interplay between the (diffusive)
acceleration and synchrotron cooling of relativistic electrons responsible for
the observed X-ray emission. The energy-dependent hard lags are in agreement
with the expectation of an energy-dependent acceleration timescale. The
inferred magnetic field (B ~ 0.11 Gauss) is consistent with the value inferred
from the Spectral Energy Distributions of the source. Future investigations
with higher quality data that whether or not the time lags are
energy-/frequency-dependent will provide a new constraint on the current models
of the TeV blazars.Comment: 11 pages, 6 figures, accepted by MNRA
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