2,800 research outputs found
Bandwidth in bolometric interferometry
Bolometric Interferometry is a technology currently under development that
will be first dedicated to the detection of B-mode polarization fluctuations in
the Cosmic Microwave Background. A bolometric interferometer will have to take
advantage of the wide spectral detection band of its bolometers in order to be
competitive with imaging experiments. A crucial concern is that interferometers
are presumed to be importantly affected by a spoiling effect known as bandwidth
smearing. In this paper, we investigate how the bandwidth modifies the work
principle of a bolometric interferometer and how it affects its sensitivity to
the CMB angular power spectra. We obtain analytical expressions for the
broadband visibilities measured by broadband heterodyne and bolometric
interferometers. We investigate how the visibilities must be reconstructed in a
broadband bolometric interferometer and show that this critically depends on
hardware properties of the modulation phase shifters. Using an angular power
spectrum estimator accounting for the bandwidth, we finally calculate the
sensitivity of a broadband bolometric interferometer. A numerical simulation
has been performed and confirms the analytical results. We conclude (i) that
broadband bolometric interferometers allow broadband visibilities to be
reconstructed whatever the kind of phase shifters used and (ii) that for
dedicated B-mode bolometric interferometers, the sensitivity loss due to
bandwidth smearing is quite acceptable, even for wideband instruments (a factor
2 loss for a typical 20% bandwidth experiment).Comment: 13 pages, 14 figures, submitted to A&
Sensitivity of a Bolometric Interferometer to the CMB power spectrum
Context. The search for B-mode polarization fluctuations in the Cosmic
Microwave Background is one of the main challenges of modern cosmology. The
expected level of the B-mode signal is very low and therefore requires the
development of highly sensitive instruments with low systematic errors. An
appealing possibility is bolometric interferometry. Aims. We compare in this
article the sensitivity on the CMB angular power spectrum achieved with direct
imaging, heterodyne and bolometric interferometry. Methods. Using a simple
power spectrum estimator, we calculate its variance leading to the counterpart
for bolometric interferometry of the well known Knox formula for direct
imaging. Results. We find that bolometric interferometry is less sensitive than
direct imaging. However, as expected, it is finally more sensitive than
heterodyne interferometry due to the low noise of the bolometers. It therefore
appears as an alternative to direct imagers with different and possibly lower
systematic errors, mainly due to the absence of an optical setup in front of
the horns.Comment: 5 pages, 3 figures. This last version matches the published version
(Astronomy and Astrophysics 491 3 (2008) 923-927). Sensitivity of Heterodyne
Interferometers modified by a factor of tw
Considerations on Neuberger's operator
We discuss new approaches to the numerical implementation of Neuberger's
operator for lattice fermions and the possible use of block spin
transformations.Comment: LATTICE 99 (Improvement and Renormalization
Saturation from nuclear pion dynamics
We construct an equation-of-state for nuclear matter based on the chiral
Lagrangian. The relevant scales are discussed and an effective chiral power
expansion scheme, which is constructed to work around the nuclear saturation
density, is presented. A realistic equation-of-state is obtained by adjusting
one free parameter, when the leading and subleading terms in the expansion are
included. The saturation mechanism is due to correlations induced by the
one-pion-exchange interaction. Furthermore, we find a substantial deviation
from the Fermi-gas estimate of the quark condensate in nuclear matter already
at the saturation density.Comment: revised version, with minor corrections, 13 pages, 3 Postscript
figure
Bandwidth in Bolometric Interferometry
Context. Bolometric interferometry is a promising new technology with potential applications to the detection of B-mode polarization fluctuations of the cosmic microwave background (CMB). A bolometric interferometer will have to take advantage of the wide spectral detection band of its bolometers to be competitive with imaging experiments. A crucial concern is that interferometers are assumed to be significantly affected by a spoiling effect known as bandwidth smearing.
Aims. We investigate how the bandwidth modifies the work principle of a bolometric interferometer and affects its sensitivity to the CMB angular power spectra.
Methods. We obtain analytical expressions for the broadband visibilities measured by broadband heterodyne and bolometric interferometers. We investigate how the visibilities must be reconstructed in a broadband bolometric interferometer and show that this critically depends on hardware properties of the modulation phase shifters. If the phase shifters produce shifts that are constant with respect to frequency, the instrument works like its monochromatic version (the modulation matrix is not modified), while if they vary (linearly or otherwise) with respect to frequency, one has to perform a special reconstruction scheme, which allows the visibilities to be reconstructed in frequency subbands. Using an angular power spectrum estimator that accounts for the bandwidth, we finally calculate the sensitivity of a broadband bolometric interferometer. A numerical simulation is performed that confirms the analytical results.
Results. We conclude that (i) broadband bolometric interferometers allow broadband visibilities to be reconstructed regardless of the type of phase shifters used and (ii) for dedicated B-mode bolometric interferometers, the sensitivity loss caused by bandwidth smearing is quite acceptable, even for wideband instruments (a factor of 2 loss for a typical 20% bandwidth experiment)
Strange and singlet form factors of the nucleon: Predictions for G0, A4, and HAPPEX-II experiments
We investigate the strange and flavor-singlet electric and magnetic form
factors of the nucleon within the framework of the SU(3) chiral quark-soliton
model. Isospin symmetry is assumed and the symmetry-conserving SU(3)
quantization is employed, rotational and strange quark mass corrections being
included. For the experiments G0, A4, and HAPPEX-II we predict the quantities
and . The dependence
of the results on the parameters of the model and the treatment of the Yukawa
asymptotic behavior of the soliton are investigated.Comment: 16 pages, 3 figures, Final version for publication in Eur. Phys. J.
Strange form factors in the context of SAMPLE, HAPPEX, and A4 experiments
The strange properties of the nucleon are investigated within the framework
of the SU(3) chiral quark-soliton model assuming isospin symmetry and applying
the symmetry conserving SU(3) quantization. We present the form factors
, and the electric and magnetic strange form
factors incorporating pion and kaon asymptotics. The results
show a fairly good agreement with the recent experimental data from the SAMPLE
and HAPPEX collaborations. We also present predictions for future measurements
including the A4 experiment at MAMI (Mainz).Comment: 10 pages with four figures. RevTeX4 is used. Few lines are changed.
Accepted for publication in Phys.Rev.
Quantum-secure message authentication via blind-unforgeability
Formulating and designing unforgeable authentication of classical messages in
the presence of quantum adversaries has been a challenge, as the familiar
classical notions of unforgeability do not directly translate into meaningful
notions in the quantum setting. A particular difficulty is how to fairly
capture the notion of "predicting an unqueried value" when the adversary can
query in quantum superposition. In this work, we uncover serious shortcomings
in existing approaches, and propose a new definition. We then support its
viability by a number of constructions and characterizations. Specifically, we
demonstrate a function which is secure according to the existing definition by
Boneh and Zhandry, but is clearly vulnerable to a quantum forgery attack,
whereby a query supported only on inputs that start with 0 divulges the value
of the function on an input that starts with 1. We then propose a new
definition, which we call "blind-unforgeability" (or BU.) This notion matches
"intuitive unpredictability" in all examples studied thus far. It defines a
function to be predictable if there exists an adversary which can use
"partially blinded" oracle access to predict values in the blinded region. Our
definition (BU) coincides with standard unpredictability (EUF-CMA) in the
classical-query setting. We show that quantum-secure pseudorandom functions are
BU-secure MACs. In addition, we show that BU satisfies a composition property
(Hash-and-MAC) using "Bernoulli-preserving" hash functions, a new notion which
may be of independent interest. Finally, we show that BU is amenable to
security reductions by giving a precise bound on the extent to which quantum
algorithms can deviate from their usual behavior due to the blinding in the BU
security experiment.Comment: 23+9 pages, v3: published version, with one theorem statement in the
summary of results correcte
AgapeZ1: a Large Amplification Microlensing Event or an Odd Variable Star Towards the Inner Bulge of M31
AgapeZ1 is the brightest and the shortest duration microlensing candidate
event found in the Agape data. It occured only 42" from the center of M31. Our
photometry shows that the half intensity duration of the event6 is 4.8 days and
at maximum brightness we measure a stellar magnitude of R=18.0 with B-R=0.80
mag color. A search on HST archives produced a single resolved star within the
projected event position error box. Its magnitude is R=22.Comment: 4 pages with 5 figure
- …