1,957 research outputs found
Symmetries of CMB Temperature Correlation at Large Angular Separations
A new analysis is presented of the angular correlation function
of cosmic microwave background (CMB) temperature at large angular separation,
based on published maps derived from {\sl WMAP} and {\sl Planck} satellite
data, using different models of astrophysical foregrounds. It is found that
using a common analysis, the results from the two satellites are very similar.
In particular, it is found that previously published differences between
measured values of near arise mainly from
different choices of masks in regions of largest Galactic emissions, and that
demonstrated measurement biases are reduced by eliminating masks altogether.
Maps from both satellites are shown to agree with to within
estimated statistical and systematic errors, consistent with an exact symmetry
predicted in a new holographic quantum model of inflation.Comment: resubmitted to ApJ Letters, with revisions in response to referee
comment
Angular correlations on causally-coherent inflationary horizons
We develop a model for correlations of cosmic microwave background anisotropy
on the largest angular scales, based on standard causal geometrical
relationships in slow-roll inflation. Unlike standard models based on quantized
field modes, it describes perturbations with nonlocal directional coherence on
spherical boundaries of causal diamonds. Causal constraints reduce the number
of independent degrees of freedom, impose new angular symmetries, and eliminate
cosmic variance for purely angular 2-point correlations. Distortions of causal
structure from vacuum fluctuations are modeled as gravitational memory from
randomly oriented outgoing and incoming gravitational null shocks, with
nonlocally coherent directional displacements on curved surfaces of causal
diamonds formed by standard inflationary horizons. The angular distribution is
determined by axially symmetric shock displacements on circular intersections
of the comoving sphere that represents the CMB photosphere with other
inflationary horizons. Displacements on thin spheres at the end of inflation
have a unique angular power spectrum that approximates the standard
expectation on small angular scales, but differs substantially at large angular
scales due to horizon curvature. For a thin sphere, the model predicts a
universal angular correlation function with an exact ``causal
shadow'' symmetry, , and significant large-angle
parity violation. We apply a rank statistic to compare models with WMAP and
Planck satellite data, and find that a causally-coherent model with no shape
parameters or cosmic variance agrees with the measured better than
a large fraction () of standard model realizations. Model-independent
tests of holographic causal symmetries are proposed
A Compact Millimeter-Wavelength Fourier-Transform Spectrometer
We have constructed a Fourier-transform spectrometer (FTS) operating between
50 and 330 GHz with minimum volume (355 x260 x64 mm) and weight (13 lbs) while
maximizing optical throughput (100 sr) and optimizing the
spectral resolution (4 GHz). This FTS is designed as a polarizing
Martin-Puplett interferometer with unobstructed input and output in which both
input polarizations undergo interference. The instrument construction is simple
with mirrors milled on the box walls and one motorized stage as the single
moving element. We characterize the performance of the FTS, compare the
measurements to an optical simulation, and discuss features that relate to
details of the FTS design. The simulation is also used to determine the
tolerance of optical alignments for the required specifications. We detail the
FTS mechanical design and provide the control software as well as the analysis
code online.Comment: Submitted to Applied Optics. [Copyright 2019 Optical Society of
America]. Users may use, reuse, and build upon the article, or use the
article for text or data mining, so long as such uses are for non-commercial
purposes and appropriate attribution is maintained. All other rights are
reserve
First measurements of high frequency cross-spectra from a pair of large Michelson interferometers
Measurements are reported of the cross-correlation of spectra of differential
position signals from the Fermilab Holometer, a pair of co-located 39 m long,
high power Michelson interferometers with flat, broadband frequency response in
the MHz range. The instrument obtains sensitivity to high frequency correlated
signals far exceeding any previous measurement in a broad frequency band
extending beyond the 3.8 MHz inverse light crossing time of the apparatus. The
dominant but uncorrelated shot noise is averaged down over
independent spectral measurements with 381 Hz frequency resolution to obtain
sensitivity to stationary
signals. For signal bandwidths kHz, the sensitivity to strain
or shear power spectral density of classical or exotic origin surpasses a
milestone where
is the Planck time.Comment: 5 pages, 3 figure
Interferometric Constraints on Quantum Geometrical Shear Noise Correlations
Final measurements and analysis are reported from the first-generation
Holometer, the first instrument capable of measuring correlated variations in
space-time position at strain noise power spectral densities smaller than a
Planck time. The apparatus consists of two co-located, but independent and
isolated, 40 m power-recycled Michelson interferometers, whose outputs are
cross-correlated to 25 MHz. The data are sensitive to correlations of
differential position across the apparatus over a broad band of frequencies up
to and exceeding the inverse light crossing time, 7.6 MHz. By measuring with
Planck precision the correlation of position variations at spacelike
separations, the Holometer searches for faint, irreducible correlated position
noise backgrounds predicted by some models of quantum space-time geometry. The
first-generation optical layout is sensitive to quantum geometrical noise
correlations with shear symmetry---those that can be interpreted as a
fundamental noncommutativity of space-time position in orthogonal directions.
General experimental constraints are placed on parameters of a set of models of
spatial shear noise correlations, with a sensitivity that exceeds the
Planck-scale holographic information bound on position states by a large
factor. This result significantly extends the upper limits placed on models of
directional noncommutativity by currently operating gravitational wave
observatories.Comment: Matches the journal accepted versio
Infrared Cloud Monitoring with UCIRC2
The second generation of the Extreme Universe Space Observatory on a Super
Pressure Balloon (EUSO-SPB2) is a balloon instrument that searched for ultra
high energy cosmic rays (UHECRs) with energies above 1 EeV and very high energy
neutrinos with energies above 1 PeV. EUSO-SPB2 consists of two telescopes: a
fluorescence telescope pointed downward for the detection of UHECRs and a
Cherenkov telescope toward the limb for the detection of PeV-scale showers
produced by neutrino-sourced tau decay (just below the limb) and by cosmic rays
(just above the limb). Clouds inside the fields of view of these
telescopes--particularly that of the fluorescence telescope--reduce EUSO-SPB2's
geometric aperture. As such, cloud coverage and cloud-top altitude within the
field of view of the fluorescence telescope must be monitored throughout
data-taking. The University of Chicago Infrared Camera (UCIRC2) monitored these
clouds using two infrared cameras centered at 10 and 12 m. By capturing
images at wavelengths spanning the cloud thermal emission peak, UCIRC2 measured
cloud color-temperatures and thus cloud-top altitudes. In this contribution, we
provide an overview of UCIRC2, including an update on its construction and
performance. We also show first results from the flight.Comment: 10 pages, 7 figures, proceedings of the 38th International Cosmic Ray
Conference (ICRC 2023). arXiv admin note: substantial text overlap with
arXiv:2112.09618, arXiv:1909.0266
EUSO-SPB2 Fluorescence Telescope Calibration and Field Tests
The Extreme Universe Space Observatory on a Super Pressure Balloon 2
(EUSO-SPB2), successfully launched from Wanaka, New Zealand on May 13, 2022, is
a precursor for a space-based astroparticle observatory such as the Probe Of
Extreme Multi-Messenger Astrophysics (POEMMA). EUSO-SPB2 flew two custom
telescopes. Both have UV/UV-visible sensitivity and feature Schmidt optics. The
Fluorescence Telescope (FT) measures ultra-high energy cosmic rays by looking
down. The \v{C}erenkov Telescope (CT) searches for neutrino signatures by
looking toward Earth's limb. The two telescopes each have a 1 m diameter
entrance pupil and segmented glass mirrors that collect light from extensive
air showers at the PeV and EeV-scale. Here we describe the FT telescope optics
together with the results of the FT field tests at the Utah Telescope Array
(TA) site from August/September 2022. The FT recorded the night sky background,
lasers, and artificial point sources. The field tests included an absolute
photometric calibration of the FT telescope that is compared to a piece-wise
laboratory calibration
Convergence towards a European strategic culture? A constructivist framework for explaining changing norms.
The article contributes to the debate about the emergence of a European strategic culture to underpin a European Security and Defence Policy. Noting both conceptual and empirical weaknesses in the literature, the article disaggregates the concept of strategic culture and focuses on four types of norms concerning the means and ends for the use of force. The study argues that national strategic cultures are less resistant to change than commonly thought and that they have been subject to three types of learning pressures since 1989: changing threat perceptions, institutional socialization, and mediatized crisis learning. The combined effect of these mechanisms would be a process of convergence with regard to strategic norms prevalent in current EU countries. If the outlined hypotheses can be substantiated by further research the implications for ESDP are positive, especially if the EU acts cautiously in those cases which involve norms that are not yet sufficiently shared across countries
- …