1,173 research outputs found
Reconstruction of primordial tensor power spectra from B-mode polarization of the cosmic microwave background
Given observations of B-mode polarization power spectrum of the cosmic
microwave background (CMB), we can reconstruct power spectra of primordial
tensor modes from the early Universe without assuming their functional form
such as a power-law spectrum. Shape of the reconstructed spectra can then be
used to probe the origin of tensor modes in a model-independent manner. We use
the Fisher matrix to calculate the covariance matrix of tensor power spectra
reconstructed in bins. We find that the power spectra are best reconstructed at
wavenumbers in the vicinity of and , which correspond to the "reionization bump" at
and "recombination bump" at of the CMB B-mode
power spectrum, respectively. The error bar between these two wavenumbers is
larger because of lack of the signal between the reionization and recombination
bumps. The error bars increase sharply towards smaller (larger) wavenumbers
because of the cosmic variance (CMB lensing and instrumental noise). To
demonstrate utility of the reconstructed power spectra we investigate whether
we can distinguish between various sources of tensor modes including those from
the vacuum metric fluctuation and SU(2) gauge fields during single-field
slow-roll inflation, open inflation and massive gravity inflation. The results
depend on the model parameters, but we find that future CMB experiments are
sensitive to differences in these models. We make our calculation tool
available on-line.Comment: 9 pages, 2 figures, 4 tables; accepted version in Phys. Rev.
Calibration System with Cryogenically-Cooled Loads for CMB Polarization Detectors
We present a novel system to calibrate millimeter-wave polarimeters for CMB
polarization measurements. This technique is an extension of the conventional
metal mirror rotation approach, however it employs cryogenically-cooled
blackbody absorbers. The primary advantage of this system is that it can
generate a slightly polarized signal ( mK) in the laboratory; this is
at a similar level to that measured by ground-based CMB polarization
experiments observing a 10 K sky. It is important to reproduce the
observing condition in the laboratry for reliable characterization of
polarimeters before deployment. In this paper, we present the design and
principle of the system, and demonstrate its use with a coherent-type
polarimeter used for an actual CMB polarization experiment. This technique can
also be applied to incoherent-type polarimeters and it is very promising for
the next-generation CMB polarization experiments.Comment: 7 pages, 9 figures Submitted to RS
Innovative Demodulation Scheme for Coherent Detectors in CMB Experiments
We propose an innovative demodulation scheme for coherent detectors used in
cosmic microwave background polarization experiments. Removal of non-white
noise, e.g., narrow-band noise, in detectors is one of the key requirements for
the experiments. A combination of modulation and demodulation is used to
extract polarization signals as well as to suppress such noise. Traditional
demodulation, which is based on the two- point numerical differentiation, works
as a first-order high pass filter for the noise. The proposed demodulation is
based on the three-point numerical differentiation. It works as a second-order
high pass filter. By using a real detector, we confirmed significant
improvements of suppression power for the narrow-band noise. We also found
improvement of the noise floor.Comment: 3 pages, 4 figure
Finding the chiral gravitational wave background of an axion-SU(2) inflationary model using CMB observations and laser interferometers
A detection of B-mode polarization of the Cosmic Microwave Background (CMB)
anisotropies would confirm the presence of a primordial gravitational wave
background (GWB). In the inflation paradigm this would be an unprecedented
probe of the energy scale of inflation as it is directly proportional to the
power spectrum of the GWB. However, similar tensor perturbations can be
produced by the matter fields present during inflation, breaking this simple
relationship. It is therefore important to be able to distinguish between
different generation mechanisms of the GWB. In this paper, we analyse the
detectability of a new axion-SU(2) gauge field model using its chiral,
scale-dependent tensor spectrum. We forecast the detectability of the resulting
CMB TB and EB cross-correlations by the LiteBIRD satellite, considering the
effects of residual foregrounds, gravitational lensing, and for the first time
assess the ability of such an experiment to jointly detect primordial TB and EB
spectra and self-calibrate its polarimeter. We find that LiteBIRD will be able
to detect the chiral signal for with denoting the
tensor-to-scalar ratio at the peak scale, and that the maximum signal-to-noise
for is . We go on to consider an advanced stage of a
LISA-like mission, and find that such experiments would complement CMB
observations by providing sensitivity to GWB chirality on scales inaccessible
to the CMB. We conclude that in order to use the CMB to distinguish this model
from a conventional vacuum fluctuation model two-point statistics provide some
power, but to achieve high statistical significance we would require higher
order statistics which take advantage of the model's non-Gaussianity. On the
other hand, in the case of a spectrum peaked at very small scales, inaccessible
to the CMB, a highly significant detection could be made using space-based
laser interferometers.Comment: 24 pages, 12 figures, accepted by PhysRev
Digital frequency domain multiplexing readout electronics for the next generation of millimeter telescopes
Frequency domain multiplexing (fMux) is an established technique for the
readout of transition-edge sensor (TES) bolometers in millimeter-wavelength
astrophysical instrumentation. In fMux, the signals from multiple detectors are
read out on a single pair of wires reducing the total cryogenic thermal loading
as well as the cold component complexity and cost of a system. The current
digital fMux system, in use by POLARBEAR, EBEX, and the South Pole Telescope,
is limited to a multiplexing factor of 16 by the dynamic range of the
Superconducting Quantum Interference Device pre-amplifier and the total system
bandwidth. Increased multiplexing is key for the next generation of large
format TES cameras, such as SPT-3G and POLARBEAR2, which plan to have on the of
order 15,000 detectors.
Here, we present the next generation fMux readout, focusing on the warm
electronics. In this system, the multiplexing factor increases to 64 channels
per module (2 wires) while maintaining low noise levels and detector stability.
This is achieved by increasing the system bandwidth, reducing the dynamic range
requirements though active feedback, and digital synthesis of voltage biases
with a novel polyphase filter algorithm. In addition, a version of the new fMux
readout includes features such as low power consumption and radiation-hard
components making it viable for future space-based millimeter telescopes such
as the LiteBIRD satellite.Comment: 15 pages, 10 figures. To be published in Proceedings of SPIE Volume
9153. Presented at SPIE Astronomical Telescopes + Instrumentation 2014,
conference 915
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