105 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.
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
Zero Casimir Force in Axion Electrodynamics and New Force Search
We point out that there is a stable configuration of metal plates where the
Casimir force is vanishing in axion electrodynamics. We consider a concrete
setup involving Weyl semimetals, which hosts an axion-like effect on the
electromagnetism, towards the measurement of the axionic effect on the Casimir
force. Our setup realizes zero Casimir force between metals and may be useful
for the search for new force mediated by light particles at the micrometer
scale.Comment: 28 pages, 9 figure
- …