11 research outputs found
Oscillations in the inflaton potential: Complete numerical treatment and comparison with the recent and forthcoming CMB datasets
Amongst the multitude of inflationary models currently available, models that
lead to features in the primordial scalar spectrum are drawing increasing
attention, since certain features have been found to provide a better fit to
the CMB data than the conventional, nearly scale invariant, primordial
spectrum. In this work, we carry out a complete numerical analysis of two
models that lead to oscillations over all scales in the scalar power spectrum.
We consider the model described by a quadratic potential which is superposed by
a sinusoidal modulation and the recently popular axion monodromy model. Since
the oscillations continue even on to arc minute scales, in addition to the WMAP
data, we also compare the models with the small scale data from ACT. Though,
both the models, broadly, result in oscillations in the spectrum,
interestingly, we find that, while the monodromy model leads to a considerably
better fit to the data in comparison to the standard power law spectrum, the
quadratic potential superposed with a sinusoidal modulation does not improve
the fit to a similar extent. We also carry out forecasting of the parameters
using simulated Planck data for both the models. We show that the Planck mock
data performs better in constraining the model parameters as compared to the
presently available CMB datasets.Comment: 10 pages, 6 figure
Primordial features due to a step in the inflaton potential
Certain oscillatory features in the primordial scalar power spectrum are
known to provide a better fit to the outliers in the cosmic microwave
background data near the multipole moments of and 40. These features
are usually generated by introducing a step in the popular, quadratic potential
describing the canonical scalar field. Such a model will be ruled out, if the
tensors remain undetected at a level corresponding to a tensor-to-scalar ratio
of, say, . In this work, in addition to the popular quadratic
potential, we investigate the effects of the step in a small field model and a
tachyon model. With possible applications to future datasets (such as PLANCK)
in mind, we evaluate the tensor power spectrum exactly, and include its
contribution in our analysis. We compare the models with the WMAP (five as well
as seven-year), the QUaD and the ACBAR data. As expected, a step at a
particular location and of a suitable magnitude and width is found to improve
the fit to the outliers (near and 40) in all these cases. We point
out that, if the tensors prove to be small (say, ), the
quadratic potential and the tachyon model will cease to be viable, and more
attention will need to be paid to examples such as the small field models.Comment: 17 pages, 6 figures, Discussion shortened, Version to appear in JCA
Statistical Isotropy violation of the CMB brightness fluctuations
Certain anomalies at large angular scales in the cosmic microwave background
measured by WMAP have been suggested as possible evidence of breakdown of
statistical isotropy(SI). Most CMB photons free-stream to the present from the
surface of last scattering. It is thus reasonable to expect statistical
isotropy violation in the CMB photon distribution observed now to have
originated from SI violation in the baryon-photon fluid at last scattering, in
addition to anisotropy of the primordial power spectrum studied earlier in
literature.
We consider the generalized anisotropic brightness distribution fluctuations,
(at conformal time ) in contrast to the
SI case where it is simply a function of and . The brightness fluctuations expanded in Bipolar Spherical Harmonic
(BipoSH) series, can then be written as where terms encode deviations from statistical isotropy. We
study the evolution of from
non-zero terms at last
scattering. Similar to the SI case, power at small spherical harmonic (SH)
multipoles of at the last
scattering, is transferred to at
larger SH multipoles. The structural similarity is more apparent in the
asymptotic expression for large values of the final SH multipoles. This
formalism allows an elegant identification of any SI violation observed today
to a possible origin in the SI violation present in the baryon-photon fluid
(eg., due to the presence of significant magnetic field).Comment: 14 pages, 4 figures, added illustrative example of SI violation in
baryon-photon fluid, matches version accepted for publication in Phys. Rev.
Design and implementation of a noise temperature measurement system for the Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX)
This paper describes the design, implementation, and verification of a
test-bed for determining the noise temperature of radio antennas operating
between 400-800MHz. The requirements for this test-bed were driven by the HIRAX
experiment, which uses antennas with embedded amplification, making system
noise characterization difficult in the laboratory. The test-bed consists of
two large cylindrical cavities, each containing radio-frequency (RF) absorber
held at different temperatures (300K and 77K), allowing a measurement of system
noise temperature through the well-known 'Y-factor' method. The apparatus has
been constructed at Yale, and over the course of the past year has undergone
detailed verification measurements. To date, three preliminary noise
temperature measurement sets have been conducted using the system, putting us
on track to make the first noise temperature measurements of the HIRAX feed and
perform the first analysis of feed repeatability.Comment: 19 pages, 12 figure
The C-Band All-Sky Survey (C-BASS):Design and capabilities
The C-Band All-Sky Survey (C-BASS) is an all-sky full-polarisation survey at
a frequency of 5 GHz, designed to provide complementary data to the all-sky
surveys of WMAP and Planck, and future CMB B-mode polarization imaging surveys.
The observing frequency has been chosen to provide a signal that is dominated
by Galactic synchrotron emission, but suffers little from Faraday rotation, so
that the measured polarization directions provide a good template for higher
frequency observations, and carry direct information about the Galactic
magnetic field. Telescopes in both northern and southern hemispheres with
matched optical performance are used to provide all-sky coverage from a
ground-based experiment. A continuous-comparison radiometer and a correlation
polarimeter on each telescope provide stable imaging properties such that all
angular scales from the instrument resolution of 45 arcmin up to full sky are
accurately measured. The northern instrument has completed its survey and the
southern instrument has started observing. We expect that C-BASS data will
significantly improve the component separation analysis of Planck and other CMB
data, and will provide important constraints on the properties of anomalous
Galactic dust and the Galactic magnetic field.Comment: 21 pages, 9 figure
Orthogonal bipolar spherical harmonics measures: Scrutinizing sources of isotropy violation
The two-point correlation function of the cosmic microwave background temperature anisotropies is generally assumed to be statistically isotropic (SI). Deviations from this assumption could be traced to physical or observational artifacts and systematic effects. Measurement of nonvanishing power in the bipolar spherical harmonic spectra is a standard statistical technique to search for isotropy violations. Although this is a neat tool allowing a blind search for SI violations in the cosmic microwave background sky, it is not easy to discern the cause of isotropy violation by using this measure. In this article, we propose a novel technique of constructing orthogonal bipolar spherical harmonic estimators, which can be used to discern between models of isotropy violation