90 research outputs found
Parity violation of primordial magnetic fields in the CMB bispectrum
We study the parity violation in the cosmic microwave background (CMB)
bispectrum induced by primordial magnetic fields (PMFs). Deriving a general
formula for the CMB bispectrum generated from not only non-helical but also
helical PMFs, we find that helical PMFs produce characteristic signals, which
disappear in parity-conserving cases, such as the intensity-intensity-intensity
bispectra arising from . For fast numerical
calculation of the CMB bispectrum, we reduce the one-loop formula to the
tree-level one by using the so-called pole approximation. Then, we show that
the magnetic anisotropic stress, which depends quadratically on non-helical and
helical PMFs and acts as a source of the CMB fluctuation, produces the
local-type non-Gaussianity. Comparing the CMB bispectra composed of the scalar
and tensor modes with the noise spectra, we find that assuming the generation
of the nearly scale-invariant non-helical and helical PMFs from the grand
unification energy scale () to the electroweak one (), the intensity-intensity-intensity bispectrum for can be observed by the WMAP experiment under the condition
that with
and being the non-helical and helical
PMF strengths smoothed on 1 Mpc, respectively.Comment: 18 pages, 2 figures. Accepted for publication in JCA
Probing the Early Universe with the CMB Scalar, Vector and Tensor Bispectrum
Although cosmological observations suggest that the fluctuations of seed
fields are almost Gaussian, the possibility of a small deviation of their
fields from Gaussianity is widely discussed. Theoretically, there exist
numerous inflationary scenarios which predict large and characteristic
non-Gaussianities in the primordial perturbations. These model-dependent
non-Gaussianities act as sources of the Cosmic Microwave Background (CMB)
bispectrum; therefore, the analysis of the CMB bispectrum is very important and
attractive in order to clarify the nature of the early Universe. Currently, the
impacts of the primordial non-Gaussianities in the scalar perturbations, where
the rotational and parity invariances are kept, on the CMB bispectrum have been
well-studied. However, for a complex treatment, the CMB bispectra generated
from the non-Gaussianities, which originate from the vector- and tensor-mode
perturbations and include the violation of the rotational or parity invariance,
have never been considered in spite of the importance of this information. On
the basis of our current studies, this thesis provides the general formalism
for the CMB bispectrum sourced by the non-Gaussianities not only in the
scalar-mode perturbations but also in the vector- and tensor-mode
perturbations. Applying this formalism, we calculate the CMB bispectrum from
two scalars and a graviton correlation and that from primordial magnetic
fields, and we then outline new constraints on these amplitudes. Furthermore,
this formalism can be easily extended to the cases where the rotational or
parity invariance is broken. We also compute the CMB bispectra from the
non-Gaussianities of the curvature perturbations with a preferred direction and
the graviton non-Gaussianities induced by the parity-violating Weyl cubic
terms. We also present some unique impacts to the violation of these
invariances on the CMB bispectrum.Comment: The final version will be published in Springer Theses
http://www.springer.com/astronomy/book/978-4-431-54179-
Violation of the Rotational Invariance in the CMB Bispectrum
We investigate a statistical anisotropy on the Cosmic Microwave Background
(CMB) bispectrum, which can be generated from the primordial non-Gaussianity
induced by quantum fluctuations of a vector field. We find new configurations
in the multipole space of the CMB bispectrum given by and their permutations, which violate the
rotational invariance, such as an off-diagonal configuration in the CMB power
spectrum. We also find that in a model presented by Yokoyama and Soda (2008),
the amplitude of the statistically anisotropic bispectrum in the above
configurations becomes as large as that in other configurations such as . As a result, it might be possible to detect these
contributions in future experiments, which would give us novel information
about the physics of the early Universe.Comment: 13 pages, 2 figures. Accepted for publication in PT
Parity violation in the CMB bispectrum by a rolling pseudoscalar
We investigate parity-violating signatures of temperature and polarization
bispectra of the cosmic microwave background (CMB) in an inflationary model
where a rolling pseudoscalar produces large equilateral tensor non-Gaussianity.
By a concrete computation based on full-sky formalism, it is shown that
resultant CMB bispectra have nonzero signals in both parity-even and parity-odd spaces, and are almost uncorrelated with usual scalar-mode equilateral
bispectra. These characteristic signatures and polarization information help to
detect such tensor non-Gaussianity. Use of both temperature and E-mode
bispectra potentially improves of the detectability with respect to an
analysis with temperature bispectrum alone. Considering B-mode bispectrum, the
signal-to-noise ratio may be able to increase by 3 orders of magnitude. We
present the uncertainties of a parameter depending on a coupling
constant and a rolling condition for the pseudoscalar expected in the and the proposed PRISM experiments.Comment: 19 pages, 5 figures. Accepted for publication in JCA
Angular dependence of primordial trispectra and CMB spectral distortions
Under the presence of anisotropic sources in the inflationary era, the
trispectrum of the primordial curvature perturbation has a very specific
angular dependence between each wavevector that is distinguishable from the one
encountered when only scalar fields are present, characterized by an angular
dependence described by Legendre polynomials. We examine the imprints left by
curvature trispectra on the bispectrum, generated by the correlation
between temperature anisotropies (T) and chemical potential spectral
distortions () of the Cosmic Microwave Background (CMB). Due to the
angular dependence of the primordial signal, the corresponding
bispectrum strongly differs in shape from sourced by the usual or local trispectra, enabling us to obtain an unbiased
estimation. From a Fisher matrix analysis, we find that, in a
cosmic-variance-limited (CVL) survey of , a minimum detectable value of
the quadrupolar Legendre coefficient is , which is 4 orders of
magnitude better than the best value attainable from the CMB
trispectrum. In the case of an anisotropic inflationary model with a
interaction (coupling the inflaton field with a vector
kinetic term ), the size of the curvature trispectrum is related to that
of quadrupolar power spectrum asymmetry, . In this case, a CVL measurement
of makes it possible to measure down to .Comment: 20 pages, 5 figures; version matching publication in JCA
Signatures of anisotropic sources in the trispectrum of the cosmic microwave background
Soft limits of -point correlation functions, in which one wavenumber is
much smaller than the others, play a special role in constraining the physics
of inflation. Anisotropic sources such as a vector field during inflation
generate distinct angular dependence in all these correlators. In this paper we
focus on the four-point correlator (the trispectrum ). We adopt a
parametrization motivated by models in which the inflaton is coupled to
a vector field through a interaction, namely
, where denotes the
Legendre polynomials. This shape is enhanced when the wavenumbers of the
diagonals of the quadrilateral are much smaller than the sides, .
The coefficient of the isotropic part, , is equal to
discussed in the literature. A interaction
generates which is, in turn, related to the quadrupole modulation
parameter of the power spectrum, , as with . We show that and can be equally well-constrained: the
expected CL error bars on these coefficients from a
cosmic-variance-limited experiment measuring temperature anisotropy of the
cosmic microwave background up to are . Therefore, we can reach by measuring the
angle-dependent trispectrum. The current upper limit on from
the temperature maps yields ( CL).Comment: 15 pages, 5 figure
Primordial trispectra and CMB spectral distortions
We study the bispectrum, generated by correlations between Cosmic
Microwave Background temperature (T) anisotropies and chemical potential
() distortions, and we analyze its dependence on primordial local
trispectrum parameters and . We cross-check our
results by comparing the full bispectrum calculation with the expectations from
a general physical argument, based on predicting the shape of -T
correlations from the couplings between short and long perturbation modes
induced by primordial non-Gaussianity. We show that and
-parts of the primordial trispectrum source a non-vanishing
signal, contrary to the auto-correlation function, which is
sensitive only to the -component. A simple Fisher matrix-based
forecast shows that a futuristic, cosmic-variance dominated experiment could in
principle detect and using
.Comment: 21 pages, 4 figures. Accepted for publication in JCA
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