58 research outputs found
Increasing evidence for hemispherical power asymmetry in the five-year WMAP data
(Abridged)Motivated by the recent results of Hansen et al. (2008) concerning
a noticeable hemispherical power asymmetry in the WMAP data on small angular
scales, we revisit the dipole modulated signal model introduced by Gordon et
al. (2005). This model assumes that the true CMB signal consists of a Gaussian
isotropic random field modulated by a dipole, and is characterized by an
overall modulation amplitude, A, and a preferred direction, p. Previous
analyses of this model has been restricted to very low resolution due to
computational cost. In this paper, we double the angular resolution, and
compute the full corresponding posterior distribution for the 5-year WMAP data.
The results from our analysis are the following: The best-fit modulation
amplitude for l <= 64 and the ILC data with the WMAP KQ85 sky cut is A=0.072
+/- 0.022, non-zero at 3.3sigma, and the preferred direction points toward
Galactic coordinates (l,b) = (224 degree, -22 degree) +/- 24 degree. The
corresponding results for l <~ 40 from earlier analyses was A = 0.11 +/- 0.04
and (l,b) = (225 degree,-27 degree). The statistical significance of a non-zero
amplitude thus increases from 2.8sigma to 3.3sigma when increasing l_max from
40 to 64, and all results are consistent to within 1sigma. Similarly, the
Bayesian log-evidence difference with respect to the isotropic model increases
from Delta ln E = 1.8 to Delta ln E = 2.6, ranking as "strong evidence" on the
Jeffreys' scale. The raw best-fit log-likelihood difference increases from
Delta ln L = 6.1 to Delta ln L = 7.3. Similar, and often slightly stronger,
results are found for other data combinations. Thus, we find that the evidence
for a dipole power distribution in the WMAP data increases with l in the 5-year
WMAP data set, in agreement with the reports of Hansen et al. (2008).Comment: 6 pages, 2 figures; added references and minor comments. Accepted for
publication in Ap
Detection of a Dipole in the Handedness of Spiral Galaxies with Redshifts z ~ 0.04
A preference for spiral galaxies in one sector of the sky to be left-handed
or right-handed spirals would indicate a parity violating asymmetry in the
overall universe and a preferred axis. This study uses 15158 spiral galaxies
with redshifts <0.085 from the Sloan Digital Sky Survey. An unbinned analysis
for a dipole component that made no prior assumptions for the dipole axis gives
a dipole asymmetry of -0.0408\pm0.011 with a probability of occurring by chance
of 7.9 x 10-4. A similar asymmetry is seen in the Southern Galaxy spin catalog
of Iye and Sugai. The axis of the dipole asymmetry lies at approx. (l, b)
=(52{\deg}, 68.5{\deg}), roughly along that of our Galaxy and close to
alignments observed in the WMAP cosmic microwave background distributions. The
observed spin correlation extends out to separations ~210 Mpc/h, while spirals
with separations < 20 Mpc/h have smaller spin correlations.Comment: To be published in Physics Letters
Searching for hidden mirror symmetries in CMB fluctuations from WMAP 7 year maps
We search for hidden mirror symmetries at large angular scales in the WMAP 7
year Internal Linear Combination map of CMB temperature anisotropies using
global pixel based estimators introduced for this aim. Two different axes are
found for which the CMB intensity pattern is anomalously symmetric (or
anti-symmetric) under reflection with respect to orthogonal planes at the
99.84(99.96)% CL (confidence level), if compared to a result for an arbitrary
axis in simulations without the symmetry. We have verified that our results are
robust to the introduction of the galactic mask. The direction of such axes is
close to the CMB kinematic dipole and nearly orthogonal to the ecliptic plane,
respectively. If instead the real data are compared to those in simulations
taken with respect to planes for which the maximal mirror symmetry is generated
by chance, the confidence level decreases to 92.39 (76.65)%. But when the
effect in question translates into the anomalous alignment between normals to
planes of maximal mirror (anti)-symmetry and these natural axes mentioned. We
also introduce the representation of the above estimators in the harmonic
domain, confirming the results obtained in the pixel one. The symmetry anomaly
is shown to be almost entirely due to low multipoles, so it may have a
cosmological and even primordial origin. Contrary, the anti-symmetry one is
mainly due to intermediate multipoles that probably suggests its
non-fundamental nature. We have demonstrated that these anomalies are not
connected to the known issue of the low variance in WMAP observations and we
have checked that axially symmetric parts of these anomalies are small, so that
the axes are not the symmetry ones.Comment: 18 pages, 10 figures, 2 tables. Consideration and discussion
expanded, 5 figures and 1 table added, main conclusions unchange
Anisotropic Inflation from Charged Scalar Fields
We consider models of inflation with U(1) gauge fields and charged scalar
fields including symmetry breaking potential, chaotic inflation and hybrid
inflation. We show that there exist attractor solutions where the anisotropies
produced during inflation becomes comparable to the slow-roll parameters. In
the models where the inflaton field is a charged scalar field the gauge field
becomes highly oscillatory at the end of inflation ending inflation quickly.
Furthermore, in charged hybrid inflation the onset of waterfall phase
transition at the end of inflation is affected significantly by the evolution
of the background gauge field. Rapid oscillations of the gauge field and its
coupling to inflaton can have interesting effects on preheating and
non-Gaussianities.Comment: minor changes, references added, figures are modified, conforms JCAP
published versio
Frequentist comparison of CMB local extrema statistics in the five-year WMAP data with two anisotropic cosmological models
We present local extrema studies of two models that introduce a preferred
direction into the observed cosmic microwave background (CMB) temperature
field. In particular, we make a frequentist comparison of the one- and
two-point statistics for the dipole modulation and ACW models with data from
the five-year Wilkinson Microwave Anisotropy Probe (WMAP). This analysis is
motivated by previously revealed anomalies in the WMAP data, and particularly
the difference in the statistical nature of the temperature anisotropies when
analysed in hemispherical partitions.
The analysis of the one-point statistics indicates that the previously
determined hemispherical variance difficulties can be apparently overcome by a
dipole modulation field, but new inconsistencies arise if the mean and the
l-dependence of the statistics are considered. The two-point correlation
functions of the local extrema, the temperature pair product and the
point-point spatial pair-count, demonstrate that the impact of such a
modulation is to over-`asymmetrise' the temperature field on smaller scales
than the wave-length of the dipole or quadrupole, and this is disfavored by the
observed data.The results from the ACW model predictions, however, are
consistent with the standard isotropic hypothesis. The two-point analysis
confirms that the impact of this type of violation of isotropy on the
temperature extrema statistics is relatively weak.
From this work, we conclude that a model with more spatial structure than the
dipole modulated or rotational-invariance breaking models are required to fully
explain the observed large-scale anomalies in the WMAP data.Comment: 10 pages, 4 figures, 3 tables, accepted for publication in MNRA
Constraints on f_nl and g_nl from the analysis of the N-pdf of the CMB large scale anisotropies
[Abridged] In this paper we explore a local non-linear perturbative model up
to third order as a general characterization of the CMB anisotropies. We focus
our analysis in large scale anisotropies. At these angular scales, the
non-Gaussian description proposed in this work defaults (under certain
conditions) to an approximated local form of the weak non-linear coupling
inflationary model. In particular, quadratic and cubic terms are governed by
the non-linear coupling parameters f_nl and g_nl, respectively. The extension
proposed in this paper allows us to directly constrain these non-linear
parameters. Applying the proposed methodology to WMAP 5-yr data, we obtain -5.6
x 10^5 < g_nl < 6.4 x 10^5, at 95% CL. This result is in agreement with
previous findings obtained for equivalent non-Gaussian models and with
different non-Gaussian estimators. A model selection test is performed,
indicating that a Gaussian model is preferred to the non-Gaussian scenario.
When comparing different non-Gaussian models, we observe that a pure f_nl model
is the most favoured case, and that a pure g_nl model is more likely than a
general non-Gaussian scenario. Finally, we have analyzed the WMAP data in two
independent hemispheres, in particular the ones defined by the dipolar pattern
found by Hoftuft et al. 2009. We show that, whereas g_nl is still compatible
with zero for both hemispheres, it is not the case for f_nl (with a p-value
0.04). However, if anisotropy of the data is assumed, the distance between the
likelihood distributions for each hemisphere is larger than expected from
Gaussian and anisotropic simulations, also for g_nl (with a p-value of 0.001 in
the case of this parameter). This result is an extra evidence for the CMB
asymmetries previously reported in WMAP data.Comment: 15 pages, 9 figures, accepted for publication in MNRAS. Corrections
made to match the final versio
Issues on Generating Primordial Anisotropies at the End of Inflation
We revisit the idea of generating primordial anisotropies at the end of
inflation in models of inflation with gauge fields. To be specific we consider
the charged hybrid inflation model where the waterfall field is charged under a
U(1) gauge field so the surface of end of inflation is controlled both by
inflaton and the gauge fields. Using delta N formalism properly we find that
the anisotropies generated at the end of inflation from the gauge field
fluctuations are exponentially suppressed on cosmological scales. This is
because the gauge field evolves exponentially during inflation while in order
to generate appreciable anisotropies at the end of inflation the spectator
gauge field has to be frozen and scale invariant. We argue that this is a
generic feature, that is, one can not generate observable anisotropies at the
end of inflation within an FRW background.Comment: V3: new references added, JCAP published versio
Can residuals of the Solar system foreground explain low multipole anomalies of the CMB ?
The low multipole anomalies of the Cosmic Microwave Background has received
much attention during the last few years. It is still not ascertained whether
these anomalies are indeed primordial or the result of systematics or
foregrounds. An example of a foreground, which could generate some non-Gaussian
and statistically anisotropic features at low multipole range, is the very
symmetric Kuiper Belt in the outer solar system. In this paper, expanding upon
the methods presented by Maris et al. (2011), we investigate the contributions
from the Kuiper Belt objects (KBO) to the WMAP ILC 7 map, whereby we can
minimize the contrast in power between even and odd multipoles in the CMB,
discussed discussed by Kim & Naselsky (2010). We submit our KBO de-correlated
CMB signal to several tests, to analyze its validity, and find that
incorporation of the KBO emission can decrease the quadrupole-octupole
alignment and parity asymmetry problems, provided that the KBO signals has a
non-cosmological dipole modulation, associated with the statistical anisotropy
of the ILC 7 map. Additionally, we show that the amplitude of the dipole
modulation, within a 2 sigma interval, is in agreement with the corresponding
amplitudes, discussed by Lew (2008).Comment: 24 pages, 9 figures, 5 tables. Matches version in JCA
A search for concentric rings with unusual variance in the 7-year WMAP temperature maps using a fast convolution approach
We present a method for the computation of the variance of cosmic microwave
background (CMB) temperature maps on azimuthally symmetric patches using a fast
convolution approach. As an example of the application of the method, we show
results for the search for concentric rings with unusual variance in the 7-year
WMAP data. We re-analyse claims concerning the unusual variance profile of
rings centred at two locations on the sky that have recently drawn special
attention in the context of the conformal cyclic cosmology scenario proposed by
Penrose (2009). We extend this analysis to rings with larger radii and centred
on other points of the sky. Using the fast convolution technique enables us to
perform this search with higher resolution and a wider range of radii than in
previous studies. We show that for one of the two special points rings with
radii larger than 10 degrees have systematically lower variance in comparison
to the concordance LambdaCDM model predictions. However, we show that this
deviation is caused by the multipoles up to order l=7. Therefore, the deficit
of power for concentric rings with larger radii is yet another manifestation of
the well-known anomalous CMB distribution on large angular scales. Furthermore,
low variance rings can be easily found centred on other points in the sky. In
addition, we show also the results of a search for extremely high variance
rings. As for the low variance rings, some anomalies seem to be related to the
anomalous distribution of the low-order multipoles of the WMAP CMB maps. As
such our results are not consistent with the conformal cyclic cosmology
scenario.Comment: 12 pages, 11 figures, 1 table. Published in MNRAS. This research was
supported by the Agence Nationale de la Recherche (ANR-08-CEXC-0002-01
Temperature and Polarization Patterns in Anisotropic Cosmologies
We study the coherent temperature and polarization patterns produced in
homogeneous but anisotropic cosmological models. We show results for all
Bianchi types with a Friedman-Robertson-Walker limit (i.e. Types I, V,
VII, VII and IX) to illustrate the range of possible behaviour. We
discuss the role of spatial curvature, shear and rotation in the geodesic
equations for each model and establish some basic results concerning the
symmetries of the patterns produced. We also give examples of the
time-evolution of these patterns in terms of the Stokes parameters , and
.Comment: 24 pages, 7 Figures, submitted to JCAP. Revised version: numerous
references added, text rewritten, and errors corrected
- …