Cosmological Alfv\'en waves in the recent CMB data, and the observational bound on the primordial vector perturbation

In the presence of the primordial magnetic field, initial vector (vorticity) perturbations produce cosmological Alfven waves and leave imprints on cosmic microwave background (CMB) temperature and polarization anisotropy. We have investigated imprints of cosmological Alfven waves in CMB anisotropy. For data constraints, we have used the power spectrum of the recent CMB observations, and correlations estimated from WMAP Internal Linear Combination (ILC) maps. Our analysis shows 3 sigma evidence of cosmological Alfven waves. Using the 3 sigma limit from our analysis and the Alfven velocity limit from the total energy density constraint, we impose a lower bound on the amplitude of primordial vector perturbation: 4*10^-12 at k_0=0.002/Mpc.Comment: v2: change in analysis method and confidence interval improved v3: typos corrected v4: a typo in Eq. 36 corrected v5: lower bound on vector perturbation in more compliant form for ease of comparison, references adde

Lack of angular correlation and odd-parity preference in CMB data

We have investigated the angular correlation in the recent CMB data. In addition to the known large-angle correlation anomaly, we find the lack of correlation at small angles with high statistical significance. We have investigated various non-cosmological contamination and additionally WMAP team's simulated data. However, we have not found a definite cause. In the angular power spectrum of WMAP data, there exist anomalous odd-parity preference at low multipoles. Noting the equivalence between the power spectrum and the correlation, we have investigated the association between the lack of large-angle correlation and the odd-parity preference. From our investigation, we find that the odd-parity preference at low multipoles is, in fact, a phenomenological origin of the lack of large-angle correlation. Futher investigation is required to find out whether the origin of the anomaly is cosmological or due to unaccounted systematics. The data from Planck surveyor, which has systematics distinct from the WMAP, will greatly help us to resolve its origin.Comment: v3: typos corrected, v4: plots updated, v5: analysis extended, v6: matched with the accepted version in ApJ (minor change

CMB data constraint on self-annihilation of dark matter particles

Recently, self-annihilation of dark matter particles is proposed to explain the "WMAP Haze" and excess of energetic positrons and electrons in ATIC and PAMELA results. If self-annihilation of dark matter occurs around the recombination of cosmic plasma, energy release from self-annihilation of dark matter delays the recombination, and hence affects CMB anisotropy. By using the recent CMB data, we have investigated the self-annihilation of dark matter particles. In this investigation, we do not find statistically significant evidence, and impose an upper bound on / m_chi. The upcoming data from Planck surveyor and the Fermi Gamma-ray telescope will allow us to break some of parameter degeneracy and improve constraints on self-annihilation of dark matter particles.Comment: a talk presented at the Invisible Universe International Conference at the Palais de l'UNESCO, Paris, v2: references adde

Parametric tension between even and odd multipole data of WMAP power spectrum: unaccounted contamination or missing parameters?

There exist power contrast in even and odd multipoles of WMAP power spectrum at low and intermediate multipole range. This anomaly is explicitly associated with the angular power spectrum, which are heavily used for cosmological model fitting. Having noted this, we have investigated whether even(odd) multipole data set is consistent with the WMAP concordance model. Our investigation shows WMAP concordance model does not make a good fit for even(odd) multipole data set, and there exist tension between two data subsets. Noting tension is highest in primordial power spectrum parameters, we have additionally considered a running spectral index, but find tension increases to even a higher level. We believe these parametric tensions may be indications of unaccounted contamination or imperfection of the model.Comment: v2: Latex error fixed, v3: matched with the accepted version in ApJL, conclusion unchange

Combined multi-frequency map for point source substraction

A method is proposed for combining multi-frequency maps in order to produce a catalogue of extragalactic point sources using data from future high-precision satellite experiments. We have found the optimal way for combining maps at different frequencies in order to maximize the signal (point sources) to noise (rest of the signal) ratio. Our approach is a natural multi-frequency generalization of the band-pass filter introduced by Tegmark and de Oliveira-Costa (1998). We show that combination of different frequency maps gives us the possibility of creating a more complete catalogue of point sources

Critical points of the cosmic velocity field and the uncertainties in the value of the Hubble constant

The existence of critical points for the peculiar velocity field is a natural feature of the correlated vector field. These points appear at the junctions of velocity domains with different orientations of their averaged velocity vectors. Since peculiar velocities are the important cause of the scatter in the Hubble expansion rate, we propose that a more precise determination of the Hubble constant can be made by restricting analysis to a subsample of observational data containing only the zones around the critical points of the peculiar velocity field, associated with voids and saddle points. On large-scales the critical points, where the first derivative of the gravitational potential vanishes, can easily be identified using the density field and classified by the behavior of the Hessian of the gravitational potential. We use high-resolution N-body simulations to show that these regions are stable in time and hence are excellent tracers of the initial conditions. Furthermore, we show that the variance of the Hubble flow can be substantially minimized by restricting observations to the subsample of such regions of vanishing velocity instead of aiming at increasing the statistics by averaging indiscriminately using the full data sets, as is the common approach.Comment: 17 pages, 6 figures and 2 tables, minor modifications after receiving several useful comment

Symmetry and anti-symmetry of the CMB anisotropy pattern

Given an arbitrary function, we may construct symmetric and antisymmetric functions under a certain operation. Since statistical isotropy and homogeneity of our Universe has been a fundamental assumption of modern cosmology, we do not expect any particular symmetry or antisymmetry in our Universe. Besides fundamental properties of our Universe, we may also figure our contamination and improve the quality of the CMB data products, by matching the unusual symmetries and antisymmetries of the CMB data with known contaminantions. Noting this, we have investigated the symmetry and antisymmetry of CMB anisotropy pattern, which provides the deepest survey. If we let the operation to be a coordinate inversion, the symmetric and antisymmetric functions have even and odd-parity respectively. The investigation on the parity of the recent CMB data shows a large-scale odd-parity preference, which is very unlikely in the statistical isotropic and homogeneous Universe. We have investigated the association of the WMAP systematics with the anomaly, but not found a definite non-cosmological cause. Additionally, we have investigated the phase of even and odd multipole data respectively, and found the behavior distinct from each other. Noting the odd-parity preference anomaly, we have fitted a cosmological model respectively to even and odd multipole data, and found significant parametric tension. Besides anomalies explicitly associated with parity, there are anomalous lack of large-scale correlation in CMB data. Noting the equivalence between the power spectrum and the correlation, we have investigated the association between the lack of large-angle correlation and the odd-parity preference of the angular power spectrum. From our analysis, we find that the odd-parity preference at low multipoles is, in fact, phenomenologically identical with the lack of large-angle correlation.Comment: review articl

Noise residuals for GW150914 using maximum likelihood and numerical relativity templates

We reexamine the results presented in a recent work by Nielsen et al. [1], in which the properties of the noise residuals in the 40\,ms chirp domain of GW150914 were investigated. This paper confirmed the presence of strong (i.e., about 0.80) correlations between residual noise in the Hanford and Livingston detectors in the chirp domain as previously seen by us [2] when using a numerical relativity template given in [3]. It was also shown in [1] that a so-called maximum likelihood template can reduce these statistically significant cross-correlations. Here, we demonstrate that the reduction of correlation and statistical significance is due to (i) the use of a peculiar template which is qualitatively different from the properties of GW150914 originally published by LIGO, (ii) a suspicious MCMC chain, (iii) uncertainties in the matching of the maximum likelihood (ML) template to the data in the Fourier domain, and (iv) a biased estimation of the significance that gives counter-intuitive results. We show that rematching the maximum likelihood template to the data in the 0.2\,s domain containing the GW150914 signal restores these correlations at the level of $60\%$ of those found in [1]. With necessary corrections, the probability given in [1] will decrease by more than one order of magnitude. Since the ML template is itself problematic, results associated with this template are illustrative rather than final.Comment: Minor correction