Kin-Wang Ng

Effect on cosmic microwave background polarization of coupling of quintessence to pseudoscalar formed from the electromagnetic field and its dual

We present the full set of power spectra of cosmic microwave background (CMB) temperature and polarization anisotropies due to the coupling between quintessence and pseudoscalar of electromagnetism. This coupling induces a rotation of the polarization plane of the CMB, thus resulting in a nonvanishing B mode and parity-violating TB and EB modes. Using the BOOMERANG data from the flight of 2003, we derive the most stringent constraint on the coupling strength. We find that in some cases the rotation-induced B mode can confuse the hunting for the gravitational lensing-induced B mode.

Weak-field expansion for processes in a homogeneous background magnetic field

The weak-field expansion of the charged fermion propagator under a uniform magnetic field is studied. Starting from Schwingers proper-time representation, we express the charged fermion propagator as an infinite series corresponding to different Landau levels. This infinite series is then reorganized according to the powers of the external field strength B. For illustration, we apply this expansion to

The Sky Polarization Observatory

\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}}\ensuremath{\nu}\overline{\ensuremath{\nu}}

Quantum noise and large-scale cosmic microwave background anisotropy

and

Correlation functions of CMB anisotropy and polarization

\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\nu}}\ensuremath{\nu}\ensuremath{\gamma}

Spherical collapse model with non-clustering dark energy

decays, which involve charged fermions in the internal loop. The leading and subleading magnetic-field effects to the above processes are computed.

Growth index with the exact analytic solution of sub-horizon scale linear perturbation for dark energy models with constant equation of state

Abstract The Sky Polarization Observatory (SPOrt) is an ASI-funded experiment specifically designed to measure the sky polarization at 22, 32 and 90 GHz, which was selected in 1997 by ESA to be flown on the International Space Station. Starting in 2006 and for at least 18 months, it will be taking direct and simultaneous measurements of the Stokes parameters Q and U at 660 sky pixels, with FWHM=7°. Due to development efforts over the past few years, the design specifications have been significantly improved with respect to the first proposal. Here we present an up-to-date description of the instrument, which now warrants a pixel sensitivity of 1.7 μK for the polarization of the cosmic background radiation, assuming two years of observations. We discuss SPOrt scientific goals in the light of WMAP results, in particular in connection with the emerging double-reionization cosmological scenario.

Decaying superheavy dark matter and subgalactic structure of the Universe

We propose a new source for the cosmological density perturbation which is passive fluctuations of the inflaton driven dynamically by a coloured quantum noise as a result of its coupling to other massive quantum fields. The created fluctuations grow with time during inflation before horizon-crossing. However, the larger-scale modes cross the horizon earlier, thus resulting in a suppression of their density perturbation as compared with those on small scales. By using current observed CMB data to constrain the parameters introduced, we find that a significant contribution from the noise-driven perturbation to the density perturbation is still allowed. It in turn gives rise to a suppression of the large-scale CMB anisotropy that may be relevant to the observed low quadrupole in the WMAP CMB anisotropy data. We also briefly discuss the implications to the energy scale of inflation and the spectral index and the non-Gaussianity of the density perturbation.

Effects of a preinflation radiation-dominated epoch to CMB anisotropy

We give a full analysis of the auto- and cross-correlations between the Stokes parameters of the cosmic microwave background. In particular, we derive the windowing function for an antenna with Gaussian response in polarization experiment, and construct correlation function estimators corrected for instrumental noise. They are applied to calculate the signal to noise ratios for future anisotropy and polarization measurements. While the small-angular-scale anisotropy-polarization correlation would be likely detected by the MAP satellite, the detection of electric and magnetic polarization would require higher experimental sensitivity. For large-angular-scale measurements such as the being planned SPOrt/ISS, the expected signal to noise ratio for polarization is greater than one only for reionized models with high reionization redshifts, and the ratio is less for anisotropy-polarization correlation. Correlation and covariance matrices for likelihood analyses of ground-based and satellite data are also given.

Complex visibilities of cosmic microwave background anisotropies

We investigate a spherical overdensity model for the non-clustering dark energy (DE) with the constant equation of state, ωde in a flat universe. In this case, the exact solution for the evolution of the scale factor is obtained for general ωde. We also obtain the exact (when ωde = −1/3) and the approximate (when ωde≠−1/3) solutions for the ratio of the overdensity radius to its value at the turnaround epoch (y≡R/Rta) for general cosmological parameters. Also the exact and approximate solutions of the overdensity at the turnaround epoch ζ = (ρcluster/ρm)|z = zta are obtained for general ωde. Thus, we are able to obtain the non-linear overdensity Δ≡1+δNL = ζ(x/y)3 at any epoch for the given DE model. The non-linear overdensity at the virial epoch Δvir = ζ(xvir/yvir)3 is obtained by using the virial theorem and the energy conservation. The non-linear overdensity of every DE model converges to that of the Einstein de Sitter universe ΔvirEdS = 18π2((1/2π)+(3/4))2 147 when zvir increases. We find that the observed quantities at high redshifts are insensitive to the different ωde models. The low-redshift cluster (zvir ~ 0.04, i.e., zta ~ 0.7) shows the most model dependent feature and it should be a suitable object for testing DE models. Also as ΩM0 increases, the model dependence of the observed quantities decreases. The error in the approximate solutions is at most 2% for a wide range of the parameter space. Even though the analytic forms of y and ζ are obtained for the constant ωde, they can be generalized to the slowly varying ωde. Thus, these analytic forms of the scale factor, y, and ζ provide a very accurate and useful tool for measuring the properties of DE.