arXiv subjects

Ka Lok Ng

Publications and source records attributed to Ka Lok Ng.

4 recordsLinked to original sources

arXiv1996

Stokes Parameters in Cosmic Microwave Background Measurements

We compute numerically the scalar- and tensor-mode induced Stokes parameters of the cosmic microwave background, by taking into account the basis rotation effects. It is found that the tensor contribution to the polarization power spectrum get enhanced and dominates over the scalar contribution for low multipoles in a universe with or without recombination. Furthermore, we show that all full-sky averaged two-point cross-correlation functions of the Stokes parameters vanish. We thus comment on the cross-correlation between the anisotropy and polarization of the CMB, and calculate the expected signal to noise ratio for the polarization experiment underway.

astro-ph↗

arXiv1995

Large-angle Polarization of the Cosmic Microwave Background Radiation and Reionization

We discuss the effect of matter reionization on the large-angular-scale anisotropy and polarization of the cosmic microwave background radiation (CMBR) in the standard CDM model. We separate three cases in which the anisotropy is induced by pure scalar, pure tensor, and mixed metric perturbations respectively. It is found that, if reionization occurs early enough, the polarization can reach a detectable level of sequentially $6\%$, $9\%$, and $6.5\%$ of the anisotropy. In general, a higher degree of polarization implies a dominant contribution from the tensor mode or reionization at high redshift. Since early reionization will suppress small-scale CMBR anisotropies and polarizations significantly, measuring the polarization on few degree scales can be a direct probe of the reionization history of the early universe.

astro-ph↗

arXiv1994

Gravitational Wave Induced Large-scale Polarization of \\Cosmic Microwave Background Radiation

We discuss the contribution of gravitational wave to the cosmic microwave background radiation (CMBR) anisotropy and polarization. It is found that the large-scale polarization of CMBR is less than 1\% for a standard recombination universe. The effect of matter reionization will enhance the CMBR polarization to a 10\% level. We have computed the CMBR polarization for two extreme cases (not absolutely ruled out) and found that further enhancement of the ratio is possible. We conclude that measuring the polarization of CMBR on large-angular scales can probe the ionization history of the early universe, set constraints on baryon density and the spectral index of the gravitational waves.

astro-ph↗

arXiv1994

Large-scale Polarization of the Cosmic Microwave Background Radiation

The anisotropy and polarization of the cosmic microwave background radiation (CMBR) induced by the scalar and tensor metric perturbations are computed in the long-wavelength limit. It is found that the large-scale polarization of CMBR induced by the decaying tensor mode can reach a few percents. This is different from the scalar or inflation-induced tensor mode, whereas the polarization is at least two orders of magnitude lower. The effect of matter re-ionization on CMBR is also considered. We conclude that measuring the polarization of CMBR on large-angular scales can probe the ionization history of the early Universe, and test different cosmological models.

astro-ph↗