Guo-Chin Liu

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.

Correlation functions of CMB anisotropy and polarization

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.

The AMiBA Hexapod Telescope Mount

The Array for Microwave Background Anisotropy (AMiBA) is the largest hexapod astronomical telescope in current operation. We present a description of this novel hexapod mount with its main mechanical components—the support cone, universal joints, jack screws, and platform—and outline the control system with the pointing model and the operating modes that are supported. The AMiBA hexapod mount performance is verified based on optical pointing tests and platform photogrammetry measurements. The photogrammetry results show that the deformations in the inner part of the platform are less than 120 μm rms. This is negligible for optical pointing corrections, radio alignment, and radio phase errors for the currently operational seven-element compact configuration. The optical pointing error in azimuth and elevation is successively reduced by a series of corrections to about 0 4 rms which meets our goal for the seven-element target specifications.

OBSERVATIONAL STRATEGIES OF COSMIC MICROWAVE BACKGROUND TEMPERATURE AND POLARIZATION INTERFEROMETRY EXPERIMENTS

We have simulated the interferometric observation of the cosmic microwave background (CMB) temperature and polarization fluctuations. We have constructed data pipelines from the time-ordered raw visibility samples to the CMB power spectra that utilize the methods of data compression, maximum likelihood analysis, and optimal subspace filtering. They are customized for three observational strategies: the single pointing, the mosaicking, and the drift-scanning. For each strategy, derived are the optimal strategy parameters that yield band power estimates with minimum uncertainty. The results are general and can be applied to any close-packed array on a single platform such as the CBI and the forthcoming AMiBA experiments. We have also studied the effect of rotation of the array platform on the band power correlation by simulating the CBI single-pointing observation. It is found that the band power anticorrelations can be reduced by rotating the platform and thus densely sampling the visibility plane. This enables us to increase the resolution of the power spectrum in the l-space down to the limit of the sampling theorem (Δl = 226 ≈ π/θ), which is narrower by a factor of about than the resolution limit (Δl ≈ 300) used in the recent CBI single-pointing observation. The validity of this idea is demonstrated for a two-element interferometer that samples visibilities uniformly in the uv-annulus. From the fact that the visibilities are the Fourier modes of the CMB field convolved with the beam, a fast unbiased estimator (FUE) of the CMB power spectra is developed and tested. It is shown that the FUE gives results very close to those from the quadratic estimator method without requiring large computer resources even though uncertainties in the results increase.

AMiBA WIDEBAND ANALOG CORRELATOR

A wideband analog correlator has been constructed for the Yuan-Tseh Lee Array for Microwave Background Anisotropy. Lag correlators using analog multipliers provide large bandwidth and moderate frequency resolution. Broadband intermediate frequency distribution, back-end signal processing, and control are described. Operating conditions for optimum sensitivity and linearity are discussed. From observations, a large effective bandwidth of around 10 GHz has been shown to provide sufficient sensitivity for detecting cosmic microwave background variations.

Primordial Quadrupole-induced Polarization from Filamentary Structures and Galaxy Clusters

We present the first computation of the cosmic microwave background (CMB) polarization power spectrum from galaxy clusters and filaments using hydrodynamic simulations of large-scale structure. We give the E- and B-mode power spectra of the CMB quadrupole-induced polarization between l ~ 560 and 20,000. We find that the contribution from warm ionized gas in filamentary structures dominates the polarized signal from galaxy clusters by more than 1 order of magnitude on large scales (below l ~ 1000) and by a factor of about 2 on small scales (l 10,000). We study the dependence of the power spectra with σ8. Assuming the power spectra vary as σ, we find n = 3.2-4.0 for filaments and n = 3.5-4.6 for clusters.

Progress of the array of microwave background anisotropy (AMiBA)

The Academia Sinica, Institute for Astronomy and Astrophysics (ASIAA) is installing the AMiBA interferometric array telescope at the Mauna Loa Observatory, Hawaii. The 6-meter carbon fiber fully steerable platform is mounted on the Hexapod Mount. After integration and equipment with dummy weights, the platform has been measured by photogrammetry to verify its behavior predicted by Finite Element Analysis. The Hexapod servo control is now operational and equipment of the platform with the initial 7 60-cm dishes, the correlator and electronics is underway. Pointing has started with the aid of the optical telescope. We present the status of the telescope after the servo and initial pointing tests have been carried out. We also present the results of platform measurements by photogrammetry.

THE AMIBA PROJECT

The Array for Microwave Background Anisotropy is a 7-element interferometer to be sited on Mauna Loa, Hawaii. The seven 1.2m telescopes are mounted on a 6-meter platform, and operates at 3mm wavelength. At the time of this meeting, the telescope is under construction at the Vertex factory in Germany. It is due to be delivered in the middle of 2004. A 2-element prototype instrument has already been deployed to Mauna Loa where initial tests are underway.

Effects on the two-point correlation function from the coupling of quintessence to dark matter

We investigate the effects of the nonminimal coupling between the scalar field dark energy (quintessence) and the dark matter on the two-point correlation function. It is well known that this coupling shifts the turnover scale as well as suppresses the amplitude of the matter power spectrum. However, these effects are too small to be observed when we limit the coupling strength to be consistent with observations. Since the coupling of quintessence to baryons is strongly constrained, species-dependent coupling may arise. This results in a baryon bias that is different from unity. Thus, we investigate the correlation function in this coupled model. We are able to observe the enhancement of the baryon acoustic oscillation (BAO) peak due to the increasing bias factor of baryon from this species-dependent coupling. In order to avoid the damping effect of the BAO signature in the matter power spectrum due to nonlinear clustering, we consider the coupling effect on the BAO bump in the linear regime. This provides an alternative method to constrain the coupling of dark energy to dark matter.

Cosmic birefringence fluctuations and cosmic microwave background B -mode polarization

Abstract Recently, BICEP2 measurements of the cosmic microwave background (CMB) B-mode polarization has indicated the presence of primordial gravitational waves at degree angular scales, inferring the tensor-to-scalar ratio of r = 0.2 and a running scalar spectral index, provided that dust contamination is low. In this Letter, we show that the existence of the fluctuations of cosmological birefringence can give rise to CMB B-mode polarization that fits BICEP2 data with r 0.11 and no running of the scalar spectral index. When dust contribution is taken into account, we derive an upper limit on the cosmological birefringence, A β 2 0.0075 , where A is the amplitude of birefringence fluctuations that couple to electromagnetism with a coupling strength β.