arXiv subjects

Jiun-Huei Proty Wu

Publications and source records attributed to Jiun-Huei Proty Wu.

27 records · Page 2Linked to original sources

arXiv2008

Tests of AMiBA Data Integrity

We describe methods used to validate data from the Y.T. Lee Array for Microwave Background Anisotropy (AMiBA), an interferometric array designed to measure the Sunyaev-Zel'dovich effect and the anisotropy of the Cosmic Microwave Background (CMB). We perform several statistical tests on data from pointed galaxy cluster observations taken in 2007 and noise data from long-term blank sky observations and measurements with the feeds covered by the absorbers. We apply power spectrum analysis, cross power spectrum analysis among different outputs with different time lags in our analog correlator, and sample variance law tests to noise data. We find that (1) there is no time variation of electronic offsets on the time scale of our two-patch observations (~10 minutes); (2) noise is correlated by less than 10% between different lags; and (3) the variance of noise scales with the inverse of time. To test the Gaussianity of the data, we apply Kolmogorov-Smirnov (K-S) tests to cluster data, and find that a 5% significance level efficiently detects data sets with known hardware problems without rejecting an excess of acceptable data. We also calculate third- and fourth-order moments and cumulants for the noise residual visibilities and find that about 95% of our data are within the 99% confidence regions of Gaussianity.

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arXiv2005

Coherence Constraint on the Existence of Cosmic Defects

We devise a measure n(r) to quantify a robust feature in the coherent cosmic perturbations, namely the narrowness of the first peak in the power spectrum of the Cosmic Microwave Background (CMB) anisotropy. A maximum-likelihood analysis using the WMAP data shows that the power fraction of any defect models at the first peak is persistently less than 4.5% at the 68% confidence. Our approach and results are insensitive to the uncertainties in the theoretical predictions for defect models, and thus the most robust to date. We show that to convert these results into realistic constraints on theories such as inflation, string cosmology, and SUSY GUTs, a more robust study for the cosmic-string-induced CMB around the degree scale is required.

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arXiv2003

Recent Results from the MAXIMA Experiment

MAXIMA is a balloon-borne platform for measuring the anisotropy of the Cosmic Microwave Background (CMB). It has measured the CMB power spectrum with a ten-arcminute FWHM beam, corresponding to a detection of the power spectrum out to spherical harmonic multipole l~1000. The spectrum is consistent with a flat Universe with a nearly scale-invariant initial spectrum of adiabatic density fluctuations. Moreover, the MAXIMA data are free from any notable non-Gaussian contamination and from foreground dust emission. In the same region, the WMAP experiment observes the same structure as that observed by MAXIMA, as evinced by analysis of both maps and power spectra. The next step in the evolution of the MAXIMA program is MAXIPOL, which will observe the polarization of the CMB with comparable resolution and high sensitivity over a small patch of the sky.

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arXiv2001

New method of extracting non-Gaussian signals

We propose a new general method of extracting non-Gaussian features in a given field. It sets the mean of the field to zero and renormalizes its Fourier (or multipole) power to white noise, while keeping the phase information unchanged. Using simulated cosmic microwave background (CMB) as an example, we demonstrate the power of this method under many challenging circumstances. In particular, we show its capability of detecting cosmic strings in the CMB.

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arXiv2001

New method of extracting non-Gaussian signals in the CMB

Searching for and charactering the non-Gaussianity (NG) of a given field has been a vital task in many fields of science, because we expect the consequences of different physical processes to carry different statistical properties. Here we propose a new general method of extracting non-Gaussian features in a given field, and then use simulated cosmic microwave background (CMB) as an example to demonstrate its power. In particular, we show its capability of detecting cosmic strings.

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arXiv2001

Cosmological matter perturbations with causal seeds

We investigate linear matter density perturbations in models of structure formation with causal seeds. Under the fluid approximation, we obtain the analytic solutions using Green-function technique. Some incorrect solutions in the literature are corrected here. Based on this, we analytically prove that the matter density perturbations today are independent of the way the causal seeds were compensated into the background contents of the universe when they were first formed. We also find that the compensation scale depends not only on the dynamics of the universe, but also on the properties of the seeds near the horizon scale. It can be accurately located by employing our Green-function solutions.

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arXiv2001

Cluster abundance and large-scale structure

We use the presently observed number density of large X-ray clusters and linear mass power spectra to constrain the shape parameter ($Γ$), the spectral index ($n$), the amplitude of matter density perturbations on the scale of $8 h^{-1}$Mpc ($σ_8$), and the redshift distortion parameter ($β$). The non-spherical-collapse model as an improvement to the Press-Schechter formula is used and yields significantly lower $σ_8$ and $β$. An analytical formalism for the formation redshift of halos is also derived.

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arXiv2000

Cosmological matter perturbations

We investigate matter density perturbations in models of structure formation with or without causal/acausal source. Under the fluid approximation in the linear theory, we first derive full perturbation equations in flat space with a cosmological constant $Λ$. We then use Green-function technique to obtain analytic solutions for matter perturbations in a flat $Λ=0$ model. Some incorrect solutions in the literature are corrected here. A simple yet accurate extrapolation scheme is then proposed to obtain solutions in curved or $Λ\neq 0$ cosmologies. Some general features of these solutions are revealed. In particular, we analytically prove that the resulting matter density perturbations are independent of the way the causal source was compensated into the background contents of the universe when it was first formed. We also use our Green-function solutions to investigate the compensation mechanism for perturbations with causal seeds, and yield a mathematically and physically explicit formin interpreting it. We found that the compensation scale depends not only on the dynamics of the universe, but also on the properties of the seeds near the horizon scale. It can be accurately located by employing our Green functions.

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arXiv2000

Cluster abundance and large scale structure

We use the presently observed number density of large X-ray clusters and the linear mass power spectra to constrain $σ_8$ and the redshift distortion parameter $β$, in both OCDM and $Λ$CDM models. The best fit to the observed mass power spectra gives $n=0.84\pm 0.67$ and $Γ=0.27^{+0.42}_{-0.16}$, with the theoretically expected degeneracy $Γ'=0.247Γ\exp(1.4n)=0.220^{+0.036}_{-0.031}$ (all at 95% confidence level). Based on this, we then calculate the cluster-abundance-normalized $σ_8$, using different models of mass function: Press & Schechter (1974), Sheth & Tormen (1999), and Lee & Shandarin (1999). The $σ_8$ based on the non-spherical-collapse models (ST & LS) are significantly lower, mainly due to the larger mass function within the scale range of our interest. In particular, we found $σ_{8{\rm (ST+LS)}}=0.477Ω_{\rm m0}^α$, where $α=-0.3-0.17Ω_{\rm m0}^{0.34}-0.13Ω_{Λ0}$. We also derive the probability distribution function of cluster formation redshift using the Lacey-Cole formalism (1993), but with modifications to incorporate non-spherical collapse. The uncertainties in our $σ_8$ are mainly contributed from the normalization in the virial mass-temperature relation. We also obtain for the IRAS galaxies $σ_{8\rm (I)}=0.78\pm 0.06$ (at 95% confidence level), and found $β_{\rm I(ST+LS)}=0.613Ω_{\rm m0}^{0.24-0.16(Ω_{\rm m0}+Ω_{Λ0})}$. This is more consistent with the recent observations than the result based on the PS formalism.

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