A Detection of the Integrated Sachs-Wolfe Effect

We have detected statistically significant correlations between the cosmic microwave background and two tracers of large-scale structure, the HEAO1 A2 full sky hard X-ray map and the NVSS 1.4 GHz, nearly full sky radio galaxy survey. The level of correlations in these maps is consistent with that predicted for the integrated Sachs-Wolfe (ISW) effect in the context of a Lambda CDM cosmological model and, therefore, provides independent evidence for a cosmological constant. A maximum likelihood fit to the amplitude of the ISW effect relative to the predicted value is 1.13 +- 0.35 (statistical error only).Comment: 4 pages, 4 figures, presented at 6th UCLA Dark Matter/Dark Energy Symposiu

Crossing Statistic: Bayesian interpretation, model selection and resolving dark energy parametrization problem

By introducing Crossing functions and hyper-parameters I show that the Bayesian interpretation of the Crossing Statistics [1] can be used trivially for the purpose of model selection among cosmological models. In this approach to falsify a cosmological model there is no need to compare it with other models or assume any particular form of parametrization for the cosmological quantities like luminosity distance, Hubble parameter or equation of state of dark energy. Instead, hyper-parameters of Crossing functions perform as discriminators between correct and wrong models. Using this approach one can falsify any assumed cosmological model without putting priors on the underlying actual model of the universe and its parameters, hence the issue of dark energy parametrization is resolved. It will be also shown that the sensitivity of the method to the intrinsic dispersion of the data is small that is another important characteristic of the method in testing cosmological models dealing with data with high uncertainties.Comment: 14 pages, 4 figures, discussions extended, 1 figure and two references added, main results unchanged, matches the final version to be published in JCA

Harmonic E/B decomposition for CMB polarization maps

The full sky cosmic microwave background polarization field can be decomposed into 'electric' (E) and 'magnetic' (B) components that are signatures of distinct physical processes. We give a general construction that achieves separation of E and B modes on arbitrary sections of the sky at the expense of increasing the noise. When E modes are present on all scales the separation of all of the B signal is no longer possible: there are inevitably ambiguous modes that cannot be separated. We discuss the practicality of performing E/B decomposition on large scales with realistic non-symmetric sky-cuts, and show that separation on large scales is possible by retaining only the well supported modes. The large scale modes potentially contain a great deal of useful information, and E/B separation at the level of the map is essential for clean detection of B without confusion from cosmic variance due to the E signal. We give simple matrix manipulations for creating pure E and B maps of the large scale signal for general sky cuts. We demonstrate that the method works well in a realistic case and give estimates of the performance with data from the Planck satellite. In the appendix we discuss the simple analytic case of an azimuthally symmetric cut, and show that exact E/B separation is possible on an azimuthally symmetric cut with a finite number of non-intersecting circular cuts around foreground sources.Comment: Fixed numerical bug in tensor C_l: Planck detection probability results updated (supersedes PRD version). Sample code and additional examples available at http://cosmologist.info/polar

Correlations in Cosmic String Networks

We investigate scaling and correlations of the energy and momentum in an evolving network of cosmic strings in Minkowski space. These quantities are of great interest, as they must be understood before accurate predictions for the power spectra of the perturbations in the matter and radiation in the early Universe can be made. We argue that Minkowski space provides a reasonable approximation to a Friedmann background for string dynamics and we use our results to construct a simple model of the network, in which it is considered to consist of randomly placed segments moving with random velocities. This model works well in accounting for features of the two-time correlation functions, and even better for the power spectra.Comment: 20pp Plain LaTeX, 11 EPS figures, uses epsf.st

Testing the tidal alignment model of galaxy intrinsic alignment

Weak gravitational lensing has become a powerful probe of large-scale structure and cosmological parameters. Precision weak lensing measurements require an understanding of the intrinsic alignment of galaxy ellipticities, which can in turn inform models of galaxy formation. It is hypothesized that elliptical galaxies align with the background tidal field and that this alignment mechanism dominates the correlation between ellipticities on cosmological scales (in the absence of lensing). We use recent large-scale structure measurements from the Sloan Digital Sky Survey to test this picture with several statistics: (1) the correlation between ellipticity and galaxy overdensity, w_{g+}; (2) the intrinsic alignment auto-correlation functions; (3) the correlation functions of curl-free, E, and divergence-free, B, modes (the latter of which is zero in the linear tidal alignment theory); (4) the alignment correlation function, w_g(r_p,theta), a recently developed statistic that generalizes the galaxy correlation function to account for the angle between the galaxy separation vector and the principle axis of ellipticity. We show that recent measurements are largely consistent with the tidal alignment model and discuss dependence on galaxy luminosity. In addition, we show that at linear order the tidal alignment model predicts that the angular dependence of w_g(r_p,theta) is simply w_{g+}*cos(2*theta) and that this dependence is consistent with recent measurements. We also study how stochastic nonlinear contributions to galaxy ellipticity impact these statistics. We find that a significant fraction of the observed LRG ellipticity can be explained by alignment with the tidal field on scales >~10 h^-1 Mpc. These considerations are relevant to galaxy formation and evolution.Comment: 23 pages, 5 figures, minor changes to reflect published version, including updated figures and a minor correction to the measured error

Correlations Between the Cosmic X-ray and Microwave Backgrounds: Constraints on a Cosmological Constant

In universes with significant curvature or cosmological constant, cosmic microwave background (CMB) anisotropies are created very recently via the Rees-Sciama or integrated Sachs-Wolfe effects. This causes the CMB anisotropies to become partially correlated with the local matter density (z < 4). We examine the prospects of using the hard (2-10 keV) X-ray background as a probe of the local density and the measured correlation between the HEAO1 A2 X-ray survey and the 4-year COBE-DMR map to obtain a constraint on the cosmological constant. The 95% confidence level upper limit on the cosmological constant is \Omega_\Lambda \leq 0.5, assuming that the observed fluctuations in the X-ray map result entirely from large scale structure. (This would also imply that the X-rays trace matter with a bias factor of b_x = 5.6 \Omega_m^{0.53}.) This bound is weakened considerably if a large portion of the X-ray fluctuations arise from Poisson noise from unresolved sources. For example, if one assumes that the X-ray bias is b_x = 2., then the 95% confidence level upper limit is weaker, \Omega_\Lambda \leq 0.7. More stringent limits should be attainable with data from the next generation of CMB and X-ray background maps.Comment: 27 pages; Latex; 5 postscript figures; submitted to New Astronomy, uses elsart.sty and harvard.sty package

Cross-Correlation of the Cosmic Microwave Background with the 2MASS Galaxy Survey: Signatures of Dark Energy, Hot Gas, and Point Sources

We cross-correlate the Cosmic Microwave Background (CMB) temperature anisotropies observed by the Wilkinson Microwave Anisotropy Probe (WMAP) with the projected distribution of extended sources in the Two Micron All Sky Survey (2MASS). By modelling the theoretical expectation for this signal, we extract the signatures of dark energy (Integrated Sachs-Wolfe effect;ISW), hot gas (thermal Sunyaev-Zeldovich effect;thermal SZ), and microwave point sources in the cross-correlation. Our strongest signal is the thermal SZ, at the 3.1-3.7 \sigma level, which is consistent with the theoretical prediction based on observations of X-ray clusters. We also see the ISW signal at the 2.5 \sigma level, which is consistent with the expected value for the concordance LCDM cosmology, and is an independent signature of the presence of dark energy in the universe. Finally, we see the signature of microwave point sources at the 2.7 \sigma level.Comment: 35 pages (preprint format), 8 figures. In addition to minor revisions based on referee's comments, after correcting for a bug in the code, the SZ detection is consistent with the X-ray observations. Accepeted for publication in Physical Review

Cosmological Effects of Radion Oscillations

We show that the redshift of pressureless matter density due to the expansion of the universe generically induces small oscillations in the stabilized radius of extra dimensions (the radion field). The frequency of these oscillations is proportional to the mass of the radion and can have interesting cosmological consequences. For very low radion masses $m_b$ ($m_b\sim10-100 H_0\simeq10^{-32} eV$) these low frequency oscillations lead to oscillations in the expansion rate of the universe. The occurrence of acceleration periods could naturally lead to a resolution of the coincidence problem, without need of dark energy. Even though this scenario for low radion mass is consistent with several observational tests it has difficulty to meet fifth force constraints. If viewed as an effective Brans-Dicke theory it predicts $\omega=-1+\frac{1}{D}$ ($D$ is the number of extra dimensions), while experiments on scales larger than $1mm$ imply $\omega>2500$. By deriving the generalized Newtonian potential corresponding to a massive toroidally compact radion we demonstrate that Newtonian gravity is modified only on scales smaller than $m_b^{-1}$. Thus, these constraints do not apply for $m_b>10^{-3} eV$ (high frequency oscillations) corresponding to scales less than the current experiments ($0.3mm$). Even though these high frequency oscillations can not resolve the coincidence problem they provide a natural mechanism for dark matter generation. This type of dark matter has many similarities with the axion.Comment: Accepted in Phys. Rev. D. Clarifying comments added in the text and some additional references include

Local Constraints on the Oscillating G Model

We analyze the observational constraints on the effective Brans-Dicke parameter and on the temporal variation of the effective gravitational constant within the context of the oscillating G model, a cosmological model based on a massive scalar field non-minimally coupled to gravity. We show that these local constraints cannot be satisfied simultaneously once the values of the free parameters entering the model become fixed by the global attributes of our Universe. In particular, we show that the lower observational bound for the effective Brans-Dicke parameter and the upper bound of the variation of the effective gravitational constant lead to a specific value of the oscillation amplitude which lies well below the value required to explain the periodicity of 128 Mpc h^{-1} in the galaxy distribution observed in the pencil beam surveys.Comment: PRD, subm., 12 pages, 1 figur

Planck-scale quintessence and the physics of structure formation

In a recent paper we considered the possibility of a scalar field providing an explanation for the cosmic acceleration. Our model had the interesting properties of attractor-like behavior and having its parameters of O(1) in Planck units. Here we discuss the effect of the field on large scale structure and CMB anisotropies. We show how some versions of our model inspired by "brane" physics have novel features due to the fact that the scalar field has a significant role over a wider range of redshifts than for typical "dark energy" models. One of these features is the additional suppression of the formation of large scale structure, as compared with cosmological constant models. In light of the new pressures being placed on cosmological parameters (in particular H_0) by CMB data, this added suppression allows our "brane" models to give excellent fits to both CMB and large scale structure data.Comment: 18 pages, 12 figures, submitted to PR