We present a global measurement of the integrated Sachs-Wolfe (ISW) effect obtained by cross correlating all relevant large-scale galaxy data sets with the cosmic microwave background radiation map provided by the Wilkinson Microwave Anisotropy Probe. With these measurements, the overall ISW signal is detected at the $4:5 level. We also examine the cosmological implications of these measurements, particularly the dark energy equation of state w, its sound speed c s , and the overall curvature of the Universe. The flat ÃCDM model is a good fit to the data and, assuming this model, we find that the ISW data constrain m ¼ 0:20 þ0:19 À0:11 at the 95% confidence level. When we combine our ISW results with the latest baryon oscillation and supernovae measurements, we find that the result is still consistent with a flat ÃCDM model with w ¼ À1 out to redshifts z > 1.

The fluctuations in the cosmic microwave background (CMB) have proved an invaluable tool for uncovering the nature of our universe. The recent dramatic data provided by the WMAP satellite [1] have confirmed previous indications that the expansion of the universe may be accelerating [2], driven by a cosmological constant or similar dark energy component. One consequence of dark energy is the suppression of the rate of gravitational collapse of matter at relatively recent times. This causes fluctuations in the CMB to be created as the photons pass through nearby large scale structures, a phenomenon known as the integrated Sachs-Wolfe (ISW) effect. The result is additional large scale fluctuations in the CMB which are correlated with the relatively nearby (i.e., at redshift z ∼ 1) matter distribution [3]. Here we report evidence of correlations between the WMAP data and two all sky probes of large scale structure, the hard X-ray background observed by the HEAO-1 satellite [4] and the NVSS survey of radio galaxies [5]. Both observed correlations are consistent with an ISW origin, indicating that we are seeing the impact of dark energy on the growth of structure.In the standard model of the origin of structure, most of the fluctuations were imprinted on the CMB at the epoch of last scattering, when the universe was 400,000 years old (z ≃ 1100.) The ISW effect induces extra fluctuations only when matter domination ends and the dark energy becomes important dynamically (z ∼ 1.) When this happens, the gravitational potentials of large, diffuse concentrations and rarefactions of matter begin to decay and the energy of photons passing through them changes by an amount that depends on the depth of the potentials. The amplitude of these ISW fluctuations tends to be small compared to the fluctuations originating at the epoch of last scattering except on very large scales. However, since ISW fluctuations were created more recently, it is expected that the CMB fluctuations should be partially correlated with tracers of the large scale matter distribution, e.g., with the distribution of distant galaxies.Detecting the relatively weak correlation of the CMB with the distribution of galaxies requires nearly full sky surveys out to redshifts z ∼ 1. Focus has thus has been on luminous active galaxies, which are believed to trace the mass distribution on large scales. While active galaxies emit at a wide range of frequencies, the most useful maps are in the hard X-rays (2-10 KeV), where they dominate the X-ray sky, and 1

Freeman Dyson has questioned whether any conceivable experiment in the real universe can detect a single graviton. If not, is it meaningful to talk about gravitons as physical entities? We attempt to answer Dyson's question and find it is possible concoct an idealized thought experiment capable of detecting one graviton; however, when anything remotely resembling realistic physics is taken into account, detection becomes impossible, indicating that Dyson's conjecture is very likely true. We also point out several mistakes in the literature dealing with graviton detection and production.

We present a new limit on the cosmological constant based on the absence of correlations between the cosmic microwave background (CMB) and the distribution of distant radio sources. In the cosmological constant-cold dark matter (ΛCDM) models currently favored, such correlations should have been produced via the integrated Sachs-Wolfe effect, assuming that radio sources trace the local (z ∼ 1) matter density. We find no evidence of correlations between the COBE 53Hz microwave map and the NVSS 1.4 GHz radio survey, and obtain an upper limit for the normalized crosscorrelation of δNδT / δN 2 δT 2 ≤ 0.067 at the 95% CL. This corresponds to an upper limit on the cosmological constant of ΩΛ ≤ 0.74, which is in marginal agreement with the values suggested by recent measurements of the CMB anisotropy and type-IA supernovae observations, ΩΛ 0.6 − 0.7. If the cosmological model does lie in this range, then the integrated Sachs-Wolfe effect should be detectable with upcoming CMB maps and radio surveys.PACS numbers: 98.80. Es, 95.85.Nv, 98.70.Vc, Recent observations of supernovae light curves [1] suggest that the expansion of the universe is accelerating rather than decelerating. Combined with evidence from the cosmic microwave background (CMB) [2][3][4] and a number of other observations [5], this suggests the universe is spatially flat and dominated by a cosmological constant, Ω Λ ≡ Λ/3H 2 0 0.6 − 0.7, where H 0 is the Hubble expansion parameter. Such a low value of Λ is difficult to explain from fundamental grounds, so it is vital that we try to confirm this result by other means.CMB anisotropies can arise via the integrated SachsWolfe effect (ISW) [6] as the photons travel through the time-dependent gravitational potentials of collapsing structures. One consequence of a large cosmological constant is that such time-dependent potentials exist even on very large scales where the collapse is linear, which is not the case for a flat, matter dominated universe. These fluctuations are likely to be small compared to those imprinted at the surface of last scattering (redshifts z ∼ 1000) and are difficult to detect directly, however, they can be observed by looking for spatial correlations between the CMB and the nearby matter density [7,8]. This requires a probe of the matter density out to redshifts of z ∼ 2 and suggested candidates include radio galaxies, quasars and the x-ray background.Other processes can also lead to correlations between the CMB and the local matter density. These include gravitational lensing, scattering from hot electrons (the Sunyaev-Zeldovich effect) and photons passing through the time-dependent potentials of non-linear collapsing structures (the Rees-Sciama effect). While the study of these effects can also benefit from cross correlation analyses [9], the ISW effect is unique in that it occurs on very large scales (θ > 1• ) where the fluctuations are simple and linear.In the first attempt to detect this effect, Boughn, Crittenden, and Turok [10] cross-correlated the CMB with the hard (>2 keV) x-ray b...

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