Constraints on the CMB temperature redshift dependence from SZ and distance measurements

The relation between redshift and the CMB temperature, $T_{CMB}(z)=T_0(1+z)$ is a key prediction of standard cosmology, but is violated in many non-standard models. Constraining possible deviations to this law is an effective way to test the $\Lambda$CDM paradigm and search for hints of new physics. We present state-of-the-art constraints, using both direct and indirect measurements. In particular, we point out that in models where photons can be created or destroyed, not only does the temperature-redshift relation change, but so does the distance duality relation, and these departures from the standard behaviour are related, providing us with an opportunity to improve constraints. We show that current datasets limit possible deviations of the form $T_{CMB}(z)=T_0(1+z)^{1-\beta}$ to be $\beta=0.004\pm0.016$ up to a redshift $z\sim 3$. We also discuss how, with the next generation of space and ground-based experiments, these constraints can be improved by more than one order of magnitude.Comment: 27 pages, 11 figure

Expressing the equation of state parameter in terms of the three dimensional cosmic shear

We study the functional dependence of the spin-weighted angular moments of the two-point correlation function of the three dimensional cosmic shear on the expansion history of the universe. We first express the redshift dependent total equation of state parameter in terms of the growing mode of the gauge invariant metric perturbation in the conformal-Newtonian gauge for the case of adiabatic perturbations. We then express the redshift dependent angular moments of the shear two-point correlation function as an integral in terms of the metric perturbation. We present the final explicit expression for the case of a Harrison-Zeldovich spectrum of primordial perturbations. Our analysis is restricted to the linear regime. We use our results to make a preliminary study of the required sensitivity that will allow cosmic shear observations to add significant information about the expansion history of the universe.Comment: Final version to appear in JCAP. Substantial improvements include added preliminary numerial results and a realistic transfer functio

Direct Dark Matter Search using CCDs

There is currently vast evidence for Dark Matter (DM) from astronomical observations. However, in spite of tremendous efforts by large experimental groups, there is no confirmed direct detection of the dark matter in our galaxy. Recent experimental results and theoretical developments suggest the possibility of a DM particle with mass below 10 GeV, such a particle would escape most of the direct searches due to the large thresholds for the detection of nuclear recoils typically used. In this work we study the possibility of a new Dark Matter search with an unprecedented low threshold for the detection of nuclear recoils using high-resistivity CCD detectors (hr-CCD). Due to their extremely low readout noise and the relatively large active mass, these detectors present a unique opportunity in this field.Comment: paper presented at the Taup2009 Conferenc

Supernova / Acceleration Probe: A Satellite Experiment to Study the Nature of the Dark Energy

The Supernova / Acceleration Probe (SNAP) is a proposed space-based experiment designed to study the dark energy and alternative explanations of the acceleration of the Universe's expansion by performing a series of complementary systematics-controlled measurements. We describe a self-consistent reference mission design for building a Type Ia supernova Hubble diagram and for performing a wide-area weak gravitational lensing study. A 2-m wide-field telescope feeds a focal plane consisting of a 0.7 square-degree imager tiled with equal areas of optical CCDs and near infrared sensors, and a high-efficiency low-resolution integral field spectrograph. The SNAP mission will obtain high-signal-to-noise calibrated light-curves and spectra for several thousand supernovae at redshifts between z=0.1 and 1.7. A wide-field survey covering one thousand square degrees resolves ~100 galaxies per square arcminute. If we assume we live in a cosmological-constant-dominated Universe, the matter density, dark energy density, and flatness of space can all be measured with SNAP supernova and weak-lensing measurements to a systematics-limited accuracy of 1%. For a flat universe, the density-to-pressure ratio of dark energy can be similarly measured to 5% for the present value w0 and ~0.1 for the time variation w'. The large survey area, depth, spatial resolution, time-sampling, and nine-band optical to NIR photometry will support additional independent and/or complementary dark-energy measurement approaches as well as a broad range of auxiliary science programs. (Abridged)Comment: 40 pages, 18 figures, submitted to PASP, http://snap.lbl.go

The signature of dark energy perturbations in galaxy cluster surveys

All models of dynamical dark energy possess fluctuations, which affect the number of galaxy clusters in the Universe. We have studied the impact of dark energy clustering on the number of clusters using a generalization of the spherical collapse model and the Press-Schechter formalism. Our statistical analysis is performed in a 7-parameter space using the Fisher matrix method, for several hypothetical Sunyaev-Zel'dovich and weak lensing (shear maps) surveys. In some scenarios, the impact of these fluctuations is large enough that their effect could already be detected by existing instruments such as the South Pole Telescope, when its data is combined with WMAP and SDSS. Future observations could go much further and probe the nature of dark energy by distinguishing between different models on the basis of their perturbations, not only their expansion histories.Comment: 5 pages, 4 figure

A New Approach to Testing Dark Energy Models by Observations

We propose a new approach to the consistency test of dark energy models with observations. To test a category of dark energy models, we suggest introducing a characteristic Q(z) that in general varies with the redshift z but in those models plays the role of a (constant) distinct parameter. Then, by reconstructing dQ(z)/dz from observational data and comparing it with zero we can assess the consistency between data and the models under consideration. For a category of models that passes the test, we can further constrain the distinct parameter of those models by reconstructing Q(z) from data. For demonstration, in this paper we concentrate on quintessence. In particular we examine the exponential potential and the power-law potential via a widely used parametrization of the dark energy equation of state, w(z) = w_0 + w_a z/(1+z), for data analysis. This method of the consistency test is particularly efficient because for all models we invoke the constraint of only a single parameter space that by choice can be easily accessed. The general principle of our approach is not limited to dark energy. It may also be applied to the testing of various cosmological models and even the models in other fields beyond the scope of cosmology.Comment: 19 pages, 5 figure