Calibrating Dark Energy

Exploring the diversity of dark energy dynamics, we discover a calibration relation, a uniform stretching of the amplitude of the equation of state time variation with scale factor. This defines homogeneous families of dark energy physics. The calibration factor has a close relation to the standard time variation parameter w_a, and we show that the new, calibrated w_a describes observables, i.e. distance and Hubble parameter as a function of redshift, typically to an accuracy level of 10^{-3}. We discuss implications for figures of merit for dark energy science programs.Comment: 9 pages, 10 figure

CMB Lensing Constraints on Neutrinos and Dark Energy

Signatures of lensing of the cosmic microwave background radiation by gravitational potentials along the line of sight carry with them information on the matter distribution, neutrino masses, and dark energy properties. We examine the constraints that Planck, PolarBear, and CMBpol future data, including from the B-mode polarization or the lensing potential, will be able to place on these quantities. We simultaneously fit for neutrino mass and dark energy equation of state including time variation and early dark energy density, and compare the use of polarization power spectra with an optimal quadratic estimator of the lensing. Results are given as a function of systematics level from residual foreground contamination. A realistic CMBpol experiment can effectively constrain the sum of neutrino masses to within 0.05 eV and the fraction of early dark energy to 0.002. We also present a surprisingly simple prescription for calculating dark energy equation of state constraints in combination with supernova distances from JDEM.Comment: 18 pages, 14 figures. Small changes made to match version to be published in Phys. Rev.

To Bin or Not To Bin: Decorrelating the Cosmic Equation of State

The physics behind the acceleration of the cosmic expansion can be elucidated through comparison of the predictions of dark energy equations of state to observational data. In seeking to optimize this, we investigate the advantages and disadvantages of using principal component analysis, uncorrelated bandpowers, and the equation of state within redshift bins. We demonstrate that no one technique is a panacea, with tension between clear physical interpretation from localization and from decorrelated errors, as well as model dependence and form dependence. Specific lessons include the critical role of proper treatment of the high redshift expansion history and the lack of a unique, well defined signal-to-noise or figure of merit.Comment: 26 pages, 28 figure

Weak Lensing Science, Surveys, and Systematics

Weak gravitational lensing is one of the key probes of the cosmological model, dark energy, and dark matter, providing insight into both the cosmic expansion history and large scale structure growth history. Taking into account a broad spectrum of physics affecting growth - dynamical dark energy, extended gravity, neutrino masses, and spatial curvature - we analyze the cosmological constraints. Similarly we consider the effects of a range of systematic uncertainties, in shear measurement, photometric redshifts, and the nonlinear power spectrum, on cosmological parameter extraction. We also investigate, and provide fitting formulas for, the influence of survey parameters such as redshift depth, galaxy number densities, and sky area. Finally, we examine the robustness of results for different fiducial cosmologies.Comment: 11 pages, 9 figure

Future CMB Constraints on Early, Cold, or Stressed Dark Energy

We investigate future constraints on early dark energy (EDE) achievable by the Planck and CMBPol experiments, including cosmic microwave background (CMB) lensing. For the dark energy, we include the possibility of clustering through a sound speed c_s^2 <1 (cold dark energy) and anisotropic stresses parameterized with a viscosity parameter c_vis^2. We discuss the degeneracies between cosmological parameters and EDE parameters. In particular we show that the presence of anisotropic stresses in EDE models can substantially undermine the determination of the EDE sound speed parameter c_s^2. The constraints on EDE primordial energy density are however unaffected. We also calculate the future CMB constraints on neutrino masses and find that they are weakened by a factor of 2 when allowing for the presence of EDE, and highly biased if it is incorrectly ignored.Comment: 12 pages, 19 figure

Inflationary Freedom and Cosmological Neutrino Constraints

The most stringent bounds on the absolute neutrino mass scale come from cosmological data. These bounds are made possible because massive relic neutrinos affect the expansion history of the universe and lead to a suppression of matter clustering on scales smaller than the associated free streaming length. However, the resulting effect on cosmological perturbations is relative to the primordial power spectrum of density perturbations from inflation, so freedom in the primordial power spectrum affects neutrino mass constraints. Using measurements of the cosmic microwave background (CMB), the galaxy power spectrum and the Hubble constant, we constrain neutrino mass and number of species for a model-independent primordial power spectrum. Describing the primordial power spectrum by a 20-node spline, we find that the neutrino mass upper limit is a factor 3 weaker than when a power law form is imposed, if only CMB data are used. The primordial power spectrum itself is constrained to better than 10% in the wave vector range k≈0.01−0.25  Mpc^(−1) . Galaxy clustering data and a determination of the Hubble constant play a key role in reining in the effects of inflationary freedom on neutrino constraints. The inclusion of both eliminates the inflationary freedom degradation of the neutrino mass bound, giving for the sum of neutrino masses Σm_ν<0.18  eV (at 95% confidence level, Planck+BOSS+H_0), approximately independent of the assumed primordial power spectrum model. When allowing for a free effective number of species, N_(eff) , the joint constraints on Σm_ν and N_(eff) are loosened by a factor 1.7 when the power law form of the primordial power spectrum is abandoned in favor of the spline parametrization

Induced Gravity and the Attractor Dynamics of Dark Energy/Dark Matter

Attractor solutions that give dynamical reasons for dark energy to act like the cosmological constant, or behavior close to it, are interesting possibilities to explain cosmic acceleration. Coupling the scalar field to matter or to gravity enlarges the dynamical behavior; we consider both couplings together, which can ameliorate some problems for each individually. Such theories have also been proposed in a Higgs-like fashion to induce gravity and unify dark energy and dark matter origins. We explore restrictions on such theories due to their dynamical behavior compared to observations of the cosmic expansion. Quartic potentials in particular have viable stability properties and asymptotically approach general relativity.Comment: 11 pages, 10 figures, accepted in JCAP, results unchanged, an explanation added on perfect fluids for general spinor Lagrangian

Shifting the Universe: Early Dark Energy and Standard Rulers

The presence of dark energy at high redshift influences both the cosmic sound horizon and the distance to last scattering of the cosmic microwave background. We demonstrate that through the degeneracy in their ratio, early dark energy can lie hidden in the CMB temperature and polarization spectra, leading to an unrecognized shift in the sound horizon. If the sound horizon is then used as a standard ruler, as in baryon acoustic oscillations, then the derived cosmological parameters can be nontrivially biased. Fitting for the absolute ruler scale (just as supernovae must be fit for the absolute candle magnitude) removes the bias but decreases the leverage of the BAO technique by a factor 2.Comment: 6 pages, 3 figure