Aspects of Dark Energy and Cosmic Curvature Patrice M. OKOUMA UCT/AIMS/SAAO
A Fundamental Uncertainty in The BAO Scale from Isocurvature Modes Physics Letters B. 696 (2011), pp. 433437The sensitivity of BAO Dark Energy Constraints to General Isocurvature Perturbations arXiv:1111.2572v1 Work(s) With C. Zunckel, S. MuyaKasanda, K. Moodley (UKZN, SA) ; B.A. BASSETT (AIMS/UCT/SAAO, SA)
Motivation our current understanding of Baryon Acoustic Oscillations (BAO) relies on a set of restrictive assumptions about the initial conditions. Question : Assuming more general initial conditions, by how much could this assumption alter/bias our understanding of DE via the BAO scale ?
Initial Conditions space Adiabatic (curvature) perturbationsIsocurvature (entropy) perturbations space
Bias in DE params. estimates for stage IIIIV like survey parameters 7σ (10σ) incorrect measurement of Wo and as much as 23σ (12σ) for Wa if ignoring isocurvature modes
BAO are a firm prediction of CDM models and one keytopic of the science programme for SKA; Even for isocurvature amplitudes undetectable by PLANCK, the presence of multiple isocurvature modes could lead to biases in the DE parameters that exceed 7 sigma on average, if the analysis is done assuming isocurvature initial conditions; Accounting for all isocurvature modes corrects for this bias but degrades the DE figure of merit by at least 50% in the case of the BOSS experiment;BAO data also provide much stronger constraints on the nature of the primordial perturbations than from the CMB alone.
The curvaturedark energy(geometric) degeneracy through the CMB Work with Y. Fantaye (SISSA, Italy) & B. A. BASSETT (AIMS/UCT/SAAO, SA)
OUTLINECurvature, lnflation? What is the Geometric Degeneracy?Some results Summary
MotivationThe current model of Inflation predicts that spatial sections of spacetime (the Universe) are flat; Current datasets are consistent with this paradigm IF the dark energy is a cosmological constant; We study the impact of allowing for a general evolution of the dark energy on the geometry of the Universe and extract some new constraints on cosmological parameters.
Curvature ? R R X (radius of) Curvature = 1/R > 0(radius of) Curvature = 1/R K = 1 K = 1 Curvature density parameter K = 0
Inflation : a solution to some Big Bang puzzles Larson et al. (2011) AIMS 2012 18
What is the curvaturedark energy(geometric) Degeneracy?
The Basic Geometric Degeneracy : Okouma et al., 2012. In prep K = Ωk and Wde effects can cancel each other 1 Using WMAP7 data only, >same angular power spectrum for K = 1 IF WDE = 1, Then IF different sets of these parameters. Larson et al., 2011K = 0
The curvaturedark energy(geometric) degeneracy through the CMB
Bayes Theorem: MetropolisHastings algorithm for the sampling of the posterior pdf > Random walk in parameter space using a modified CosmoMCData: WMAP7yr , Supernovae, BBN, HST (+ ACT data) B. Bassett stat. lectures 5 chains of 300 000 steps each ran
Large open models with dynamical DE which fit the first CMB peak do exist, but the strong Integrated SachsWolfe (ISW) effect in such models means that low multipoles of the CMB power spectrum is very poorly fit, hence these models are discarded. The vast ~ 30dimensional parameter volume explored is an additional limitation.
A significantly nonphantom (Wde > 1) leads to a strong reduction in the volume of possible curved models; A general dynamical dark energy model adds nothing significant in terms of allowing for curved models; Strong constraints on cosmic curvature remain despite the extra dark energy freedom. However, these constraints now come from a mixture of dynamical constraints (ISW effect) and distance measurements.
Summary A general dynamical dark energy model adds nothing significant in terms of allowing for curved models; Strong constraints on cosmic curvature remain despite the extra dark energy freedom. However, these constraints now come from a mixture of dynamical constraints (Integrated SachsWolfe effect) and distance measurements.