aspects of dark energy and cosmic curvature
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Aspects of Dark Energy and
Cosmic Curvature
Patrice M. OKOUMAUCT/AIMS/SAAO
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A Fundamental Uncertainty inThe BAO Scale from Isocurvature Modes
Physics Letters B. 696 (2011), pp. 433437
The 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)
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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 muchhow much could this assumption alter/bias
our understanding of DE via the BAO scale ?
Motivation
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space
Isocurvature (entropy) perturbations
Adiabatic (curvature) perturbations
Initial Conditions space
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“ Fingerprints ” on
Large Scale Structure
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r0r0
r0
In adiabatic mode :In adiabatic mode :
Eisenstein et al. (2005)
�
r0 = Standard ruler
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Fisher formalism applied to galaxy power spectrumIf likelihood function of band powers of galaxy power spectrum is Gaussian
(Tegmark et al. 1997; Seo & Eisenstein 2003)
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Fisher formalism applied to galaxy power spectrum – cont'd
Minimum error on parameter =
+ Isocurvature parameters
Gaussian Likelihood
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FoM alterations for stage IIIIV like survey parameters
1.5, 1.2
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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
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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.
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r0
r0 = Standard ruler
In adiabatic mode :In adiabatic mode :
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The curvaturedark energy(geometric) degeneracy through
the CMB
Work with Y. Fantaye (SISSA, Italy) & B. A. BASSETT (AIMS/UCT/SAAO, SA)
&
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OUTLINE
Curvature, lnflation?
What is the Geometric Degeneracy?
Some results
Summary
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Motivation
The current model of Inflation predicts that spatial sections of spacetime (the Universe) are flat;
Current datasets are consistent with this paradigm
IFIF 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.
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Curvature ?Curvature ?
XX
RR
(radius of) Curvature = 1/R
RR
(radius of) Curvature = 1/R > 0
K = 0
K = 1
K = 1
Curvature density parameter
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AIMS 2012 18
Inflation : a solution to some Big Bang puzzles
Larson et al. (2011)
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What is the curvaturedark energy
(geometric) Degeneracy?
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AIMS 2012 21
D. Larson et al. (2010)
l1l1
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k and Wde effects can cancel each other Ω>same angular power spectrum for different sets of these parameters.
The Basic Geometric Degeneracy :
K = 0
K = 1
K = 1
Okouma et al., 2012. In prepUsing WMAP7 data only, IFIF WDE = 1, Then
Larson et al., 2011
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The general geometric degeneracy
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The curvaturedark energy(geometric) degeneracy through the
CMB
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Bayes Theorem:
MetropolisHastings algorithmMetropolisHastings algorithm for the sampling of the posterior pdf > Random walk in parameter space using a modified CosmoMCData: WMAP7yrWMAP7yr , Supernovae, BBN, HST (+ ACT data) B
. Bassett stat. lectures
5 chains of 300 000 steps each ran5 chains of 300 000 steps each ran
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Some ResultsOkouma et al., 2012. In prep
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AIMS 2012 27
Oohh Look !
H0 = 71 (km/s)/Mpc,Ok = 0.15
Okouma et al., 2011. In prep
H0 = 56.36 (km/s)/Mpc,Ok = 0.06
using CAMB
Okouma et al., 2012. In prep
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?
Okouma et al., 2012. In prep
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Okouma et al., 2012. In prep
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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.
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√√
X
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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.
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Okouma et al., 2012. In prep
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JQ Xia & M. Viel , 2009
Okouma et al., 2012. In prep
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Okouma et al., 2012. In prep
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Okouma et al., 2012. In prep
Kom
atsu et al., 2008
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Okouma et al., 2012. In prep
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Prospects with Growth Information
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Summary
A general dynamical dark energy model adds nothingsignificant in terms of allowing for curved models;
Strong constraints on cosmic curvature remain despitethe extra dark energy freedom.
However, these constraints now come from a mixture of dynamical constraints (Integrated SachsWolfe effect) and distance measurements.
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Thank you for
your attention
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