3. A Fundamental Uncertainty in
The 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)
4. 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 ?
5. Initial Conditions space
Adiabatic (curvature) perturbations
Isocurvature (entropy) perturbations
space
12.
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.
22. 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., 2011
K = 0
25. Bayes Theorem:
MetropolisHastings algorithm for the sampling of the posterior pdf
> Random walk in parameter space using a modified CosmoMC
Data: WMAP7yr , Supernovae, BBN, HST (+ ACT data)
B. Bassett stat. lectures
5 chains of 300 000 steps each ran
27. Oohh Look !
Okouma et al., 2012. In prep
Okouma et al., 2011. In prep
using CAMB
H0 = 71 (km/s)/Mpc,
Ok = 0.15
H0 = 56.36 (km/s)/Mpc,
Ok = 0.06 AIMS 2012 27
30. 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.
32.
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.
41. 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.
