2 research outputs found
Using BBN in cosmological parameter extraction from CMB: a forecast for Planck
Data from future high-precision Cosmic Microwave Background (CMB)
measurements will be sensitive to the primordial Helium abundance . At the
same time, this parameter can be predicted from Big Bang Nucleosynthesis (BBN)
as a function of the baryon and radiation densities, as well as a neutrino
chemical potential. We suggest to use this information to impose a
self-consistent BBN prior on and determine its impact on parameter
inference from simulated Planck data. We find that this approach can
significantly improve bounds on cosmological parameters compared to an analysis
which treats as a free parameter, if the neutrino chemical potential is
taken to vanish. We demonstrate that fixing the Helium fraction to an arbitrary
value can seriously bias parameter estimates. Under the assumption of
degenerate BBN (i.e., letting the neutrino chemical potential vary), the
BBN prior's constraining power is somewhat weakened, but nevertheless allows us
to constrain with an accuracy that rivals bounds inferred from present
data on light element abundances.Comment: 14 pages, 4 figures; v2: minor changes, matches published versio
WMAP 5-year constraints on lepton asymmetry and radiation energy density: Implications for Planck
In this paper we set bounds on the radiation content of the Universe and
neutrino properties by using the WMAP-5 year CMB measurements complemented with
most of the existing CMB and LSS data (WMAP5+All),imposing also self-consistent
BBN constraints on the primordial helium abundance. We consider lepton
asymmetric cosmological models parametrized by the neutrino degeneracy
parameter and the variation of the relativistic degrees of freedom, due to
possible other physical processes occurred between BBN and structure formation
epochs. We find that WMAP5+All data provides strong bounds on helium mass
fraction and neutrino degeneracy parameter that rivals the similar bounds
obtained from the conservative analysis of the present data on helium
abundance. We also find a strong correlation between the matter energy density
and the redshift of matter-radiation equality, z_re, showing that we observe
non-zero equivalent number of relativistic neutrinos mainly via the change of
the of z_re, rather than via neutrino anisotropic stress claimed by the WMAP
team. We forecast that the CMB temperature and polarization measurements
observed with high angular resolutions and sensitivities by the future Planck
satellite will reduce the errors on these parameters down to values fully
consistent with the BBN bounds