A new wa parametrization

1
A new w(a) parametrization
W(a)-1?2f(a/ac)

• Zhiqi Huang
• Supervisors Dick Bond Lev Kofman

2
Dark Energy Equation of State (EOS)
Scale factor a1/(1z)
Observationally SNe, BAO, CL, WL, CMB (Albrecht
et al White Paper) constraints on w depend on
the data set, parametrization, and statistics
(ref. Spergel et al 2006, Riess et al 2006,
Seljak et al 2006, etc.) We roughly know
w-1.0 0.2

• Theoretical Models --
• Cosmological Constant (w-1)
• Quintessence (-1w1)
• Phantom field (w-1)
• Tychyon fields (-1 w 0)
• K-essence ( no prior on w)

3
Old joke A party of famous physicists

• Everyone gravitated toward Newton, but he just
  kept moving around at a constant velocity and
  showed no reaction.
• Pauli came late, but was mostly excluded from
  things, so he split.
• Pascal was under too much pressure to enjoy
  himself.
• Ohm spent most of the time resisting Ampere's
  opinions on current events.
• .
• Heisenberg may or may not have been there.
• .

4
Dark energy may or may not be cosmological
constant
Standard parametrization degeneracy between two
parameters
Seljak et al 2005
Liddle et al 2006
5
Break the degeneracy between w0 and wa

• One-parameter parametrization.
• Physically motivated.
• Quintessence model

slow roll conditions ?
6
Slow roll conditions
? varies slowly ?V is exponential-like
Examples Ve-?f, VCfa, a1 VABf
7
Include the phantom field

• f -gt if ? ?2lt 0

8
In all 3 figures, I use fiducial Om0.3
9
Run my MCMC codes (SNe CMB prior BAO prior LSS
prior)
Dark shade 68 contour. Light shade 95
contour.