Early-universe constraints on a Primordial Scaling Field

Abstract

In the past years 'quintessence' models have been considered which can produce the accelerated expansion in the universe suggested by recent astronomical observations. One of the key differences between quintessence and a cosmological constant is that the energy density in quintessence, $Ω_φ$, could be a significant fraction of the overall energy even in the early universe, while the cosmological constant will be dynamically relevant only at late times. We use standard Big Bang Nucleosynthesis and the observed abundances of primordial nuclides to put constraints on $Ω_φ$ at temperatures near $T \sim 1MeV$. We point out that current experimental data does not support the presence of such a field, providing the strong constraint $Ω_φ(MeV) < 0.045$ at $2σ$ C.L. and strengthening previous results. We also consider the effect a scaling field has on CMB anisotropies using the recent data from Boomerang and DASI, providing the CMB constraint $Ω_φ\le 0.39$ at $2σ$ during the radiation dominated epoch.

Figures (4)

• Figure 1: Top panel: Time behaviour of the fractional energy density $\Omega_{\phi}$ for the Albrecht and Skordis model together with the constraints presented in the paper. The parameters of the models are (assuming $h=0.65$ and $\Omega_{\phi}=0.65$) $\lambda=3$, $\phi_0=87.089$, $A=0.01$ and $\lambda=8$, $\phi_0=25.797$, $A=0.01$. Bottom panel: Time behaviour for the overall equation of state parameter $w_{tot}$ for the two models. Luminosity distance data will not be useful in differentiating the two models.
• Figure 2: $1,2$ and $3 \sigma$ likelihood contours in the $(\Omega_b h^2, \Omega_\phi (1 \hbox{MeV}))$ parameter space derived from $^4He$ and $D$ abundances.
• Figure 3: CMB anisotropy power spectra for the Albrecht-Skordis models with $\lambda=3$, $\phi_0=87.22$ and $A=0.009$ (long dash), $\lambda=8$, $\phi_0=32.329$ and $A=0.01$ (short dash) (both with $\Omega_{\phi}=0.65$ and $h=0.65$), and a cosmological constant with $\Omega_{\Lambda}=0.65$, $N_{\nu}=3.04$ (full line) and $N_{\nu}$=7.8(dash-dot).
• Figure 4: Matter power spectra for 3 models in fig. 3. The predictions support those in the CMB spectra, the quintessence model in agreement with BBN $\lambda=8$ (short dash) mimics the $\Omega_\Lambda=0.65$ spectrum with $N_\nu$=3.0 (full line). The model with $\lambda=3$ (long dash) is in clear disagreement with observations.