Testing coupled dark energy with next-generation large-scale observations

Coupling dark energy to dark matter provides one of the simplest way to effectively modify gravity at large scales without strong constraints from local (i.e. Solar System) observations. Models of coupled dark energy have been studied several times in the past and are already significantly constrained by cosmic microwave background experiments. In this paper we estimate the constraints that future large-scale observations will be able to put on the coupling and in general on all the parameters of the model. We combine cosmic microwave background, tomographic weak lensing, redshift distortions and power spectrum probes. We show that next-generation observations can improve the current constraint on the coupling to dark matter by two orders of magnitude; this constraint is complementary to the current Solar System bounds on a coupling to baryons.

Figure 1

Evolution of $w_{\mathrm{eff}}$ for various values of $\beta$.

Figure 2

CMB unlensed TT temperature spectra for three values of $\beta$. Data are taken from WMAP7 [53].

Figure 3

Predicted confidence contours for the cosmological parameter set $\Theta \equiv \{{\beta }^2,\alpha ,{\Omega }_c,h,{\Omega }_b,n_s,\log A\}$ using CMB Planck specifications. We plot here a selection of various parameters vs ${\beta }^2$. Each plot is obtained marginalizing over all parameters except the ones on the $x$ and $y$ axes.

Figure 4

Predicted confidence contours for the cosmological parameter set $\Theta \equiv \{{\beta }^2,\alpha ,{\Omega }_c,h,{\Omega }_b,n_s,\log A\}$ using CMB Planck specifications. We plot here a selection of various parameters vs $\alpha$. Each plot is obtained marginalizing over all parameters except the ones on the $x$ and $y$ axes.

Figure 5

Predicted confidence contours for the cosmological parameter set $\Theta \equiv \{{\beta }^2,\alpha ,{\Omega }_c,h,{\Omega }_b,n_s,\log A\}$ (in black, equal to Fig. 3) using CMB Planck specifications. Overplotted in dashed are the predicted confidence contours for the cosmological parameter set $\{{\beta }^2,\alpha ,{\Omega }_c,{\Omega }_b,n_s,\log A\}$, with $h$ fixed to the reference value.

Figure 6

Predicted confidence contours for the cosmological parameter set $\Theta \equiv \{{\beta }^2,\alpha ,{\Omega }_c,h,{\Omega }_b,n_s,\log A\}$ (in black, equal to Fig. 5) using CMB Planck specifications. Overplotted are the predicted confidence contours for the cosmological parameter set $\{{\beta }^2,\alpha ,{\Omega }_c,{\Omega }_b,n_s,\log A\}$ (dashed contours, with $h$ fixed to the reference values) and the cosmological parameter set $\{{\beta }^2,\alpha ,{\Omega }_c,{\Omega }_b,\log A\}$ (dotted contours, with $h$ and $n_s$ fixed to the reference values).

Figure 7

The combination $G(z)f(z)$ that appears as the amplitude of the power spectrum, for various values of $\beta$. $G(z)$ is normalized to unity today.

Figure 8

BAO oscillations in $P(k)$ for three values of $\beta$. The curves show the ratio $P(k)/P_s(k)$, where $P_s(k)$ is the corresponding smooth power spectrum.

Figure 9

Predicted confidence contours for the cosmological parameter set $\Theta \equiv \{{\beta }^2,\alpha ,{\Omega }_c,h,{\Omega }_b,n_s,{\sigma }_8\}$ using the galaxy power spectrum. We plot here a selection of various parameters vs ${\beta }^2$. Each plot is obtained marginalizing over all parameters except the ones on the $x$ and $y$ axes.

Figure 10

Predicted confidence contours for the cosmological parameter set $\Theta \equiv \{{\beta }^2,\alpha ,{\Omega }_c,h,{\Omega }_b,n_s,{\sigma }_8\}$ using the galaxy power spectrum. We plot here a selection of various parameters vs $\alpha$. Each plot is obtained marginalizing over all parameters except the ones on the $x$ and $y$ axes.

Figure 11

The convergence power spectra $P_{11}$ and $P_{55}$ for three values of $\beta$.

Figure 12

Predicted confidence contours for the cosmological parameter set $\Theta \equiv \{{\beta }^2,\alpha ,{\Omega }_c,h,{\Omega }_b,n_s,{\sigma }_8\}$ using weak lensing Euclid-like specifications. We plot here a selection of various parameters vs ${\beta }^2$. Each plot is obtained marginalizing over all parameters except the ones on the $x$ and $y$ axes.

Figure 13

Predicted confidence contours for the cosmological parameter set $\Theta \equiv \{{\beta }^2,\alpha ,{\Omega }_c,h,{\Omega }_b,n_s,{\sigma }_8\}$ using weak lensing Euclid-like specifications. We plot here a selection of various parameters vs $\alpha$. Each plot is obtained marginalizing over all parameters except the ones on the $x$ and $y$ axes.

Figure 14

Comparison among predicted confidence contours for the cosmological parameter set $\Theta \equiv \{{\beta }^2,\alpha ,{\Omega }_c,h,{\Omega }_b,n_s,{\sigma }_8,log(A)\}$ using CMB (Planck, blue contours), $P(k)$ (pink-violet contours) and weak lensing (orange-red contours) with Euclid-like specifications. We plot here a selection of various parameters vs ${\beta }^2$. Each plot is obtained marginalizing over all parameters except the ones on the $x$ and $y$ axes.

Figure 15

Comparison among predicted confidence contours for the cosmological parameter set $\Theta \equiv \{{\beta }^2,\alpha ,{\Omega }_c,h,{\Omega }_b,n_s,{\sigma }_8,log(A)\}$ using CMB (Planck, blue contours), $P(k)$ (pink-violet contours) and weak lensing (orange-red contours) with Euclid-like specifications. We plot here a selection of various parameters vs $\alpha$. Each plot is obtained marginalizing over all parameters except the ones on the $x$ and $y$ axes.

Figure 16

Combined predicted confidence contours for the cosmological parameter set $\Theta \equiv \{{\beta }^2,\alpha ,{\Omega }_c,h,{\Omega }_b,n_s,{\sigma }_8,\log (A)\}$ from CMB (Planck), $P(k)$ and weak lensing (Euclid-like) specifications. We plot here a selection of various parameters vs $\alpha$. Each plot is obtained marginalizing over all parameters except the ones on the $x$ and $y$ axes.

Figure 17

Combined predicted confidence contours for the cosmological parameter set $\Theta \equiv \{{\beta }^2,\alpha ,{\Omega }_c,h,{\Omega }_b,n_s,{\sigma }_8,\log (A)\}$ from CMB (Planck), $P(k)$ and weak lensing (Euclid-like) specifications. We plot here a selection of various parameters vs $\alpha$. Each plot is obtained marginalizing over all parameters except the ones on the $x$ and $y$ axes.