Domain Wall Dominated Universes

Abstract

We consider a cosmogony with a dark matter component consisting of a network of frustrated domain walls. Such a network provides a solid dark matter component with $p=-(2/3)ρ$ that remains unclustered on small scales and with $Ω_{\rm dw}\approx 0.7$ can reconcile a spatially flat universe with the many observations indicating $Ω_{\rm m}\approx 0.3.$ Because of its large negative pressure, this component can explain the recent observations indicating an accelerating universe without recourse to a non-vanishing cosmological constant. We explore the viability of this proposal and prospects for distinguishing it from other kinds of proposed dark matter with significant negative pressure.

Figures (2)

• Figure 1: Rescaled CMB Moments for SDM Models. In the first four panels $\ell (\ell +1)C_\ell$ versus $\ell$ is plotted for $w=-1/3, -1/2, -2/3, -5/6$ for several values of the longitudinal sound speed for a universe with $\Omega_{\rm m}=0.3, \Omega_{\rm sdm}=0.7.$ The solid curve corresponds to $c_s=0.0$ and $c_s=0.2, 0.4, 0.6, 0.8$ are indicated by the line styles dotted, dashed, dot-dash, and dot-dot-dash, respectively. rescaled so that the horizon size at recombination subtends the same angle in the sky today as for a $w=-1$ model with the same $\Omega _{\rm m}.$ The bottom middle panel indicates the rescaled and renormalized moments for the quintessence models with $w=-1/3, -1/2, -2/3, -5/6,$ and the bottom right panel shows all models of the previous panels for comparison.
• Figure 2: Domain wall dominated models compatible with constraints on $\sigma_8$ from X-ray clusters. The solid line indicates the stringent lower limit and the dotted line the upper limit, which can be weakened by including a tensor component. The vertical and horizontal axes are $h$ and $\Omega_{\rm m},$ respectively. The left and right panels indicate the spectral indices $n=1.0$ and $n=1.1$, respectively. In both cases the longitudinal sound speed is $c_s=0.2.$