Are Domain Walls ruled out ?
  Recent analysis of the combined data of cosmic microwave background, galaxy clustering and supernovae type Ia observations have set strong constraints on the equation of state parameter $w_X$. The upper bound $w_X < -0.82$ at 95% c.l. rules out an important class of models, the domain walls ($-2/3 < w_X < -1/3$). Here we revisit the issue of domain walls as a possible alternative to the standard $\Lambda$-CDM model by questioning the assumptions made in the choice of priors of the data analysis. The results of our investigation show that domain walls can provide a good fit to the WMAP data for a different choice of priors with ``lower'' values of the Hubble parameter ($h<0.65$), (as indicated by Sunyaev-Zeldovich and time delays for gravitational lensing observations), and ``higher'' values of the matter density ($\Omega_m > 0.35$), (in agreement with recent measurements of the temperature-luminosity relation of distant clusters observed with the XMM-Newton satellite). In this new perspective, their existence would lead to important implications for the CMB constraints on cosmological and inflationary parameters. 
Luca Conversi, Alessandro Melchiorri, Laura Mersini, Joseph Silk