Are domain walls ruled out?

Recent analysis of the combined data of cosmic microwave background, galaxy clustering and supernovae type la 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, the existence of domain walls would lead to important implications for CMB constraints on cosmological and on inflationary parameters. (C) 2004 Elsevier B.V. All rights reserved.