Topological defects as effective dynamical dark energy

Abstract: In this work, we consider the possibility that the dynamical dark energy hinted at by recent DESI data may be mimicked by the effects of additional components in the universe, potentially arising from topological defects. We find that the data does not show a particular preference for the existence of cosmic strings. However, a domain wall contribution at the percent level can improve the fit, yielding a $\Delta \chi^2= -1.72$ compared to the $\Lambda \rm{CDM}$ model. The improvement indicates that topological defects remain a viable and interesting extension to $\Lambda\rm{CDM}$, meriting further investigation with future cosmological data.