Frustrated expectations: Defect networks and dark energy

We discuss necessary conditions for a network of cosmic domain walls to have a chance of providing the dark energy that might explain the recent acceleration of the Universe. We derive a strong bound on the curvature of the walls, which shows that viable candidate networks must be fine-tuned and nonstandard. We also discuss various requirements that any stable lattice of frustrated walls must obey. We conjecture that, even though one can build (by hand) lattices that would be stable, no such lattices will ever come out of realistic domain wall forming cosmological phase transitions. We provide some simple numerical simulations that illustrate our results and correct some misconceptions in the published literature, but a detailed numerical analysis is left for a companion paper.