dark energy equation of state

why can the equation of state \(w\) of dark energy in a scalar field model never be larger than \(+1\) and never be more negative than \(-1\)? are there physical arguments why this would be weird? what would happen to distance measures and to structure growth if \(w\) were outside this range? bonus question: does the Higgs-mechanism in quantum field theory give rise to mass or to inertia? second bonus question: why is dark matter called dark matter if it does not interact with light? if that was the reason, it should rather be called transparent matter, don’t you agree?