## Wednesday, October 10, 2012

### 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?

1. in a scalar field model the dark energy eos $w$ depends on the balance between kinetic energy $\dot{\varphi}^2/2$ and potential energy $V(\varphi)$ of the quintessence field $\varphi$:
consequently, if there's only kinetic energy and no potential energy, $w$ would be equal to $+1$, and if there's only potential energy and no kinetic energy, $w$ would be $-1$, which corresponds to the slow roll conditions needed for accelerated expansion.