Probing the equation of state of the early universe with a space laser interferometer

Abstract

We propose a method to probe the equation of state of the early universe and its evolution, using the stochastic gravitational wave background from inflation. A small deviation from purely radiation dominated universe ($w= 1/3$) would be clearly imprinted on the gravitational wave spectrum $Ω_{GW}(f)$ due to the nearly scale invariant nature of inflationary generated waves.

Figures (1)

• Figure 1: Energy spectrum of the gravitational wave background, $\Omega_{GW}(f,a_0)$, in a chaotic inflationary model driven by a massive scalar field. Solid line represents the case with no entropy production. Dash-dotted line depicts the case with $\Gamma_\chi=10^{-7}$ GeV and the entropy increase factor $F=10^3$. Three intermediate curves are for $F=10$ with $\Gamma_\chi=10^{-5}$ GeV (short-dashed line), $\Gamma_\chi=10^{-6}$ GeV (dotted line), and $\Gamma_\chi=10^{-7}$ GeV (long-dashed line), respectively.