Dark Energy as Double N-Flation--Observational Predictions
  We propose a simple model for dark energy useful for comparison with
observations. It is based on the idea that dark energy and inflation should be
caused by the same physical process. As motivation, we note that Linde's simple
chaotic inflation $V=(1/2)m^{2}\phi^{2}$ produces values of $n_{s}=0.967$ and
$r=0.13$, which are consistent with the WMAP 1-sigma error bars. We therefore
propose $V=(1/2)m_{2}^{2}\phi_{2}^{2}+(1/2)m_{1}^{2}\phi_{1}^{2}$ with
$m_{1}\sim10^{-5}$ and $m_{2}\leq10^{-60}$, where $c=1=\hbar$ and the reduced
Planck mass is set to unity. The field $\phi_{1}$ drives inflation and has
damped by now ($\phi_{1,0}=0$), while $\phi_{2}$ is currently rolling down its
potential to produce dark energy. Using this model, we derive the formula
$\delta w(z)\equiv w(z)+1=\delta w_{0}(H_0/H(z))^2$ via the slow-roll
approximation. Our numerical results from exact and self-consistent solution of
the equations of motion for $\phi_2$ and the Friedmann equations support this
formula, and it should hold for any slow-roll dark energy.
  Our potential can be easily realized in N-flation models with many fields,
and is easily falsifiable by upcoming experiments -- for example, if Linde's
chaotic inflation is ruled out. But if $r$ values consistent with Linde's
chaotic inflation are detected then one should take this model seriously
indeed.
