No-boundary wave function for two-field inflation
  In this paper, we investigate the no-boundary wave function and the complex-valued instantons for two-field inflation models that have different masses. If there is a relatively massive direction, to classicalize the massive field, the solution should start from the slow direction with relatively larger vacuum energy. Therefore, the existence of the massive direction implies the increase of expected $e$-foldings. The most probable $e$-foldings are approximately $\mathcal{N} \simeq (m_{2}/m_{1})^{2} \times \mathcal{O}(1)$ in the $m_{1} \ll m_{2}$ limit. Therefore, as long as there is a sufficient mass hierarchy, the no-boundary wave function can reasonably explain large $e$-foldings, so to speak more than 50 $e$-foldings. 
Dong-il Hwang, Soo A Kim, Dong-han Yeom
gr-qc astro-ph.CO hep-th