Inconsistency of an inflationary sector coupled only gravitationally. (arXiv:1811.04093v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Figueroa_D/0/1/0/all/0/1">Daniel G. Figueroa</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tanin_E/0/1/0/all/0/1">Erwin H. Tanin</a>
From a model-building perspective, the inflationary sector might very well
have no direct couplings to other species, apart from inevitable gravitational
interactions. In such a case, a thermal universe can still emerge after
inflation if: $i)$ some radiation sector is excited towards the end of
inflation, and $ii)$ the post-inflationary equation of state becomes
sufficiently stiff $w geq w_{rm RD}gtrsim 0.57$, with $w_{rm RD}$ a
threshold depending on the inflationary scale $H_*$ and the initial
radiation-to-inflaton energy ratio $Delta_*$. Furthermore, a stiff period in
the expansion history enhances significantly the inflationary gravitational
wave (GW) spectrum, making this signal (potentially) observable by aLIGO, LISA
and other GW observatories. The very same enhancement leads however to an
inconsistency of the scenario: the energy of the GWs becomes too large compared
to the rest of the radiation sector, violating standard BBN and CMB bounds on
GW backgrounds. Except for unappealing initial radiation sectors, our result is
independent of $w$, $H_*$ and $Delta_*$, suggesting that in order to reheat
the universe, the inflationary sector must necessarily be coupled directly to
other particle species.
From a model-building perspective, the inflationary sector might very well
have no direct couplings to other species, apart from inevitable gravitational
interactions. In such a case, a thermal universe can still emerge after
inflation if: $i)$ some radiation sector is excited towards the end of
inflation, and $ii)$ the post-inflationary equation of state becomes
sufficiently stiff $w geq w_{rm RD}gtrsim 0.57$, with $w_{rm RD}$ a
threshold depending on the inflationary scale $H_*$ and the initial
radiation-to-inflaton energy ratio $Delta_*$. Furthermore, a stiff period in
the expansion history enhances significantly the inflationary gravitational
wave (GW) spectrum, making this signal (potentially) observable by aLIGO, LISA
and other GW observatories. The very same enhancement leads however to an
inconsistency of the scenario: the energy of the GWs becomes too large compared
to the rest of the radiation sector, violating standard BBN and CMB bounds on
GW backgrounds. Except for unappealing initial radiation sectors, our result is
independent of $w$, $H_*$ and $Delta_*$, suggesting that in order to reheat
the universe, the inflationary sector must necessarily be coupled directly to
other particle species.
http://arxiv.org/icons/sfx.gif
