The Inflaton Portal to a Highly decoupled EeV Dark Matter Particle. (arXiv:1905.05191v1 [hep-ph])

The Inflaton Portal to a Highly decoupled EeV Dark Matter Particle. (arXiv:1905.05191v1 [hep-ph])
<a href="http://arxiv.org/find/hep-ph/1/au:+Heurtier_L/0/1/0/all/0/1">Lucien Heurtier</a>, <a href="http://arxiv.org/find/hep-ph/1/au:+Huang_F/0/1/0/all/0/1">Fei Huang</a>

We explore the possibility that the dark-matter relic abundance is generated
in a context where the inflaton is the only mediator between the visible and
the hidden sectors of our universe. Due to the relatively large mass of the
inflaton field, such a portal leads to an extremely feeble interaction between
the dark and the visible sectors suggesting that the dark sector cannot reach
any thermal equilibrium with the visible sector. After the two sectors are
populated by the decay of the inflaton, a heavy dark-matter particle thermally
decouples within the dark sector. Later, a lighter dark particle, whose decay
width is naturally suppressed by the inflaton propagator, decays into the
visible sector after it dominates the energy density of universe. This process
dilutes the dark-matter relic density by injecting entropy in the visible
sector. We show that an inflaton mass of $mathcal{O}(10^{13})$ GeV together
with couplings of order one are fully compatible with a dark-matter relic
abundance $Omega h^2sim 0.1$. As a general feature of the model, the entropy
dilution mechanism is accompanied by a period of early matter domination, which
modifies the amount of e-folds of inflation necessary to accommodate Planck
data. Moreover, the coupling of the inflaton to the dark and visible sectors
brings loop contributions to the inflationary potential which can destabilize
the inflation trajectory. Considering all these complementary constraints, we
show that, in the context of a plateau-inflation scenario such as the
$alpha$-attractor model, the inflaton can constitute a viable mediator between
the visible sector and a $sim 10$ EeV dark-matter candidate. Furthermore, we
show that improved constraints on the tensor-to-scalar ratio and spectral index
could potentially rule out dark-matter scenarios of this sort in the future.

We explore the possibility that the dark-matter relic abundance is generated
in a context where the inflaton is the only mediator between the visible and
the hidden sectors of our universe. Due to the relatively large mass of the
inflaton field, such a portal leads to an extremely feeble interaction between
the dark and the visible sectors suggesting that the dark sector cannot reach
any thermal equilibrium with the visible sector. After the two sectors are
populated by the decay of the inflaton, a heavy dark-matter particle thermally
decouples within the dark sector. Later, a lighter dark particle, whose decay
width is naturally suppressed by the inflaton propagator, decays into the
visible sector after it dominates the energy density of universe. This process
dilutes the dark-matter relic density by injecting entropy in the visible
sector. We show that an inflaton mass of $mathcal{O}(10^{13})$ GeV together
with couplings of order one are fully compatible with a dark-matter relic
abundance $Omega h^2sim 0.1$. As a general feature of the model, the entropy
dilution mechanism is accompanied by a period of early matter domination, which
modifies the amount of e-folds of inflation necessary to accommodate Planck
data. Moreover, the coupling of the inflaton to the dark and visible sectors
brings loop contributions to the inflationary potential which can destabilize
the inflation trajectory. Considering all these complementary constraints, we
show that, in the context of a plateau-inflation scenario such as the
$alpha$-attractor model, the inflaton can constitute a viable mediator between
the visible sector and a $sim 10$ EeV dark-matter candidate. Furthermore, we
show that improved constraints on the tensor-to-scalar ratio and spectral index
could potentially rule out dark-matter scenarios of this sort in the future.

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