Speaker
Description
The relic abundance of the dark matter (DM) particle $d$
is studied in a secluded DM scenario, in which the $d$ number
decreasing process dominantly occurs not through the pair annihilation
of $d$ into the standard model particles, but via the $dd \to mm$
scattering process with a subsequently decaying mediator particle $m$.
It is pointed out that the cosmologically observed relic abundance of DM
can be accomplished even with a massive mediator having a mass $m_m$
non-negligibly heavy compared with the DM particle mass $m_d$.
In the degenerated $d$-$m$ case
($m_d=m_m$),
the DM relic abundance is realized by adjusting
the $dd \to mm$ scattering amplitude large enough and by choosing
an appropriate mediator particle life-time.
The DM evolution in the early universe exhibits characteristic
"terrace" behavior, or two-step number density decreasing behavior,
having a ``fake'' freeze-out at the first step.
Based on these observations, a novel possibility of the DM model
buildings is introduced
in which the mediator particle $m$ is unified with the DM particle
$d$ in an approximate dark symmetry multiplet.
A pionic DM model is proposed to illustrate this idea
in a renormalizable field theory framework.
S. Okawa, M. Tanabashi and M. Yamanaka,
``Relic Abundance in Secluded Dark Matter Scenario with Massive Mediator,''
arXiv:1607.08520 [hep-ph].
Summary
The relic abundance of the dark matter (DM) particle $d$
is studied in a secluded DM scenario, in which the $d$ number
decreasing process dominantly occurs not through the pair annihilation
of $d$ into the standard model particles, but via the $dd \to mm$
scattering process with a subsequently decaying mediator particle $m$.
It is pointed out that the cosmologically observed relic abundance of DM
can be accomplished even with a massive mediator having a mass $m_m$
non-negligibly heavy compared with the DM particle mass $m_d$.
In the degenerated $d$-$m$ case
($m_d=m_m$),
the DM relic abundance is realized by adjusting
the $dd \to mm$ scattering amplitude large enough and by choosing
an appropriate mediator particle life-time.
The DM evolution in the early universe exhibits characteristic
"terrace" behavior, or two-step number density decreasing behavior,
having a ``fake'' freeze-out at the first step.
Based on these observations, a novel possibility of the DM model
buildings is introduced
in which the mediator particle $m$ is unified with the DM particle
$d$ in an approximate dark symmetry multiplet.
A pionic DM model is proposed to illustrate this idea
in a renormalizable field theory framework.
