Black Holes and WIMPs: All or Nothing or Something Else. (arXiv:2011.01930v4 [astro-ph.CO] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Carr_B/0/1/0/all/0/1">Bernard Carr</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kuhnel_F/0/1/0/all/0/1">Florian Kuhnel</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Visinelli_L/0/1/0/all/0/1">Luca Visinelli</a>
We consider constraints on primordial black holes (PBHs) in the mass range $(
10^{-18}text{-}10^{15} ),M_{odot}$ if the dark matter (DM) comprises weakly
interacting massive particles (WIMPs) which form halos around them and generate
$gamma$-rays by annihilations. We first study the formation of the halos and
find that their density profile prior to WIMP annihilations evolves to a
characteristic power-law form. Because of the wide range of PBH masses
considered, our analysis forges an interesting link between previous approaches
to this problem. We then consider the effect of the WIMP annihilations on the
halo profile and the associated generation of $gamma$-rays. The observed
extragalactic $gamma$-ray background implies that the PBH DM fraction is
$f^{}_{rm PBH} lesssim 2 times 10^{-9},( m_{chi} / {rm TeV} )^{1.1}$ in
the mass range $2 times 10^{-12},M_{odot},( m_{chi} / {rm TeV} )^{-3.2}
lesssim M lesssim 5 times 10^{12},M_{odot},( m_{chi} / {rm TeV}
)^{1.1}$, where $m_{chi}$ and $M$ are the WIMP and PBH masses, respectively.
This limit is independent of $M$ and therefore applies for any PBH mass
function. For $M lesssim 2times 10^{-12},M_{odot},( m_{chi}/ {rm TeV}
)^{-3.2}$, the constraint on $f^{}_{rm PBH}$ is a decreasing function of $M$
and PBHs could still make a significant DM contribution at very low masses. We
also consider constraints on WIMPs if the DM is mostly PBHs. If the merging
black holes recently discovered by LIGO/Virgo are of primordial origin, this
would rule out the standard WIMP DM scenario. More generally, the WIMP DM
fraction cannot exceed $10^{-4}$ for $M > 10^{-9},M_{odot}$ and $m_{chi} >
10,$GeV. There is a region of parameter space, with $M lesssim
10^{-11},M_{odot}$ and $m_{chi} lesssim 100,$GeV, in which WIMPs and PBHs
can both provide some but not all of the DM, so that one requires a third DM
candidate.
We consider constraints on primordial black holes (PBHs) in the mass range $(
10^{-18}text{-}10^{15} ),M_{odot}$ if the dark matter (DM) comprises weakly
interacting massive particles (WIMPs) which form halos around them and generate
$gamma$-rays by annihilations. We first study the formation of the halos and
find that their density profile prior to WIMP annihilations evolves to a
characteristic power-law form. Because of the wide range of PBH masses
considered, our analysis forges an interesting link between previous approaches
to this problem. We then consider the effect of the WIMP annihilations on the
halo profile and the associated generation of $gamma$-rays. The observed
extragalactic $gamma$-ray background implies that the PBH DM fraction is
$f^{}_{rm PBH} lesssim 2 times 10^{-9},( m_{chi} / {rm TeV} )^{1.1}$ in
the mass range $2 times 10^{-12},M_{odot},( m_{chi} / {rm TeV} )^{-3.2}
lesssim M lesssim 5 times 10^{12},M_{odot},( m_{chi} / {rm TeV}
)^{1.1}$, where $m_{chi}$ and $M$ are the WIMP and PBH masses, respectively.
This limit is independent of $M$ and therefore applies for any PBH mass
function. For $M lesssim 2times 10^{-12},M_{odot},( m_{chi}/ {rm TeV}
)^{-3.2}$, the constraint on $f^{}_{rm PBH}$ is a decreasing function of $M$
and PBHs could still make a significant DM contribution at very low masses. We
also consider constraints on WIMPs if the DM is mostly PBHs. If the merging
black holes recently discovered by LIGO/Virgo are of primordial origin, this
would rule out the standard WIMP DM scenario. More generally, the WIMP DM
fraction cannot exceed $10^{-4}$ for $M > 10^{-9},M_{odot}$ and $m_{chi} >
10,$GeV. There is a region of parameter space, with $M lesssim
10^{-11},M_{odot}$ and $m_{chi} lesssim 100,$GeV, in which WIMPs and PBHs
can both provide some but not all of the DM, so that one requires a third DM
candidate.
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