Jun 1 – 2, 2023
ZiF | Bielefeld University
Europe/Berlin timezone

Reviewing the prospect of fermion triplets as dark matter and source of baryon asymmetry in non-standard cosmology

Jun 1, 2023, 2:00 PM
Plenarsaal (ZiF | Bielefeld University)


ZiF | Bielefeld University

Methoden 1 33615 Bielefeld


Sarif Khan (ITP, University of Goettingen)


The indirect searches of Dark Matter (DM), in conjugation with the
so called `missing track searches' at the collider seems to confine fermion
triplet DM mass within a narrow range around $1$ TeV. The canonical picture of
pure triplet fermionic dark matter is in tension since it is under-abundant for
the said mass range. Several preceding studies have shown that the existence of
an extra species over the radiation background composed of the Standard Model particles,
prior to the Big Bang Nucleosynthesis, leads to a fast expanding Universe driven by
an enhanced Hubble parameter. This faster (than radiation) expansion has the potential
to revive the under-abundant fermion triplet ($\mathbb{Z}_2$ odd, lightest generation)
WIMP dark matter scenario by causing freeze-out earlier without modifying the interaction
strength between dark matter and thermal bath. Although the CP asymmetry, produced due to the
decay of $\mathbb{Z}_2$ even heavier generations of the triplet, remains unaffected by
the modification of cosmology, the evolution of the same receives significant non-trivial
effect. It has been observed through numerical estimations that the minimum mass
of the decaying triplet, required to produce sufficient baryon asymmetry, can be lowered
up to two orders (compared to the standard cosmology) in this fast expansion scenario. The
non-standard parameters $n$ and $T_r$, which simultaneously control the dark matter relic abundance
as well the frozen value of baryon asymmetry, are tightly constrained due to consecutive
imposition of experimental bounds on relic density followed by observed value of baryon
asymmetry of the Universe. It has been found that $n$ is strictly bounded within the
interval $0.4\lesssim n \lesssim 1.8$. The upper bound is imposed by the
baryon asymmetry constraint whereas the lower bound arises to satisfy the
correct relic abundance of the DM. The restriction on the other non-standard
parameter $T_r$ is not so stringent as it can vary from sub GeV to few tens of GeV.

Primary author

Sarif Khan (ITP, University of Goettingen)

Presentation materials