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After revisiting the heterotic string-derived low-energy effective model of cite{Ashfaque:2016ydg, Athanasopoulos:2014bba, Faraggi:2016xnm, Ashfaque:2016jha} constructed in the four-dimensional free fermionic formulation, we find two axions which are either harmful or massive. As a direct consequence, they can not solve the strong $CP$ problem which is in complete agreement with cite{Lopez:1990iq, Halyo:1993xn}. We also explore the possibility of the self-interacting dark matter residing in the non-Abelian gauge group present in the hidden sector cite{Faraggi:2000pv}. We find that the low-energy string-derived model naturally welcomes the self-interacting dark matter as $4$ copies of the non-Abelian, hidden $SU(2)$ gauge group factor are present.
The production and the subsequent decay of the SM singlet via heavy vector--like colour triplets and electroweak doublets in one--loop diagrams can shed light on the recent observation of diphoton excess at the LHC. In this paper, the $E_6$ GUT is co
In this paper, $E_6$ and especially $E_7$ GUT are considered in the F-theory setting in view of the free fermionic construction of the $4D$ heterotic string. In particular, the NAHE-Based LRS model of cite{Cleaver:2000ds, Cleaver:2002ps} is revisited
In models of multi-component dark matter, the lighter component of dark matter can be boosted by annihilations of the heavier state if mass splitting is large enough. Such relativistic dark matter can be detectable via large neutrino detectors such a
We investigate cosmological implications of an energy density contribution arising by elastic dark matter self-interactions. Its scaling behaviour shows that it can be the dominant energy contribution in the early universe. Constraints from primordia
We explore the phenomenology of having a second epoch of dark matter annihilation into dark radiation long after the standard thermal freeze-out. Such a hidden reannihilation process could affect visible sectors only gravitationally. As a concrete re