sonant
Region Keywords: dark matter, IIMI
PACS: 95.35,+d
DO1:10.108/1674-1137/42/7/073101
I Introduction
Weakly interacting massive particles (WIMPS)are
the most popular solution to the puzzle of dark mat
ter (DM)(1-3). In Tev scale(LHC scale)new physics, de
DM particles follow the thermal scenario in which they
reach thermal and chemical equilibrium with the bath on
particles but lose it at the freeze-out temperature(which 1
is around mpw/20)and experience decoupling trom the the
Universe plasma. WIMP candidates such as the neu
14) and Kaluza-klein particle (5, 6 are found in
R
tra. lino
heories such as the minimal supersymmetric Standard
Model(MSSM )and universal extra dimensions(UED), sl
respectively, and also in other extensions of the Standard
Model(SM)such as singlet scalar [7 10)(or fermionic u
11-13)DM. In spite of their popularity, WIMPS have 3)
not yet been detected in direct experiments
nd well-motivated hypothesis to ex-.
plain the DM problem is that there is such a feeble inter
action that DM particles can never be abundant enough
to thermalize. In this so-called freeze-in mechanism 14
16), feebly interacting massive particles (FINIPS)have
been slowly produced in the early Universe through the
Received 31 January 2018, Revised 20 April 2018, Published online
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