  Positron excess observed by PAMELA, Fermi and AMS02 may be due to dark matter
(DM) pair annihilation or decay dominantly into muons. In this paper, we
consider a scenario with thermal fermionic DM ($\chi$) with mass $\sim O(1-2)$
TeV decaying into a dark Higgs ($\phi$) and an active neutrino ($\nu_a$)
instead of the SM Higgs boson and $\nu_a$. We first present a renormalizable
model for this scenario with local dark $U(1)_X$ gauge symmetry, in which the
DM $\chi$ can be thermalized by Higgs portal and the gauge kinetic mixing.
Assuming the dark Higgs ($\phi$) mass is in the range $2 m_\mu < m_\phi < 2
m_{\pi^0}$, the positron excess can be fit in a natural manner without conflict
with constraints from antiproton and gamma ray fluxes or direct detection
experiments. Also having such a light dark Higgs, the self-interaction of DM
can be enhanced to some extent, and three puzzles in the CDM paradigm can be
somewhat relaxed.
