Asymmetric Dark Matter Bound State
  We propose an interesting framework for asymmetric scalar dark matter (ADM),
which has novel collider phenomenology in terms of an unstable ADM bound state
(ADMonium) produced via Higgs portals. ADMonium is a natural consequence of the
basic features of ADM: the (complex scalar) ADM is charged under a dark local
$U(1)_d$ symmetry which is broken at a low scale and provides a light gauge
boson $X$. The dark gauge coupling is strong and then ADM can annihilate away
into $X$-pair effectively. Therefore, the ADM can form bound state due to its
large self-interaction via $X$ mediation. To explore the collider signature of
ADMonium, we propose that ADM has a two-Higgs doublet portal. The ADMonium can
have a sizable mixing with the heavier Higgs boson, which admits a large cross
section of ADMonium production associated with $b\bar b$. The resulting
signature at the LHC depends on the decays of $X$. In this paper we consider a
case of particular interest: $pp\ra b\bar b+ {\rm ADMonium}$ followed by ${\rm
ADMonium}\ra 2X\ra 2e^+e^-$ where the electrons are identified as (un)converted
photons. It may provide a competitive explanation to heavy di-photon resonance
searches at the LHC.
