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Top-phobic heavy Higgs boson as the 750 GeV diphoton resonance

A hint of a new resonance at a mass of 750\,GeV has been observed in the diphoton channel of LHC Run 2 at $\sqrt{s}=13$ TeV. The signal rate is too large to interpret it as a new Higgs boson in the context of weakly-coupled renormalizable models. One way is to reduce its total decay rate, which is possible if the CP-even heavy Higgs boson $H^0$ in the aligned two Higgs doublet model becomes top-phobic. To ensure sufficient gluon fusion production, we introduce vector-like quarks (VLQ). The Higgs precision data as well as the exclusion limits from no excesses in other 8 TeV LHC searches of $Zγ$, $b\bar{b}$, $τ^+τ^-$, and $jj$ channels are simultaneously included. In Type I, top-phobic $H^0$ cannot explain the 750\,GeV diphoton signal and the Higgs precision data simultaneously since the universal Yukawa couplings of the up-type and down-type VLQs always make more contribution to $h^0$ than to $H^0$. In Type II, small Yukawa coupling of the up-type VLQ but sizable Yukawa coupling for the down-type VLQ is shown to explain the signal while satisfying other LHC exclusion limits.