  Jet propagation is shown to produce Mach-cone-like medium excitation inside a
quark-gluon plasma. However, only deflection of such medium excitation and jet
shower partons by radial flow leads to double-peaked dihadron correlation in
high-energy heavy-ion collisions. Dihadron correlations from harmonic flow, hot
spots and dijets are studied separately within the AMPT Monte Carlo model and
all lead to double-peaked dihadron azimuthal correlation. The $\gamma$-hadron
correlation has similar double-peak feature but is free of the contributions
from harmonic flow and hot spots. Dihadron and $\gamma$-hadron correlations are
compared to shed light on jet-induced medium excitation and hot spots in an
expanding medium.
