  To understand the decaying phase of outbursts in the black hole (BH) X-ray
binaries (BH-XRBs), we performed very long general relativistic
magneto-hydrodynamic (GRMHD) simulations of a geometrically thin accretion disk
around a Kerr BH with slowly rotating matter injected from outside. We
thoroughly studied the flow properties, dynamical behavior of the accretion
rate, magnetic flux rate, and jet properties during the temporal evolution. Due
to the interaction between the thin disk and injected matter, the accretion
flow near the BH goes through different phases. The sequence of phases is: soft
state $\rightarrow$ soft-intermediate state $\rightarrow$ hard-intermediate
state $\rightarrow$ hard state $\rightarrow$ quiescent state. For the accretion
rate (and hence the luminosity) to decrease (as observed) in our model, the
mass injection should not decay slower than angular momentum injection. We also
observed quasi-periodic oscillations (QPOs) in the accretion flow. Throughout
the evolution, we observed low-frequency QPOs (~10Hz) and high-frequency QPOs
(\sim 200Hz). Our simple unified accretion flow model for state transitions is
able to describe outbursts in BH-XRBs.
