Capital growth and public debt growth depend on the deficit ratio and on the
debt-capital ratio. Both growth rates stay constant if the debt–capital ratio is
constant. In the steady state, public debt and capital grow at the same rate, so
the debt–capital ratio and both growth rates are constant. There is a critical
deficit ratio. First assume that the deficit ratio is below the critical level. In this
case there are two steady states. One of them is locally stable, and the other
is unstable. There is a critical initial debt–capital ratio. If the initial debt–
capital ratio is below the critical level, the stable steady state will be reached.
However, if the initial debt–capital ratio is above the critical level, then capital
growth declines continuously, becomes negative at some point of time, and
deteriorates further. Capital is driven to zero in finite time. Now assume that
the economy is in the stable steady state. Consider an increase in the deficit
ratio. First assume that the deficit ratio stays below the critical level. Then,
the increase in the deficit ratio leads to a new steady state. Capital growth and
public debt growth are lower than in the original steady state. Second assume
that the deficit ratio exceeds the critical level. In this case there is no steady
state. Capital growth declines continuously, and capital is driven to zero in