Negative Rates: Handgun or Distress Signal?

The negative nominal rates currently applied to some sovereign and banks, which refinance at negative interest rates offered by some central banks, have swept aside the zero-lower bound assumption. Although they seem to increase the leeway of monetary policy, are the negative rates a controlled consequence of the unconventional monetary policy? Or do they much more reflect the threats of deflation and the unfavorable macroeconomic situation, or even worse, do they appear as an early warning of secular stagnation? What if the recovery relied more on the yield of productive investment (i.e. the natural rate as defined by Wicksell) than the level of market interest rates? This return to the Wicksell’s natural interest rate approach brings a key issue: to prevent both deflation and secular stagnation, should the monetary rate be perpetually cut to new lows? Or should we try to raise the natural rate? In that case, how to raise the natural rate?