这篇文章值得细细一读:Central banks using options as a monetary policy tool
http://ftalphaville.ft.com/blog/2011/04/18/548381/more-on-the-literal-bernanke-put/
In theory the Federal Reserve is now the largest volatility trader in the world because current monetary policy is akin to shorting massive amounts of volatility and assuming tail risk. The current regime of monetary and fiscal stimulus is similar to writing a naked put on the entire financial system with margin backed by the US debt. The premium received from the sale of the naked put is financed via demand for our debt and redistributed to the investor class to re-flate underlying asset prices and depress volatility. The theory is that the reinvestment of this premium by investors into underling risk assets ensures the Fed’s naked put is never exercised. In effect, the Federal Reserve is constantly shorting vega on a systematic level. This stimulus regime socializes “tail risk” to generate short-term prosperity. If asset prices drop the Fed is forced to sell more volatility to artificially support prices.