Edit: pstuartb, You are right that 5 - 10B are nothing compared to market cap and total trading. It is just an opinion, not backed by any data or analysis. When FED pump a big amount, a rally comes out from no where between 10:30 and 11:00 and typically runs NDX up by 1 - 3%. See the NDX is already up 0.80% (0.30% net) from where the rally started.
The money they inject works as catalyst in chemical reaction. It just starts with furious buying, which results in short covering and then momo buyers to jump in etc ....
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