The Dow closed down 512 points, or 4.3 percent, to 11383.68, a new low for this year. Markets were spooked by the spending cuts agreed upon in the debt talks and worried over fears of a double-dip recession. There are also concerns about Europe’s continuing debt crisis, which threatens to widen to Italy and Spain. The Standard & Poor’s 500 was down 60 points, or 4.78 percent, to 1200. The Nasdaq was down 136, or 5 percent, to 2556. It was the biggest percentage drop since February 2009. In one day, the three major U.S. indexes had erased all of the gains made so far in 2011.