The economic downturn Wall Street has been fearing may have already arrived, according to Moody's top economist. Mark Zandi , the chief economist at Moody's Analytics, said he's been looking at one signal in particular that suggests the US economy may have already tipped into a recession . It's called the Vicious Cycle Index — an economic gauge that Zandi said he and his team at Moody's created, which recently flashed a positive signal for a recession. The indicator is loosely based on the Sahm