By Ryan Vlastelica NEW YORK Mon Apr 14, 2014 6:02pm EDT (Reuters) – U.S. stocks closed higher on Monday as Citigroup’s earnings and strong retail sales gave investors reasons to buy equities despite a resurgence of geopolitical uncertainties. Equities opened higher as strong results from Citigroup and bullish retail sales data lifted sentiment, though shares lost ground in the last hour of trading. Both the Nasdaq and the S&P 500 briefly turned negative, though they […]