Romney wins Nevada caucuses
Mitt Romney swept to a convincing win in the Nevada caucuses, maintaining his momentum as frontrunner in the race for the Republican nomination and leaving Newt Gingrich in a tussle with Ron Paul for second place
Facebook chief faces tax bill of $1.5bn
Money will fall due on a profit of nearly $5bn that Mark Zuckerberg plans to take on stock options he was handed in 2005