What to Watch in the Day Ahead - Wednesday, Jan. 28

(The Day Ahead is an email and PDF publication that includes the day's major stories and events, analyses and other features. To receive The Day Ahead, Eikon users can register at . Thomson One users can register at RT/DAY/US. All times in ET/GMT) Facebook's stock soared in 2014 as the company's mobile ad revenue exploded. There are signs that revenue growth may slow in the coming quarters and Facebook has warned that spending will rise in 2015 as it embarks on a hiring spree and invests in oth