UK stocks are expected to open unchanged on Tuesday after a strong rally the previous session, as investors turn cautious ahead of a much-anticipated Federal Reserve meeting.City sources predict the FTSE 100 will open more or less flat on Monday's close of 6,804.08.The Fed will kick off its two-day policy meeting later on with a decision expected at 18:00 on Wednesday evening. While no change is expected in policy, markets will be watching the central bank's forward guidance closely, given recent speculation that policymakers could hike interest rates sooner than expected.Analysts at Rabobank said the Federal Open Market Committee (FOMC) is likely to remove the word 'patient' from its statement this week on the timing of policy tightening."Given the better-than-expected labour market data [over January and February], the FOMC is likely to open the door to a June rate hike. In fact, the Fed seems intent on preparing the markets for the first rate hike," they said.Stocks to watchProfits at copper miner Antofagasta sank more than expected after lower production and weaker commodity prices were met with higher costs, as the company slashed its dividend by 77.4%. EBITDA dropped 17.8% to $2.22bn, missing the market forecast of around $2.3bn. The company did not address recent rumours that it may have to close its flagship Los Pelambres project in Chile.Sainsbury's posted a 1.9% fall in fourth-quarter like-for-like sales excluding fuel, as it cut prices on over 1,100 items. Total sales were down 0.3% and the supermarket group expects the market to remain challenging for the foreseeable future, with food deflation and competitive pressures likely to persist for the rest of this calendar year.BHP Billiton, the world's largest mining group, has recommended shareholders to approve its proposed demerger as it spins off its non-core activities into a new company called South32. It will cost the company a one-off bill of $738m to go through with the demerger, though it has promised to maintain a progressive dividend policy and doesn't plant to rebase its payout to shareholders following the demerger, implying a higher payout ratio.Sky has invested an extra $5m into on-demand video start-up company 1Mainstream. The funds will take the shape of a convertible debt security, adding to the $2m invested back in August 2013.