Indian benchmark indices BSE Sensex and NSE Nifty50 are likely to make a gap-up start on Monday tracking gains across global markets, as investors awaited the outcome of a policy review by the Fed wherein the US central bank is widely expected to decide on a hike in the benchmark interest rates.Singapore Exchange (SGX) Nifty futures — an early indicator of the Nifty index — jumped as much as 196 points or 1.1 percent to 18,030.5 ahead of the opening bell on Dalal Street.