Indian equity benchmarks BSE Sensex and NSE Nifty50 are likely to make a gap-down start to the week, tracking weakness across most global peers as nervousness persisted ahead of a key Fed rate decision due this week. Singapore Exchange (SGX) Nifty futures — an early indicator of the Nifty index — fell as much as 108 points or 0.6 percent to 16,617 ahead of the opening bell on Dalal Street.