The primary market is expected to remain vibrant, with at least 10 companies, including supermart major Vishal Mega Mart and Blackstone-owned diamond grading firm International Gemmological Institute (India) Ltd expected to raise a combined Rs 20,000 crore in the next month, merchant bankers said.Education-focused NBFC Avanse Financial Services, TPG Capital-backed Sai Life Sciences, hospital chain operator Paras Healthcare, and investment bank DAM Capital Advisors are also among the companies planning to launch their IPOs in December, they added.The companies aim to raise a total of Rs 20,000 crore through their public offerings.