Apart from Mumbai spinner Harmeet, the IPL side added talented Kerala batsmen Sachin Baby and Sanju Samson and Jharkhand paceman Rahul Shukla to their squad.
20-year-old Harmeet has represented India in two Under-19 ICC World Cups in 2010 and 2012. In the 2012 U-19 World Cup, he was one of the main pillars of India, helping win the title with his economy rate of 3.02.
Kerala's 18-year-old wicket-keeper Samson has been representing his state team since his Ranji debut in 2011 against Vidarbha.
Baby has been a consistent performer for Kerala in the last few years and was among the top run-scorers in the invitational Buchi Babu Tournament and Vijay Hazare Trophy for his state.
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The 24-year-old has played 14 first class and domestic matches, and has scored 492 runs with a highest score of 104 at an average of 49.20.
Rahul Dravid, Captain, Rajasthan Royals, said, "The IPL has been an excellent platform for encouraging the growth of fresh talent in our country. These four confident players will provide more depth and variation to our team during IPL 2013.