By Jonathan Stempel NEW YORK (Reuters) – Nomura Securities was sued in New York by a former quantitative researcher who said she was underpaid relative to men and fired after insisting that her team “should stop discriminating against women.” Xue Feng filed her lawsuit on Monday in federal court in Manhattan, seeking unspecified damages for alleged violations of federal civil rights, equal pay and medical leave laws, and New York state and city human rights laws. Nomura had no immediate comment on Tuesday. Feng, who is known Heidi, said she had worked in Nomura’s otherwise all-male Global Equi…