By Tom Hals and Sheila Dang WILMINGTON, Del. (Reuters) -Elon Musk is under a federal investigation related to his $44 billion takeover deal for Twitter Inc, the social media company said in a court filing made public on Thursday. Twitter said it requested for months that Musk’s attorneys produce their communications with federal authorities but they had not done so, and asked a Delaware judge to order the attorneys to provide the documents. In late September, Musk’s attorneys provided a “privilege log” identifying documents to be withheld from discovery. The log referenced drafts of a May 13 e…