ROME — An independent researcher claimed on Wednesday that a marble bust of Christ in a Roman church is by Michelangelo , the latest purported attribution to the  Renaissance genius  who is one of the most imitated artists in the world. The unverified claims by Valentina Salerno have unsettled Renaissance scholars, especially since a recent sketch of a foot that was attributed to Michelangelo , but disputed by some as a copy, recently fetched $27.2 million at a  Christie’s auction. Given the