Fifty-nine of the country’s top computer scientists and election security experts rebuked President Trump’s baseless claims of voter fraud and hacking on Monday, writing that such assertions are “unsubstantiated or are technically incoherent.”

The rebuttal, in a letter to be published on various websites, did not mention Mr. Trump by name but amounted to another forceful corrective to the torrents of disinformation that he has posted on Twitter.

“Anyone asserting that a U.S. election was ‘rigged’ is making an extraordinary claim, one that must be supported by persuasive and verifiable evidence,” the scientists wrote. In the absence of evidence, they added, it is “simply speculation.”

“To our collective knowledge, no credible evidence has been put forth that supports a conclusion that the 2020 election outcome in any state has been altered through technical compromise,” they wrote.