Actor Charlie Sheen pleaded not guilty to domestic violence charges Monday, nearly three months after his wife told Colorado police in a 911 call he put a knife to her throat and threatened to kill her. Sheen showed little emotion and said nothing during his brief arraignment in Pitkin County District Court. The plea was entered by Richard Cummins, a Colorado attorney who represents Sheen. The star of “Two and a Half Men” on CBS is charged with menacing, criminal mischief and assault. Menacing, the most serious charge, carries a possible sentence of one to three years in prison. A judge scheduled a jury trial for July 21.