There is no sound reason to require voters to register at least 20 days before an election. Media coverage escalates, races tighten, and voter interest intensifies as election day nears. That kind of electoral energy should be directed into the state’s 2,166 precincts. But too often it gets lost in registration technicalities. A soon-to be-released study by the New York-based Demos research organization estimates that turnout in the November presidential election in Massachusetts could rise by 226,000 voters, or 4.9 percent, if people had the opportunity to register at their polling places on election day. Turnout among those ages 18 to 25 could increase by 9.7 percent, according to the study.