Students arriving on the former campuses of Northern Vermont University, Castleton University and Vermont Technical College for the start of classes last week were greeted with banners, T-shirts and pennants bearing a different name: Vermont State University, accompanied by the slogan “We Are One.” It was also the first day of classes for the newly unified VSU, a consolidation of three four-year institutions in the Vermont State Colleges System that was formally born this summer after two-plus years of planning. System leaders hope the bold transformation will boost rapidly declining enrollment, whittle down a $25 million deficit and stave off college closures that just a few years ago seemed inevitable.