CEOs are fighting back. Chief executives of big U.S. companies, including Sprint, JPMorgan Chase and Hewlett Packard, yesterday warned that heavy regulation, legislation and litigation triggered by recent scandals could have a chilling effect on corporate decision-making and the economy. The comments are among the first public signals that top executives want to get back to business, even as prosecutors and regulators are increasing their high-profile efforts to punish corporate malpractice.