Public fretting by some U.S. central bankers over excessively low inflation aside, the current bout of sub-par U.S. inflation isn’t that unusual and will likely be cured as employment rises, according to a study published Monday by the San Francisco Federal Reserve Bank. U.S. inflation has lingered below the Fed’s 2-percent target for more than three years, and policymakers such as Chicago Fed President Charles Evans have pointed to that shortfall as reason to hold short-term borrowing costs near zero until well into next year.