Few U.S. banks protected themselves against rising interest rates during the Federal Reserve’s monetary-tightening campaign last year, according to a research paper that says unhedged securities holdings are more widespread than investors might realize, the Wall Street Journal reported. The paper — “Limited Hedging and Gambling for Resurrection by U.S. Banks During the 2022 Monetary Tightening?” — contends that hundreds of other banks share that risk, which played a role in the collapse last month of Silicon Valley Bank. The paper didn’t single out individual institutions, instead presenting an analysis of aggregate data. Investors this week are taking a fresh look at the health of U.S. banks such as Bank of America Corp., Zions Bancorp of Utah and Comerica Inc. of Texas as they report first-quarter results. The authors — professors Erica Jiang of the University of Southern California’s Marshall School of Business, Gregor Matvos of Northwestern University’s Kellogg School of Management, Tomasz Piskorski of Columbia Business School and Amit Seru of Stanford Graduate School of Business — say Silicon Valley Bank and parent SVB Financial weren’t alone in declining to shield assets against rising rates. Across the banking sector, only about 6% of bank assets were protected by interest-rate swaps, contracts a bank can purchase to ease the pain of rising rates, the professors found, drawing on public financial filings.