8月6日,三大评级机构之一标准普尔首次取消了美国债务保持了70年之久的AAA评级,把美国主权债务评级降至A A+,美国三大股指跌幅均超过4%,全球股市迎来了2008年金融危机以来最黑暗的一天。一个很有意思的现象,美国中长期国债价格在信用评级下调后的第一个交易日价格上涨,国债收益率降至2009年以来的最低点,全球投资者依然看多美债。换句话说,信用下降,美国的借债成本不但没有上升反而下降了。这个在理论上看似“悖论”的现象,可以从欧洲找到答案。作为美债最主要替代产品,欧债风险更大。西班牙、意大利国债收益一度 On August 6, S & P, one of the top three rating agencies, first canceled its 70-year-old AAA rating on U.S. debt and downgraded the US sovereign debt to A A +. The three major U.S. stock indexes both dropped more than 4%. Global stock markets Ushered in the darkest day since the 2008 financial crisis. A very interesting phenomenon. Prices of medium and long-term US treasury bonds rose on the first trading day after the credit rating cut. The yield of government bonds fell to its lowest level since 2009, and global investors still looked for more U.S. debt. In other words, as credit goes down, the cost of borrowing in the United States has declined instead of rising. This seemingly “paradox ” phenomenon in theory can find the answer from Europe. As the most important substitute for the U.S. debt, the European debt is even more risky. Spanish, Italian government bond yields once