FT SeriesNegative yields: Getting to grips with the great bond rallyHow negative rates are upending the rules of finance© FT montage; Sir John Tenniel/CCNegative rates: investors go through looking glass to sub-zero yieldsRoughly one-quarter of the global debt market is trading at levels once thought improbableNegative yields: Sweden leads the world below zeroCentral bank argues that the policy has been a success but others are unconvincedNegative yields: Charting the surge in sliding ratesWhat was once an anomaly has become commonplace since the financial crisisHow hedge funds are thriving in a world of negative-yielding debtThe unnerving world of sub-zero rates still offers managers ways to eke out gainsNegative yields force investors to plunge into riskier debtFeeble returns from safer bonds steer funds into longer, shakier instrumentsNegative interest rates take investors into surreal territoryThe markets are vulnerable to potential nasty losses if rates suddenly shoot up