The paper explores the implications of the Dark Energy Spectroscopic Instrument (DESI) data, combined with cosmic microwave background (CMB) data, on the sum of neutrino masses. The analysis places an upper limit on the sum of neutrino masses, $\sum m_{\nu} < 70$ meV (95\%), and peaks at $\sum m_{\nu} = 0$, suggesting that the minimum sum of 58 meV is excluded at 2$\sigma$. The authors extend the DESI analysis to allow for negative neutrino masses, finding $\sum m_{\nu} = -160 \pm 90$ meV (68\%), which excludes the minimum sum of 58 meV at 99\% confidence. They discuss how this preference for negative masses affects the measurement of cosmic parameters, particularly the optical depth, and explore models of new physics in the neutrino sector, including decay, annihilation, cooling, and time-dependent masses. These models are consistent with current observations but imply new physics accessible in various experiments. The paper also considers the possibility that the apparent signal of negative neutrino masses could arise from new long-range forces in the dark sector or a primordial trispectrum resembling CMB lensing.The paper explores the implications of the Dark Energy Spectroscopic Instrument (DESI) data, combined with cosmic microwave background (CMB) data, on the sum of neutrino masses. The analysis places an upper limit on the sum of neutrino masses, $\sum m_{\nu} < 70$ meV (95\%), and peaks at $\sum m_{\nu} = 0$, suggesting that the minimum sum of 58 meV is excluded at 2$\sigma$. The authors extend the DESI analysis to allow for negative neutrino masses, finding $\sum m_{\nu} = -160 \pm 90$ meV (68\%), which excludes the minimum sum of 58 meV at 99\% confidence. They discuss how this preference for negative masses affects the measurement of cosmic parameters, particularly the optical depth, and explore models of new physics in the neutrino sector, including decay, annihilation, cooling, and time-dependent masses. These models are consistent with current observations but imply new physics accessible in various experiments. The paper also considers the possibility that the apparent signal of negative neutrino masses could arise from new long-range forces in the dark sector or a primordial trispectrum resembling CMB lensing.