Weighing Neutrinos by the Cosmic Web express
The Universe is a colossal web of invisible dark matter and galaxies, stretched by the expansion of space. Neutrinos, nearly intangible ghost particles, barely cling to the threads, but their collective mass subtly shifts the tension of the entire network.
Instead of bright nodes, scientists studied the voids between the strands. The shape of these "gaps" turned out to be highly sensitive to neutrino mass: heavier particles smooth out their edges. Using a method akin to unraveling a complex tapestry into individual stitches, researchers, even on a tiny patch of simulation (a cube half a billion light-years across), managed to estimate the neutrino mass with an error of 0.05 electronvolts — millions of times lighter than an electron.
Real sky surveys will allow us to check whether the Standard Model of physics is breaking down.
Original abstract
as written by the authors arXiv:2604.02300
Cosmological constraints on neutrino mass offer a promising avenue for advancing our understanding of both fundamental particle physics and the evolution of cosmic large-scale structure. To overcome challenges associated with traditional probes of neutrino mass, particularly degeneracies with other parameters, we consider topological summaries of the cosmic web based on the formalism of persistent homology. We introduce persistence strips, a novel representation that segments Betti curves by topological persistence, effectively condensing two-dimensional persistence diagrams into a set of one-dimensional curves. Applied to the FLAMINGO suite of cosmological simulations, these topological descriptors demonstrate pronounced sensitivity to neutrino mass. By constructing an emulator spanning a 10-dimensional $$w_0 w_a\text{CDM} + u$$ cosmological parameter space that includes parameters degenerate with neutrino masses in conventional approaches, assuming a volume of only $$(350 \, \mathrm{Mpc})^3$$, we obtain neutrino mass constraints with an uncertainty of $$0.05 \, \mathrm{eV}$$ for the total matter field and $$0.13 \, \mathrm{eV}$$ for the dark matter-only field, with the strongest constraints coming from void topology. Persistence strips exhibit roughly twice the constraining power of unbinned Betti curves and, through their multi-scale, environment-dependent sensitivity, systematically break degeneracies between neutrino mass and other cosmological parameters. We pinpoint the precise physical origin of the signal, identifying two equally important contributions: sensitivity to the neutrino mass fraction, which is highest in underdense regions, and the impact of neutrinos on the distribution of dark matter. Our findings highlight the particular promise of applying topological statistics to weak lensing measurements, which directly probe the total matter distribution.
Every second, about a hundred billion neutrinos pass through a human fingernail without a single collision.