Cosmogenic neutrinos are produced when ultra-high-energy cosmic rays ( UHECRs ) interact with cosmological photon fields .
Limits on the diffuse flux of these neutrinos can be used to constrain the fraction of protons arriving at Earth with energies E _ { p } \gtrsim 30 \text { EeV } , thereby providing bounds on the composition of UHECRs without fully relying on hadronic interaction models .
We show to which extent current neutrino telescopes already constrain this fraction of protons and discuss the prospects for next-generation detectors to further constrain it .
Additionally , we discuss the implications of these limits for several popular candidates for UHECR source classes .