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We thoroughly study the photo-disintegration of $^4$He on the cosmicmicrowave background using the most recent cross-section data both from theinclusive measurement observing the analog of the giant dipole resonance in$^4$He through the charge-exchange spin-flip $^4$He ($^7$Li,$^7$Be) reactionand from measurements of exclusive two-body and three-body processes: $^4{\rmHe} \, (\gamma,p)\, ^3{\rm H}$, $^4{\rm He} \, (\gamma,n) \, ^3{\rm He}$, and$^4$He $(\gamma, pn)$ $^2$H. We show that the present-day (redshift $z=0$) meanfree path of ultra-relativistic (Lorentz factor $\sim 10^{10}$) helium nucleiincreases by more that $15\%$ with respect to previous estimates adopted asbenchmarks for Monte Carlo simulation codes of ultrahigh-energy cosmic raypropagation. This implies that the physical survival probability of $^4$Henuclei would be larger than predicted by existing event generators. Forexample, for $E \sim 10^{10.8}~{\rm GeV}$ and a propagation distance of 3.5Mpc, the $^4$He intensity would be $35\%$ larger than the output of CRPropa 3program and $42\%$ larger than the output of SimProp v2r4 program. We providenew parametrizations for the two-body and three-body photo-disintegrationcross-sections of $^4$He, $^3$He, tritium, and deuterium.

The photo-disintegration of $^4$He on the cosmic microwave background is less severe than earlier thought