We report on our calculation of the hypertriton partial decay rate Γ(Hyp --> 3He + π^-).Our calculation uses full three-body hypertriton and 3He wave functions,computed with the no-core shell model (NCSM) and taking as input the NNLOsim NN+NNN and LO YN effective field theory Hamiltonians.

The hypertriton wave function includes Σ-Λ admixtures,and we consider both weak vertices in the matrix element, Λ→N + πand Σ→N+π. The small Sigma probability in the hypertriton, P<0.5%,enhances the decay rate by about 10%. This effect is morethan countered when the Coulomb distortion of the outgoingpion wave is considered, which decreases the rate by ~15%.

Considering both effects, the decay rate evaluates to Γ=1.265 GHz.Γ is found to be strongly correlated with the Lambda separation energyB(Λ), not precisely determined by the state of the art nuclear Hamiltonians.This can be tracked down to the main contribution to the matrix element,coupling the deuteron-baryon components of hypertriton and ^3He amplitudes.Using the world average ratio R_3=Γ(Hyp --> 3Ηe+ π^-)/Γ_{π^-}(Hyp)=0.35 ± 0.04and the isospin ΔI=1/2 rule, we derive a value for the hypertriton lifetimeand show how it correlates with B(Λ).