Alpha-particle condensation in light hypernuclei

Gas-like α-cluster states are investigated in light Λ hypernuclei. The α condensate-type microscopic cluster model wave function is introduced to describe Λ hypernuclei. In particular, the analogous state to the famous Hoyle state, the second ^{0 +} state in ¹²C, is investigated in ¹³_ΛC, with the use of the new type wave function. The Hoyle state is known to have a gas-like 3α cluster structure, where the 3α particles are condensed into an identical S orbit. The second 1/^{2 +} state in ¹³_ΛC is shown to have the 3α + Λ structure. A strong shrinkage effect by adding the Λ particle is seen for the state, reducing the rms radius from 3.8 fm in the Hoyle state to 2.8 fm. In spite of the shrinkage effect, the α condensate fraction of about 60% still survives, though it is reduced by about 20% from the Hoyle state.