Survey of the He8 properties within a microscopic multiphonon approach

Bulk properties, spectrum, and nuclear response of $^{8}\mathrm{He}$ are investigated within the equation of motion phonon method, which generates an orthonormal basis of $n$-phonon states ($n=0,1,2,3...$) whose constituents are Tamm-Dancoff phonons. The basis is free of any contamination induced by the center-of-mass motion, in virtue of a procedure exploiting the singular value decomposition of rectangular matrices. A self-consistent calculation is performed within a space spanned by a basis of $n$-phonon states up to $n=3$ using a potential derived from the chiral effective field theory. The Hartree-Fock single-particle states are obtained from a harmonic-oscillator space including all major shells up to ${N}_{max}=12$. The calculation is exact up to $n=2$, whereas the three-phonon ($n=3$) states are assumed to be composed of noninteracting $n=1$ and $n=2$ constituent phonons. It yields bulk and spectroscopic observables consistent with the available experimental data and provides an electric dipole response exhibiting distinctive signatures.