Spectral function for 4He using the Chebyshev expansion in coupled-cluster theory

We compute spectral function for 4He by combining coupled-cluster theory with an expansion of integral transforms into Chebyshev polynomials. Our method allows us to estimate the uncertainty of spectral reconstruction. The properties of the Chebyshev polynomials make the procedure numerically stable and considerably lower in memory usage than the typically employed Lanczos algorithm. We benchmark our predictions with other calculations in the literature and with electron-scattering data in the quasi-elastic peak. The spectral function formalism allows one to extend ab initio lepton-nucleus cross sections into the relativistic regime. This makes it a promising tool for modeling this process at higher-energy transfers. The results we present open the door for studies of heavier nuclei, important for the neutrino oscillation programs.

Automated summary

We computed the spectral function for 4He using coupled-cluster theory and an expansion of integral transforms into Chebyshev polynomials. Our method provides an estimation of the uncertainty in spectral reconstruction. The Chebyshev polynomials make the procedure numerically stable and more memory efficient than the commonly used Lanczos algorithm. We compared our predictions with other calculations and electron-scattering data, and found good agreement. The spectral function formalism has the potential to extend lepton-nucleus cross sections into the relativistic regime, making it a valuable tool for modeling processes with higher-energy transfers. These results are significant for neutrino oscillation programs, as they open the door for studying heavier nuclei.