  We formulate microscopic optical potentials for nucleon-nucleus scattering
from chiral two- and three-nucleon forces. The real and imaginary central terms
of the optical potentials are obtained from the nucleon self energy in infinite
nuclear matter at a given density and isospin asymmetry, calculated
self-consistently to second order in many-body perturbation theory. The real
spin-orbit term is extracted from the same chiral potential using an improved
density matrix expansion. The density-dependent optical potential is then
folded with the nuclear density distributions of 40Ca, 42Ca, 44Ca, and 48Ca
from which we study proton-nucleus elastic scattering and total reaction cross
sections using the reaction code TALYS. We compare the results of the
microscopic calculations to those of phenomenological models and experimental
data up to projectile energies of E = 180 MeV. While overall satisfactory
agreement with the available experimental data is obtained, we find that the
elastic scattering and total reaction cross sections can be significantly
improved with a weaker imaginary optical potential, particularly for larger
projectile energies.
