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Register a new userMicroscopic optical potential for exotic isotopes from chiral effective field theory
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We compute the isospin-asymmetry dependence of microscopic optical model potentials from realistic chiral two- and three-body interactions over a range of resolution scales $Lambda simeq 400-500$,MeV. We show that at moderate projectile energies, $E_{rm inv} = 110 - 200$,MeV, the real isovector part of the optical potential changes sign, a phenomenon referred to as isospin inversion. We also extract the strength and energy dependence of the imaginary isovector optical potential and find no evidence for an analogous phenomenon over the range of energies, $E leq 200$,MeV, considered in the present work. Finally, we compute for the first time the leading corrections to the Lane parametrization for the isospin-asymmetry dependence of the optical potential and observe an enhanced importance at low scattering energies.
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The energy- and density-dependent single-particle potential for nucleons is constructed in a medium of infinite isospin-symmetric nuclear matter starting from realistic nuclear interactions derived within the framework of chiral effective field theory. The leading-order terms from both two- and three-nucleon forces give rise to real, energy-independent contributions to the nucleon self-energy. The Hartree-Fock contribution from the two-nucleon force is attractive and strongly momentum dependent, in contrast to the contribution from the three-nucleon force which provides a nearly constant repulsive mean field that grows approximately linearly with the nuclear density. Together, the leading-order perturbative contributions yield an attractive single-particle potential that is however too weak compared to phenomenology. Second-order contributions from two- and three-body forces then provide the additional attraction required to reach the phenomenological depth. The imaginary part of the optical potential, which is positive (negative) for momenta below (above) the Fermi momentum, arises at second-order and is nearly inversion-symmetric about the Fermi surface when two-nucleon interactions alone are present. The imaginary part is strongly absorptive and requires the inclusion of an effective mass correction as well as self-consistent single-particle energies to attain qualitative agreement with phenomenology.
A microscopic optical potential (OP) is derived from NN chiral potentials at the first-order term within the spectator expansion of the multiple scattering theory and adopting the impulse approximation. The performances of our OP are compared with those of a phenomenological OP in the description of elastic proton scattering data on different isotopic chains. An analogous scheme is adopted to construct a microscopic OP for elastic antiproton-nucleus scattering. The results of our OPs are in reasonably good agreement with the experimental data, for both elastic proton and antiproton-nucleus scattering.
Since the pioneering work of Weinberg, Chiral Effective Field Theory ($chi$EFT) has been widely and successfully utilized in nuclear physics to study many-nucleon interactions and associated electroweak currents. Nuclear $chi$EFT has now developed into an intense field of research and is applied to study light to medium mass nuclei. In this contribution, we focus on the development of electroweak currents from $chi$EFT and present applications to selected nuclear electroweak observables.
We construct nucleonic microscopic optical potentials by combining the Greens function approach with the coupled-cluster method for $rm{^{40}Ca}$ and $rm{^{48}Ca}$. For the computation of the ground-state of $rm{^{40}Ca}$ and $rm{^{48}Ca}$, we use the coupled-cluster method in the singles-and-doubles approximation, while for the A = $pm 1$ nuclei we use particle-attached/removed equation-of-motion method truncated at two-particle-one-hole and one-particle-two-hole excitations, respectively. Our calculations are based on the chiral nucleon-nucleon and three-nucleon interaction $rm{NNLO_{sat}}$, which reproduces the charge radii of $^{40}$Ca and $^{48}$Ca, and the chiral nucleon-nucleon interaction $rm{NNLO_{opt}}$. In all cases considered here, we observe that the overall form of the neutron scattering cross section is reproduced for both interactions, but the imaginary part of the potential, which reflects the loss of flux in the elastic channel, is negligible. The latter points to neglected many-body correlations that would appear beyond the coupled-cluster truncation level considered in this work. We show that, by artificially increasing the parameter $eta$ in the Greens function, practical results can be further improved.
The Pauli rearrangement potential given by the second-order diagram is evaluated for a nucleon optical model potential (OMP) with $G$ matrices of the nucleon-nucleon interaction in chiral effective field theory. The results obtained in nuclear matter are applied for $^{40}$Ca in a local-density approximation. The repulsive effect is of the order of 5MeV at the normal density. The density dependence indicates that the real part of the microscopic OMP becomes shallower in a central region, but is barely affected in a surface area. This improves the overall resemblance of the microscopic OMP to the empirical one.
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