Subleading contributions to the nuclear scalar isoscalar currents

We extend our recent analyses of the nuclear vector, axial-vector and pseudoscalar currents and derive the leading one-loop corrections to the two-nucleon scalar current operator in the framework of chiral effective field theory using the method of unitary transformation. We also show that the scalar current operators at zero momentum transfer are directly related to the quark mass dependence of the nuclear forces.Comment: 14 pages, 6 figure

Ground state energy of dilute neutron matter at next-to-leading order in lattice chiral effective field theory

We present lattice calculations for the ground state energy of dilute neutron matter at next-to-leading order in chiral effective field theory. This study follows a series of recent papers on low-energy nuclear physics using chiral effective field theory on the lattice. In this work we introduce an improved spin- and isospin-projected leading-order action which allows for a perturbative treatment of corrections at next-to-leading order and smaller estimated errors. Using auxiliary fields and Euclidean-time projection Monte Carlo, we compute the ground state of 8, 12, and 16 neutrons in a periodic cube, covering a density range from 2% to 10% of normal nuclear density.Comment: 34 pages, 8 figures, journal version to appear in Eur. Phys. J.

Lattice chiral effective field theory with three-body interactions at next-to-next-to-leading order

We consider low-energy nucleons at next-to-next-to-leading order in lattice chiral effective field theory. Three-body interactions first appear at this order, and we discuss several methods for determining three-body interaction coefficients on the lattice. We compute the energy of the triton and low-energy neutron-deuteron scattering phase shifts in the spin-doublet and spin-quartet channels using Luescher's finite volume method. In the four-nucleon system we calculate the energy of the alpha particle using auxiliary fields and projection Monte Carlo.Comment: 33 pages, 9 figure

Towards consistent nuclear interactions from chiral Lagrangians I: The path-integral approach

Low-energy nuclear interactions have been extensively studied in the framework of chiral effective field theory. The corresponding potentials have been worked out using dimensional regularization to evaluate ultraviolet divergent loop integrals. An additional cutoff is then introduced in the nuclear Schr\"odinger equation to calculate observables. Recently, we have shown that such a mixture of two regularization schemes violates chiral symmetry when applied beyond the two-nucleon system and/or to processes involving external probes. To solve this issue, three- and four-nucleon forces as well as exchange current operators need to be re-derived using symmetry-preserving cutoff regularization. While it is possible to introduce a symmetry-preserving cutoff already in the effective chiral Lagrangian, the appearance of high-order time derivatives of the pion field, caused by the regulator, makes the standard Hamiltonian-based methods not well suited for the calculation of nuclear potentials. Here, we propose a new approach to derive nuclear interactions using the path integral method with no reliance on the canonical quantization. To this aim, the interaction part of the action is brought to an instantaneous form via suitably chosen nonlocal field redefinitions. Loop contributions to the nuclear potentials are then generated through the functional determinant, induced by the field redefinitions. We discuss in detail the application of these ideas to the case of a regularized Yukawa-type model of pion-nucleon interactions. Our new method allows to perform a systematic quantum mechanical reduction within the quantum field theory framework and opens the way for deriving consistently regularized nuclear forces and current operators from the effective chiral Lagrangian.Comment: 22 pages, 2 figure

Finite volume effects in low-energy neutron-deuteron scattering

We present a lattice calculation of neutron-deuteron scattering at very low energies and investigate in detail the impact of the topological finite-volume corrections. Our calculations are carried out in the framework of pionless effective field theory at leading order in the low-energy expansion. Using lattice sizes and a lattice spacing comparable to those employed in nuclear lattice simulations, we find that the topological volume corrections must be taken into account in order to obtain correct results for the neutron-proton S-wave scattering lengths.Comment: 16 pages, 6 figure