Quantum Monte Carlo calculations with chiral effective field theory interactions
The neutron-matter equation of state connects several physical systems over a wide density range, from cold atomic gases in the unitary limit at low densities, to neutron-rich nuclei at intermediate densities, up to neutron stars which reach supranuclear densities in their core. An accurate descr...
| Main Author: | |
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| Format: | Others |
| Language: | English en |
| Published: |
2015
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| Online Access: | https://tuprints.ulb.tu-darmstadt.de/5011/1/phd_final.pdf Tews, Ingo <http://tuprints.ulb.tu-darmstadt.de/view/person/Tews=3AIngo=3A=3A.html> (2015): Quantum Monte Carlo calculations with chiral effective field theory interactions.Darmstadt, Technische Universität, [Ph.D. Thesis] |
| Summary: | The neutron-matter equation of state connects several physical systems over a wide density
range, from cold atomic gases in the unitary limit at low densities, to neutron-rich nuclei at
intermediate densities, up to neutron stars which reach supranuclear densities in their core. An
accurate description of the neutron-matter equation of state is therefore crucial to describe these
systems. To calculate the neutron-matter equation of state reliably, precise many-body methods
in combination with a systematic theory for nuclear forces are needed. Chiral effective field theory (EFT) is such a theory. It provides a systematic framework for the description of low-energy
hadronic interactions and enables calculations with controlled theoretical uncertainties. Chiral
EFT makes use of a momentum-space expansion of nuclear forces based on the symmetries of
Quantum Chromodynamics, which is the fundamental theory of strong interactions. In chiral
EFT, the description of nuclear forces can be systematically improved by going to higher orders
in the chiral expansion. On the other hand, continuum Quantum Monte Carlo (QMC) methods
are among the most precise many-body methods available to study strongly interacting systems
at finite densities. They treat the Schrödinger equation as a diffusion equation in imaginary time
and project out the ground-state wave function of the system starting from a trial wave function
by propagating the system in imaginary time. To perform this propagation, continuum QMC
methods require as input local interactions. However, chiral EFT, which is naturally formulated
in momentum space, contains several sources of nonlocality.
In this Thesis, we show how to construct local chiral two-nucleon (NN) and three-nucleon (3N)
interactions and discuss results of first QMC calculations for pure neutron systems. We have
performed systematic auxiliary-field diffusion Monte Carlo (AFDMC) calculations for neutron
matter using local chiral NN interactions. By comparing these results with many-body perturbation theory (MBPT), we can study the perturbative convergence of local chiral interactions.
We have shown that soft, low-cutoff potentials converge well and can be reliably used in MBPT,
while harder potentials are less perturbative and have to be treated within AFDMC. We have
also derived consistent local chiral 3N interactions and study these forces in detail. Our results
show that local regulators lead to less repulsion from 3N forces compared to nonlocal 3N forces.
Finally, we present the neutron-matter equation of state based on local chiral NN and 3N interactions using the AFDMC method as well as results for light nuclei and neutron drops. This
work paves the way for systematic QMC calculations with chiral EFT interactions for nuclei and
nucleonic matter. |
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