Ab initio methods (nuclear physics): Difference between revisions

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{{Nuclear physics}}

In [[nuclear physics]], '''ab initio methods''' seek to describe the [[atomic nucleus]] from the groundbottom up by solving the non-relativistic [[Schrödinger equation]] for all constituent [[nucleon]]s and the forces between them. This is done either exactly for very light nuclei (up to four nucleons) or by employing certain well-controlled approximations for heavier nuclei. Ab initio methods constitute a more fundamental approach compared to e.g. the [[nuclear shell model]]. Recent progress has enabled ab initio treatment of heavier nuclei such as [[isotopes of nickel|nickel]].<ref name=navratil2016>{{cite journal|first1=P.|last1=Navrátil|first2=S.|last2=Quaglioni|first3=G.|last3=Hupin|first4=C.|last4=Romero-Redondo|first5=A.|last5=Calci|title=Unified ab initio approaches to nuclear structure and reactions|journal=Physica Scripta|volume=91|issue=5|pages=053002|year=2016|doi=10.1088/0031-8949/91/5/053002|arxiv=1601.03765|bibcode=2016PhyS...91e3002N}}</ref>

A significant challenge in the ab initio treatment stems from the complexities of the inter-nucleon interaction. The [[nuclear force|strong nuclear force]] is believed to emerge from the [[strong interaction]] described by [[quantum chromodynamics]] (QCD), but QCD is non-perturbative in the low-energy regime relevant to nuclear physics. This makes the direct use of QCD for the description of the inter-nucleon interactions very difficult (see [[lattice QCD]]), and a model must be used instead. The most sophisticated models available are based on [[chiral perturbation theory|chiral effective field theory]]. This [[effective field theory]] (EFT) includes all interactions compatible with the symmetries of QCD, ordered by the size of their contributions. The degrees of freedom in this theory are nucleons and [[pion]]s, as opposed to [[quark]]s and [[gluon]]s as in QCD. The effective theory contains parameters called low-energy constants, which can be determined from scattering data.<ref name=navratil2016 /><ref name=machleidt2011>