## Pairing Forces in Quantum Dimer Bound States Studied

by Tommy on 29/12/2016This result has helped me immensely, and it actually got some press already.

https://arxiv.org/abs/1612.08004

Effective forces between quantum bound states, Alexander Rokash, Evgeny Epelbaum, Hermann Krebs and Dean Lee (23 December 2016)

Recent ab initio lattice studies have found that the interactions between alpha particles (

^{4}He nuclei) are quite sensitive to the details of the nucleon-nucleon force. In order to understand the underlying physics, we study a simple model involving two-component fermions in one spatial dimension. We probe the interaction between two bound dimers for several different particle-particle interactions. We measure an effective potential between the dimers using external point potentials which act as numerical tweezers. We find that the strength and range of the local or nearly local part of the particle-particle interactions play a large role in shaping the interactions between the dimers and can even determine the overall sign of the effective potential.

**See also**: https://arxiv.org/abs/1602.04539

http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.117.132501

Nuclear binding near a quantum phase transition, Serdar Elhatisari, Ning Li, Alexander Rokash, Jose Manuel Alarcón, Dechuan Du, Nico Klein, Bing-nan Lu, Ulf-G. Meißner, Evgeny Epelbaum, Hermann Krebs, Timo A. Lähde, Dean Lee and Gautam Rupak, Phys. Rev. Lett., 117, 132501 (19 September 2016), doi:10.1103/PhysRevLett.117.132501

lifeform@charter.netHow do protons and neutrons bind to form nuclei? This is the central question of ab initio nuclear structure theory. While the answer may seem as simple as the fact that nuclear forces are attractive, the full story is more complex and interesting. In this work we present numerical evidence from ab initio lattice simulations showing that nature is near a quantum phase transition, a zero-temperature transition driven by quantum fluctuations. Using lattice effective field theory, we perform Monte Carlo simulations for systems with up to twenty nucleons. For even and equal numbers of protons and neutrons, we discover a first-order transition at zero temperature from a Bose-condensed gas of alpha particles (

^{4}He nuclei) to a nuclear liquid. Whether one has an alpha-particle gas or nuclear liquid is determined by the strength of the alpha-alpha interactions, and we show that the alpha-alpha interactions depend on the strength and locality of the nucleon-nucleon interactions. This insight should be useful in improving calculations of nuclear structure and important astrophysical reactions involving alpha capture on nuclei. Our findings also provide a tool to probe the structure of alpha cluster states such as the Hoyle state responsible for the production of carbon in red giant stars and point to a connection between nuclear states and the universal physics of bosons at large scattering length.

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