Two Nucleon Interactions and Their Effect on the Visible Universe and the Dark Universe

Project Overview

Our universe as we see it around us today has beautiful structures, galaxies, stars, planets, and life. It all started from a featureless primordial soup of particles called quarks and gluons. As the universe expanded and cooled down the quarks and gluon coalesced into the familiar nuclear particles, the protons, and neutrons (collectively called nucleons) under the very strong force of quantum chromodynamics (QCD). As time passed, the universe evolved to what it is today. That evolution would not have been the same, or not have happened at all if the parameters of nature were not tuned and were even a little bit different. The existence of this tuning is a tantalizing mystery and a most prominent question in physics. Chief among those parameters are the ones resulting from the interaction of protons and neutrons that allow them to combine to larger structures and form the nuclei of all elements. In contrast, dark matter, a mysterious invisible substance that permeates our universe, did not evolve the same way. Gravitational observations suggest that it is mainly featureless (no structure). Why did dark matter evolve to not have structure, but ordinary matter does? Is it possible that the dark matter parameters were not tuned in a way that it could develop structure today?

We used Lawrence Livermore National Laboratory's fastest supercomputers and the methods of lattice gauge theory to calculate the interactions of ordinary protons and neutrons, as well as generate the vacuum states of their possible "dark matter" counterparts. These simulations were possible for the first time because of the new generation of supercomputers (Lassen), and the highly efficient codes and algorithms we developed. We have found that ordinary matter interactions depend on the value of the quark mass in an important way. For heavy, unphysical, quark mass, ordinary matter does not form the first nuclear bound state, the deuteron, which is comprised of a proton and a neutron. Without the deuteron our world would have been drastically different, and we wouldn't exist today. In nature, the quark mass is light, and the deuteron exists as a bound state. Therefore, we have found clear evidence of tuning in the quark mass. In addition, we performed the very first numerical simulations of the vacuum states of our dark matter theory, stealth dark matter (SDM). These will serve as the starting point of further investigations of SDM.

Mission Impact

This research shed light on one of the most prominent questions in physics: the tuning in the interactions of protons and neutrons that allow them to combine to larger nuclei, such as the deuteron, the lightest stable nuclear particle consisting of one proton and one neutron. It also shed light on the theory of stealth dark matter (SDM) by exhibiting that the theory can be in the non-plasma, cold, phase. In addition, this work is the first and necessary step towards building our quantitative understanding of nuclear physics upon the fundamental theory of quarks and gluons, QCD (quantum chromodynamics) using lattice gauge theory methods (LQCD). Following this effort there are many quantities of interest, which are not constrained well from experiment, but where LQCD can provide critical input. This can enable us to make predictions of the structure and reactions of nuclei directly from QCD coupled with theories of ab initio nuclear physics and produce nuclear data for Livermore's libraries. This is aligned with Livermore's mission. The algorithms that were developed can be used by a wider group of researchers and have pointed to the benefits of the new direction of machine learning, a prominent new direction at the Laboratory. The research was published in a refereed scientific journal (Physical Review C) and was presented in two talks at the 38th International Symposium on Lattice Field Theory, adding to Livermore's already high scientific visibility. Furthermore, research conducted in this LDRD opened a wealth of research that is fully aligned with the DOE Office of Science Nuclear Physics and High Energy Physics stated missions. Finally, this research continued fostering and growing the two large U.S. lattice collaborations that the principal investigator and external collaborators have established and are leading, the CalLat (California Lattice) and Lattice Strong Dynamics (LSD) collaborations.

Publications, Presentations. and Patents

CalLat collaboration, "Two-nucleon S-wave interactions at the SU(3) flavor-symmetric point: a first lattice QCD calculation with the stochastic Laplacian Heaviside method," Phys. Rev. C, vol. 103, no. 014003, 2021.

B. Hoerz, "Spectroscopy and Hadron Interactions," Presented and to appear in the Proceedings of the 38th International Symposium on Lattice Field Theory , 2021.

K. Cushman, "BB scattering at Nc=4 for Stealth Dark Matter," Presented and to appear in the Proceedings of the 38th International Symposium on Lattice Field Theory, 2021.