Nuclear and Particle Physics, Astrophysics, and Cosmology

Leading research in nuclear, particle, astrophysics, and cosmology theory and simulations

We study the most fundamental physics of the Universe from the tiniest to the largest scales in Nature

Studying the most fundamental physics of the Universe from the tiniest to the largest scales in Nature. We develop and employ the most modern theoretical and computational tools to probe everything from quarks and gluons in nuclei, to dramatic black hole and neutron star mergers emitting gravitational waves; from nuclear structure to rare isotopes; from nuclear fission to nuclear fusion for energy and security; from ghostly neutrinos to the mysterious dark matter in the Universe.

Our group performs research in the following areas:

Astrophysics, Heliophysics & Space Physics

Fan Guo
Hui Li
Xiaocan Li

T2-Plasma Astrophysics Research

Basic Nuclear Theory

Joe Carlson
Stefano Gandolfi
Christopher Lee
Emanuele Mereghetti
Duff Neill
Ingo Tews
Ivan Vitev

The basic nuclear theory effort spans the range of phenomena from quarks & gluons that make up protons & hadrons, to the strongly-interacting plasma of unconfined quarks and gluons that existed shortly after the Big Bang; from the structure and energy levels of nuclei to the equations of state and structure of massive neutron stars and the gravitational wave radiation emitted when they merge dramatically with one another or with black holes; from the study of tiny asymmetries in the charge distributions in neutrons that also reveal the existence of physics beyond the Standard Model, to the origin of the excess matter in the Universe that survived over the antimatter to make up everything we see today.

These studies utilize and advance state-of-the-art theoretical methods and frameworks, including quantum field theory [(in particular, Quantum Chromodynamics (QCD)] to describe the interactions of particles in the nuclear and subnuclear realm, in systems and processes that often exhibit large separations of scales that are rigorously separated into calculable pieces, with controllable uncertainties, through the modern techniques of effective field theory. Large-scale numerical or Monte Carlo calculations, utilizing LANL HPC resources, solving many-body quantum mechanical or field theoretic equations of motion tell us the structure and energy levels of nuclei and the effect of high-order quantum loop corrections to scattering of elementary particles in colliders.

These theoretical studies are tied to, motivate, and are motivated by concurrent and upcoming experimental efforts in the US, some with several billion dollars of expected investment. These include the Relativistic Heavy-Ion Collider (RHIC) and its successor the Electron-Ion Collider (EIC) at Brookhaven; the Facility for Rare-Isotope Beams (FRIB) at Michigan State; the Laser-Interferometer Gravitational-Wave Observatory (LIGO); the LEGEND experiment to search for neutrinoless double beta decay; the Ultracold Neutron (UCN) experiments at LANSCE (the highest intensity UCN sources in the world); and more.

Many of these experiments have heavy LANL involvement and leadership, in both experimental effort and connected theory initiatives. Most of these efforts at LANL involve close, ongoing collaboration between T and P Divisions.

Fundamental Symmetries

Nuclear Structure & Nuclear Astrophysics

Quantum Chromodynamics

High-Energy Physics

Daniele Alves
Tanmoy Bhattacharya
Michael Graesser
Rajan Gupta

Elementary particle or high-energy physics is defined by the quest to discover, at the heart of Nature, the most fundamental particles and forces that govern or underlie all physical phenomena in our Universe. Although the Standard Model (SM) of particle physics (the three known families of quarks & leptons, Higgs boson, and carriers of the electroweak and strong forces) has spectacularly passed every experimental test thrown at it on earth, by itself it signals its own incompleteness as it fails to explain enormous features of our Universe such as the nature of dark matter, the amount of ordinary matter in the Universe, or how gravity, the weakest and yet most influential force on large scales in the Universe, fits in a consistent quantum description with the other particles and forces.

The quest to uncover signals of new physics beyond the SM is shared with nuclear physics (NP), especially the fundamental symmetry thrust in NP. High-energy physics strategies for discovering new physics are focused on high-energy particle colliders that attempt to directly create new particles by creating enormous energy that may convert into new heavy particles, as well as large-scale, heavy, or novel detectors that may register signatures of interactions with elusive dark matter particles (such as axions). The detection of such subtle signatures requires innovation in quantum sensing technologies, in computational technologies to tease small signals out of enormously large data sets, and high-precision field theoretic computations of SM backgrounds to ensure maximal signal-to-background ratios. 

The NPAC group performs research into developing theoretical models of new physics particles and forces, motivating new detection methods and technologies to expand the parameter space of dark matter or new physics particles that we can have sensitivity to, and, notably, in large-scale lattice computations of fundamental quantities in quantum field theory (QFT) that must be known precisely in order to make predictions for observations aimed at BSM discoveries and to interpret measurements in terms of fundamental theoretical descriptions.

These areas of leadership in lattice QCD/QFT and BSM model building are closely linked to the expertise of the nuclear theory team in Effective Field Theory (especially Standard Model EFT and chiral EFT) that ties together physics at low-energy scales where many observations are made (and properties and interactions of neutrons, protons, and other hadrons are computed in lattice QCD) to the high-energy scales where new physics particles and forces should exist. EFT makes these connections across scales in a rigorous, calculable manner with computable uncertainties, crucial for reliable scientific interpretation and discoveries.

Particle, nuclear, and astrophysics all bear on and are intertwined in the quest to find BSM physics, and new computational technologies not only in classical lattice field theory but also machine-learning-enhanced techniques and quantum computing techniques will be required to tackle the numerical and nonperturbative predictions required in this effort.

Lattice Gauge Theory

Physics Beyond the Standard Model, Dark Matter, Neutrinos

Nuclear Reactions and Nuclear Data

Gerald Hale
Michal Herman
Toshihiko Kawano
Amy Lovell
Mark Paris
Hirokazu Sasaki

The T-2 Nuclear Data team develops the underlying physical theory for fission and fusion reactions, and our evaluation of the world’s data on nuclear reactions provides the cross sections that are used in simulations crucial for the weapons and stockpile modernization programs of the Laboratory. Our effort in radiochemistry diagnostics of inertial confinement fusion experiments use nuclear physics to open a window into the core of these reactions that are otherwise inaccessible to observation.

Light Elements

Left: nuclear reactivities in light element fusion, credit: M. Paris. Right: Experimental data on neutron emission from ICF reaction, credit: [ask Mark]

Heavy Elements 

Supercomputer simulations of fission and emission of neutrons, credit: I. Stetcu and collaborators

Uncertainty Quantification

Applications of Nuclear, Particle & Astrophysics

Anna Hayes-Sterbenz
Gerard Jungman
Hui Li
Joshua Martin
Mark Paris

Inertial Confinement Fusion

Inside the target chamber of the National Ignition Facility at Lawrence Livermore National Laboratory, 192 ultraviolet lasers converge on a small target assembly containing a fuel capsule just a few millimeters in diameter. CREDIT: Lawrence Livermore National Laboratory / 1663 Magazine

A deuterium-tritium fusion reaction produces a helium nucleus and a 14-megaelectronvolt (MeV) neutron. This high-energy neutron usually flies out of the fuel capsule, but on rare occasion, the neutron collides with another nucleus—deuterium, say—outside the core where fusion normally takes place, giving the deuterium nucleus extra energy.

If the deuterium then collides with a tritium nucleus, the collision carries sufficient energy to spawn another fusion reaction, producing an even higher-energy neutron, up to 30 MeV. By using special thulium and bismuth foils, the passage of the neutron and some information about its energy can be recorded. From that information, scientists can tease out key properties of the matter undergoing fusion. Credit: 1663 Magazine

Electron densities in plasmas at National Ignition Facility [left] and brown dwarf stars [right].