Lawrence Livermore National Laboratory



Pavlos Vranas

Overview

This project addressed one of the central questions in physics today: the lack of antimatter relative to matter in the universe. If antimatter and matter existed in equal amounts, they would have annihilated into radiation and we would not exist today. The DOE is funding experiments to investigate processes that could lead to a lepton number violation (to explain the matter–antimatter imbalance) and the resulting neutrino-less double beta (0νββ) decay signal that may be observed. However, even if the 0νββ decay is detected in these experiments, the physics mechanism that violates the lepton number would not be known as there are several candidates.

Calculating the event rate for 0νββ decays for candidate theories involving heavy particle exchange requires large-scale lattice simulations of the underlying fundamental theory of quantum chromodynamics (QCD). We performed these simulations on Lawrence Livermore National Laboratory's supercomputers and calculated the necessary matrix elements of short-range operators that arise from the exchange of heavy mediators that contribute to 0νββ decay via the leading pion exchange diagrams. Our published results can be used as input to field theory calculations to calculate the 0νββ decay rate for the nuclei involved in the various experimental detectors.

To perform this research, we developed codes for the new CPU-GPU CORAL machines. Our innovative and highly optimized code and methods were selected as one of the six international finalists for the 2018 Gordon Bell Prize competition, the highest prize in scientific supercomputing. Our efforts supported the preparation of the Laboratory's new Sierra and Lassen supercomputers by identifying hardware and software problems. Aiming towards the next step of this research, involving the sub-leading nucleon–nucleon direct vertex, we developed algorithms and codes that will play a significant role in future lattice QCD calculations involving nucleon–nucleon interactions.

Impact on Mission

Our work supports the Laboratory's core competencies in nuclear, chemical, and isotopic science and technology and advances Livermore's core competencies in high-performance computing, simulation, and data science. Our results are also relevant to DOE's search for the 0νββ decay and future nuclear systems research.

Publications, Presentations, Etc.

Appelquist, T., et al. 2018. "Nonperturbative Investigations of SU(3) Gauge Theory with Eight Dynamical Flavors." Physical Review D. LLNL-JRNL-753511.

Berkowitz, E., et al. 2017. "Mobius Domain-Wall Fermions on Gradient-Flowed Dynamical HISQ Ensembles." Physical Review D. LLNL-JRNL-719521.

——— . 2017. "Calm Multi-Baryon Operators." LATTICE 2017, Granada, Spain, June 2018. LLNL-PROC-763057.

——— . 2017. "An Accurate Calculation of the Nucleon Axial Charge with Lattice Quantum Chromodynamics." Nature. LLNL-JRNL-719521.

——— . 2018. "Simulating the Weak Death of the Neutron in a Femtoscale Universe with Near-Exascale Computing." Supercomputing 2018: LLNL-JRNL-749850.

——— . 2018. "Gauged and Ungauged: A Nonperturbative Test." Journal of High Energy Physics. LLNL-JRNL-747004.

——— . 2018. "Simulating the Weak Death of the Neutron in a Femtoscale Universe with Near-Exascale Computing." Supercomputing 2018. LLNL-JRNL-749850.

Monge-Camacho, H., et al. 2018. "Short Range Operator Contributions to 0vBB Decay from LQCD.2." The 36th Annual International Symposium on Lattice Field Theory LATTICE 2018, East Lansing, MI. LLNL-PROC-772237.

Nicholson, A., et al. 2018. "Symmetries and Interactions from Lattice QCD." Conference on the Intersections of Particle and Nuclear Physics, Palm Springs, CA, May/June 2018. LLNL-CONF-764382.

—— 2018. "Heavy Physics Contributions to Neutrinoless Double Beta Decay from QCD." Physical Review Letters 121 (17): 172501. LLNL-JRNL-751220.

Vranas, P. 2018. "Toward Holographic Reconstruction of Bulk Geometry from Lattice Simulations." J. High Energy Phys. doi: 10.1007/JHEP02(2018)042. LLNL-JRNL-732009.