NPLQCD
Nuclear Physics with Lattice QCD

Nuclear Physics with Lattice QCD

Quantum Chromodynamics (QCD) is the underlying theory governing the interaction between quarks and gluons, the strong force, and therefore, responsible for all the states of matter in the Universe. Analytical solutions of QCD in the low energy regime cannot be obtained due to the complexity of the quark-gluon dynamics. The only known non-perturbative method that systematically implements QCD from first principles is its formulation on a discretized space-time, lattice QCD. This numerical simulation of the theory consists in a Monte Carlo evaluation of a functional integral. Our goal is to extract information on hadronic interactions, relevant to nuclear processes, through Lattice QCD, using the enormous computing capabilities that the most modern supercomputers offer us, specially on those sectors where experiments are difficult to perform.

Recent results:

In Evidence for a Bound H Dibaryon from Lattice QCD (Phys. Rev. Lett. 106, 162001 (2011)) we presented evidence for the existence of a bound H-dibaryon, an I=0, J=0, s=-2 state with valence quark structure uuddss. The infinite volume extrapolation of the results of Lattice QCD calculations performed on four ensembles of anisotropic clover gauge-field configurations, with spatial extents of 2.0, 2.5, 3.0 and 3.9 fm at a spatial lattice spacing of 0.123 fm, lead to an H-dibaryon bound by 16.6 ± 2.1 ± 4.6 MeV at a pion mass of 389 MeV. In the figure, the results of the Lattice QCD calculations of -i cot(δ) versus (q/m_π)² at the two larger lattice sizes, along with the infinite-volume extrapolation (red point). The dark (blue) (light (green)) lines correspond to the statistical (systematic and statistical uncertainties combined in quadrature) 68% coincidence intervals calculated.

Recent results:

In I=2 ππ S-wave Scattering Phase Shift from Lattice QCD we calculated the π⁺π⁺ scattering amplitude using Lattice QCD over a range of momenta below the inelastic threshold. In the figure, we compare the experimental data with our Lattice QCD prediction for the phase shift at the physical value of the pion mass, m_π ∼ 140 MeV using NLO χPT, as a function of the squared center-of-mass momentum. The statistical and systematic uncertainties have been combined in quadrature. The red vertical line denotes the inelastic 4π threshold. Our predictions for the threshold scattering parameters, and hence the leading three terms in the Effective Range Expansion, are consistent with determinations using the Roy equations (inner blue and purple bands in the figure) and the predictions of χPT (solid purple curve).