# Theoretical Nuclear, Particle, Astrophysics, and Cosmology (NPAC)

**Why is there more matter than antimatter in the universe?**

**What unseen forces were present at the birth of the cosmos but disappeared from view as the universe evolved?**

**Are neutrinos their own antiparticles? How did neutrinos shape the evolution of the cosmos?**

**What is the nature of dark matter and dark energy?**

**Why is the cosmological constant so small?**

The NPAC Theory Group research focuses on questions like these that lie at the interface of nuclear physics, particle physics, astrophysics, and cosmology. This interdisciplinary work encompasses a broad range of topics ranging from physics beyond the Standard Model of fundamental interactions and the elementary particle physics of the early universe to the substructure of protons, neutrons and nuclei as they emerge from Quantum Chromodynamics.

This breadth of research includes a diverse range of topics, including supersymmetry, grand unified theories, and extra spacetime dimensions; theories of electroweak symmetry-breaking and the Higgs boson; the origin of cosmic baryonic matter and dark matter; quantum field theory in non-equilibrium environments and curved spacetime; string cosmology; neutrino properties and interactions; supernovae and Big Bang nucleosynthesis; tests of fundamental symmetries such as CP and lepton number; perturbative QCD and effective field theories. Tying these diverse strands together is a common quest to explain the microphysics of the early universe at the most fundamental level.

NPAC Theory Group members maintain close collaborations with members of the Phenomenology Institute and String Theory group, as well as experimental groups in high energy physics, nuclear and neutrino physics, astrophysics, and cosmology. The next decade promises to be an era of exciting discoveries in these fields, with the possibilities of finding new particles at the Large Hadron Collider, breakdowns of fundamental symmetries in precise low-energy experiments with atomic nuclei, new properties of neutrinos in oscillation experiments and double beta-decay searches, and new properties of the early universe with increasingly detailed maps of the cosmic microwave background.

NPAC Theory Group members are playing leading roles in providing both theoretical guidance to these discovery oriented experimental activities as well as the expertise needed to interpret the results.

We welcome you to join us in this compelling enterprise!