What is the fine-grained topic of the following text: Observations of the CMB can be used to gather evidence for gravitational waves released by an early period of inflation, and can be used to constrain the neutrino mass and the understand the growth of structure and dark energy. Only return the topic.
Observations of the Cosmic Microwave Background (CMB) for Evidence of Gravitational Waves and Understanding Neutrino Mass, Structure Growth, and Dark Energy