Snowmass 2021 Cosmic Frontier White Paper: Cosmology with
  Millimeter-Wave Line Intensity Mapping
  Next-generation tests of fundamental physics and cosmology using large scale
structure require measurements over large volumes of the Universe, including
high redshifts inaccessible to present-day surveys. Line intensity mapping, an
emerging technique that detects the integrated emission of atomic and molecular
lines without resolving sources, can efficiently map cosmic structure over a
wide range of redshifts. Observations at millimeter wavelengths detect far-IR
emission lines such as CO/[CII], and take advantage of observational and
analysis techniques developed by CMB experiments. These measurements can
provide constraints with unprecedented precision on the physics of inflation,
neutrino masses, light relativistic species, dark energy and modified gravity,
and dark matter, among many other science goals. In this white paper we
forecast the sensitivity requirements for future ground-based mm-wave intensity
mapping experiments to enable transformational cosmological constraints. We
outline a staged experimental program to steadily improve sensitivity, and
describe the necessary investments in developing detector technology and
analysis techniques.
