[SME-JP] Unveiling cosmic origins with the CMB

Unveiling cosmic origins with the CMB

Organiser(s):

David Alonso, Peter Barry, Erminia Calabrese, Anthony Challinor, Jens Chluba

Session type:

Regular

Description:

The cosmic microwave background (CMB) is the most pristine cosmological probe of the early Universe. Travelling since ~400,000 years after the Big Bang, shortly after the Universe became neutral, it contains relic signatures of the physical processes that took place much earlier, at incredibly high energies, as well as unique features allowing us to determine precisely the abundances of the main constituents of our Universe, which govern its evolution on large scales. Fundamental science can be extracted from the CMB in multiple ways. The angular fluctuations in the intensity of the CMB map the density and gravitational potential of the Universe. The anisotropies in the CMB polarisation, unencumbered by emission from late-time extragalactic sources, also carry significant information and are able to place strong constraints on the abundance of particles at early times. Furthermore, the production of gravitational waves in the early Universe would leave a distinct parity-odd signature in the CMB polarisation ("B-modes"). Detecting these B-modes, or placing a sufficiently strong constraint on their amplitude, would be revolutionary to understand cosmic origins, potentially providing evidence for an inflationary origin and giving us a window to study the quantum nature of gravity. Finally, the detailed study of the CMB frequency spectrum - a unique probe not yet unlocked by existing experiments - would allow us to shed light on interactions deep into the pre-recombination era. This could deliver a new test of inflation at scales far smaller than currently observed, and a direct way to study the dynamics of the recombination process, potentially uncovering new physical effects that relate to the tensions in cosmology. 

In the near future, a series of ground-based and satellite-borne CMB experiments promise to deliver new breakthroughs in cosmology and fundamental physics. In the Chilean Atacama Desert, the Simons Observatory will provide wide-area, high-resolution, and high-sensitivity maps of the CMB intensity and polarisation. These will target the small-scale signatures of the early Universe, as well as the evolution of density structures at later times that leave imprints on the CMB through gravitational lensing and scattering processes. Several high-sensitivity small-aperture telescopes will instead specifically measure the large-scale polarised signal, targeting a detection of primordial gravitational waves. The same goal will be sought from space by the LiteBIRD satellite. With a wide frequency coverage and unprecedented sensitivity at large scales, LiteBIRD is poised to detect or rule out entire classes of inflation models. In addition to these, multiple CMB spectrometers are being actively discussed and developed with the ultimate goal to supersede the current long-standing distortion limits by many orders of magnitude and lead to a detection of the expected standard model distortion signals. The UK CMB community is strongly involved in the development of these experiments (with UKRI and UKSA support for participation into Simons Observatory and LiteBIRD), leading key contributions in instrumentation and data analysis. 

This session will cover the most important CMB science cases targeting the primordial Universe, the latest results from current experiments, and the prospects of these near-future observations.

Topic:

Cosmology