Probing Cosmic Inflation with the LiteBIRD Cosmic Microwave Background Polarization Survey (2202.02773v3)

Abstract: LiteBIRD, the Lite (Light) satellite for the study of B-mode polarization and Inflation from cosmic background Radiation Detection, is a space mission for primordial cosmology and fundamental physics. The Japan Aerospace Exploration Agency (JAXA) selected LiteBIRD in May 2019 as a strategic large-class (L-class) mission, with an expected launch in the late 2020s using JAXA's H3 rocket. LiteBIRD is planned to orbit the Sun-Earth Lagrangian point L2, where it will map the cosmic microwave background (CMB) polarization over the entire sky for three years, with three telescopes in 15 frequency bands between 34 and 448 GHz, to achieve an unprecedented total sensitivity of 2.2$\mu$K-arcmin, with a typical angular resolution of 0.5$^\circ$ at 100 GHz. The primary scientific objective of LiteBIRD is to search for the signal from cosmic inflation, either making a discovery or ruling out well-motivated inflationary models. The measurements of LiteBIRD will also provide us with insight into the quantum nature of gravity and other new physics beyond the standard models of particle physics and cosmology. We provide an overview of the LiteBIRD project, including scientific objectives, mission and system requirements, operation concept, spacecraft and payload module design, expected scientific outcomes, potential design extensions and synergies with other projects.

• The paper demonstrates how LiteBIRD’s multi-frequency CMB polarization measurements can detect primordial gravitational waves to test inflationary hypotheses.
• The paper explains the mission’s advanced instrumentation and techniques, including continuously-rotating half-wave plates and cryogenic detectors, to minimize systematic errors.
• The paper projects tightening the tensor-to-scalar ratio constraint to around 10⁻³, offering key insights into the energy scale and dynamics of cosmic inflation.

Probing Cosmic Inflation with the Cosmic Microwave Background Polarization Survey

The paper under discussion presents an analysis of the forthcoming LiteBIRD (Lite satellite for the paper of $B$-mode polarization and Inflation from cosmic background Radiation Detection) mission, which is set to enhance our understanding of cosmic inflation by probing the Cosmic Microwave Background (CMB) $B$-mode polarization. This research aims to provide additional constraints on inflationary models and investigate the fundamental physics associated with the early universe.

Mission Overview and Objectives

LiteBIRD, led by the Japan Aerospace Exploration Agency (JAXA), is a space mission targeted to launch in the late 2020s. It aims to orbit the Sun-Earth Lagrangian point L2 and conduct a CMB polarization survey over the entire sky for three years. This mission is designed to achieve unprecedented sensitivity of $2.2$\,$\mu$K-arcmin with fifteen frequency bands ranging from 34 to 448 GHz. The principal scientific goal of the mission is to detect the $B$-mode polarization signature that indicates the presence of primordial gravitational waves, thus permitting a direct observational test of cosmic inflationary theory.

Technical Specifications and Instrumentation

LiteBIRD is equipped with three telescopes for different frequency ranges: the Low-Frequency Telescope (LFT), the Mid-Frequency Telescope (MFT), and the High-Frequency Telescope (HFT). These instruments employ advanced technologies, such as continuously-rotating half-wave plates (HWPs), to achieve sensitivity and control systematic errors. The mission also utilizes multiple cryogenic cooling stages down to 0.1 K to minimize thermal noise in the detectors, which consist of multichroic transition-edge sensor (TES) arrays. The entire system is designed to mitigate systematic errors such as instrumental polarization, beam asymmetries, and temperature-to-polarization leakage.

Significance and Expected Outcomes

A significant outcome of the LiteBIRD mission will be the measurement of the tensor-to-scalar ratio $r$, which quantifies the relative magnitude of primordial gravitational waves to density fluctuations. Current constraints on $r$ are below 0.036, and LiteBIRD aims to further tighten these constraints or detect $r$ with a precision on the order of $10^{-3}$. Such measurements will have profound implications for the energy scale of inflation, predicted to be near the grand unified theory scale ($10^{16}$ GeV), and for the understanding of the dynamics of inflation, including the inflationary potential and field trajectory.

Moreover, the full-sky survey enabled by LiteBIRD will also allow detection of both the recombination peak ($\ell \approx 80$) and reionization peak ($\ell \approx 4$) in $B$-mode power spectra. Firm detections of these peaks offer a higher confidence level in confirming any inflationary $B$-mode signal, distinguishing it from potential astrophysical foreground contributions.

Interactions with Future Data Sets

The paper discusses strategies for improving the detection of primordial $B$-modes using external data for delensing, which involves removing lensing-induced $B$-modes using high-resolution data from ground-based CMB experiments. A multi-tracer approach with extensive sky overlap (e.g., with ground-based collaborations such as Simons Observatory or CMB-S4) may further facilitate this process and enhance the constraints on $r$.

Conclusion

LiteBIRD represents a critical step forward in cosmic inflation research, promising to deliver precise measurements that could validate the inflationary paradigm. The success of LiteBIRD would not only confirm aspects of our current cosmological models but might also uncover new physics by probing eras of the universe and energies that cannot be accessed by particle accelerators. The mission's results will be a valuable complement to both prior and future CMB experiments, contributing significantly to the field of cosmology and particle physics.

Further progress in simulations and analyses allied with real-time data are warranted to rebound on the success expectations expressed in this work. The technological development associated with LiteBIRD sets a promising premise for CMB polarization studies as a frontier for uncovering the universe's deepest secrets.