Probing primordial gravitational waves: Ali CMB Polarization Telescope.

Hong Li,Cong-Zhan Liu,Fang-Jun Lu,Yong-Jie Zhang,Chao-Lin Kuo,Yong-Ping Li,Si-Yu Li,Zu-Hui Fan,Yong-Qiang Yao,Yifu Cai,Xinmin Zhang,Gong-Bo Zhao,Yang Liu,Zheng-Wei Li,He Xu,Mingzhe Li,Di Wu

doi:10.1093/nsr/nwy019

Abstract

In this paper, we will give a general introduction to the Ali CMB Polarization Telescope (AliCPT) project, which is a Sino–US joint project led by the Institute of High Energy Physics and involves many different institutes in China. It is the first ground-based Cosmic Microwave Background (CMB) polarization experiment in China and an integral part of China's Gravitational-wave Program. The main scientific goal of the AliCPT project is to probe the primordial gravitational waves (PGWs) originating from the very early Universe. The AliCPT project includes two stages. The first stage, referred to as AliCPT-1, is to build a telescope in the Ali region of Tibet at an altitude of 5250 meters. Once completed, it will be the highest ground-based CMB observatory in the world and will open a new window for probing PGWs in the northern hemisphere. The AliCPT-1 telescope is designed to have about 7000 transition-edge sensor detectors at 95 GHz and 150 GHz. The second stage is to have a more sensitive telescope (AliCPT-2) with more than 20 000 detectors. Our simulations show that AliCPT will improve the current constraint on the tensor-to-scalar ratio r by one order of magnitude with three years' observation. Besides the PGWs, AliCPT will also enable a precise measurement of the CMB rotation angle and provide a precise test of the CPT symmetry. We show that three years' observation will improve the current limit by two orders of magnitude.

Highlights

Searching for gravitational waves (GWs) has long been the cornerstone of cosmology and astrophysics since Einstein proposed the General Relativity (GR) in early 20th century
Different from the GWs detected by LIGO and Virgo, the PGWs arise from quantum fluctuations and carry important information about the very early Universe, for example, the physics of inflation, bouncing and emergent Universe
ALICPT AND ITS SCIENTIFIC GOALS we provide a brief introduction to the main contents and scientific goals of the AliCPT project

Summary

INTRODUCTION

Searching for gravitational waves (GWs) has long been the cornerstone of cosmology and astrophysics since Einstein proposed the General Relativity (GR) in early 20th century. LIGO and Virgo have announced other three events of black hole [2,3,4] and one event of neutron stars GWs [5] These achievements make the GWs study to enter a new era and were awarded the Nobel Prize in Physics in 2017. Different from the GWs detected by LIGO and Virgo, the PGWs arise from quantum fluctuations and carry important information about the very early Universe, for example, the physics of inflation, bouncing and emergent Universe. The CMB B-mode polarization induced by the tensor fluctuations generated in the early Universe, i.e., the PGWs, still have not been detected conclusively. The CMB B-mode polarization induced by the tensor fluctuations generated in the early Universe, i.e., the PGWs, still have not been detected conclusively1 This has become a key scientific goal of CMB.

OVERVIEW OF THE ALICPT SITE

Sensitivity on r and its implication on the Early Universe Physics

Findings

SUMMARY