ABSTRACT
The Planck mission measures the cosmic microwave background (CMB) with unprecedentedly precision. The angular spectra extracted from Planck's CMB measurements can be used to test gravitational theories and cosmological models. This is done by comparing the observational results with theoretical predictions that can be calculated by solving together the Boltzmann equation governing the evolution of the distribution of photons and the Einstein field equations governing the evolution of the metric tensor of the universe. Programs to do the theoretical calculations in general relativity (GR) have been well-developed. The representative ones are CAMB (Code for Anisotropies in the Microwave Background) and CLASS (Cosmic Linear Anisotropy Solving System). In my work I would like to do the calculation in a modified gravity theory that has not been studied yet. As the first step, I manage to build up a prototype program for calculating the CMB temperature spectrum in GR. Once the set of the Einstein field equations are replaced by the modified Einstein field equations, the program will be able to calculate predictions in the modified gravity theory that I study. In this talk, I will explain the key elements for going from the equations to the workable numerical code, and demonstrate the prototype code by comparing its calculations with the results from CAMB.
BIO
Rui Xu has been a postdoc in Prof. Dandan Xu's group since the April in 2023. He obtained a Bachelor's degree in astronomy from Nanjing University in 2012, and a PhD degree in physics from Indiana University Bloomington in 2019. Then he was a postdoc at the Kavli Institue of Astronomy and Astrophysic in Peking University before coming to Tsinghua. His research focuses on black holes and neutron stars in modified gravity theories, investigating spacetime structures of these compact objects and their motions in binary systems. Recently he has started to explore cosmology in modified gravity theories, calculating FLRW solutions and CMB anisotropies.
