HET Seminar | Dark Energy and Time Reparametrizations

The cosmological constant’s quantum origin is a famous open problem in theoretical physics and cosmology. Its observed value and theoretical prediction exhibit a large 120-order discrepancy. In this talk, we first summarize the current state of research on the cosmological constant problem and review the Schwarzian theory of time reparametrizations in the literature. Inspired by an early work by Gary Gibbons and our recent attempts to solve various formidable problems (e.g., color confinement in SYM, fluid/gravity correspondence at low temperatures, etc.) via the JT gravity/Schwarzian theory duality, we apply the Schwarzian theory of time reparametrizations and its ensemble average to the cosmological constant problem and propose a new approach to resolving it. We will show that this new method, at leading order, yields a theoretical value that exactly matches the observed value of the cosmological constant. However, recent results from dark energy observations (such as DESI) suggest a dynamical dark energy. Starting from the leading-order constant value, we will take into account matter-gravity interactions and develop a more realistic dynamical dark energy model based on time reparametrizations that can fit observational data with comparable precision to other models (e.g., LCDM and CPL). We also provide some falsifiable predictions for future more precise observations. This talk is based on my recent paper arXiv:2602.17476 and another upcoming work.

Brief Biography:
Jun Nian is an assistant professor at the International Centre for Theoretical Physics Asia-Pacific (ICTP-AP), University of Chinese Academy of Sciences. He received a Diplom degree from the University of Heidelberg in 2009 and a Ph.D. degree from Stony Brook University in 2015. Before joining ICTP-AP in 2021, he was a postdoctoral fellow at Institut des Hautes Etudes Scientifiques (IHES), the University of Michigan, and the University of Milan. His research interests include quantum field theory, gravity theory, and string theory, with a recent focus on the quantum-gravitational effects in black holes and cosmology.