Time：14:00-15:30, Tuesday, August 26 2025
Venue：E4-233
Host：Hongguang Liu, ITS
Speaker：Minxi He, Institute for Basic Science
Biography：Minxi He is a senior researcher at Institute for Basic Science (IBS) in South Korea. He graduated from University of Science and Technology of China in 2015 and received his PhD in 2021 at The University of Tokyo. After that, he worked at a postdoc at KEK in Japan from 2021 to 2023 and moved to IBS from 2023. His main research interest is cosmology and high-energy physics. So far, he has been working on cosmic inflation and reheating of the early Universe, primordial black hole, modified gravity, and astrophysical probe of new particles beyond the Standard Model.
Title：Geometry of target space and unitarity of Higgs inflation
Abstract：The Higgs inflation is the minimal inflation model within general relativity and the Standard Model of particle physics, and gives predictions on cosmic microwave background favored by the Planck experiment. However, the validity of this model as an effective field theory (EFT) is jeopardized by its low UV cutoff, because unitarity is violated during preheating. Due to the multi-field nature of this model, the UV cutoff is determined by the geometry of the target space as in the non-linear sigma model, which is independent of field redefinition. However, this uniqueness is obscured by the freedom of redefinition of the spacetime metric in the presence of gravity. To unambiguously calculate the cutoff scale which is essential for the EFT discussion, we propose an extended target space whose geometry is independent of the conformal transformation of the spacetime metric. I will discuss the application of this new method to the Higgs inflation in the metric and the Einstein-Cartan formalism. I may also briefly discuss the preheating process.
