Topic:Hubble-Delayed Vacuum Decay and Its Gravitational-Wave Signatures

Speaker: Assoc.Prof.Haipeng An

Coordinates: Classroom 5204, 16:00, Friday,  September 11

Abstract:      

The particle nature of dark matter remains one of the central questions in fundamental physics. Although a wide range of direct and indirect detection strategies have been developed, no compelling evidence has yet been found for nongravitational interactions between dark matter and Standard Model particles. This has motivated dark-sector models, in which the Universe may contain multiple sectors coupled to one another predominantly through gravity. In this picture, the Standard Model constitutes only one sector, while dark matter consists of particles or states belonging to another. If this framework is correct, how can we detect signatures of these hidden sectors and test the underlying picture?

From the perspective of dark energy, the cosmological constant problem remains among the most profound puzzles in fundamental physics. The anthropic principle, when applied within a landscape of vacua, offers one possible explanation, but its physical testability remains an open question.

In this talk, I will show that combining the dark-sector framework with the vacuum-landscape picture naturally gives rise to a new class of first-order cosmological phase transitions:Hubble-delayed vacuum decay. Such transitions may have occurred during the history of the Universe. I will discuss the resulting stochastic gravitational-wave background, demonstrate that it may be detectable by proposed gravitational-wave observatories, and highlight distinctive spectral features that could distinguish this mechanism from conventional first-order phase transitions.

Speaker Profile: 

Haipeng An received his B.S. in Physics from Peking University in 2006, along with a minor in Mathematics. He earned his Ph.D. in Physics from the University of Maryland in 2011.From 2011 to 2014, he was a postdoctoral fellow at the Perimeter Institute for Theoretical Physics. He then joined Caltech as a Walter Burke Fellow, where he worked from 2014 to 2017.In 2017, he joined Tsinghua University and was promoted to tenured Associate Professor in 2024. His research focuses on particle phenomenology and cosmology.