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HET Seminar Dec 8th: Rashmish Mishra
Rashmish Mishra: Holographic Phase Transitions in the early Universe
Strongly coupled confining theories are well-motivated in many BSM frameworks. The early universe cosmological history of these theories provides possibilities for observable signals. These theories undergo confinement deconfinement phase transition in the early universe, which can result in gravitational wave signals, observable in upcoming experiments. Using AdS/CFT, these theories have been studied in the Randall-Sundrum framework, and various quantitative aspects of the phase transition have been calculated. In the models that have been considered, the rate of transition from the hot phase to the confined phase is very small and leads to a period of supercooling. This enhances the gravitational wave signal, but presents a tension between a low confinement scale and fitting to the standard picture of BBN. In this talk, I will revisit these features and argue that some of the issues are specific to the simplified models that have been studied. I will present two modifications that are expected on general grounds and argue that both of them enhance the rate. I will also present the effect on the resulting phenomenology. The talk will be based on 2309.10090 and an ongoing work.
Colloquium Dec 5th: Scott Ransom
Patience is a virtue: The 15-year NANOGrav Gravitational Wave Result
Earlier this summer, the pulsar timing array community announced strong evidence for the presence of a stochastic background of nanoHertz frequency gravitational waves. This has been the primary goal of the community for the past two decades, and it took thousands of hours of telescope time, over 500,000 pulse arrival times from ~70 millisecond pulsars, and a highly sophisticated and very computationally demanding analysis effort to accomplish. While we can't yet say for certain what is causing the gravitational waves, our best guess is a population of slowly merging super-massive black hole binaries throughout the universe. But it is possible that the signal also heralds new physics. So what does it all mean and what are we expecting next? And what other cool things can we do with all of this high-precision pulsar data?
Colloquium Nov 7th: Cora Dvorkin
Cora Dvorkin: The Universe as a Lab for New Physics Across Cosmic Times
The remarkable progress in cosmology over the last decades has been driven by the close interplay between theory and observations. Cosmological observations and galaxy dynamics have shown us that 84% of all matter in the universe is composed of dark matter, which is not accounted for by the Standard Model of particle physics. The properties and interactions of dark matter remain one of the great puzzles of fundamental physics. In this talk, I will discuss new ways to use current and upcoming astrophysical observations to improve our understanding of the nature of dark matter.
HET Seminar Oct 20th: Nils Schonenberg
Nils Schoneberg: A Hubble tension status update
The standard model of cosmology (LCDM) involving cold dark matter and dark energy has been wildly successful in predicting astrophysical observations across a wide range of scales. Despite this success, the precise nature of its ingredients has so far remained elusive. To this end, a vast experimental effort has been undertaken to measure observables in the local and distant universe to unprecedented precision. These promising measurements have only deepened the mysteries of cosmology, however, as they revealed a growing tension between the current expansion rate of the Universe (the Hubble constant) measured through the local distance ladder and that inferred from the cosmic microwave background. Now that the formal significance of this discrepancy has reached a level of five sigma significance, it is crucial to thoroughly re-examine both the astrophysical observations as well as the theoretical models used to analyze the data. In this talk, I introduce the experimental pillars of this Hubble tension and highlight the crucial role that current and future large-scale structure surveys play in this quest. I further discuss the status of the theoretical proposals for easing the Hubble tension, with a focus on a critical examination of the different mechanisms at play in these models.
Colloquium Oct 3rd: Matias Zaldarriaga
Matias Zaldarriaga: "Cosmology into the next decade"
In this talk, I will be reviewing the observations that have contributed to the development of the Standard Cosmological Model. I will argue that as we seek to address many of the remaining questions, the field of observational Cosmology is transitioning to a more complex phase, where we are attempting to gather information from the late Universe on smaller scales. Specifically, I will be focusing on the challenging task of modeling galaxy clustering, and presenting some of the recent results in this area. Finally, I will be discussing the prospects for future theoretical developments. Pre-Colloquium Reception at 3:00 pm in SCI 101