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Colloqiua & Seminars
Preliminary Cosmology Results from the Dark Energy Survey Supernova Program
Rick Kessler, The University of Chicago
We have recently completed 5 seasons of the Dark Energy Survey (DES), and cosmology results starting coming out last summer. Here I will discuss new cosmology results based on a subset of spectroscopically confirmed SNIa, and describe advances in the analysis aimed for much larger samples in DES and beyond. Finally, I will briefly describe other science projects using the DES transient-search pipeline.
Science, Politicians, and the Public: What's the Story?
Rush D Holt, AAAS
With many public decisions being made on the basis of political partisanship rather than scientific evidence, what storyline should scientists follow and what difference does it make for the practicing researcher?
Dark Matter in the Universe
Katherine Freese, University of Michigan
"What is the Universe made of?" This question is the longest outstanding problem in all of modern physics, and it is one of the most important research topics in cosmology and particle physics today. The bulk of the mass in the Universe is thought to consist of a new kind of dark matter particle, and the hunt for its discovery in on. I'll start by discussing the evidence for the existence of dark matter in galaxies, and then show how it fits into a big picture of the Universe containing 5% atoms, 25% dark matter, and 70% dark energy. Neutrinos only constitute ½% of the content of the Universe, but much can be learned about neutrino properties from cosmological data. Leading candidates for the dark matter are Weakly Interacting Massive Particles (WIMPs), axions, and sterile neutrinos. WIMPs are a generic class of particles that are electrically neutral and do not participate in strong interactions, yet have weak-scale interactions with ordinary matter. There are multiple approaches to experimental searches for WIMPS: at the Large Hadron Collider at CERN in Geneva; in underground laboratory experiments; with astrophysical searches for dark matter annihilation products, and upcoming searches with the James Webb Space Telescope for Dark Stars, early stars powered by WIMP annihilation. Current results are puzzling and the hints of detection will be tested soon. At the end of the talk I'll briefly turn to dark energy and its effect on the fate of the Universe.
From Emergent Gravity to Dark Energy and Dark Matter
Erik P. Verlinde, University of Amsterdam
The observed deviations from the laws of gravity of Newton and Einstein in galaxies and clusters can logically speaking be either due to unseen dark matter or due to a change in the way gravity works. Until recently there was little reason to doubt that general relativity correctly describes gravity in these circumstances. In the past few years insights from black hole physics and string theory have lead to a new theoretical framework in which the gravitational laws are derived an underlying microscopic quantum description of spacetime. An essential ingredient in the derivation of the Einstein equations is that the quantum entanglement of the vacuum obeys an area law, a condition that is known to hold in Anti-de Sitter space. In a Universe that is dominated by positive dark energy, like de Sitter space, the microscopic entanglement entropy contains, in addition to the area law, a volume law contribution whose total contribution equals the Bekenstein-Hawking entropy associated with the cosmological horizon. We will argue that this extra volume law contribution leads to modifications in the emergent laws of gravity, and provide evidence for the fact that these modifications explain the observed phenomena in galaxies and clusters currently attributed to dark matter. We end with a discussion of the possible implications for early cosmology, the CMB and structure formation.
Journey to the Beginning of Time: Turning Metaphysics into Physics
Lawrence M Krauss, Arizona State University
Even a generation ago, fundamental existential questions such as, "How did the Universe Begin?, How will it End?, Are we Alone, and, Are there OTHER Universes?," and other less grand but no less interesting questions such as "Do Black Holes Exist?" may have appeared as forever inaccessible metaphysical questions. Gravitational waves have now been discovered by LIGO, opening up a vast new window on the Universe. I will explain how we might eventually unambiguously detect a gravitational signal from moments after the Big Bang, pushing our direct empirical handle on the Universe back in time by 49 orders of magnitude, and revealing what we might learn about own origins, the nature of gravity, grand unification, and even the possible existence of other universes.
The Limits of Cosmology
Joe Silk, IAP/JHU
One of our greatest challenges in cosmology is understanding the origin of the structure of the universe, and in particular the formation of the galaxies. I will describe how the fossil radiation from the beginning of the universe, the cosmic microwave background, has provided a window for probing the initial conditions from which structure evolved and seeded the formation of the galaxies, and the outstanding issues that remain to be resolved. I will address our optimal choice of future strategy in order to make further progress on understanding our cosmic origins.
First observation of coherent elastic neutrino-nucleus scattering
Grayson C Rich, Triangle Universities Nuclear Lab
The process of coherent elastic neutrino-nucleus scattering (CEvNS) was predicted in 1974 by D.Z. Freedman, who suggested that attempts to detect CEvNS “may be an act of hubris” due to several profound experimental challenges. More than 40 years after its initial description, the world’s smallest functional neutrino detector has been used by the COHERENT Collaboration to produce the first observation of the process: a 14.6-kg CsI[Na] scintillator was deployed to the Spallation Neutron Source of Oak Ridge National Lab and observed, with high significance, evidence for a CEvNS process in agreement with the prediction of the Standard Model. I will discuss CEvNS and its connection to a range of exciting physics, including: its potential role in supernova dynamics; the possibility to use neutrinos as a tool for studying nuclear structure and neutron stars; its relationship to upcoming direct searches for WIMP dark matter; and the ways in which CEvNS could offer insight into physics beyond the Standard Model. The experimental program and the recent result from the COHERENT Collaboration will be presented along with ongoing efforts within the collaboration and future plans.