Talks & Events
KICP Wednesday Colloquia - Usually Wednesdays, 3 PM, BSLC 115, unless otherwise specified. Reception starts at 4 PM in LASR conference room. For more information visit the KICP website.
Past KICP Colloquia
Baryogenesis and New Physics
Although physical reality seems to be well described by the Standard Models of Particle Physics and Cosmology, there are many open questions that do not have a direct answer within this framework. An important one is why is there Matter and not Antimatter in the Universe. The conditions for a dynamical generation of the asymmetry between matter and antimatter (baryogenesis) are well known, but cannot be fulfilled within the Standard Models framework. I will explain what are the basic conditions that must be fulfilled for baryogenesis to occur, some general classes of models in which baryogenesis is realized and the possible tests of these models in the near future.
Sterile Neutrinos in Particle Physics and Cosmology
The matter particle with the smallest mass, the neutrino, is also the most abundant in the Universe. Since their discovery, neutrinos have continually surprised us. Every time we think we understand the full scope of neutrino physics, data prove us wrong. We now understand the full scope of neutrino physics and can explain almost all observations with a simple 3-flavor model. Will upcoming data from accelerators and the cosmos prove us wrong yet again?
Overview of the 2015 Planck full mission results
The Planck collaboration has released the results from the full mission including polarisation. The Planck space mission has fulfilled its initial goal of extracting essentially all the cosmological information in the temperature map of the Cosmic Microwave Background. It has also detected the polarisation cosmological signals with unprecedented sensitivity over the whole sky.
The Planck mission performances will be illustrated by some spectacular improvements in calibration and reduction of polarized sytematic effects. The Planck view of the polarized microwave sky will be presented. The extreme stability of the L-CDM cosmological parameters determined either from the temperature or polarization data is leading to a Â« standard cosmolgy model Â». This includes also parameters related to the primordial universe physics. The polarised foreground emission from interstellar dust has been mapped with a spectacular accuracy. The claim for detection of primordial gravity waves from the BICEP2 team using CMB data aquired from south pole will be discussed in the light of the dust B modes signal observed by Planck and the recent BICEP2-Plkanck paper. The future of the search for primordial B modes will be discussed.
Baryon Acoustic Oscillations: A Robust and Precise Route to the Cosmological Distance Scale
I will discuss how the acoustic oscillations that propagate in the photon-baryon fluid during the first million years of the Universe provide a robust method for measuring the cosmological distance scale. The distance that the sound can travel can be computed to high precision and creates a signature in the late-time clustering of matter that serves as a standard ruler. Galaxy clustering results from the Sloan Digital Sky Survey reveal this feature, giving geometric distances to a wide range of redshifts and producing an accurate measurement of the abundance of dark energy. I will review our recent work on the theory and practice of the acoustic oscillation method and our latest cosmology results from SDSS-III on the expansion history of the Universe.
CMB Polarization and the BICEP / Keck Program
The theory of cosmic inflation postulates that the initial conditions of our observable universe arose from quantum fluctuations during a very early burst of exponential expansion. The BICEP / Keck Array experiments are a series of cosmic microwave background (CMB) polarimeters specifically designed to search for gravitational waves predicted by inflation by looking for the faint B-mode patterns they would imprint on degree-scale CMB polarization. Observing from the South Pole between 2010 and 2012, the BICEP2 telescope made maps of unprecedented sensitivity at degree angular scales over 2% of the sky, In March 2014 the BICEP2 team reported a high signal-to-noise detection of B-mode polarization at 150 GHz, at a level well above typical predictions of galactic foreground models for that region of sky, and consistent with a large contribution from inflationary gravitational waves. However, later last year high-frequency results reported by the Planck satellite indicated levels of polarized emission from galactic dust potentially high enough to account for the entire BICEP2 signal. In a recently published joint analysis that combines data from BICEP2, the Keck Array, and the Planck satellite, we find that there is not currently significant evidence for a gravitational wave signal, and we set the tightest constraints yet on its possible level. I will describe our current results and the continuing hunt for inflationary gravitational waves with the BICEP / Keck Array experimental program.
A Galactic Scale Gravitational Wave Observatory
Pulsars are rapidly rotating neutron stars with phenomenal rotational stability that can be used as celestial clocks in a variety of fundamental physics experiments. One of these experiments involves using an array of precisely timed millisecond pulsars to detect perturbations due to gravitational waves. The gravitational waves detectable through pulsar timing will most likely result from an ensemble of supermassive black hole binaries. I will describe the efforts of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), a collaboration which monitors an array of over 40 millisecond pulsars with the Green Bank Telescope and Arecibo Observatory. The most recent limits on various types of gravitational wave sources will be presented, and I will show how these limits are already constraining models for galaxy formation and evolution and the tension of cosmic strings. I will then describe the dramatic gains in sensitivity that are expected from discoveries of millisecond pulsars, more sensitive instrumentation, improved detection algorithms, and international collaboration and show that detection is possible before the end of the decade.
News on the search for Milky Way satellite galaxies
The population of Milky Way satellite galaxies includes the least luminous, least chemically evolved, and most dark matter dominated galaxies in the known universe. These extreme objects have reshaped how we define a "galaxy" and provide a unique testing ground for both galaxy formation models and the cold dark matter paradigm. The current census of satellite galaxies surrounding the Milky Way is almost certainly incomplete. Ongoing and near-future wide-field optical imaging surveys are anticipated to find hundreds of ultra-faint Milky Way companions at lower luminosities, greater distances, and in less explored regions of the sky. A dozen new stellar systems have already been reported in 2015, and at least one these, Reticulum II, has now been dynamically and chemically confirmed as a galaxy. I will place these recent results in context and discuss how the emergent population of Milky Way satellites might enhance the sensitivity of indirect dark matter searches.
Double Disk Dark Matter
I will describe Partially Interacting Dark Matter and a possible consequence, Double Disk Dark Matter in which a dark matter disk is embedded in the baryonic disk. I will discuss possible implications and observational consequences and constraints, including implications for the satellites of the Andromeda Galaxy.
Frank B. Baird, Jr., Professor of Science, Harvard University
Photo credit: Tsar Fodorsky.