KICP Seminars & Colloquia, Current and Future

Seminar schedule for Spring 2020
May 19, 2020
Wednesday colloquium
Fabian Schmidt
Max-Planck-Institut fur Astrophysik
New Approaches to Galaxy Clustering   [Abstract]
May 22, 2020
Friday noon seminar
Ke Fang
Stanford University
Multi-messenger Astrophysics: Probing Compact Objects with Cosmic Particles   [Abstract]
May 29, 2020
Friday noon seminar
Nirmal Raj Krishna
TRIUMF
Nucleons, Electrons, and Pasta: Discovering Dark Matter by Reheating the Neutron Star Soup   [Abstract]
June 5, 2020
Friday noon seminar
Hongwan Liu
Princeton University and New York University
Dark Photon Oscillations in our Inhomogeneous Universe   [Abstract]
 
COLLOQUIA

  • May 19, 2020 | 12:00 PM | Zoom Room (online) | Wednesday colloquium
    New Approaches to Galaxy Clustering
    Fabian Schmidt, Max-Planck-Institut fur Astrophysik

    All large-scale structure cosmologists are faced with the question: how do we robustly extract cosmological information, such as on dark energy, gravity, and inflation, from tracers such as galaxies whose astrophysics is extremely complex and incompletely understood? Based on advances in our theoretical understanding of large-scale structure, we now know how to absorb these complexities into free "nuisance" parameters on large scales. This opens up the possibility for physically robust cosmology inference from galaxy clustering. However, to really make use of the power of this approach, we have to go beyond current analyses based on the power spectrum. I will describe a novel approach that attempts to extract the information in the entire galaxy density field, rather than compressing it into summary statistics, while robustly marginalizing over the complexities of galaxy formation.

 
FRIDAY NOON SEMINARS

  • May 22, 2020 | 12:00 PM | Zoom Room (online) | Friday noon seminar
    Multi-messenger Astrophysics: Probing Compact Objects with Cosmic Particles
    Ke Fang, Stanford University

    The study of compact stellar remnants such as black holes and neutron stars is an important component of modern astrophysics. Recent observations of the first neutron star merger event and an active galactic nucleus as a potential high-energy neutrino source open a new way to study compact objects using multi-messengers. The key to coordinated detection and interpretation of multiple messenger signals, namely, electromagnetic radiation, cosmic rays, neutrinos, and gravitational waves, is to understand the link between the messengers. We try to answer this question from both theoretical and observational perspectives. We study high-energy particle propagation in the vicinity of magnetar-powered transients and black hole jets using numerical simulation. We also investigate analysis frameworks aiming to exploit data across multiple wavelengths and messengers. We close the talk by overlooking the future of Multi-messenger Astrophysics, in light of upcoming facilities such as SWGO and IceCube-Gen2, as well as new questions brought by recent observations.
  • May 29, 2020 | 12:00 PM | Zoom Room (online) | Friday noon seminar
    Nucleons, Electrons, and Pasta: Discovering Dark Matter by Reheating the Neutron Star Soup
    Nirmal Raj Krishna, TRIUMF

    I present a largely model-independent probe of dark matter interactions with nucleons and electrons. Accelerated by gravity to relativistic speeds, local dark matter scattering against old neutron stars deposits kinetic energy at a rate that heats them to infrared blackbody temperatures. The resulting radiation is detectable by next generation telescopes such as James Webb, the Thirty Meter Telescope, and the European Extremely Large Telescope. I treat neutron star capture of dark matter by scattering (a) in the various layers of the well-understood stellar crust, on nucleonic and nuclear constituents, which include non-spherical "pasta" phases, (b) in the less understood stellar core, on nucleons and muons using non-relativistic kinematics, and on electrons using relativistic kinematics. I show that the (non-)observation of dark kinetic heating of neutron stars would overcome several limitations of terrestrial searches for dark matter, and advance challenging frontiers by orders of magnitude.
  • June 5, 2020 | 12:00 PM | Zoom Room (online) | Friday noon seminar
    Dark Photon Oscillations in our Inhomogeneous Universe
    Hongwan Liu, Princeton University and New York University

    The dark photon is a well-motivated extension of the Standard Model which can mix with the regular photon. This mixing is enhanced whenever the dark photon mass matches the primordial plasma frequency, leading to resonant conversions between photons and dark photons at specific redshifts. These conversions can produce observable cosmological signatures, including distortions to the cosmic microwave background blackbody spectrum. Until recently, constraints on the dark photon based on these effects have been derived assuming a homogeneous universe. In this talk, I will review the physics of photon/dark-photon mixing, and introduce a new analytic formalism that can account for the inhomogeneous distribution of matter in our universe. Using this formalism, we obtain new limits on the dark photon mixing parameter, significantly correcting and extending earlier results.