Talks & Events
KICP Friday Noon Seminars
Current & Future KICP Seminars
Past KICP Seminars
Helical Magnetic Fields in the Cosmos
It is often necessary to study cosmological phase transitions, such as inflation and thermal symmetry-breaking phenomena, through the relics that they leave behind. In this sense, the cosmological magnetic field may be a powerful probe of the early universe, which has yet to be tapped. In this talk, I will survey various topics related to primordial magnetic fields (PMFs) with helicity. We will ask: how might a PMF have been generated in the early universe, how would it have evolved in the cosmological medium, and how could it be detected today? In the first part, we discuss the interesting connection between baryogenesis and magnetogenesis, which may link the sign of the cosmological baryon asymmetry to the sign of the magnetic helicity. In the second part, we discuss the interplay between the PMF and other magnetically-active objects, such as monopoles and axions. Finally we turn to detection prospects, with an emphasis on the frontier field of magnetically-broadened TeV blazar halos.
Modified gravity inside astrophysical bodies: breaking of the Vainshtein mechanism
Any infrared modification of gravity, which explains the current cosmic acceleration, should not spoil the successes of general relativity in solar-system observations. In many theories of modified gravity, it is ensured by the Vainshtein mechanism that works near dense sources. Recently, it has been found that the Vainshtein mechanism can be broken inside a dense source, although not outside, in a general class of scalar-tensor theories. In this talk, after reviewing how the Vainshtein mechanism can be broken, I will discuss its impact on the density profile of a star, modeling simply it as a polytropic sphere. I also show the existence of a universal upper bound on the amplitude of this type of modification, independently of the details of the equation of state.
New tests of not-so-dark matter
The nature of dark matter remains one of the major unsolved problems in physics, and one must leave no stone unturned when exploring empirical probes. In this talk I will discuss two different test of dark matter properties. First, I will show that dark matter interactions with standard model particles at high redshift can be probed through spectral distortions of the cosmic microwave background. In particular, I will show that upper limits from FIRAS measurements allow to constrain dark matter interactions for masses below 0.1 MeV. In the second part, I will discuss an interesting possible consequence of clumpy dark matter: flares following tidal compression events by supermassive black holes.
A 3D view of the Dark Universe: illuminating intergalactic gas at high redshift with fluorescent Lyman-alpha emission
Gravitational collapse during the Universe's first billion years transformed a nearly homogeneous matter distribution into a network of filaments - the Cosmic Web - where galaxies form and evolve. Because most of this material is too diffuse to form stars, its study has been limited so far to absorption probes against background sources. In this talk, I will present the results of a new program to directly detect and study high-redshift cosmic gas in emission using bright quasars and galaxies as external "source of illumination’’. In particular, I will show results from ultra-deep narrow-band imaging and recent integral-field-spectroscopy as a part of the MUSE Guaranteed Time of Observation program that revealed numerous giant Lyman-alpha emitting filaments around quasars and bright galaxies. Finally, I will discuss how the unexpectedly high luminosities of the giant Lyman-alpha filaments, together with the constraints from Helium and metal extended emission, present a serious challenge for our current understanding of the Intergalactic and Circumgalactic media based on hydrodynamical cosmological simulations.
Putting the Cosmology in "21 cm Cosmology"
21 cm cosmology -- the concept of using radio telescopes to observe the highly redshifted 21 cm line of neutral hydrogen on cosmological scales -- is a field on the verge of a breakthrough. The first generation of 21 cm cosmology experiments (LOFAR, MWA, and PAPER, among others) have been operating for several years, and first results at the level of design sensitivity are potentially forthcoming. In this talk, I will focus on the work needed to establish the reliability of any putative detection of the cosmological signal and the paths forward for bringing 21 cm experiments into the "precision cosmology" fold, alongside the CMB and galaxy surveys. Recent results from the MWA and PAPER will be presented, including the first limits on the z = 8.4 IGM temperature from PAPER.
Quantifying discordance in the 2015 Planck CMB spectrum
Gravity at the horizon: from the cosmic dawn to ultra-large scales
Recent advances in cosmology provide both the motivation and the data to probe gravity on the largest scales available to observation. I will revise the landscape of gravitational theories, focusing on modern scalar-tensor theories and their cosmological implications. Then I will present the ongoing effort to test gravity in novel regimes such as the early universe, non-linear effects and ultra-large scales. I will also introduce the hi_class code (www.hiclass-code.net), which is central to this program.