# Cosmology & Gravitation

This series consists of talks in the areas of Cosmology, Gravitation and Particle Physics.

## Seminar Series Events/Videos

Nov 3 2020 - 11:00am
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Nov 10 2020 - 11:00am
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Nov 17 2020 - 11:00am
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## GW190521 - Discovery of Black Holes that Should Not Exist

Tuesday Oct 27, 2020
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The new gravitational-wave signal GW190521in LIGO and Virgo marks the first observational detection of the elusive intermediate-mass black holes. The detection also confirms there exist a new class of black holes in the mass gap predicted by the pair-instability supernovae theory. In this talk, I will discuss the process that went behind inferring the astrophysical properties of this historic discovery. I would briefly address the alternative scenarios we looked into for a possible exotic origin of this signal, including any violation of General Relativity.

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## The boundary of clusters

Tuesday Oct 20, 2020
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The outskirts of accreting dark matter haloes exhibit a sudden drop in density delimiting the virialized region. After briefly describing the physics shaping this feature and how it is measured, I will discuss its applications. I will examine its connection to structure formation and how it can constrain the screening mechanisms of beyond-GR models of gravity.

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## Strong gravitational lensing as a cosmological probe: new ways of constraining dark

Tuesday Oct 13, 2020
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Studying the smallest self-bound dark matter structure in our Universe can yield important clues about the fundamental particle nature of dark matter, and galaxy-scale strong gravitational lensing provides a unique way to detect and characterize dark matter on small scales at cosmological distances from the Milky Way. Research in this field can be broadly separated into works that aim to directly detect individual perturbers and works that aim to statistically constrain the matter distribution by looking at collective perturbations caused by an unresolved population of perturbers.

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## Cosmology from current and future spectroscopic galaxy surveys

Tuesday Oct 06, 2020
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Mapping of galaxy density fluctuations on large scales is one of the most important goals of observational cosmology in this decade. These observations can significantly improve our knowledge of the universe, its origins and composition. In this talk I will review some of the science goals of the ongoing and future spectroscopic galaxy surveys and explain how these goals can be met. In particular, I will focus on some recent progress in theoretical modelling of the nonlinear structure formation and show how it can be used to extract cosmology from observations of the cosmic web.

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## Search for Lensed Gravitational Waves from LIGO/Virgo Binary Black Hole Mergers: Intriguing Candidates in O2

Tuesday Sep 29, 2020
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Current and forthcoming observing runs at ground-based laser interferometry detectors are starting to uncover gravitational waves from binary black hole (BBH) mergers at cosmological distances, and a fraction of them are expected to be gravitationally lensed by intervening galaxy or cluster lenses with multiple images. Such strongly lensed events, if discovered, may offer a precious opportunity to localize BBH host galaxies and probe global and small-scale property of the lens mass profile.

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## Halo gas thermodynamics from the cosmic microwave background: implications for large-scale structure and galaxy formation

Tuesday Sep 22, 2020
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Understanding galaxy formation is an outstanding problem in Astrophysics. The feedback processes that drive it, exploding stars and accretion onto supermassive black holes, are poorly understood. This results in an order unity uncertainty in the distribution of the gas inside halos, the missing baryon problem''. Because baryons are 15% of the total mass in the universe, this baryonic uncertainty is the largest theoretical systematics for percent precision weak lensing surveys like DES, HSC, Rubin Observatory, Roman Observatory and Euclid.

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## CMB lensing and new constraints on the early universe

Tuesday Sep 15, 2020
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Measurements of gravitational lensing in the cosmic microwave background (CMB) allow the dark matter distribution to be mapped out to uniquely high redshifts. After giving a brief overview of current and upcoming CMB lensing measurements, I will focus on two new ways of using CMB lensing, in combination with galaxy surveys, to constrain the early universe. First, I will explore how CMB lensing and galaxy surveys could provide insights into current discrepancies in measurements of the Hubble constant.

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## Cosmology from the SDSS

Tuesday Jul 28, 2020
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On Monday July 20th, we announced the final results from extended Baryon Oscillation Spectroscopic Survey (eBOSS), the last large-scale structure galaxy survey to be undertaken within the umbrella of the Sloan Digital Sky Survey (SDSS). This marks the culmination of 20 years of galaxy surveys undertaken using the Sloan Foundation Telescope.

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## Relieving the Hubble tension with primordial magnetic fields

Tuesday Jul 14, 2020
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The standard cosmological model determined from the accurate cosmic microwave background measurements made by the Planck satellite implies a value of the Hubble constant H0 that is 4.2 standard deviations lower than the one determined from Type Ia supernovae. The Planck best fit model also predicts lower values of the matter density fraction Om and clustering amplitude S8 compared to those obtained from the Dark Energy Survey Year 1 data.

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## Space time fluctuations in AdS/CFT and Extensions to Minkowski

Tuesday Jul 07, 2020
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Based on recent work arXiv:1902.08207 and arXiv:1911.02018 with E. Verlinde.

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