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Cosmology & Gravitation

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

Seminar Series Events/Videos

TBA
sep 4 2018 - 11:00am
Room #: 400
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TBA
sep 10 2018 - 11:00am
Room #: 400
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TBA
oct 2 2018 - 2:00pm
Room #: 405
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TBA
oct 9 2018 - 11:00am
Room #: 400
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Jeudi juil 05, 2018
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I will first outline an effective field theory for cosmology (EFTC) that is based on the Standard Model coupled to General Relativity and improved with Weyl symmetry. Any version of quantum gravity (QG), including string theory, must include the same improvement, otherwise QG will not be geodesically complete.

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Mardi juin 26, 2018
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Burst phenomena are ubiquitous in astrophysics. Understanding the origin of bright and rapid bursts, like FRBs, is an important goal of contemporary astrophysics.  We apply Dicke's superradiance, a coherent quantum mechanical radiation mechanism, to explain these burst phenomena. We show that bursts lasting from a few milliseconds (FRBs) to a few years (e.g. OH masers) can be produced by very large groups of entangled atoms/molecules. This is in contrast with the common assumption that, in the interstellar medium, the atoms/molecules in a radiating gas act independently from each other.

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Mardi juin 12, 2018

Axions are attractive candidates for theories of large-field inflation that are capable of generating observable primordial gravitational wave backgrounds. These fields enjoy shift-symmetries that protect their role as inflatons from being spoiled by coupling to unknown UV physics. This symmetry also restricts the couplings of these axion fields to other matter fields. At lowest order, the only allowed interactions are derivative couplings to gauge fields and fermions.

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Mercredi mai 23, 2018
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The next frontiers in cosmic microwave background (CMB) science include a detailed mapping of the CMB polarization anisotropy, with goals of detecting the inflationary B-mode signal and reconstructing high-fidelity maps of the matter distribution via CMB lensing, as well as a first detection of CMB spectral distortions.  At this level of precision (~nK), Galactic and extragalactic foregrounds may be the ultimate limiting factor in deriving cosmological constraints.  I will discuss biases due to foregrounds in CMB lensing measurements, including the first calculation of the lensing bias due

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Mardi mai 01, 2018
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Gravitational lensing of the cosmic microwave background has emerged as a powerful cosmological probe, made possible by the development and characterization of nearly-optimal estimators for extracting the lensing signal from temperature and polarization maps. One can ask whether similar tools can be applied to upcoming "intensity maps" of emission lines at other wavelengths (e.g. 21cm). In this talk, I will present recent work in this direction, focusing in particular on the impact of gravitational nonlinearities on standard quadratic lensing estimators.

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Mardi avr 24, 2018
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The lensing convergence measurable with future CMB experiments will be highly correlated with the clustering of galaxies that will be observed by imaging surveys such as LSST. I will discuss prospects for using that cross-correlation signal to constrain local primordial non-Gaussianity, the amplitude of matter fluctuations as a function of redshift, halo bias, and possibly the sum of neutrino masses. A key limitation for such analyses and large-scale structure analyses in general is that the mapping from initial conditions to observables is nonlinear for wavenumbers k>0.1h/Mpc.

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Mardi mar 06, 2018
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In 2020 the European Space Agency (ESA) will launch the Euclid satellite mission. Euclid is an ESA medium class astronomy and astrophysics space mission, and will undertake a galaxy redshift survey over the redshift range 0.9 < z < 1.8, while simultaneously performing an imaging survey in both visible and near infrared bands. The complete survey will provide hundreds of thousands images and several tens of Petabytes of data.

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Mardi fév 27, 2018
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In classical General Relativity (GR), an observer falling into an astrophysical black hole (BH) is not expected to experience anything dramatic as she crosses the event horizon. However, tentative resolutions to problems in quantum gravity, such as the cosmological constant problem or the black hole information paradox, invoke significant departures from classicality in the vicinity of the horizon. I outline theoretical and phenomenological arguments for these departures.

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Mardi fév 13, 2018
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Large scale structure surveys are one of our primary tools for answering open questions in cosmology like: What is the physics behind dark energy? Is gravity well described by general relativity on cosmological scales, or does that description need to be extended? In order to take full advantage of the information contained in survey data, however, we must ensure that we understand our data’s sensitivity to new physics and that our analyses are not biased by systematics. In my talk I’ll describe work I have been doing in this aim for the Dark Energy Survey (DES).

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Mardi fév 06, 2018
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If a black hole horizon has its microscopic structure as is conjectured by the candidates of quantum gravity, the dispersion relation of gravitational waves (GWs) near the horizon may be drastically modified since its wavelength can be comparable to the size of the microscopic structure because of its infinite gravitational blue-shift near the horizon.  We investigate ringdown-GWs from a perturbed black hole with such a modified dispersion relation and found that the change of modified dispersion relation near the horizon would lead to the partial reflection of infalling GWs at the horizon

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