# Cosmology & Gravitation

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

## Seminar Series Events/Videos

Currently there are no upcoming talks in this series.

## Dissipation during inflation

Tuesday Mar 15, 2016
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I will discuss phenomena associated with particle production and field excitation during inflation. In the first part of the talk I will present several

signatures that can originate from the coupling of an axion inflaton to gauge fields. In the second part I will test the robustness of the standard

implications associated with the detection of a gravity wave (GW) signal at CMB scales, by discussing what conditions can allow a visible

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## Testing gravity using astrophysics

Tuesday Mar 08, 2016
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Alternative theories of gravity are popular alternatives to the LCDM model because they can self-accelerate without a cosmological constant. On smaller scales, consistency with solar system tests of gravity is achieved by utilising screening mechanisms, which act to hide fifth-forces locally. This makes them difficult to distinguish from general relativity. In this talk I will describe recent work using astrophysical objects---stars, galaxies, and clusters---as new and novel probes of alternative gravity theories.

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## Astrophysical and Cosmological consequences of recent and future kSZ measurements

Tuesday Feb 16, 2016

The kinetic Sunyaev-Zel'dovich effect is a direct probe of the distribution and velocity of electrons on cosmological scales. Recent progress in Cosmic Microwave Background observations allow statistical detections of this subtle effect originating from a number of different tracers populations. In my talk, I will review the observational status, highlight the consequences for astrophysics and cosmology and discuss future directions.

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## Interferometry and the Global 21-cm Signal

Tuesday Feb 09, 2016
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The global redshifted 21-cm radiation background is expected to be a powerful probe of the re-heating and re-ionization of the intergalactic medium. However, its measurement is technically challenging: one must extract the small, frequency-dependent signal from under much brighter and spectrally smooth foregrounds. Traditional approaches to study the global signal have used single-antenna systems, where one must calibrate out frequency-dependent structure in the overall system gain, as well as remove the noise bias from auto-correlating a single amplifier output.

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## Highlights from the Atacama Cosmology Telescope

Tuesday Feb 02, 2016
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The Atacama Cosmology Telescope (ACT) has been pushing our measurements of the Cosmic Microwave Background on small scales to high resolution and deeper sensitivity since 2008. While ACT stopped taking temperature-only measurements in 2010, ACTPol is now operating with polarisation-sensitive detectors. I will present some of the current ACTPol results in terms of the power spectrum constraints.

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## Reheating Predictions in Single Field Inflation

Thursday Jan 14, 2016
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One possibility for studying reheating is to link the duration and final temperature after reheating, and its equation of state, to inflationary observables. By restricting the equation of state to lie within a broad physically allowed range, one can bracket an allowed range of $n_s$ and $r$ for models of inflation. The results are similar to, but do a little better, than requiring the length of inflation lie between 50 and 60 efolds. The added constraints can help break degeneracies between inflation models that otherwise overlap in their predictions.

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## Modified Gravity (MOG), Dark Matter, and Black Holes

Thursday Jan 14, 2016
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According to the standard model of cosmology 96% of the matter and energy in the universe is invisible. The dark matter particles comprising the invisible material have so far not been detected in laboratory and astrophysical experiments.  The dark energy responsible for the acceleration of the universe is still a controversial issue. A modified gravity theory is presented that can potentially fit current cosmological and astrophysical data. The black holes and their shadows predicted by MOG can differ from the predictions of Einstein gravity.

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## Fast radio bursts as probes of large-scale structure

Tuesday Jan 12, 2016

Fast radio bursts (FRBs) are bright, broadband, non-repeating, millisecond flashes of unknown astronomical origin.

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## Alternatives to Inflation – Non-Minimal Ekpyrosis & Conflation

Tuesday Dec 15, 2015
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In this talk I derive the evolution equations for two scalar fields with non-canonical field space metric up to third order in perturbation theory, employing the covariant formalism. These equations can be used to calculate the local bi- and trispectra of the non-minimal ekpyrotic model. Remarkably, the nearly scale-invariant entropy perturbations have vanishing bi- and trispectra during the ekpyrotic phase.

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## Can We Identify the Theory of Dark Matter with Direct Detection?

Tuesday Dec 08, 2015

In light of the upcoming Generation 2 (G2) direct-detection experiments attempting to record dark matter scattering with nuclei in underground detectors, it is timely to inquire about their ability to single out the correct theory of dark-matter-baryon interactions, in case a signal is observed. I will present a recent study in which we perform statistical analysis of a large set of direct-detection simulations, covering a wide variety of operators that describe scattering of fermionic dark matter with nuclei.

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## RECENT PUBLIC LECTURE

### Emily Levesque: The Weirdest Stars in the Universe

Speaker: Emily Levesque