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# 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.

## Highlights from the Atacama Cosmology Telescope

Mardi fév 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

Jeudi 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

Jeudi 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

Mardi 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

Mardi déc 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?

Mardi déc 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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## On the Statistics of Biased Tracers and BAO in the Effective Field Theory of Large Scale Structures

Mardi déc 01, 2015
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With the completion of the Planck satellite, in order to continue collecting cosmological information it is

important to gain a precise understanding of the formation of Large Scale Structures (LSS) of the universe.

The Effective Field Theory of LSS (EFTofLSS) offers a consistent theoretical framework that aims to develop

an analytic understanding of LSS at long distances, where inhomogeneities are small. We present the recent

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## Axionic Band Structure of the Cosmological Constant

Jeudi nov 19, 2015
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We argue that theories with multiple axions generically contain a large
number of vacua that can account for the smallness of the cosmological
constant. In a theory with N axions, the dominant instantons with charges Q
determine the discrete symmetry of vacua. Subleading instantons break the
leading periodicity and lift the vacuum degeneracy. For generic integer charges
the number of distinct vacua is given by |det(Q)|~exp(N). Our construction
motivates the existence of a landscape with a vast number of vacua in

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## Beyond the CMB: The Effective Field Theory of Large Scale Structure

Mardi nov 17, 2015
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The next hope to constrain cosmological parameters observationally is in surveys of the large scale structure (LSS) of the universe. LSS has the potential to rival the CMB in cosmological constraints because the number of modes scales like the volume, but the nonlinear clustering due to gravity makes it more difficult to extract primordial parameters. In order to take full advantage of the constraining power of LSS, we must understand it in the quasi-nonlinear regime.

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## Cosmic Neutrinos and Other Light Relics

Mardi nov 10, 2015
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Cosmic neutrinos carry a wealth of information about both cosmology and particle physics, but they are notoriously difficult to observe. Rapid advancement in measurements of the cosmic microwave background, however, have allowed us to indirectly constrain some properties of the cosmic neutrino background. I will discuss the current status and future prospects for improving constraints on cosmic neutrinos, focusing in part of the phase shift of acoustic peaks in the cosmic microwave background which results from neutrino fluctuations.

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## RECENT PUBLIC LECTURE

### Molly Shoichet: Engineering Change in Medicine

Speaker: Molly Shoichet