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.

 

Thursday Jun 02, 2016
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We have great certainty on how gravity works around our solar system: General Relativity (GR) has been found to be very accurate at these small scales. On large scales though, we still have a considerable lack of understanding about the evolution of the universe, and its constituents. While the LCDM model is in good agreement with cosmological data, this might change in the future. For this reason, we need to test GR on these scales.



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Tuesday May 31, 2016

I will discuss how we constrain properties of the universe using two

tracers of large scale structure measured by the BOSS (Baryon

Oscillations Spectroscopic Experiment): galaxies and Lyman-alpha

forest. I will show recent results from baryonic acoustic oscillations

measured in both tracers and discuss cosmological implications. I

will briefly mention other measurements and consider forecasts for

quasar-forest bispectrum to constrain primordial non-Gaussianity.

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Thursday May 12, 2016
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Spectral distortions of the CMB provide a powerful new probe of early Universe processes. Even if so far no average spectral distortion has been seen, LCDM does predict several signals that are within reach of current technology. In this talk, I will give a broad brush overview of our most recent understanding of the formation and evolution of distortions in the early Universe, highlighting guaranteed LCDM signals and what we hope to learn from them about the Universe we live in.

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Tuesday May 10, 2016
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Gravitational lensing by matter clumps can magnify various transient bursts in the sky, making them more detectable from the high redshift Universe. For one example, chirping gravitational waves from stellar-mass black hole binary mergers, as first detected by LIGO recently, can appear louder due to intervening galaxies.

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Monday May 09, 2016
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In the last few years, we have made remarkable progress in understanding the properties of our observable Universe which appears to have evolved from a hot Big Bang 13.7 billion years ago. The fine-tuning of initial conditions required to reproduce our present day Universe suggests that our Universe may merely be a region within an eternally inflating super-region. Many other regions could exist beyond our observable Universe with each such region governed by a different set of physical parameters than the ones we have measured for our Universe.

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Tuesday Apr 26, 2016
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Planck's full-mission data, released in 2015, provides a high-resolution whole-sky polarization and temperature maps of the CMB and astrophysical components. I will talk about implications of Planck 2015 results for inflation, why cosmic dust is important, and what we are currently doing to study it. I will also highlight some tests of the statistical isotropy and Gaussianity of the cosmic microwave background (CMB) anisotropies we have done with observations made by the Planck satellite.

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Tuesday Apr 05, 2016
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Tuesday Mar 29, 2016
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Since the Universe was filled with hydrogen atoms at early times, the

most promising method for observing the epoch of the first stars is to

measure the hyperfine line of hydrogen at a wavelength of 21 cm. Such

an observation of the "cosmic dawn" era was considered speculative

when I helped lay out the theoretical predictions a decade ago, but

there is now an enormous, promising observational effort (in which I

am involved within the Square Kilometre Array). There is also an
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Tuesday Mar 22, 2016
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I will discuss the cosmology of galileon models with a Minkowski limit and discuss whether they can account for the currently observed cosmological model. The full galileon model predicts the speed of gravitational waves to be different from that of photons. I will discuss this and compare with observations. I will then discuss a subdominant galileon model which is compatible. Finally I will discuss the shape dependence of screening in galileon models, showing that the fifth force is unscreened for planar objects.

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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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