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.

 

Tuesday Jul 16, 2019
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I’ll discuss the issue of how we can tell which quantum state might be the “right “ one for inflationary quantum fluctuations. I’ll then use a new class of states that entangle curvature fluctuations with those of a spectator scalar field and discuss potential observational signatures of such states.

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Tuesday Jun 25, 2019
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It is generally believed that modification of general relativity inevitably introduce extra physical degree(s) of freedom.
In this talk I argue that this is not the case by constructing modified gravity theories with two local physical degrees of freedom. After classifying such theories into two types, I show explicit examples and discuss their cosmology and phenomenology.

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Tuesday Jun 11, 2019
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Modified gravity theories typically feature numerous additional parameters and functions as compared to general relativity, which are unmotivated by observations and challenging to meaningfully constrain. We instead propose a new theory of gravity with the startling property of having *fewer* degrees of freedom than general relativity with a cosmological constant, by invoking a duality property within a first-order formulation that supports torsion.

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Thursday May 23, 2019
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Tuesday May 21, 2019
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The history of the baryonic (normal) matter in the universe is an excellent probe of the  formation of cosmic structures and the evolution of galaxies.  Over the last decade, considerable effort has gone into investigating the physics of baryonic material, particularly after the epoch of Cosmic Dawn: signalling the birth of the earliest stars and 

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Tuesday May 14, 2019
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Fundamental physics traditionally views the dynamical laws governing the world as time reversal invariant. The evident arrow of time of nature is then held to be an accident, emerging as we coarse grain and originating in the improbable choice of initial conditions. The main pillar which supports this time-symmetric lifestyle is the fluctuation-dissipation theorem, which connects purely time-symmetric microscopic equations to the emergence of a macroscopic arrow of thermodynamics.

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Tuesday Apr 09, 2019
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Large scale B-mode patterns in CMB polarization, if detected, would constitute a “smoking gun” signature of primordial gravitational waves generated during an inflationary phase in the early universe. In this talk, I will discuss other sources of B-modes, such as primordial magnetic fields, axion-like fields and cosmic strings, and prospects of isolating their distinguishing features with future CMB measurements.

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Tuesday Mar 26, 2019
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I'll discuss recent work on finding time-dependent solutions of a black hole interacting with a scalar field. I'll discuss two distinct cases where the back-reaction of the scalar can be found. First, in the case that the scalar is slowly rolling (such as in inflation) the scalar field can be found in terms of super-advanced time coordinate, regular on both horizons. The scalar back-reacts on the geometry, with the black hole accreting and growing more or less as expected.

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Tuesday Mar 12, 2019
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Quasars are among the most powerful light sources in the universe and, as such, can be seen at cosmological distances. Is some rare occasions (although not that rare), a massive galaxy on their line of sight can act as a gravitational lens and produce multiple images of distant quasars. These can be used both for cosmology and astrophysics by measuring the so-called time delays between the lensed images from photometric monitoring, a quantity directly related to the Hubble-Lemaître parameter H0.

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Tuesday Feb 05, 2019
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Quantum decay of false vacuum states via the nucleation of bubbles may 
have played an important role in the early history of our Universe.  For 
example, in multiverse models that utilize false vacuum eternal 
inflation, the Big Bang of our observable Universe corresponds to one of 
these bubble nucleation events.  Further, our observable Universe may 
have undergone a series of symmetry-breaking first-order phase 
transitions as it cooled, which may have produced a remnant background 
of gravitational waves.

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