Collection Number S004
Collection Type Series
This series consists of talks in the area of Cosmology and Gravitation.

High-redshift astrophysics using every photon

Patrick Breysse Canadian Institute for Theoretical Astrophysics (CITA)

Large galaxy surveys have dramatically improved our understanding of astrophysics and cosmology in the high-redshift universe, but they are fundamentally limited by the need to integrate long enough to detect each individual source. Line intensity mapping has recently arisen as a powerful alternative to these surveys, offering access to fainter sources and larger volumes than conventional techniques. There has been a surge of experimental interest in this technique, with surveys planned or in progress across the electromagnetic spectrum.

The MESS and dualities of cosmological perturbations

Antonio Enea Romano National Taiwan University

We introduce two new effective quantities for the study of comoving curvature perturbations ζ: the space dependent effective sound speed (SESS) and the momentum dependent effective sound speed (MESS) . We use the SESS and the MESS to derive a new set of equations,  not involving explicitly entropy or anisotropies, which can be applied to any system described by an effective stress-energy-momentum tensor (EST), including any multi-fields systems, supergravity and modified gravity theories.

Entangled Inflationary States

Richard Holman Minerva Schools at KGI

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.

Minimalism in modified gravity

Shinji Mukohyama Yukawa Institute for Theoretical Physics

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.

Simplifying general relativity

Andrew Liddle University of Lisbon

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.

Mapping the baryonic universe: from reionization to present-day galaxies

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 

Our time-symmetric lifestyle

Marina Cortes University of Lisbon

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.

Slow Roll with a Black Hole (and other scalar tails)

Ruth Gregory Durham Academy

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.

Astrophysics and cosmology with gravitationally lensed quasars

Frederic Courbin L'Ecole Polytechnique Federale de Lausanne (EPFL)

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.