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

A New Real-Time Picture of Vacuum Decay

Jonathan Braden Canadian Institute for Theoretical Astrophysics (CITA)

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.

A new probe to axion-like particles from upcoming CMB experiments

Suvodip Mukherjee Institut d’Astrophysique de Paris

Cosmic Microwave Background (CMB) is a powerful probe to the Universe which carries signatures of cosmic secrets over a vast range of redshifts. Along with spatial fluctuations, spectral distortions of CMB blackbody are also a rich source of cosmological information. In my talk, I will introduce a new kind of spectral distortion of CMB which can arise due to the conversion of CMB photons into Axion-Like Particles (ALPs) in the presence of an external magnetic field.

Conformal Horizon Fluctuations in de Sitter Space, Dynamical Dark Energy & the CMB

Emil Mottola Los Alamos National Laboratory

Infrared sensitivity of the de Sitter decay rate due to particle creation requires that gravitational backreaction be taken into account on the horizon scale. At lowest order, backreaction can be studied by Linear Response of the geometry to quantum matter perturbations around the Bunch-Davies state. In Linear Response the scalar degree of freedom derived from the conformal anomaly gives rise to scalar gravitational waves that grow without bound on the de Sitter horizon scale,  which implies substantial non-linear quantum backreaction effects in cosmology.

Instability of de Sitter Space & Dynamical Dark Energy

Emil Mottola Los Alamos National Laboratory

Cosmological vacuum energy does not remain constant for the same reason that a uniform electric field cannot persist indefinitely in the presence of quantum fluctuations. The decay rate of the Bunch-Davies state of QFT in de Sitter space due to particle creation is calculated in real time by the same method as that for an electric field, giving Schwinger’s result.  In both the electric field and de Sitter cases the particles created are verified to be real, in that they persist in the final asymptotic region if the background field is switched off.

Inflation from spontaneously broken Weyl invariance in theories with torsion

Stefano Lucat Utrecht University

Introduction of the torsion tensor on the space-time manifold  leads to a Weyl invariant geometry, in which t e torsion trace acts as a "U(1)" compensating field for the conformal transformations. Such  symmetry can be extended to the whole matter sector included in the  standard model by coupling the Higgs scalar (and all other possible  fundamental scalars) to the torsion. A relevant question is then whether such framework can be used to describe cosmic inflation, as a spontaneous symmetry breaking phenomenon.

Large-Scale Structure with 21cm Intensity Mapping

Andrej Obuljen University of Waterloo

In this talk I will discuss several aspects of using the 21cm Intensity Mapping (IM) as a Large-Scale Structure (LSS) probe in order to better constrain the cosmological parameters. I will start with a Baryon Acoustic Oscillations (BAO) reconstruction method intended for 21cm IM observations at low redshifts. I will then present the predictions and gains of performing 21cm IM surveys at redshift range which is currently vastly unobserved (2<z<6).

CMB Beyond Planck

Martin Bucher The French National Centre for Scientific Research

In July 2018 the Planck Collaboration released its final set of cosmology results. I will discuss some of the  interesting new science that remains to be done with the CMB, including some not so often discussed topics such as the kinetic SZ effect and 21cm cross-correlations.


The Conformal Anomaly Effective Theory of Gravity III: Scalar Gravitational Waves, Black Holes and Dark Energy

Emil Mottola Los Alamos National Laboratory
In this third of 3 talks I will discuss the effects of the conformal anomaly in the low energy infrared relevant correction to General Relativity. Among the significant implications of this effective field theory of gravity are the prediction of scalar gravitational wave solutions—a spin-0 breather mode— in addition to the transversely polarized tensor waves of the classical Einstein theory.

Cosmology with the Hyper Suprime-Cam (HSC) survey

Rachel Mandelbaum Carnegie Mellon University

Hyper Suprime-Cam (HSC) is an imaging camera mounted at the Prime Focus of the Subaru 8.2-m telescope operated by the National Astronomical Observatory of Japan on the summit of Maunakea in Hawaii. A consortium of astronomers from Japan, Taiwan and Princeton University is carrying out a three-layer, 300-night, multiband survey from 2014-2019 with this instrument. In this talk, I will focus on the HSC survey Wide Layer, which will cover 1400 square degrees in five broad bands (grizy), to a 5 sigma point-source depth of r~26.