Cosmology

I will compute the probability distribution for bubble collisions in an inflating false vacuum which decays by bubble nucleation. The number of collisions in our backward lightcone can be large in realistic models without tuning. In addition, we calculate the angular position and size distribution of the collisions on the cosmic microwave background sky.

I will report results from simulations of galaxy-scale dark halos of unprecedented numerical resolution. Convergence tests demonstrate detailed convergence for (sub)structures for over six decades in mass, enabling detailed forecasts of the expected dark matter signal both in Earth-bound direct-detection experiments as well as in indirect detection experiments which attempt to image dark matter annihilation radiation in gamma rays.

Varied experimental results have recently sparked theoretical interest in the dark matter sector. I will review some of these results and the basic ideas in particle physics that might explain them, as well as some requirements for those models to work. Then I'll discuss a new model dark matter sector that can better explain many of the experimental results. I'll also mention the interesting cosmological history required in this type of model. Finally, if there's time, I'll discuss ongoing efforts at McGill to develop basic physics shared by many of the new dark matter models.

The standard cosmological framework explains an impressive range of large-scale astrophysical phenomena, but an agreement between its predictions and the properties of the dark matter halos of nearby galaxies has not been established. In this talk, I will highlight some key observables that constrain galaxy structure and some key differences between cosmological predictions and halo properties inferred from these measurements. I will also discuss proposed 'observational' solutions to some of these discrepancies, such as the role of coherent non-circular motions in spiral galaxies and the measured abundance of gas-rich, starless halos in the nearby Universe.

An astrophysical black hole is completely described with just two parameters: its mass and its dimensionless spin. A few dozen black holes have mass estimates, but until recently none had a reliable spin estimate. The first spins have now been measured for black holes in X-ray binaries.

I will discuss the possibility that a 'Wilson line' degree of freedom can play the role of an inflaton in a warped flux compactification, in the context of the DBI inflationary scenario. I will show how warped DBI Wilson line inflation offers an attractive alternative to ordinary (position field) DBI inflation, inasmuch as observational and theoretical constraints get considerably relaxed. Thus, besides the large non-Gaussianities produced in DBI scenarios, Wilson lines allow for an observable amount of gravitational waves, within consistent approximations.

We have only scratched the surface of the potential for using large-scale structure (LSS) as a probe of fundamental physics/cosmology, i.e., quantitatively, we have only measured a small fraction of a percent of the accessible LSS information. Future measurements will probe dark energy, inflation, dark matter properties, neutrino masses, modifications of gravity, etc. with unprecedented precision. I will discuss three probes of LSS: the traditional galaxy redshift survey, the Lyman-alpha forest (LyaF), and the new idea of 21 cm intensity mapping; and two future experiments that cover these probes: SDSS-III/BOSS (galaxies and LyaF) and the proposed CHIME (21 cm). I will discuss recent theoretical/phenomenological developments that promise to greatly enhance the power of LSS surveys, related to the connection between bias, redshift-space distortions, and non-Gaussianity.

Braneworlds are a fascinating way of hiding extra dimensions by confining ourselves to live on a brane. One particular model (Randall-Sundrum) has a link to string theory via living in anti de Sitter space. I'll describe how the ads/cft correspondence has been used to claim that a braneworld black hole would tell us how Hawking radiation back reacts on spacetime, thus solving one of the outstanding problems of quantum gravity - the ultimate fate of an evaporating black hole. I'll review evidence for this conjecture, ending with some recent work that shows it may be problematic.

We examine the embedding of dark energy energy models based upon supergravity. We analyse the structure of the soft supersymmetry breaking terms in presence of dark energy. We pay attention to their dependence on the quintessence field and to the electroweak symmetry breaking, ie the pattern of fermions masses at low energy within the MSSM coupled to quintessence. In particular, we compute explicitly how the fermion masses generated through the Higgs mechanism depend on the quintessence field for a general model of quintessence. Fifth force and equivalence principle violations are potentially present as the vev of the Higgs bosons become quintessence field dependent. We emphasize that equivalence principle violations are a generic consequence of the fact that, in the MSSM, the fermions couple diffeently to the two Higgs doublets. Finally, we also discuss how the scaling of the cold dark and baryonic matter energy density is modified.

Cosmology, in particular applying the physics of elementary particles to the extremely hot and violent conditions of the early universe, and exploring deep questions about the big bang, the fate of our universe, and the hope for intelligent life (here or elsewhere)

The growth of matter perturbations in the presence of dark energy with small fluctuations depends on the speed of sound of these fluctuations and the comoving scale. The growth index can differ from the value that it takes in the limit of no dark energy perturbations by an amount comparable to the accuracy of future observations. This may contribute to a better characterization of the dark energy properties.