Ben Craps, VUB & Solvay Institutes
Strings in Compact Cosmological Spaces
A formalism is proposed for perturbative string theory in spacetimes with totally compact space (and non-compact time).
Daniel Green, Stanford University
How much information is there in large scale structure?
Large scale structure contains vastly more Fourier modes than the CMB, and is therefore a promising arena for studying the early universe. One obstacle to using these modes is the non-linearity of structure formation. The amount of weakly coupled information available is therefore very sensitive to scale at which non-linear effects become important and simulations become necessary. Using effective field theory techniques, I will present evidence that the perturbative description of dark matter is much better behaved than previously thought. I will discuss the implications for improving constraints on non-gaussian initial conditions.
Marc Henneaux, Solvay Institute
Remarks on Gravitational Duality
Renee Hlozek, Princeton University
The Microwave Background on small scales: Cosmological parameters from three seasons of data of the Atacama Cosmology Telescope (ACT).
The Atacama Cosmology Telescope (ACT) has mapped the microwave sky to
arcminute scales. We present constraints on parameters from the observations at 148 and 217 GHz respectively by ACT from three years of observations. Efficient map-making and spectrum-estimation techniques allow us to probe the acoustic peaks deep into the damping tail, and allow for confirmation of the concordance model, and tests for deviations from the standard cosmological picture. We fit a model of primary cosmological and secondary foreground parameters to the dataset, including contributions from both the thermal and kinetic Sunyaev-Zel'dovich effect, Poisson distributed and correlated infrared sources, radio sources and a term modeling the correlation between the thermal SZ effect and the Cosmic Infrared Background. We will describe the multi-frequency likelihood for the ACT data, and present constraints on a variety of cosmological parameters using this
complete dataset, and put these results in context with the recent results from the Planck satellite.
David Langlois, APC Paris
A unifying approach to dark energy models
This talk will present an effective description of single field dark energy/modified gravity models, which encompasses most existing proposals. The starting point is a generic Lagrangian expressed in terms of the lapse and of the extrinsic and intrinsic curvature tensors of the uniform scalar field hypersurfaces. By expanding this Lagrangian up to quadratic order, one can describe the homogeneous background and the dynamics of linear perturbations. In particular, one can identify seven Lagrangian operators that lead to equations of motion containing at most second order derivatives, the time-dependent coefficients of three of these operators characterizing the background evolution. I will illustrate this approach with Horndeski's---or generalized Galileon---theories. Finally, I will discuss the link between this effective approach and observations.
Paul McFadden, Perimeter Institute
Precision Holographic Cosmology
We discuss holography for cosmology, focusing on a class of slow-roll inflationary spacetimes that are holographically dual to a perturbative RG flow between two nearby CFTs. The cosmological power spectrum and non-Gaussianities may be calculated directly from the dual QFT using conformal perturbation theory, even when the dual QFT is strongly coupled. Holography thus offers new methods for computing cosmological observables. To illustrate, we show how to recover the power spectrum to second order in slow roll.
Sean McWilliams, Princeton University
Gravitational waves and stalled satellites from massive galaxy mergers at z < 1
Pulsar timing arrays (PTAs), which are currently operating around the world and achieving remarkable sensitivities in the ~1--‐100 nHz band, will observe supermassive black holes (SMBHs) at redshifts z < ~1. Until now, all estimates of the anticipated signal strength of these sources have relied primarily on simulations to predict the relevant merger rates. I will present results from a completely new approach, which combines observational data and a fully self--‐consistent numerical evolution of the galaxy mass function. This method, which we will argue is superior to past estimates in several key ways, predicts a merger rate for massive galaxies that is ~10 times larger than that implied by previous calculations. I will explain why previous methods applied to this problem may systematically underestimate this merger rate, and one way in which our method may overestimate the rate, so that our approach has complementary systematic uncertainties in the worst case, and is an overall improvement in the best case. Finally, I will show that the new rate implies a range of possible signal strengths that is already in mild tension with PTA observations, with our model predicting a detection at the 95% confidence level as early as 2016. This could make PTAs the first instruments to directly detect gravitational waves, and will provide unprecedented information about the dynamics of merging galaxies, and merging bulges and supermassive black holes within those galaxies.
Shinji Mukohyama, Kavli IPMU
Massive gravity and cosmology
Ue-Li Pen, CITA
21cm cosmology
I will overview the progress of 21cm cosmology, with emphasis on intensity mapping. Current and future experiments have the potential for precision measurements of dark energy, neutrino mass, and gravitational waves.
Suvrat Raju, International Centre for Theoretical Sciences
The Information Paradox and an an Infalling Observer in AdS/CFT
Neil Turok, Perimeter Institute
Resolution of Cosmic Singularities and Bounces
The AdS/CFT correspondence provides new insights and tools to answer previously inaccessible questions in quantum gravity. Among the most interesting is whether it is possible to describe a cosmological "bounce" in a mathematically complete and consistent way. In the talk, I'll discuss joint work with M. Smolkin, developing the dual description of the simplest possible 4d M-theory cosmology in the stringy regime, employing the full quantum dynamics of its dual CFT. I'll also present evidence that the description extends to the Einstein-gravity regime.
Tanmay Vachaspati, Arizona State University
Cosmological Magnetic Fields
