Adam Brown, Princeton University

Bubbles of nothing and the big bang

Alejandra Castro, McGill University

The partition function of quantum de Sitter

We propose that quantum gravity in de Sitter space should be defined by fixing boundary conditions at the location of an observer. This provides a notion of holography  in de Sitter space which can be defined strictly in terms of observable quantities. We  consider the partition function for the three dimension de Sitter gravity defined with  such boundary conditions. We argue that the partition function has an interpretation as a sum over Euclidean geometries, and that the partition function must therefore be  modular invariant. This partition function can be computed in the semiclassical limit, where it reproduces the Bekenstein-Hawking entropy of de Sitter space. We comment on the exact computation using a Chern-Simons formulation.

Frederik Denef, Harvard University

Complexity in Fundamental Physics

Xi Dong, Stanford University

An effective Field Theory Dual of FRW Spacetime

We investigate a simple FRW spacetime realized by a brane construction. This also comes from a Coleman-de Luccia decay from a metastable de Sitter. We motivate a dual description in terms of a low energy effective field theory (EFT) on FRW in one lower dimensions. This EFT is coupled to gravity with a time-dependent Planck mass that grows to infinity at late times. We investigate the entropy bound, correlation functions, and various particle/brane probes as first steps to understand the degrees of freedom building up the EFT. This is work in collaboration with B. Horn, S. Matsuura, E. Silverstein, and G. Torroba.

Willy Fischler, University of Texas

Challenges in Cosmology

An attempt at describing some of the shortcomings in our present understanding of cosmology.

Ben Freivogel, UC, Berkeley

Predictions from geometric cutoffs in Eternal Inflation

Daniel Lord Harlow, Stanford University

Liouville theory and Holographic Cosmology

I will explain how Liouville theory with complex values of its parameters arises naturally in speculative holographic cosmologies.  We will encounter Liouville theory of both the ``spacelike'' and ``timelike'' variety.  I will then use this as motivation to present some new results on the analytic continuation of Liouville theory recently obtained with Maltz and Witten.

Patrick Hayden, McGill University

On the fast scrambling conjecture

Motivated by the consistency of black hole complementarity, Sekino and Susskind have conjectured that no physical system can "scramble" its internal degrees of freedom in time faster than (1/T) log S, where T is temperature and S the system's entropy. By considering a number of toy examples and general Lieb-Robinson-type causality bounds, I'll explore the range of validity of the conjecture. Some of these examples suggest that nonlocal Hamiltonians can delocalize information at rates exceeding the fast scrambling bound, but the physical relevance of these examples is unclear. Joint work with Nima Lashkari and Douglas Stanford.

Simeon Hellerman, IPMU

Bubble Popper

In the context of the AdS/CFT correspondence, I will discuss model-independent properties shared by bulk theories of gravity with consistent dual descriptions.  I will then discuss the prospects of extending these ideas to non-conformal theories, in particular to attempts to realize cosmological theories holographically.  I will address the status of in-principle falsifiability of various holographic proposals through internal consistency conditions of the boundary theory.

Bart Horn, Stanford University

Micromanaging and Accounting in de Sitter Holography

I will discuss recent work engineering "semi-holographic" constructions of de Sitter space in string theory, using elliptic fibrations and orientifolds to uplift known Freund-Rubin compactifications.  The dual brane construction is compact and provides a microscopic realization of the dS/dS correspondence of Alishahiha et al., realizing de Sitter space in d dimensions as a warped compactification down to d-1 dimensional de Sitter space coupled to a pair of large N matter sectors.  This provides a parametric microscopic accounting of the Gibbons-Hawking entropy.  I will discuss an explicit example in three dimensions as well as ongoing work in four dimensions.

Stefan Leichenauer, University of California, Berkeley

Eternal inflation predicts that time will end

Present treatments of eternal inflation regulate infinities by imposing a geometric cutoff. We point out that some matter systems reach the cutoff in finite time. This implies a nonzero probability for a novel type of catastrophe. According to the most successful measure proposals, our galaxy is likely to encounter the cutoff within the next 5 billion years.

Hong Liu, MIT

Inside the horizon with holographic Wilsonian RG

Alex Maloney, McGill University

A de Sitter Farey Tail

We compute the partition function of quantum Einstein gravity in three dimensional de Sitter space. The Euclidean path integral is formulated as a sum over geometries, including both perturbative loop and non-perturbative instanton corrections coming from geometries with non-trivial topology. These non-trivial geometries have a natural physical interpretation and lead to deviations from the standard thermal behaviour of the de Sitter horizon; this is the de Sitter analog of the celebrated "black hole Farey tail." Perturbative quantum corrections are computed to all orders in perturbation theory and the vacuum partition function, including all instanton and perturbative corrections, is shown to diverge in a way which can not be regulated using standard field theory techniques.  Thus the Hartle-Hawking state is not normalizable.

Juan Maldacena, IAS

The semiclassical wavefunction of the universe near de Sitter space

We make some remarks about the semiclassical wavefunction of the universe around de-Sitter space. In five dimensional gravity with a positive cosmological constant it is possible to compute the full semiclassical measure for arbitrary geometries at superhorizon scales. In four dimensions, the same computation can be reformulated as a problem in conformal gravity.

Daniel Park, MIT

Lessons on Quantum Supergravity from Six-Dimensions

Six dimensional (1, 0) supergravity theories have received recent attention due to the fact that the strong constraints coming from anomalies severely restrict the theory. These constraints are restrictive enough that it is possible to get a rather good handle on the space of theories that do not exhibit any (known) inconsistencies. Many useful observations can be made by studying this space of theories. In particular, the process of comparing these theories with six-dimensional string vacua turns out to be fruitful in many aspects. I will be presenting the lessons learned from research in this direction.

Joe Polchinski, UC, Santa Barbara

Bulk Physics from CFT

Gauge/gravity duality is our most complete construction of quantum gravity, but it gives in a simple way only the observations of an observer at the AdS boundary.  I discuss various issues regarding the representation of the bulk physics.

John Preskill, Callifornia University of Technology

Simulating the universe with a quantum computer

I'll discuss some recent insights regarding the complexity of simulating highly entangled quantum systems using classical and quantum computers, and what these advances might imply about the quantum state of the early universe.

Mark van Raamsdonk, University of British Columbia

A toy model of quantum gravity in cosmological spacetimes

In this talk, I attempt to gain insight into the description of quantum gravity on cosmological spacetimes by considering the physics of families of accelerating observers in spacetimes which admit non-perturbative descriptions vis AdS/CFT.

Yasuhiro Sekino, Okayam Institute for Quantum Physics

Correlation functions in FRW/CFT duality

FRW/CFT duality is a proposal for a holographic dual description for universe created by bubble nucleation.  For (3+1) dimensional universe, the dual theory is defined on 2-sphere at the boundary of open universe.  I will study correlation functions and explain essential features of FRW/CFT duality: One bulk field corresponds to a tower of CFT operators  The boundary theory contains 2D gravity, and the Liouville field plays the role of time.  Energy-momentum tensor has dimension 2, as required from the 2D conformal symmetry.

Eva Silverstein, Stanford University

Uplifting AdS/CFT to Cosmology

Starting from AdS/CFT, one can introduce ingredients which produce cosmological solutions, including metastable de Sitter and its decay to FRW.  In the de Sitter case, this produces a compact brane construction which mirrors the dS/dS correspondence realizing de Sitter as a pair of warped throats coupled to gravity.  In the FRW case, I will present simple solutions sourced by magnetic flavor branes and explore their holographic description.  The basic strategy is to exhibit a time-dependent warped metric on the solution and test the interpretation of the resulting region of gravitational redshift as a low energy effective field theory (EFT) by analyzing particle dynamics and correlation functions.  

At finite times, the EFT has a finite cutoff since system has a propagating lower dimensional graviton and a finite covariant entropy bound, but the graviton decouples at late times as the Planck mass goes off to infinity along with the entropy.  This is work in collaboration with X. Dong, B. Horn, S. Matsuura, and G. Torroba.  Along the way I will make some comments on the role of microscopic (UV complete) physics in cosmological holography and mention several different approaches to deriving landscape duals.

Douglas Stanford, Stanford University

Dictionaries and Wavefunctions in dS/CFT and AdS/CFT

Dual AdS/CFT correlators can be computed in two equivalent ways: differentiate the bulk partition function with respect to boundary conditions, or extrapolate bulk correlation functions to the boundary. By contrast, dS/CFT analogues of the two dictionaries are inequivalent. I will discuss the relation of these dictionaries to each other, and to AdS and FRW holography. Work done with Daniel Harlow.

Neil Turok, Perimeter Institute

A Canonical Measure for Inflation

Erik Verlinde, Utrecht University

The Hidden Phase Space of our Universe

By combining insights from black holes and string theory we argue for the existence of a hidden phase space associated with an underlying fast dynamical system, which is largely invisible from a macroscopic point of view.  The dynamical system is influenced by slow macroscopic observables, such as positions of objects. This leads to a collection of reaction forces, whose leading order Born Oppenheimer force is determined by the general principle that the phase space volume of the underlying system is preserved. We propose that this adiabatic force is responsible for inertia and gravity.  This fact allows us to calculate the hidden phase space volume from the known laws of inertia and gravity. We find that in a cosmological setting the appearance of dark energy is naturally explained by the finite temperature of  the underlying system.  The adiabatic approximation that leads to the usual laws of inertia and gravity breaks down in the neighborhood of horizons. In this regime the reaction force degenerates into an entropic force, and the laws of inertia and gravity receive corrections due to thermal effects. A simple estimate of these effects leads to the conclusion that they coincide with observed phenomena attributed to dark matter.

Herman Verlinde, Princeton University

Fuzzy Twistors and Emergent Gravity

In this talk, I explain how twistors can be used to provide a covariant UV cut-off for 4-D gauge theory. I'll then motivate the conjecture that the cut-off gauge theory automatically contains 4-D Einstein gravity. As evidence, I describe how the theory reproduces the gravitational MHV amplitudes.

Alex Vilenkin, Tufts University 

Holographic multiverse and the measure problem.

We explore the duality, conjectured in earlier work, between the wave function of the multiverse and a 3D Euclidean field theory on the future boundary of spacetime.  We propose that a measure for the multiverse, which is needed in order to extract quantitative probabilistic predictions, can be derived in terms of the boundary theory by imposing a UV cutoff. In the inflationary bulk, this measure corresponds to a cutoff at surfaces of constant comoving apparent horizon.

I Sheng Yang, Columbia University

Exploring the Landscape with Classical Transitions

Classical transition is one of the simplest consequences of cosmic bubble collisions.  In quite a few simple toy  model landscapes, collisions always result in classical transitions.  Can it be generalized to the "real" string  theory landscape?  If so, does it imply some sort of hidden structure of the landscape?