- Organized by
Gregory Gabadadze, Ph.D.
Eva Silverstein, Ph.D.Stanford University
Paul Steinhardt, Ph.D.Princeton University
The first annual meeting of the Origins of the Universe program will bring together three diverse groups of theoretical cosmologists, each addressing the history of the universe in their own ways. The themes of the presentations and discussions will include inflationary dynamics and its observational probes, bouncing cosmologies, and other proposals for geodesically past-complete classical models.
THURSDAY, SEPTEMBER 20
8:30 AM CHECK-IN & BREAKFAST 9:30 AM Paul Steinhardt | Introduction to Bouncing Cosmology 10:30 AM BREAK 11:00 AM Anna Ijjas | Recent Advances in Constructing Smooth Cosmological Bounces 12:00 PM LUNCH 1:30 PM Leonardo Senatore | Field Theory, Geometry and Data in Cosmology 2:30 PM BREAK 3:00 PM Liam McAllister | Inflationary Theory and Quantum Gravity 4:00 PM BREAK 4:30 PM Benjamin Wallisch | Signatures of the Early Universe in the BAO Spectrum 4:50 PM Jonathan Braden | Curvature Perturbations from Entropy Generation on Ballistic Trajectories 5:10 PM DAY ONE CONCLUDES
FRIDAY, SEPTEMBER 21
8:30 AM CHECK-IN & BREAKFAST 9:30 AM Frans Pretorius | Numerical Approaches to Bouncing Cosmologies 10:10 AM BREAK 10:40 AM Claudia de Rham | Physics Under the Gravitational Rainbow 11:40 AM LUNCH 12:40 PM David Pirtskhalava | Violation of the Null Energy Condition and the Early Universe Cosmology 1:40 PM BREAK 1:50 PM Greg Gabadadze | Strong Coupling and Early Universe in Beyond Einstein Theories 2:30 PM MEETING CONCLUDES
Introduction to Bouncing Cosmology
This talk will explain how models that replace the big bang with a classical, non-singular transition from contraction to expansion can address many of the fundamental problems of cosmology.
Recent Advances in Constructing Smooth Cosmological Bounces
In this talk, I will describe newly discovered, smooth, non-singular bounce solutions. In particular, I will focus on how adapting insights and tools from mathematical relativity has been crucial for these constructions and why it will also be a central focus looking ahead.
Numerical Approaches to Bouncing Cosmologies
In this talk, I will give an introduction to numerical solutions of the Einstein equations, focusing on their application to bouncing cosmologies. I will review some work that has been done and discuss some of the challenges going forward that will need to be overcome to fully investigate generic, non-perturbative regimes in non-singular bounce models.
Field Theory, Geometry and Data in Cosmology
I will discuss several applications of geometry and field theory to cosmology and how they can affect our understanding of the cosmological data. In the context of geometry, I will show how Thurston’s geometrization classification and mean curvature flow, together with advanced numerical techniques in general relativity, are used to shed light on how inflation starts out of completely inhomogenous initial conditions. I will also discuss a rigorous formalism that allows us to compute correlation functions of fields that are light during inflation and that are endowed with a nontrivial potential, for which naïve perturbation theory is IR divergent. In a multifield landscape of scalar fields, we derive a strongly non-Gaussian tail of the distribution of primordial perturbations, exhibiting factorial growth of N point correlators. I will then show how these results allow us to identify novel inflationary signatures and connect to some cosmological data, exploring CMB and primordial black hole signals.
Signatures of the Early Universe in the BAO Spectrum
Many aspects of the early universe are currently probed through the cosmic microwave background. Due to theoretical developments and an increase in survey sensitivity, these measurements can now be complemented by large-scale structure observations. In this talk, I will advocate the spectrum of baryon acoustic oscillations (BAO) as a new observable for early universe cosmology beyond its use as a standard ruler. I will present the first measurement of the cosmic neutrino background as imprinted in the BAO spectrum of galaxy clustering obtained by BOSS. As a second example, I will discuss a new search for oscillatory features of the primordial power spectrum in the same observable.
Curvature Perturbations from Entropy Generation on Ballistic Trajectories
Inflation provides a dynamical mechanism to produce the primordial density perturbations that seed the formation of structure in the Universe through gravitational collapse. However, during the inflationary phase, the Universe is in a nearly homogeneous and low-entropy state, which must eventually give rise to the dense thermal plasma of the standard hot big bang. This transition, known as (p)reheating, is a necessary ingredient in inflationary theory. Microscopic models of this transition typically lead to strong instabilities and the eventual onset of highly complex, nonlinear mode-mode coupled behavior.
I will introduce a novel viewpoint on preheating dynamics — the ballistic approximation — where the derivatives coupling nearby points in spacetime (separated by less than Hubble scales) are ignored and individual points in spacetime evolve independently. Remarkably, this approximation captures the relevant dynamics obtained in full lattice simulations. We define a nonlinear generalization of the comoving curvature perturbation that applies on subhorizon as well as superhorizon scales, allowing it be monitored at the level of individual lattice sites in a nonlinear lattice simulation. Absent couplings between trajectories, this quantity is conserved, and the production of curvature fluctuations can be identified with entropy generation. Using this viewpoint, I will argue that the production of curvature perturbations from end-of-inflation dynamics is ubiquitous, rather than occurring in only a few highly specialized models. Furthermore, our formalism can be extended to study the effects of particle production and evolution on nontrivial potential surfaces during inflation, thus providing a unifying description of both the inflationary and early post-inflationary Universe.
Inflationary Theory and Quantum Gravity
Important conceptual and technical issues in inflationary theory depend on the details of the ultraviolet completion of gravity. String theory provides a concrete framework for attacking these problems and has inspired new approaches to understanding inflation and de Sitter space. Conjectured properties of quantum gravity and features of known solutions of string theory have led to novel inflationary models and signatures. The structure of the string landscape, along with holographic duality, also feeds into ongoing research on de Sitter quantum gravity. After summarizing the status of this subject, I will describe several developments over the past year. These may include analyses of inflationary scenarios building from the geometry of string compactifications, the kinetic sector of supergravity and the large-flavor limit of string theory; careful assessments of the weak gravity conjecture and its interplay with large-field inflation; and basic quantum information theoretic properties of de Sitter space.
Claudia de Rham
Physics under the Gravitational Rainbow
The recent direct detection of gravitational waves marks the beginning of a new era for physics and astronomy with an opportunity to probe gravity at its most fundamental level. I will discuss how the behavior of gravity on large scales may differ from general relativity and its implications for early and late-time cosmology as well as the potential signatures on the spectrum of gravitational waves observable at LIGO and LISA.
Violation of the Null Energy Condition and the Early Universe Cosmology
I will review recent progress in understanding low-energy effective field theories that can consistently violate the null energy condition of general relativity. The implications of these theories for alternatives to cosmic inflation as well as the non-anthropic approaches to the cosmological constant problem will be discussed.
Strong Coupling and Early Universe in Beyond Einstein Theories
Certain cosmologically interesting field theories that, at the classical level, exhibit strongly coupled behavior can be embedded in broader theories that help the strong coupling issue. I will discuss recent developments on these theories and their possible cosmological implications.
Group AThe foundation will arrange and pay for all air and train travel to the conference for those in Group A. Please provide your travel specifications by clicking the registration link above. If you are unsure of your group, please refer to your invitation sent via email.
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Participants in Groups A & B who require accommodations are hosted by the foundation for a maximum of four nights at The Roger hotel. Any additional nights are at the attendee’s own expense.
The Roger New York
131 Madison Avenue
New York, NY 10016
(between 30th and 31st Streets)
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