publication . Preprint . Article . 2014

Simulating the universe(s): from cosmic bubble collisions to cosmological observables with numerical relativity

Wainwright, Carroll L.; Johnson, Matthew C.; Peiris, Hiranya V.; Aguirre, Anthony; Lehner, Luis; Liebling, Steven L.;
Open Access English
  • Published: 17 Mar 2014
  • Country: Italy
The theory of eternal inflation in an inflaton potential with multiple vacua predicts that our universe is one of many bubble universes nucleating and growing inside an ever-expanding false vacuum. The collision of our bubble with another could provide an important observational signature to test this scenario. We develop and implement an algorithm for accurately computing the cosmological observables arising from bubble collisions directly from the Lagrangian of a single scalar field. We first simulate the collision spacetime by solving Einstein's equations, starting from nucleation and ending at reheating. Taking advantage of the collision's hyperbolic symmetry, simulations are performed with a 1+1-dimensional fully relativistic code that uses adaptive mesh refinement. We then calculate the comoving curvature perturbation in an open Friedmann-Robertson-Walker universe, which is used to determine the temperature anisotropies of the cosmic microwave background radiation. For a fiducial Lagrangian, the anisotropies are well described by a power law in the cosine of the angular distance from the center of the collision signature. For a given form of the Lagrangian, the resulting observational predictions are inherently statistical due to stochastic elements of the bubble nucleation process. Further uncertainties arise due to our imperfect knowledge about inflationary and pre-recombination physics. We characterize observational predictions by computing the probability distributions over four phenomenological parameters which capture these intrinsic and model uncertainties. This represents the first fully-relativistic set of predictions from an ensemble of scalar field models giving rise to eternal inflation, yielding significant differences from previous non-relativistic approximations. Thus, our results provide a basis for a rigorous confrontation of these theories with cosmological data.
Comment: 52 pages, 23 figures. A four page summary of methods and results follows the introduction. Version 2 contains minor clarifications and edits to match the version accepted for publication by JCAP. Version 3 fixes a typo in Eq. 3.10 and a typo in the paragraph after Eq. 5.27. All other text, including results, remains the same
Persistent Identifiers
arXiv: General Relativity and Quantum Cosmology
free text keywords: High Energy Physics - Theory, Astrophysics - Cosmology and Nongalactic Astrophysics, General Relativity and Quantum Cosmology, Astronomy and Astrophysics, Physics, Inflaton, Scalar field, Spacetime, Numerical relativity, Universe, media_common.quotation_subject, media_common, Cosmic microwave background, Eternal inflation, Theoretical physics, False vacuum
Funded by
NSF| Collaborative Research: Loud, Bright, and Hot Compact Binary Mergers
  • Funder: National Science Foundation (NSF)
  • Project Code: 1308621
  • Funding stream: Directorate for Mathematical & Physical Sciences | Division of Physics
Understanding the Origin of Cosmic Structure
  • Funder: European Commission (EC)
  • Project Code: 306478
  • Funding stream: FP7 | SP2 | ERC
Validated by funder
  • Funder: Natural Sciences and Engineering Research Council of Canada (NSERC)
NSF| Collaborative Research: Dynamics and Gravitational Wave Production of Neutron Stars and Black Holes
  • Funder: National Science Foundation (NSF)
  • Project Code: 0969827
  • Funding stream: Directorate for Mathematical & Physical Sciences | Division of Physics

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