Theoretical Cosmology
Lead Research Organisation:
University of Portsmouth
Department Name: Institute of Cosmology and Gravitation
Abstract
In recent years there has been an explosion in the amount and precision of observational data with which we can probe models of our Universe. This enables us to test speculative ideas about the physics at work in the very early Universe, the material content of the universe today, and even the nature of gravity and spacetime. A period of rapid, accelerated expansion in the very early universe, known as cosmological inflation provides the initial conditions from which the large scale structure of our universe can subsequently evolve. Quantum fluctuations during inflation are swept up to astrophysical scales by the rapid expansion, and we can distinguish between different possible models of inflation by the spectrum of fluctuations they leave behind. We intend to study the type of density fluctuations they produce, and the statistical properties of these fluctuations both in large galaxy surveys and in the pattern of temperature fluctuations in the cosmic microwave background radiation, which survives as a relic of the hot big bang. The most dramatic discovery in science in the past decade has been the revelation that the expansion of our Universe is actually accelerating today. This implies that the expansion must be driven, not by ordinary matter but by an unknown dark energy, similar to the quantum fields that drove inflation at high energies in the very early universe. However we have no clear idea what low-energy physics could lie behind the dark energy. It is important to distinguish the whether this dark energy is a cosmological constant, or whether it could vary in space and time. The growth of structure in our Universe revealed by observational surveys will be used to study the clustering of dark energy. In particular we will use weak gravitational lensing to probe the distribution of energy density in our Universe and an effect known as the integrated Sachs-Wolfe effect which probes the evolution of the gravitational potential as structure forms. We will also develop geometrical tests of the expansion history of our Universe, preparing for the next generation of massive cosmological data-sets that will be available to researchers in Portsmouth. We will develop advanced methods for cosmological data analysis with such surveys and make projections of the accuracy of geometrical tests. We will be seeking to distinguish models of dark energy from an alternative possibility that Einstein's theory of general relativity iteslf is modified on large scales. Our view of gravity and spacetime has been revolutionised in recent years by brane-world models which propose that our observed Universe may in fact be a four-dimensional 'brane' (with three space dimensions plus time) embedded in a higher-dimensional bulk spacetime. This could reconcile our observed four-dimensional world with string theory that requires extra, hidden spatial dimensions. We will continue work to study the implications of such brane-world models through their effect on models of inflation in the early universe, the evolution of cosmological structure, and the late-time acceleration of our Universe.
Organisations
Publications
Wang A
(2010)
Cosmological perturbations in Horava-Lifshitz theory without detailed balance
in Physical Review D
Zhao G
(2010)
Probing modifications of general relativity using current cosmological observations
in Physical Review D
Wang A
(2010)
Scalar field perturbations in Horava-Lifshitz cosmology
in Journal of Cosmology and Astroparticle Physics
Pogosian L
(2010)
How to optimally parametrize deviations from general relativity in the evolution of cosmological perturbations
in Physical Review D
Majerotto E
(2010)
Adiabatic initial conditions for perturbations in interacting dark energy models
in Monthly Notices of the Royal Astronomical Society
Assadullahi H
(2010)
Constraints on primordial density perturbations from induced gravitational waves
in Physical Review D
Byrnes C
(2010)
Scale dependence of local f NL
in Journal of Cosmology and Astroparticle Physics
Väliviita J
(2010)
Observational constraints on an interacting dark energy model
in Monthly Notices of the Royal Astronomical Society
Esposito-Farèse G
(2010)
Vector theories in cosmology
in Physical Review D
Shapiro C.
(2010)
Delensing gravitational wave standard sirens with shear and flexion maps
in MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Percival W
(2010)
Baryon acoustic oscillations in the Sloan Digital Sky Survey Data Release 7 galaxy sample
in Monthly Notices of the Royal Astronomical Society
Nishimichi T
(2010)
Scale dependence of halo bispectrum from non-Gaussian initial conditions in cosmological N-body simulations
in Journal of Cosmology and Astroparticle Physics
Koyama K
(2010)
Non-Gaussianity of quantum fields during inflation
in Classical and Quantum Gravity
Song Y
(2010)
Theoretical priors on modified growth parametrisations
in Journal of Cosmology and Astroparticle Physics
Koyama K
(2010)
Pathological behaviour of the scalar graviton in Horava-Lifshitz gravity
in Journal of High Energy Physics
Pietrobon D
(2010)
Needlet bispectrum asymmetries in the WMAP 5-year data Needlet bispectrum asymmetries in the WMAP5
in Monthly Notices of the Royal Astronomical Society: Letters
Beynon E
(2010)
Weak lensing predictions for modified gravities at non-linear scales
in Monthly Notices of the Royal Astronomical Society
Wands D
(2009)
Cosmological Perturbations Through the Big Bang
in Advanced Science Letters
Malik K
(2009)
Cosmological perturbations
in Physics Reports
Hikage C
(2009)
Limits on isocurvature perturbations from non-Gaussianity in WMAP temperature anisotropy
in Monthly Notices of the Royal Astronomical Society
Cresswell J
(2009)
Scale-dependent galaxy bias in the Sloan Digital Sky Survey as a function of luminosity and colour
in Monthly Notices of the Royal Astronomical Society
Caldera-Cabral G
(2009)
The growth of structure in interacting dark energy models
in Journal of Cosmology and Astroparticle Physics
Lu T
(2009)
The cosmological background of vector modes
in Journal of Cosmology and Astroparticle Physics
Wands D
(2009)
Scale-dependent bias from primordial non-Gaussianity in general relativity
in Physical Review D
Crittenden R
(2009)
Investigating dark energy experiments with principal components
in Journal of Cosmology and Astroparticle Physics