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
Abazajian K
(2009)
THE SEVENTH DATA RELEASE OF THE SLOAN DIGITAL SKY SURVEY
in The Astrophysical Journal Supplement Series
Shapiro C
(2009)
BIASED DARK ENERGY CONSTRAINTS FROM NEGLECTING REDUCED SHEAR IN WEAK-LENSING SURVEYS
in The Astrophysical Journal
Malik K
(2009)
Cosmological perturbations
in Physics Reports
Barrow J
(2007)
Cosmology with inhomogeneous magnetic fields
in Physics Reports
TSAGAS C
(2008)
Relativistic cosmology and large-scale structure
in Physics Reports
Crittenden R
(2007)
Measuring deviations from a cosmological constant: a field-space parametrization.
in Physical review letters
Cailleteau T
(2008)
Singularities in loop quantum cosmology.
in Physical review letters
Zhao G
(2010)
Probing modifications of general relativity using current cosmological observations
in Physical Review D
Wang A
(2010)
Cosmological perturbations in Horava-Lifshitz theory without detailed balance
in Physical Review D
Cardoso A
(2008)
Generalized perturbation equations in bouncing cosmologies
in Physical Review D
Wands D
(2009)
Scale-dependent bias from primordial non-Gaussianity in general relativity
in Physical Review D
Koyama K
(2008)
Brane-world inflation: Slow-roll corrections to the spectral index
in Physical Review D
Pogosian L
(2010)
How to optimally parametrize deviations from general relativity in the evolution of cosmological perturbations
in Physical Review D
De Risi G
(2007)
Graceful exit via polymerization of pre-big-bang cosmology
in Physical Review D
Hollenstein L
(2008)
Challenges for creating magnetic fields by cosmic defects
in Physical Review D
Giannantonio T
(2008)
Combined analysis of the integrated Sachs-Wolfe effect and cosmological implications
in Physical Review D
Pietrobon D
(2008)
Affine parametrization of the dark sector: Constraints from WMAP5 and SDSS
in Physical Review D
Corradini O
(2008)
Induced gravity on intersecting brane worlds. II. Cosmology
in Physical Review D
Assadullahi H
(2010)
Constraints on primordial density perturbations from induced gravitational waves
in Physical Review D
Arroja F
(2008)
Non-Gaussianity from the trispectrum in general single field inflation
in Physical Review D
Mizuno S
(2009)
Full quantum trispectrum in multifield DBI inflation
in Physical Review D
Ananda K
(2007)
Cosmological gravitational wave background from primordial density perturbations
in Physical Review D
Koyama K
(2009)
Nonlinear evolution of the matter power spectrum in modified theories of gravity
in Physical Review D
Esposito-Farèse G
(2010)
Vector theories in cosmology
in Physical Review D
Silva F
(2009)
Self-accelerating universe in Galileon cosmology
in Physical Review D