Physics of the Early Universe
Lead Research Organisation:
University of Nottingham
Department Name: Sch of Physics & Astronomy
Abstract
Cosmology spans a wide range of physics, from the very small scales and high energies of the early Universe to the large scale dynamics of galaxies. This diversity is met with a corresponding array of techniques to study various phenomena, ranging from quantum gravity to classical dynamics and analytic calculations to numerical simulations. On the largest observable scales the Cosmic Microwave Background (CMB), relic radiation from the big bang, and the clustering of galaxies allow us to probe the expansion history and constituents of the Universe. These observations suggest that most of the Universe is composed of exotic dark matter and dark energy. Understanding the nature of these components, and connecting observations of the Universe with particle physics, is a major outstanding issue for cosmology and one of the goals of our work. The standard model of particle physics is extremely successful at describing the results from various sources, including collider experiments. It does however have some conceptual problems (for instance the existance of a large number of free parameters) which motivate the study of various extensions. We will use ideas from non-commutative geometry, which provides a natural framework for the symmetries of the standard model, to constrain the free parameters and make testable predictions. Another well motivated extension of the standard model is supersymmetry which postulates a symmetry between bosons and fermions. Supersymmetry leads to different dynamics at phase transitions and bubbles can nucleate. This may explain why there is more matter than anti-matter in the Universe and we will perform numerical simulations of this process. The standard model includes the strong nuclear force, which governs the behaviour of a quark-gluon plasma. This novel state of matter is currently being probed at colliders, however it is extremely complicated to describe using orthodox methods. There has recently been great interest in the possibility that techniques derived from string theory can be employed, and we will explore the physics of these plasmas using these insights. Particle physics and general relativity both break down at extreme energies, where a unified theory of quantum gravity is expected to operate. We will test the observational consequences of two such theories, string theory and non-metric gravity. String theory allows superstrings to stretch across the Universe, altering the fluctuations in the CMB, producing gravitational waves, emmitting high energy particles and lensing galaxies, while non-metric theories of gravity may successfully reproduce the rotation curves of galaxies as well as their lensing properties. Another feature of string theory is that it offers a new set of degrees of freedom called moduli fields. The behaviour of these fields will lead to potentially observable consequences which could provide observational evidence for, or undermine, string theory. We will calculate how the moduli behave as the Universe evolves and examine their relation to dark energy and dark matter.
Publications
Padilla A
(2010)
The good, the bad and the ugly . of Horava gravity
in Journal of Physics: Conference Series
Padilla A
(2011)
Multi-Galileons, solitons, and Derrick's theorem
in Physical Review D
Pourtsidou A
(2011)
Scaling configurations of cosmic superstring networks and their cosmological implications
in Physical Review D
Saffin P
(2011)
Real-time fermions for baryogenesis simulations
in Journal of High Energy Physics
Scarinci, Carlos And Krasnov, Kirill
(2011)
The universal phase space of $AdS_3$ gravity
Torres-Gomez A
(2010)
Gravity-Yang-Mills-Higgs unification by enlarging the gauge group
in Physical Review D
Torres-Gomez A
(2011)
Unified theory of nonlinear electrodynamics and gravity
in Physical Review D
Zacchei A
(2011)
Planck early results. V. The Low Frequency Instrument data processing
in Astronomy & Astrophysics
Zibin J
(2011)
Linear kinetic Sunyaev-Zel'dovich effect and void models for acceleration
in Classical and Quantum Gravity
Description | Key breakthroughs included our work on string cosmology and cosmic superstrings - we examined the collision of two cosmic strings in a field theory model, which allows junctions to form where standard Abelian strings do not, and confirmed analytic results based on the Nambu-Goto approximation We continued to investigate the constraints on a network of cosmic superstrings, the aim being to determine their observational signatures. We determined the B-mode polarisation signature from the network, and exciting new results were obtained including the determination of the signal as a function of the string coupling and Fundamental string tension. Copeland and Kibble wrote an influential review on cosmic superstrings and showed how kinks play an important role in the build up of small scale structure on cosmic strings, solving explicitely for the sharpness distribution of the kinks on very short scales. We investigated analytically and numerically, in the thick and thin-wall regimes, the stability of Q-balls in gauge- and gravity-mediated supersymmetry breaking and found the conditions for absolute stability in a number of dimensions. We updated the limits on the abundance of primordial black holes (PBHs), translating them into model independent constraints on the amplitude of the primordial curvature perturbation. These limits, were used with an improved horizon ow analysis, to show both that PBH formation constrains models where in inflation ends via a secondary mechanism, and that gamma-rays from WIMP annihilation in ultra compact mini halos potentially place a tight constraint on the primordial curvature perturbation In dark energy, dark matter and modified gravity we developed the model of stealth acceleration, identifying a ghost in the fluctuations about the de Sitter brane, and noting it decoupled in the Minkowski limit, suggesting that the original model developed by Padilla and collaborators, may be a ghost-free gravitational alternative to dark energy. We introduced a consistent cosmological model assuming the dark sector may contain long range forces similar to electromagnetism. Failure to account for the dark charge would lead to wrong conclusions about the value of dark energy equation of state. We developed a bi-galileon theory, and showed that in contrast to the single galileon case, they give rise to self-acceleration models without any pathologies. We formulated a novel method for calculating the ultra-local dark matter distribution, and carried out a detailed study of how the accuracy with which the WIMP mass could be determined by a direct detection experiment depends on the detector configuration and WIMP properties. This work is frequently used in studies of the potential of dark matter detection for constraining models of supersymmetry. |
Exploitation Route | The work was continued in the follow up grant ST/J000388/1 and by other groups throughout the world interested in our work. |
Sectors | Education |
Description | The findings of this grant do not stretch much beyond academia. A couple of Sixty Symbols videos have emerged based on the published findings from the grant. |
First Year Of Impact | 2008 |
Sector | Education |
Impact Types | Cultural |
Description | Reintegration grant |
Amount | £84,991 (GBP) |
Funding ID | RH2772 |
Organisation | European Research Council (ERC) |
Sector | Public |
Country | Belgium |
Start | 08/2010 |
End | 09/2014 |
Description | URF |
Amount | £519,188 (GBP) |
Organisation | The Royal Society |
Sector | Charity/Non Profit |
Country | United Kingdom |
Start | 01/2013 |
End | 12/2017 |
Description | COSMOS |
Organisation | University of Cambridge |
Department | Department of Applied Mathematics and Theoretical Physics (DAMTP) |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | We have access to COSMOS supercomputer |
Collaborator Contribution | All partners have access to COSMOS to undertake basic research into cosmology |
Impact | Many publications too numerous to mention |
Description | Nottingham Masterclasses |
Form Of Engagement Activity | Participation in an open day or visit at my research institution |
Part Of Official Scheme? | Yes |
Geographic Reach | National |
Primary Audience | Schools |
Results and Impact | 60 pupils or so attend the masterclasses As well as exciting students, it has had an impact on ugd recruitment at Nottingham. |
Year(s) Of Engagement Activity | Pre-2006,2006,2007,2008,2009,2010,2011,2012,2013,2014,2015,2016 |
URL | http://www.nottingham.ac.uk/~ppzphy7/webpages/outreach/ |
Description | School talks |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | Yes |
Geographic Reach | National |
Primary Audience | Schools |
Results and Impact | Generally very positive feedback from staff and students who appreciate us bringing cutting edge research ideas into the classroom. See above. |
Year(s) Of Engagement Activity | Pre-2006,2006,2007,2008,2009,2010,2011,2012,2013,2014,2015,2016 |
Description | Sixty Symbols Videos |
Form Of Engagement Activity | A press release, press conference or response to a media enquiry/interview |
Part Of Official Scheme? | Yes |
Type Of Presentation | Keynote/Invited Speaker |
Geographic Reach | International |
Primary Audience | Public/other audiences |
Results and Impact | We have a big impact with these videos receiving thousands of comments on the videos and emails sent thanking us for the work. See above. |
Year(s) Of Engagement Activity | 2010,2011,2012,2013,2014,2015,2016 |
URL | http://www.youtube.com/user/sixtysymbols |