Spectral Regularisation: Induced Gravity and the Onset of Inflation

Using spectral regularisation, we compute the Weyl anomaly and express the anomaly generating functional of the quantum effective action through a collective scalar degree of freedom of all quantum vacuum fluctuations. Such a formulation allows us to describe induced gravity on an equal footing with the anomaly-induced effective action, in a self-consistent way. We then show that requiring stability of the cosmological constant under loop quantum corrections, Sakharov's induced gravity and Starobinsky's anomaly-induced inflation are either both present or both absent, depending on the particle content of the theory.Comment: 23 pages, 1 figure Slightly amended file to match published versio

Lattice Refining LQC and the Matter Hamiltonian

In the context of loop quantum cosmology, we parametrise the lattice refinement by a parameter, $A$, and the matter Hamiltonian by a parameter, $\delta$. We then solve the Hamiltonian constraint for both a self-adjoint, and a non-self-adjoint Hamiltonian operator. Demanding that the solutions for the wave-functions obey certain physical restrictions, we impose constraints on the two-dimensional, $(A,\delta)$, parameter space, thereby restricting the types of matter content that can be supported by a particular lattice refinement model.Comment: 15 pages, 3 figures, revtex style; amended version to match publication in Phys. Rev.

Lattice Refining Loop Quantum Cosmology and Inflation

We study the importance of lattice refinement in achieving a successful inflationary era. We solve, in the continuum limit, the second order difference equation governing the quantum evolution in loop quantun cosmology, assuming both a fixed and a dynamically varying lattice in a suitable refinement model. We thus impose a constraint on the potential of a scalar field, so that the continuum approximation is not broken. Considering that such a scalar field could play the role of the inflaton, we obtain a second constraint on the inflationary potential so that there is consistency with the CMB data on large angular scales. For a $m^2\phi^2/2$ inflationary model, we combine the two constraints on the inflaton potential to impose an upper limit on $m$, which is severely fine-tuned in the case of a fixed lattice. We thus conclude that lattice refinement is necessary to achieve a natural inflationary model.Comment: 12 pages, RevTex Two minor changes to match version to appear in Physical Review

On degenerate models of cosmic inflation

In this article we discuss the role of current and future CMB measurements in pinning down the model of inflation responsible for the generation of primordial curvature perturbations. By considering a parameterization of the effective field theory of inflation with a modified dispersion relation arising from heavy fields, we derive the dependence of cosmological observables on the scale of heavy physics $\Lambda_{\rm UV}$. Specifically, we show how the $f_{\rm NL}$ non-linearity parameters are related to the phase velocity of curvature perturbations at horizon exit, which is parameterized by $\Lambda_{\rm UV}$. Bicep2 and Planck findings are shown to be consistent with a value $\Lambda_{\rm UV} \sim \Lambda_{\rm GUT}$. However, we find a degeneracy in the parameter space of inflationary models that can only be resolved with a detailed knowledge of the shape of the non-Gaussian bispectrum.Comment: 22pp., 1 fig; v2: added some clarifications and references, corrected typos, matches published versio

Can we detect quantum gravity with compact binary inspirals?

Treating general relativity as an effective field theory, we compute the leading-order quantum corrections to the orbits and gravitational-wave emission of astrophysical compact binaries. These corrections are independent of the (unknown) nature of quantum gravity at high energies, and generate a phase shift and amplitude increase in the observed gravitational-wave signal. Unfortunately (but unsurprisingly), these corrections are undetectably small, even in the most optimistic observational scenarios.Comment: 7 pages, 0 figures; version 2 has additional discussion of our approach and 5 additional reference

Effective field theory of weakly coupled inflationary models

The application of Effective Field Theory (EFT) methods to inflation has taken a central role in our current understanding of the very early universe. The EFT perspective has been particularly useful in analyzing the self-interactions determining the evolution of co-moving curvature perturbations (Goldstone boson modes) and their influence on low-energy observables. However, the standard EFT formalism, to lowest order in spacetime differential operators, does not provide the most general parametrization of a theory that remains weakly coupled throughout the entire low-energy regime. Here we study the EFT formulation by including spacetime differential operators implying a scale dependence of the Goldstone boson self-interactions and its dispersion relation. These operators are shown to arise naturally from the low-energy interaction of the Goldstone boson with heavy fields that have been integrated out. We find that the EFT then stays weakly coupled all the way up to the cutoff scale at which ultraviolet degrees of freedom become operative. This opens up a regime of new physics where the dispersion relation is dominated by a quadratic dependence on the momentum \omega ~ p^2. In addition, provided that modes crossed the horizon within this energy range, the prediction of inflationary observables - including non-Gaussian signatures - are significantly affected by the new scales characterizing it.Comment: 36 pages, v2: references added, minor changes to match published versio

A contemporary history of the origins and development of UK Biobank, 1998-2005

Background: This thesis examines the origins and early development of UK Biobank. This is a resource funded in 2002 by the Medical Research Council, the Wellcome Trust, the Department of Health and the Scottish Executive to gather genetic and lifestyle information from half a million participants aged 4069 years old in the UK and monitor their health for up to thirty years in order to improve the prevention, diagnosis and treatment of major diseases. UK Biobank was set up following the completion of the Human Genome Project in 2001, and was one of many established at around the same time with the goal of translating the knowledge of the human genome sequence into practical benefits for human health. (National genetic databases were also set up or proposed in Iceland, Estonia, Latvia, Sweden, Singapore, Tonga, Spain, and the United States). They, and the Human Genome Project, had raised a number of important issues about access to and ownership of genetic information. Aims: The original aim of my PhD was to examine lay and professional understandings and responses to Biobank in the light of this background. However, UK Biobank took longer than expected to reach the stage of data collection, in part because of negotiations about its organisational structure. The aim therefore changed to address the question of how and why was UK Biobank initially configured in the manner it was. Organisational structure: UK Biobank was originally set up by the funders with a ‘hub’ and ‘spoke’ model, with calls for bids from UK Universities for a central ‘hub’ charged with financial management and overall control of data and samples, and ‘spokes’ who were responsible for recruitment and data collection through primary care. The selection of both was made through the procurement rules of the EU. The hub (Manchester), six regional spokes, and the CEO (from Oxford) were all appointed simultaneously in 2003 and subsequently a Board of Directors and a number of committees were appointed. The CEO resigned in late 2004, and a new CEO and Principal Investigator was appointed in 2005, after which there were significant changes to the organisational structure. Methods: I conducted 76 oral history interviews with academic scientists directly and indirectly involved in UK Biobank, representatives of all four funding bodies, and representatives of UK Biobank Limited (the company set up to manage UK Biobank). I also conducted archival analysis of the MRC’s official documents concerning the origins and development of UK Biobank. Findings: From its beginning UK Biobank was marked by tension between academic scientists on the one hand and representatives of the funding bodies and UK Biobank Limited on the other. Academic scientists criticised the funding bodies for establishing UK Biobank in a way that departed from what I have termed ‘standard academic scientific practice’. Spokes felt they should receive some privileged access to data they would contribute to collecting, and felt that the set up did not recognise the performance indicators driving scientists and universities. Lack of clarity over who was in control of UK Biobank contributed to these tensions as both spokes and funders felt that the other exerted undue influence. Some mistrust developed between academic scientists and representatives of the funding bodies and UK Biobank Limited. Discussion: The configuration of UK Biobank was difficult for academic scientists and representatives of both the funding bodies and UK Biobank alike. Organisational issues, typical of those confronting Big Science initiatives, were largely responsible for this difficult legacy. Issues of leadership, the hub and spoke model, the sequencing of funding decisions, appointment of groups and committees and protocol development, uncertainties about who was in control, and ambiguities within the organisational structure as a whole were the most significant issues in the origins and development of UK Biobank, as the organisational changes in 2005 testify

Cosmological implications of interacting Group Field Theory models: cyclic Universe and accelerated expansion

We study the cosmological implications of interactions between spacetime quanta in the Group Field Theory (GFT) approach to Quantum Gravity from a phenomenological perspective. Our work represents a first step towards understanding Early Universe Cosmology by studying the dynamics of the emergent continuum spacetime, as obtained from a fundamentally discrete microscopic theory. In particular, we show how GFT interactions lead to a recollapse of the Universe while preserving the bounce replacing the initial singularity, which has already been shown to occur in the free case. It is remarkable that cyclic cosmologies are thus obtained in this framework without any a priori assumption on the geometry of spatial sections of the emergent spacetime. Furthermore, we show how interactions make it possible to have an early epoch of accelerated expansion, which can be made to last for an arbitrarily large number of e-folds, without the need to introduce an ad hoc potential for the scalar field.Comment: 11 pages, 6 figure

Dynamics of anisotropies close to a cosmological bounce in quantum gravity

We study the dynamics of perturbations representing deviations from perfect isotropy in the context of the emergent cosmology obtained from the group field theory formalism for quantum gravity. Working in the mean field approximation of the group field theory formulation of the Lorentzian EPRL model, we derive the equations of motion for such perturbations to first order. We then study these equations around a specific simple isotropic background, characterised by the fundamental representation of \mbox{SU(2)}, and in the regime of the effective cosmological dynamics corresponding to the bouncing region replacing the classical singularity, well approximated by the free GFT dynamics. In this particular example, we identify a region in the parameter space of the model such that perturbations can be large at the bounce but become negligible away from it, i.e. when the background enters the non-linear regime. We also study the departures from perfect isotropy by introducing specific quantities, such as the surface-area-to-volume ratio and the effective volume per quantum, which make them quantitative.Comment: 45 pages, 4 figure

Constraining the Noncommutative Spectral Action via Astrophysical Observations

The noncommutative spectral action extends our familiar notion of commutative spaces, using the data encoded in a spectral triple on an almost commutative space. Varying a rather simple action, one can derive all of the standard model of particle physics in this setting, in addition to a modified version of Einstein-Hilbert gravity. Thus, noncommutative geometry provides a geometric interpretation of particle physics coupled to curvature. In this letter we use observations of pulsar timings, assuming that no deviation from General Relativity has been observed, to constrain the gravitational sector of this theory. Thus, we directly constrain noncommutative geometry, a potential grand unified theory of physics, via astrophysical observations. Whilst the bounds on the coupling constants remain rather weak, they are comparable to existing bounds on deviations from General Relativity in other settings and are likely to be further constrained by future observations.Comment: 5 pages; slightly shorter version to match the one will appear in Phys. Rev. Let