Is a Higgs Vacuum Instability Fatal for High-Scale Inflation?

We study the inflationary evolution of a scalar field $h$ with an unstable potential for the case where the Hubble parameter $H$ during inflation is larger than the instability scale $\Lambda_I$ of the potential. Quantum fluctuations in the field of size $\delta h \sim \frac{H}{2 \pi}$ imply that the unstable part of the potential is sampled during inflation. We investigate the evolution of these fluctuations to the unstable regime, and in particular whether they generate cosmological defects or even terminate inflation. We apply the results of a toy scalar model to the case of the Standard Model (SM) Higgs boson, whose quartic evolves to negative values at high scales, and extend previous analyses of Higgs dynamics during inflation utilizing statistical methods to a perturbative and fully gauge-invariant formulation. We show that the dynamics are controlled by the renormalization group-improved quartic coupling $\lambda(\mu)$ evaluated at a scale $\mu = H$, such that Higgs fluctuations are enhanced by the instability if $H > \Lambda_I$. Even if $H > \Lambda_I$, the instability in the SM Higgs potential does not end inflation; instead the universe slowly sloughs off crunching patches of space that never come to dominate the evolution. As inflation proceeds past 50 $e$-folds, a significant proportion of patches exit inflation in the unstable vacuum, and as much as 1% of the spacetime can rapidly evolve to a defect. Depending on the nature of these defects, however, the resulting universe could still be compatible with ours.Comment: 31 pages, 3 figures; v2: references added, journal versio

Probable or Improbable Universe? Correlating Electroweak Vacuum Instability with the Scale of Inflation

Measurements of the Higgs boson and top quark masses indicate that the Standard Model Higgs potential becomes unstable around $\Lambda_I \sim 10^{11}$ GeV. This instability is cosmologically relevant since quantum fluctuations during inflation can easily destabilize the electroweak vacuum if the Hubble parameter during inflation is larger than $\Lambda_I$ (as preferred by the recent BICEP2 measurement). We perform a careful study of the evolution of the Higgs field during inflation, obtaining different results from those currently in the literature. We consider both tunneling via a Coleman-de Luccia or Hawking-Moss instanton, valid when the scale of inflation is below the instability scale, as well as a statistical treatment via the Fokker-Planck equation appropriate in the opposite regime. We show that a better understanding of the post-inflation evolution of the unstable AdS vacuum regions is crucial for determining the eventual fate of the universe. If these AdS regions devour all of space, a universe like ours is indeed extremely unlikely without new physics to stabilize the Higgs potential; however, if these regions crunch, our universe survives, but inflation must last a few e-folds longer to compensate for the lost AdS regions. Lastly, we examine the effects of generic Planck-suppressed corrections to the Higgs potential, which can be sufficient to stabilize the electroweak vacuum during inflation.Comment: 26 pages, 7 figures. Clarifications added. Matches published version in JHE

Predictors of Vitamin D Supplementation Amongst Infants in Ireland Throughout The First Year of Life

A prospective observational study was conducted. Self-complete questionnaires recorded socio-demographic characteristics, health behaviours and supplementation practices for 158 mother-infant dyads at 4, 9 and 12 months post-partum. A 2-day food diary was also obtained on 12-month-old infants to examine the contribution of diet to vitamin D intakes

Spacetime Dynamics of a Higgs Vacuum Instability During Inflation

A remarkable prediction of the Standard Model is that, in the absence of corrections lifting the energy density, the Higgs potential becomes negative at large field values. If the Higgs field samples this part of the potential during inflation, the negative energy density may locally destabilize the spacetime. We use numerical simulations of the Einstein equations to study the evolution of inflation-induced Higgs fluctuations as they grow towards the true (negative-energy) minimum. These simulations show that forming a single patch of true vacuum in our past light cone during inflation is incompatible with the existence of our Universe; the boundary of the true vacuum region grows outward in a causally disconnected manner from the crunching interior, which forms a black hole. We also find that these black hole horizons may be arbitrarily elongated---even forming black strings---in violation of the hoop conjecture. By extending the numerical solution of the Fokker-Planck equation to the exponentially suppressed tails of the field distribution at large field values, we derive a rigorous correlation between a future measurement of the tensor-to-scalar ratio and the scale at which the Higgs potential must receive stabilizing corrections in order for the Universe to have survived inflation until today.Comment: 36 pages, 11 figures; revised to match published versio

Mainstreaming prevention: Prescribing fruit and vegetables as a brief intervention in primary care

This is the author's PDF version of an article published in Public health© 2005.This articles discusses a project at the Castlefields Health Centre in Halton whereby primary care professionals issue a prescription for discounts on fruit and vegetables. The prescription is explicitly linked to the five-a-day message

Aerodynamic control using distributed active bleed

A novel approach for controlling the global aerodynamic loads on lifting surfaces using regulated distributed active bleed that is driven by pressure differences across the surfaces is investigated in wind tunnel experiments. The experiments focus on the flow mechanisms that govern the interaction between the bleed and the local cross flow over a wide range of pre- and post-stall angles of attack. Particle image velocimetry (PIV) and load cell measurements indicate that low momentum quasi-steady and time-periodic bleed [momentum coefficients of O(10-4)] lead to bi-directional deflections of the time-averaged vorticity layer and effect increases or decreases in lift, drag, and pitching moment. High-speed PIV and proper orthogonal decomposition (POD) of the vorticity flux show that the bleed engenders trains of discrete vortices that advect along the surface and are associated with a local instability that is manifested by a time-averaged bifurcation of the vorticity layer near the bleed outlets. The vortices advect over several convective times and alter the vorticity flux over the airfoil and thereby the aerodynamic loads. Active bleed is also investigated on a dynamically pitching airfoil (reduced frequencies up to k = 0.42) to study the effects of modulating the evolution of vorticity concentrations during dynamic stall. Time-periodic bleed mitigates adverse pitching moment behavior (“negative damping”) that can precipitate structural instabilities while maintaining the cycle-average loads to within 5% of the base levels by segmenting the vorticity layer during upstroke and promoting early flow attachment during downstroke. The present investigations demonstrate that active bleed can be implemented for direct lift control, maneuvering, or stabilization of flexible aerostructures (airframes, flexible wings, and rotor blades).Ph.D

The Relationship Between Diet and Lifestyle Behaviours in a Sample of Higher Education Students; A Cross-Sectional Study

Transitioning into higher education (HE) impacts health behaviours. Poor dietary and lifestyle behaviours may correlate and increase risk of co-morbidities. The introduction of the Okanagan Charter detailed the important role of health promotion within a HE setting. The aim of this study was to assess the relationship between dietary quality and lifestyle behaviours of students attending HE