Regulating Eternal Inflation II: The Great Divide

In a previous paper, two of the authors presented a "regulated" picture of eternal inflation. This picture both suggested and drew support from a conjectured discontinuity in the amplitude for tunneling from positive to negative vacuum energy, as the positive vacuum energy was sent to zero; analytic and numerical arguments supporting this conjecture were given. Here we show that this conjecture is false, but in an interesting way. There are no cases where tunneling amplitudes are discontinuous at vanishing cosmological constant; rather, the space of potentials separates into two regions. In one region decay is strongly suppressed, and the proposed picture of eternal inflation remains viable; sending the (false) vacuum energy to zero in this region results in an absolutely stable asymptotically flat space. In the other region, we argue that the space-time at vanishing cosmological constant is unstable, but not asymptotically Minkowski. The consequences of our results for theories of supersymmetry breaking are unchanged.Comment: JHEP3, 19 Pages, 7 Figure

Towards a quantum theory of de Sitter space

We describe progress towards constructing a quantum theory of de Sitter space in four dimensions. In particular we indicate how both particle states and Schwarzschild de Sitter black holes can arise as excitations in a theory of a finite number of fermionic oscillators. The results about particle states depend on a conjecture about algebras of Grassmann variables, which we state, but do not prove.Comment: JHEP3 LaTex - 19 page

Counter-rotating Accretion Disks

We consider accretion disks consisting of counter-rotating gaseous components with an intervening shear layer. Configurations of this type may arise from the accretion of newly supplied counter-rotating gas onto an existing co-rotating gas disk. For simplicity we consider the case where the gas well above the disk midplane is rotating with angular rate $+\Omega$ and that well below has the same properties but is rotating with rate $-\Omega$. Using the Shakura-Sunyaev alpha turbulence model, we find self-similar solutions where a thin (relative to the full disk thickness) equatorial layer accretes very rapidly, essentially at free-fall speed. As a result the accretion speed is much larger than it would be for an alpha disk rotating in one direction. Counter-rotating accretion disks may be a transient stage in the formation of counter-rotating galaxies and in the accretion of matter onto compact objects.Comment: 7 pages, 3 figures, aas2pp4.sty, submitted to Ap

Goodbye to Projects? Briefing Paper 1: An Overview: Projects and Principles.

YesThis briefing paper reports on research exploring ten detailed case studies of livelihoods-oriented interventions operating in Tanzania, Lesotho, South Africa and Uganda. Analysing these interventions through an audit of sustainable livelihood `principles¿ (as a proxy for best practice) revealed general lessons both about the practical opportunities and challenges for employing sustainable livelihoods approaches to the design, implementation, monitoring and evaluation of development interventions and also about the changing format of development interventions.Department for International Developmen

Goodbye to Projects? - Briefing Paper 3: The changing format of development interventions.

yesThis briefing paper reports on research exploring ten detailed case studies of livelihoods-oriented interventions operating in Tanzania, South Africa, Uganda and Lesotho. As a proxy for best practice, these interventions were analysed through an audit of sustainable livelihood `principles¿. This revealed general lessons about both the practical opportunities and challenges for employing sustainable livelihoods approaches to the design, implementation, monitoring and evaluation of development interventions and also about the changing format of development interventions.Department for International Development

Goodbye to Projects? Briefing Paper 2: The Application of the SL Principles.

YesThis briefing paper reports on research exploring ten detailed case studies of livelihoods-oriented interventions operating in Tanzania, South Africa, Uganda and Lesotho. As a proxy for best practice, these interventions were analysed through an audit of sustainable livelihood `principles¿. This revealed general lessons about both the practical opportunities and challenges for employing sustainable livelihoods approaches to the design, implementation, monitoring and evaluation of development interventions and also about the changing format of development interventions.Department for International Development

Goodbye to Projects? - Briefing Paper 4: Lessons for the community-based planning interventions.

YesThis briefing paper compares two approaches to community-based planning in Tanzania, South Africa and Uganda. Analysing these interventions through an audit of sustainable livelihood `principles¿ (as a proxy for best practice) reveals general lessons about both the practical opportunities and challenges for employing sustainable livelihoods approaches to the design, implementation, monitoring and evaluation of development interventions and also about the changing format of development interventions.Department for International Developmen

Experimental Proof of a Magnetic Coulomb Phase

Spin ice materials are magnetic substances in which the spin directions map onto hydrogen positions in water ice. Recently this analogy has been elevated to an electromagnetic equivalence, indicating that the spin ice state is a Coulomb phase, with magnetic monopole excitations analogous to ice's mobile ionic defects. No Coulomb phase has yet been proved in a real magnetic material, as the key experimental signature is difficult to resolve in most systems. Here we measure the scattering of polarised neutrons from the prototypical spin ice Ho2Ti2O7. This enables us to separate different contributions to the magnetic correlations to clearly demonstrate the existence of an almost perfect Coulomb phase in this material. The temperature dependence of the scattering is consistent with the existence of deconfined magnetic monopoles connected by Dirac strings of divergent length.Comment: 18 pages, 4 fig