Absence of Anderson localization in certain random lattices

This is the final version of the article. Available from American Physical Society via the DOI in this record.We report on the transition between an Anderson localized regime and a conductive regime in a one-dimensional microwave scattering system with correlated disorder. We show experimentally that when long-range correlations are introduced, in the form of a power-law spectral density with power larger than 2, the localization length becomes much bigger than the sample size and the transmission peaks typical of an Anderson localized system merge into a pass band. As other forms of long-range correlations are known to have the opposite effect, i.e., to enhance localization, our results show that care is needed when discussing the effects of correlations, as different kinds of long-range correlations can give rise to very different behavior.J.B. acknowledge support from the Leverhulme Trust's Philip Leverhulme Prize. I.R.H. acknowledges financial support from the Engineering and Physical Sciences Research Council (EPSRC) of the United Kingdom, via the EPSRC Centre for Doctoral Training in Metamaterials (Grant No. EP/L015331/1)

D-brane potentials in the warped resolved conifold and natural inflation

In this paper we obtain a model of Natural Inflation from string theory with a Planckian decay constant. We investigate D-brane dynamics in the background of the warped resolved conifold (WRC) throat approximation of Type IIB string compactifications on Calabi-Yau manifolds. When we glue the throat to a compact bulk Calabi-Yau, we generate a D-brane potential which is a solution to the Laplace equation on the resolved conifold. We can exactly solve this equation, including dependence on the angular coordinates. The solutions are valid down to the tip of the resolved conifold, which is not the case for the more commonly used deformed conifold. This allows us to exploit the effect of the warping, which is strongest at the tip. We inflate near the tip using an angular coordinate of a D5-brane in the WRC which has a discrete shift symmetry, and feels a cosine potential, giving us a model of Natural Inflation, from which it is possible to get a Planckian decay constant whilst maintaining control over the backreaction. This is because the decay constant for a wrapped brane contains powers of the warp factor, and so can be made large, while the wrapping parameter can be kept small enough so that backreaction is under control.Comment: 41 pages, 3 appendices, 1 figure, PDFLaTex; various clarifications added along with a new appendix on b-axions and wrapped D5 branes;version matches the one published in JHE

Stabilizing All Kahler Moduli in Type IIB Orientifolds

We describe a simple and robust mechanism that stabilizes all Kahler moduli in Type IIB orientifold compactifications. This is shown to be possible with just one non-perturbative contribution to the superpotential coming from either a D3-instanton or D7-branes wrapped on an ample divisor. This moduli-stabilization mechanism is similar to and motivated by the one used in the fluxless G_2 compactifications of M-theory. After explaining the general idea, explicit examples of Calabi-Yau orientifolds with one and three Kahler moduli are worked out. We find that the stabilized volumes of all two- and four-cycles as well as the volume of the Calabi-Yau manifold are controlled by a single parameter, namely, the volume of the ample divisor. This feature would dramatically constrain any realistic models of particle physics embedded into such compactifications. Broad consequences for phenomenology are discussed, in particular the dynamical solution to the strong CP-problem within the framework.Comment: RevTeX, 24 pages, 2 tables, 1 figure

M5 spikes and operators in the HVZ membrane theory

In this note we study some aspects of the so-called dual ABJM theory introduced by Hanany, Vegh & Zaffaroni. We analyze the spectrum of chiral operators, and compare it with the spectrum of functions on the mesonic moduli space M=C^2\times C^2/Z_k, finding expected agreement for the coherent branch. A somewhat mysterious extra branch of dimension N^2 opens up at the orbifold fixed point. We also study BPS solutions which represent M2/M5 intersections. The mesonic moduli space suggests that there should be two versions of this spike: one where the M5 lives in the orbifolded C^2 and another where it lives in the unorbifolded one. While expectedly the first class turns out to be like the ABJM spike, the latter class looks like a collection of stacks of M5 branes with fuzzy S^3 profiles. This shows hints of the appearance of the global SO(4) at the non-abelian level which is otherwise not present in the bosonic potential. We also study the matching of SUGRA modes with operators in the coherent branch of the moduli space. As a byproduct, we present some formulae for the laplacian in conical CY_4 of the form C^n\times CY_{4-n}.Comment: 22 pages, 1 figure. Published version with corrected typos

Dark Radiation and Dark Matter in Large Volume Compactifications

We argue that dark radiation is naturally generated from the decay of the overall volume modulus in the LARGE volume scenario. We consider both sequestered and non-sequestered cases, and find that the axionic superpartner of the modulus is produced by the modulus decay and it can account for the dark radiation suggested by observations, while the modulus decay through the Giudice-Masiero term gives the dominant contribution to the total decay rate. In the sequestered case, the lightest supersymmetric particles produced by the modulus decay can naturally account for the observed dark matter density. In the non-sequestered case, on the other hand, the supersymmetric particles are not produced by the modulus decay, since the soft masses are of order the heavy gravitino mass. The QCD axion will then be a plausible dark matter candidate.Comment: 27 pages, 4 figures; version 3: version published in JHE

The effectiveness of public health interventions to reduce the health impact of climate change:a systematic review of systematic reviews

Climate change is likely to be one of the most important threats to public health in the coming years. Yet despite the large number of papers considering the health impact of climate change, few have considered what public health interventions may be of most value in reducing the disease burden. We aimed to evaluate the effectiveness of public health interventions to reduce the disease burden of high priority climate sensitive diseases

Index for three dimensional superconformal field theories with general R-charge assignments

We derive a general formula of an index for three dimensional N=2 superconformal field theories with general R-charge assignments to chiral multiplets by using the localization method in S^2xS^1 background. As examples we compute the index for theories in a few mirror pairs, and confirm the agreement of the indices in each mirror pair.Comment: 22 pages, no figure; v2: refs added, the definition of the index changed; v3: chemical potentials for monopole charges introduced, Sec. 5 improved, a reference adde

Soft branes in supersymmetry-breaking backgrounds

We revisit the analysis of effective field theories resulting from non-supersymmetric perturbations to supersymmetric flux compactifications of the type-IIB superstring with an eye towards those resulting from the backreaction of a small number of anti-D3-branes. Independently of the background, we show that the low-energy Lagrangian describing the fluctuations of a stack of probe D3-branes exhibits soft supersymmetry breaking, despite perturbations to marginal operators that were not fully considered in some previous treatments. We take this as an indication that the breaking of supersymmetry by anti-D3-branes or other sources may be spontaneous rather than explicit. In support of this, we consider the action of an anti-D3-brane probing an otherwise supersymmetric configuration and identify a candidate for the corresponding goldstino.Comment: 36+5 pages. References added, minor typos correcte

Sequential innovation, naked exclusion, and upfront lump-sum payments

We present a potentially benign naked exclusion mechanism that can be applied to sequential innovation; a non-patentable original innovation by the incumbent supplier fosters derivative innovation by rivals. In the absence of an appropriate legal framework, the original innovator’s equilibrium exclusivity contracts block subsequent efficient entry even if there is (leader-follower) competition in the contracting phase. However, the legal framework may maximize social welfare by imposing a ban on upfront lumps-sum payments in exclusivity contracts (by all suppliers) combined with an outright ban on exclusivity contracts by the derivative innovator. The former ban precludes the exclusion of socially beneficial derivative innovation by causing the incumbent supplier to resort to accommodation, rather than to pure exclusion, strategies. The latter ban complements the former by preventing inefficient or excessive derivative innovation