Cultivating equality: delivering just and sustainable food systems in a changing climate

T oday, the world faces a greater challenge perhaps than ever before: tackling hunger and malnutrition in the face of climate change and increasing natural resource scarcity. Civil society, governments, researchers, donors, and the private sector are simultaneously debating and collaborating to find solutions. But the dialogue is over-emphasizing food production. Improving yields is important, particularly in places where there is not enough food or where food producers live in poverty. But simply producing more is not enough to tackle hunger. Furthermore, acknowledging that lack of food is not the sole cause of hunger is important. Inequality shapes who has access to food and the resources to grow it and buy it. It governs who eats first and who eats worst. Inequality determines who can adapt more readily to a changing climate. Hunger and poverty are not an accident – they are the result of social and economic injustice and inequality at all levels, from household to global. The reality of inequality is no truer for anyone than it is for women – half the world’s population, with far less than their fair share of the world’s resources. If we are to achieve the new Sustainable Development Goal of ending hunger by 2030, we must address the underlying inequalities in food systems. In a changing climate, agriculture and food systems must be sustainable and productive – but our efforts cannot end there. They must be profitable for those for whom it is a livelihood; they must be equitable, to facilitate a level playing field in the market, to secure rights to resources for food producers, and to ensure access to nutritious food for all; they must be resilient to build the capacity of populations vulnerable to economic shocks, political instability, and increasing, climate-induced natural hazards to recover and still lift themselves out of poverty

The background scale Ward identity in quantum gravity

We show that with suitable choices of parametrization, gauge fixing and cutoff, the anomalous variation of the effective action under global rescalings of the background metric is identical to the derivative with respect to the cutoff, i.e. to the beta functional, as defined by the exact RG equation. The Ward identity and the RG equation can be combined, resulting in a modified flow equation that is manifestly invariant under global background rescalings

Gauges and functional measures in quantum gravity I: Einstein theory

We perform a general computation of the off-shell one-loop divergences in Einstein gravity, in a two-parameter family of path integral measures, corresponding to different ways of parametrizing the graviton field, and a two-parameter family of gauges. Trying to reduce the gauge- and measure-dependence selects certain classes of measures and gauges respectively. There is a choice of two parameters (corresponding to the exponential parametrization and the partial gauge condition that the quantum field be traceless) that automatically eliminates the dependence on the remaining two parameters and on the cosmological constant. We observe that the divergences are invariant under a Z2 \u201cduality\u201d transformation that (in a particularly important special case) involves the replacement of the densitized metric by a densitized inverse metric as the fundamental quantum variable. This singles out a formulation of unimodular gravity as the unique \u201cself-dual\u201d theory in this class. \ua9 2016, The Author(s)

Beta functions of topologically massive supergravity

We compute the one-loop beta functions of the cosmological constant, Newton's constant and the topological mass in topologically massive supergravity in three dimensions. We use a variant of the proper time method supplemented by a simple choice of cutoff function. We also employ two different analytic continuations of AdS3 and consider harmonic expansions on the 3-sphere as well as a 3-hyperboloid, and then show that they give the same results for the beta functions. We find that the dimensionless coefficient of the Chern-Simons term, 28, has vanishing beta function. The flow of the cosmological constant and Newton's constant depends on 28; we study analytically the structure of the flow and its fixed points in the limits of small and large ?. Open Access, \ua9 2014 The Authors

On the physical mechanism underlying Asymptotic Safety

We identify a simple physical mechanism which is at the heart of Asymptotic Safety in Quantum Einstein Gravity (QEG) according to all available effective average action-based investigations. Upon linearization the gravitational field equations give rise to an inverse propagator for metric fluctuations comprising two pieces: a covariant Laplacian and a curvature dependent potential term. By analogy with elementary magnetic systems they lead to, respectively, dia- and paramagnetic-type interactions of the metric fluctuations with the background gravitational field. We show that above 3 spacetime dimensions the gravitational antiscreening occurring in QEG is entirely due to a strong dominance of the ultralocal paramagnetic interactions over the diamagnetic ones that favor screening. (Below 3 dimensions both the dia- and paramagnetic effects support antiscreening.) The spacetimes of QEG are interpreted as a polarizable medium with a "paramagnetic" response to external perturbations, and similarities with the vacuum state of Yang-Mills theory are pointed out. As a by-product, we resolve a longstanding puzzle concerning the beta function of Newton's constant in 2+{\epsilon} dimensional gravity.Comment: 43 pages, 8 figures; clarifying remarks added; to appear in JHE

The nonperturbative functional renormalization group and its applications

The renormalization group plays an essential role in many areas of physics, both conceptually and as a practical tool to determine the long-distance low-energy properties of many systems on the one hand and on the other hand search for viable ultraviolet completions in fundamental physics. It provides us with a natural framework to study theoretical models where degrees of freedom are correlated over long distances and that may exhibit very distinct behavior on different energy scales. The nonperturbative functional renormalization-group (FRG) approach is a modern implementation of Wilson's RG, which allows one to set up nonperturbative approximation schemes that go beyond the standard perturbative RG approaches. The FRG is based on an exact functional flow equation of a coarse-grained effective action (or Gibbs free energy in the language of statistical mechanics). We review the main approximation schemes that are commonly used to solve this flow equation and discuss applications in equilibrium and out-of-equilibrium statistical physics, quantum many-particle systems, high-energy physics and quantum gravity.Comment: v2) Review article, 93 pages + bibliography, 35 figure