BRST cohomology of the Chapline-Manton model

We completely compute the local BRST cohomology $H(s|d)$ of the combined Yang-Mills-2-form system coupled through the Yang-Mills Chern-Simons term ("Chapline-Manton model"). We consider the case of a simple gauge group and explicitely include in the analysis the sources for the BRST variations of the fields ("antifields"). We show that there is an antifield independent representative in each cohomological class of $H(s|d)$ at ghost number 0 or 1. Accordingly, any counterterm may be assumed to preserve the gauge symmetries. Similarly, there is no new candidate anomaly beside those already considered in the literature, even when one takes the antifields into account. We then characterize explicitly all the non-trivial solutions of the Wess-Zumino consistency conditions. In particular, we provide a cohomological interpretation of the Green-Schwarz anomaly cancellation mechanism.Comment: Latex file, no figures, 15 page

On the instability of the magnetohydrodynamic pipe flow subject to a transverse magnetic field

The linear stability of a fully-developed liquid-metal MHD pipe flow subject to a transverse magnetic field is studied numerically. Because of the lack of axial symmetry in the mean velocity profile, we need to perform a BiGlobal stability analysis. For that purpose, we develop a two-dimensional complex eigenvalue solver relying on a Chebyshev-Fourier collocation method in physical space. By performing an extensive parametric study, we show that in contrast to Hagen-Poiseuille flow known to be linearly stable for all Reynolds numbers, the MHD pipe flow with transverse magnetic field is unstable to three-dimensional disturbances at sufficiently high values of the Hartmann number and wall conductance ratio. The instability observed in this regime is attributed to the presence of velocity overspeeds in the so-called Roberts layers and the corresponding inflection points in the mean velocity profile. The nature and characteristics of the most unstable modes are investigated, and we show that they vary significantly depending on the wall conductance ratio. A major result of this paper is that the global critical Reynolds number for the MHD pipe flow with transverse magnetic field is $Re=45230$, and it occurs for a perfectly conducting pipe wall and the Hartmann number $Ha=19.7$

A Theorem on First-Order Interaction Vertices for Free p-Form Gauge Fields

The complete proof of a theorem announced in [1] on the consistent interactions for (non-chiral) exterior form gauge fields is given. The theorem can be easily generalized to the analysis of anomalies. Its proof amounts to computing the local BRST cohomology H^0(s|d) in the space of local n-forms depending on the fields, the ghosts, the antifields and their derivatives.Comment: 18 pages, no figures, misquotes in references correcte

Couplings of gravity to antisymmetric gauge fields

We classify all the first-order vertices of gravity consistently coupled to a system of 2-form gauge fields by computing the local BRST cohomology H(s|d) in ghost number 0 and form degree n. The consistent deformations are at most linear in the undifferentiated two-form, confirming the previous results of [1] that geometrical theories constructed from a nonsymmetric gravity theory are physically inconsistent or trivial. No assumption is made here on the degree of homogeneity in the derivatives nor on the form of the gravity action.Comment: 11 pages, no figures, Latex2.0

Goltz, Andreas, Barbar – König – Tyrann. Das Bild Theoderichs des Großen in der Überlieferung des 5. bis 9. Jahrhunderts

En raison de son destin exceptionnel, le roi ostrogoth Théodoric s’est très tôt imposé comme une figure marquante de la fin de l’Antiquité tardive. De nombreux auteurs du haut Moyen Âge, tant grecs que latins, n’ont dès lors pas manqué d’en traiter dans leurs ouvrages, contribuant à façonner une image complexe et plurielle de ce souverain hors norme. C’est à l’étude de cette image qu’Andreas Goltz a consacré sa thèse de doctorat soutenue en 2005 à la Freie Universität de Berlin, et désormais..

Correcting cold wire measurements in isotropic turbulence with a DNS database

We estimate the effect of the finite spatial resolution of a cold wire for scalar measurements, using a database from direct numerical simulations (DNS). These are for homogeneous isotropic turbulence at low Taylor-microscale Reynolds number (≃ 42) and Schmidt number unity. Correction factors for the scalar variance, scalar mean dissipation rate, and mixed velocity-scalar derivative skewness are evaluated, for a sensor length of up to 15 times the Batchelor length scale. The largest attenuation effect is found on the dissipation rate, followed by the scalar variance. The mixed skewness,which is affected the least, is overestimated

challenges to multi-level capacity building

Communities facing the effects of climate change are actively trying to boost their resilience. At the same time, governments are mainstreaming climate change into their development frameworks. Close examination of current practice, however, points at a disconnect between government policy and community initiatives. This study explores how strengthening specific capabilities at various levels can ensure synchronization of policy and practice and further community resilience in face of climate change. Choosing an approach that appreciates the interplay of top-­‐down and bottom-­‐up logics towards performance under stress, it illust rates that understanding resilience in terms of capacity opens the door to practical thinking on policies as well as practices. Evidence is taken from case studies in Chile and Vietnam to show how governments can play an enabling role when connecting their efforts to initiatives taken by communities. At the same time, top-­‐down structures, such as the United Nations Framework Convention on Climate Change (UNFCCC) and the Sustainable Development Goals (SDGs), can help to break silos between different (inter)national political agendas and underscore the need to link top-­‐down and bottom-­‐up approaches to ensure resilience. This paper contends that improving communities' adaptive capacity demands bridging the disconnect between multiple levels of policy and practice. In doing so, different, and too often conflicting, values, interests, and political agendas need to be aligned. Moreconcretely, we found that resilience, as an emergent property of human systems, can be enhanced when government and local stakeholders work together in a number of specific areas. For instance, combining multi-­‐stakeholder platforms in which diverse actors – ranging from policy-­‐makers to researchers to community representatives – translate lessons learned at the community level intolocal and national policy, with initiatives aimed at strengthening capacitiesand ensuring access to relevant assets at the community level