Wilson line correlators in two-dimensional noncommutative Yang-Mills theory

We study the correlator of two parallel Wilson lines in two-dimensional noncommutative Yang-Mills theory, following two different approaches. We first consider a perturbative expansion in the large-N limit and resum all planar diagrams. The second approach is non-perturbative: we exploit the Morita equivalence, mapping the two open lines on the noncommutative torus (which eventually gets decompacted) in two closed Wilson loops winding around the dual commutative torus. Planarity allows us to single out a suitable region of the variables involved, where a saddle-point approximation of the general Morita expression for the correlator can be performed. In this region the correlator nicely compares with the perturbative result, exhibiting an exponential increase with respect to the momentum p.Comment: 21 pages, 1 figure, typeset in JHEP style; some formulas corrected in Sect.3, one reference added, results unchange

Extreme and rapid bursts of functional adaptations shape bite force in amniotes

Adaptation is the fundamental driver of functional and biomechanical evolution. Accordingly, the states of biomechanical traits (absolute or relative trait values) have long been used as proxies for adaptations in response to direct selection. However, ignoring evolutionary history, in particular ancestry, passage of time and the rate of evolution, can be misleading. Here, we apply a recently developed phylogenetic statistical approach using significant rate shifts to detect instances of exceptional rates of adaptive changes in bite force in a large group of terrestrial vertebrates, the amniotes. Our results show that bite force in amniotes evolved through multiple bursts of exceptional rates of adaptive changes, whereby whole groups—including Darwin's finches, maniraptoran dinosaurs (group of non-avian dinosaurs including birds), anthropoids and hominins (fossil and modern humans)—experienced significant rate increases compared to the background rate. However, in most parts of the amniote tree of life, we find no exceptional rate increases, indicating that coevolution with body size was primarily responsible for the patterns observed in bite force. Our approach represents a template for future studies in functional morphology and biomechanics, where exceptional rates of adaptive changes can be quantified and potentially linked to specific ecological factors underpinning major evolutionary radiation

Ultra-high brilliance multi-MeV γ\gamma-ray beam from non-linear Thomson scattering

We report on the generation of a narrow divergence ($\theta\approx 2.5$ mrad), multi-MeV ($E_\text{MAX} = 18$ MeV) and ultra-high brilliance ($\approx 2\times10^{19}$ photons s$^{-1}$ mm$^{-2}$ mrad $^{-2}$ 0.1\% BW) $\gamma$-ray beam from the scattering of an ultra-relativistic laser-wakefield accelerated electron beam in the field of a relativistically intense laser (dimensionless amplitude $a_0\approx2$). The spectrum of the generated $\gamma$-ray beam is measured, with MeV resolution, seamlessly from 6 MeV to 18 MeV, giving clear evidence of the onset of non-linear Thomson scattering. The photon source has the highest brilliance in the multi-MeV regime ever reported in the literature

Z_2-gradings of Clifford algebras and multivector structures

Let Cl(V,g) be the real Clifford algebra associated to the real vector space V, endowed with a nondegenerate metric g. In this paper, we study the class of Z_2-gradings of Cl(V,g) which are somehow compatible with the multivector structure of the Grassmann algebra over V. A complete characterization for such Z_2-gradings is obtained by classifying all the even subalgebras coming from them. An expression relating such subalgebras to the usual even part of Cl(V,g) is also obtained. Finally, we employ this framework to define spinor spaces, and to parametrize all the possible signature changes on Cl(V,g) by Z_2-gradings of this algebra.Comment: 10 pages, LaTeX; v2 accepted for publication in J. Phys.

Variational formulas of higher order mean curvatures

In this paper, we establish the first variational formula and its Euler-Lagrange equation for the total $2p$-th mean curvature functional $\mathcal {M}_{2p}$ of a submanifold $M^n$ in a general Riemannian manifold $N^{n+m}$ for $p=0,1,...,[\frac{n}{2}]$. As an example, we prove that closed complex submanifolds in complex projective spaces are critical points of the functional $\mathcal {M}_{2p}$, called relatively $2p$-minimal submanifolds, for all $p$. At last, we discuss the relations between relatively $2p$-minimal submanifolds and austere submanifolds in real space forms, as well as a special variational problem.Comment: 13 pages, to appear in SCIENCE CHINA Mathematics 201

Capital Fixity and Mobility in Response to the 2008-09 Crisis: Variegated Neoliberalism in Mexico and Turkey

The article examines the 2008-9 crisis responses in Mexico and Turkey as examples of variegated neoliberalism. The simultaneous interests of corporations and banks relative to the national fixing of capital and their mobility in the form of global investment heavily influenced each state authority’s policy responses to the crisis at the expense of the interests of the poor, workers, and peasantry. Rather than pitching this as either evidence of persistent national differentiation or some Keynesian state resurgence, we argue from a historical materialist geographical framework that the responses of capital and state authorities in Mexico and Turkey actively constitute and reconstitute the global parameters of market regulatory design and neoliberal class rule through each state’s distinct domestic policy formation and crisis management processes. While differing in specific content the form of Mexico and Turkey’s state responses to the crisis ensured continuity in their foregoing neoliberal strategies of development and capital accumulation, most notably in the continued oppression of workers. That is, the prevailing strategy of accumulation continues to be variegated neoliberalism

Consistency Conditions for Orientifolds and D-Manifolds

We study superstrings with orientifold projections and with generalized open string boundary conditions (D-branes). We find two types of consistency condition, one related to the algebra of Chan-Paton factors and the other to cancellation of divergences. One consequence is that the Dirichlet 5-branes of the Type I theory carry a symplectic gauge group, as required by string duality. As another application we study the Type I theory on a $K3$ $Z_2$ orbifold, finding a family of consistent theories with various unitary and symplectic subgroups of $U(16) \times U(16)$. We argue that the $K3$ orbifold with spin connection embedded in gauge connection corresponds to an interacting conformal field theory in the Type I theory.Comment: Reference added. 27 pages LaTeX, 2 epsf figures. To appear in Phys.Rev.D (15Jly96

Investigating the New Landscapes of Welfare: Housing Policy, Politics and the Emerging Research Agenda

As debates about housing form an increasingly important arena of political controversy, much has been written about the new fissures that have appeared as governments not only struggle to reduce public expenditure deficits but also attempt to address problems such as affordability and homelessness. It is widely anticipated that new conflicts will be played out in the private rental market as access to homeownership becomes unrealistic and the supply of social housing diminishes. However, what other tensions might surface; that hitherto have not been subject to the critical gaze of housing research? In this paper, we provide some thoughts on the nascent policy issues as well as the ideological schisms that are likely to develop in coming years, offering suggestions as to how the focus of housing policy research might be reoriented towards a “politics” framework to capture and better understand the conflicts that are likely to arise

Testing Non-commutative QED, Constructing Non-commutative MHD

The effect of non-commutativity on electromagnetic waves violates Lorentz invariance: in the presence of a background magnetic induction field b, the velocity for propagation transverse to b differs from c, while propagation along b is unchanged. In principle, this allows a test by the Michelson-Morley interference method. We also study non-commutativity in another context, by constructing the theory describing a charged fluid in a strong magnetic field, which forces the fluid particles into their lowest Landau level and renders the fluid dynamics non-commutative, with a Moyal product determined by the background magnetic field.Comment: 14 pages, LaTeX; minor corrections, references adde