Hopf instantons, Chern-Simons vortices, and Heisenberg ferromagnets

The dimensional reduction of the three-dimensional fermion-Chern-Simons model (related to Hopf maps) of Adam et el. is shown to be equivalent to (i) either the static, fixed--chirality sector of our non-relativistic spinor-Chern-Simons model in 2+1 dimensions, (ii) or a particular Heisenberg ferromagnet in the plane.Comment: 4 pages, Plain Tex, no figure

Galilean Lee Model of the Delta Function Potential

The scattering cross section associated with a two dimensional delta function has recently been the object of considerable study. It is shown here that this problem can be put into a field theoretical framework by the construction of an appropriate Galilean covariant theory. The Lee model with a standard Yukawa interaction is shown to provide such a realization. The usual results for delta function scattering are then obtained in the case that a stable particle exists in the scattering channel provided that a certain limit is taken in the relevant parameter space. In the more general case in which no such limit is taken finite corrections to the cross section are obtained which (unlike the pure delta function case) depend on the coupling constant of the model.Comment: 7 pages, latex, no figure

Non-SVEA models for supercontinuum generation

We know that the modified Korteweg-de Vries (mKdV), the sine-Gordon (sG), and the mKdV-sG models can describe few-cycle optical pulse propagation beyond the slowly-varying-envelope approximation in transparent media. We show numerically that these models are also able to describe the generation of supercontinua with spectral bandwidths of several octaves. Several mechanisms of spectral broadening are highlighted, involving self-phase modulation, parametric interactions of high harmonics, and few-cycle-soliton generation

COVID-19: A turning point to further sanitation justice?

Sanitation has received increased attention during the COVID-19 pandemic, but the heterogeneity of infrastructures, investments, practices and needs that exist on the ground, have often been overlooked. Consequently, the intersecting inequalities shaping how COVID-19 and sanitation interact remain unaddressed. This paper suggests it is possible to move beyond ‘deficit narratives’, and to support pathways towards just sanitation for all women and men, girls and boys during and beyond the pandemic. Tracking down past, ongoing and projected sanitary arrangements, exploring the political economy of both grid and off-grid investments and promises, and paying attention to the diversity of needs and practices from an intersectional perspective that considers, among other things, class, gender, age, ethnicity and ability, are three directions to do so. Together, these three directions can account for how illness or health, poverty or prosperity, suffering or well-being, stigma or respect are generated for different people who are dependent on, or who are providing, sanitation services. COVID-19 marks a turning point to critically reframe how we talk and act upon just sanitation and to challenge long-term inequalities