Searching for dark matter with plasma haloscopes

We summarize the recent progress of the Axion Longitudinal Plasma Haloscope (ALPHA) Consortium, a new experimental collaboration to build a plasma haloscope to search for axions and dark photons. The plasma haloscope is a novel method for the detection of the resonant conversion of light dark matter to photons. ALPHA will be sensitive to QCD axions over almost a decade of parameter space, potentially discovering dark matter and resolving the strong CP problem. Unlike traditional cavity haloscopes, which are generally limited in volume by the Compton wavelength of the dark matter, plasma haloscopes use a wire metamaterial to create a tuneable artificial plasma frequency, decoupling the wavelength of light from the Compton wavelength and allowing for much stronger signals. We develop the theoretical foundations of plasma haloscopes and discuss recent experimental progress. Finally, we outline a baseline design for ALPHA and show that a full-scale experiment could discover QCD axions over almost a decade of parameter space

How Local are Spatial Density Externalities? Neighbourhood Effects in Agglomeration Economies

Andersson M., Klaesson J. and Larsson J. P. How local are spatial density externalities? Neighbourhood effects in agglomeration economies, Regional Studies. The geographic scale at which density externalities operate is analysed in this paper. Using geocoded high-resolution data, the analysis is focused on exogenously determined within-city squares (‘neighbourhoods’) of 1 km2. The analysis confirms a city-wide employment density–wage elasticity and an economically significant density–wage elasticity at the neighbourhood level that attenuate sharply with distance. Panel estimates over 20 years suggest a neighbourhood density–wage elasticity of about 3%, while the city-wide elasticity is about 1%. It is argued that the neighbourhood level is more prone to capture learning, e.g. through knowledge and information spillovers. This interpretation is supported by (1) significantly larger neighbourhood elasticities for university educated workers and (2) sharper attenuation with distance of the effect for such workers

The sources of the urban wage premium by worker skills: Spatial sorting or agglomeration economies?

We estimate the respective importance of spatial sorting and agglomeration economies in explaining the urban wage premium for workers with different sets of skills. Sorting is the main source of the wage premium. Agglomeration economies are in general small, but are larger for workers with skills associated with non-routine job tasks. They also appear to involve human capital accumulation, as evidenced by the change in the wage of workers moving away from denser regions. For workers with routine jobs, agglomeration economies are virtually non-existent. Our results provide further evidence of spatial density bringing about productivity advantages primarily in contexts when problem-solving and interaction with others are important