Effective Spin Foam Models for Four-Dimensional Quantum Gravity.

A number of approaches to four-dimensional quantum gravity, such as loop quantum gravity and holography, situate areas as their fundamental variables. However, this choice of kinematics can easily lead to gravitational dynamics peaked on flat spacetimes. We show that this is due to how regions are glued in the gravitational path integral via a discrete spin foam model.

The Economic Costs of COVID-19 in Sub-Saharan Africa: Insights from a Simulation Exercise for Ghana.

Globally, countries have resorted to social distancing, travel restrictions and economic lockdowns to reduce transmission of COVID-19. The socioeconomic costs of these blunt measures are expected to be high, especially in sub-Saharan Africa where many live hand-to-mouth and lack social safety nets. Social Accounting Matrix multiplier model results show that Ghana's urban lockdown, although in force for only three weeks in April 2020, has likely caused GDP to fall by 27.