Friedmann branes with variable tension

We introduce braneworlds with nonconstant tension, strengthening the analogy with fluid membranes, which exhibit a temperature dependence according to the empirical law established by E\"otv\"os. This new degree of freedom allows for evolving gravitational and cosmological constants, the latter being a natural candidate for dark energy. We establish the covariant dynamics on a brane with variable tension in full generality, by considering asymmetrically embedded branes and allowing for nonstandard model fields in 5-dimensional space-time. Then we apply the formalism for a perfect fluid on a Friedmann brane, which is embedded in a 5-dimensional charged Vaidya-anti-de Sitter space-time.