  A new universality in optimization of trade-off between power and efficiency
for low-dissipation Carnot cycles is presented. It is shown that any trade-off
measure expressible in terms of efficiency and the ratio of power to its
maximum value can be optimized independently of most details of the dynamics
and of the coupling to thermal reservoirs. The result is demonstrated on two
specific trade-off measures. The first one is designed for finding optimal
efficiency for a given output power and clearly reveals diseconomy of engines
working at maximum power. As the second example we derive universal lower and
upper bounds on the efficiency at maximum trade-off given by the product of
power and efficiency. The results are illustrated on a model of a
diffusion-based heat engine. Such engines operate in the low-dissipation regime
given that the used driving minimizes the work dissipated during the isothermal
branches. The peculiarities of the corresponding optimization procedure are
reviewed and thoroughly discussed.
