Dark matter + dark energy = fluid with negative mass?

Physicists introduced the concept of dark matter after they determined that, among other things, galaxies didn’t have enough mass to explain their rotation. Dark energy with its strange properties is needed to explain, for example, the evolution of the universe during its early childhood when it must have experienced a sudden, tremendous growth spurt. Both concepts are incorporated into the current model of the universe called Lambda-CDM.

This model, however, has a small disadvantage: it says...