A New Model of Holographic Dark Energy with Action Principle
  We propose a new model of holographic dark energy with an action. It is the
first time that one can derive a HDE model from the action principle. The
puzzles of causality and circular logic about HDE have been completely solved
in this model. The evolution of the universe only depends on the present state
of the universe, clearly showing that it obeys the law of causality.
Furthermore, the use of future event horizon as a present cut-off is not an
input but automatically follows from equations of motion. Interestingly, this
new model is very similar to the initial one of Li except a new term which may
be explained as dark radiation.
