Null energy condition violation: Tunneling versus the Casimir effect

We show that tunneling between two degenerate minima, as allowed in a finite volume, leads to a nonextensive symmetric ground state. This results in a null energy condition violation for sufficiently low temperatures, when a continuous set of momenta in the box containing the field is assumed. Taking into account discrete momenta can modify this picture and is achieved via the addition of the Casimir energy to the tunneling-induced ground state energy. Focusing on zero-temperature, these nontrivial effects are found to compete, depending on the typical length scales involved.