Is there a mechanism for creation of negative energy density

[Christofer Br]

Excuse me for bad wording in the title, but there is only so much you can do with the character limit.
So, has there ever been a proposal for a mechanism through which negative energy density could be created? Or the only possibility considered so far was that it would have been created in the beginning of the universe?

 

[mfb]

We don't know of anything with a negative energy density. It is possible to interpret the space between nearby conductors as region of negative energy density due to the Casimir effect, but that is mainly a mathematical bookkeeping tool.

 

[JordBruno]

The Janus Cosmological Model predicts existence of negative mass matter in space, which would account for the effects attributed to dark matter and dark energy. Negative mass matter means negative energy. Maybe it's an answer , if I'm getting your question right.