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## Main Question or Discussion Point

Which of the following do you prefer as possible solution to the cosmological constant problem or why QFT computes vacuum energy density that is 120 magnitude more than from observational data? Sometimes I think the metric (1.a) needs to change, but on other days I think QFT needs to change (2.a).. the CC problem would indeed be directly relevant to search for physics beyond the standard model.

http://arxiv.org/pdf/hep-th/0012253v1.pdf

Can you add others not mentioned above?

http://arxiv.org/pdf/hep-th/0012253v1.pdf

Schwinger’s source theory is that in the absence of matter and measurement settings, there are no quantum fields avoiding the 120 magnitude discrepancy, how many even consider this possibility?1.A modification of GR. The problem could be either

(a) ‘internal’ in the sense that a change is needed in the GR formalism itself (e.g. changing the role of the metric), or

(b) ‘external’ in the sense that GR is still considered effectively correct, but that it needs to be embedded in an extended framework to address the question (e.g. quantum cosmology).

2.A modification of QFT. Again, the problem could be either

(a) ‘internal’ in the sense that a change in, or a reinterpretation of, the QFT formalism which gives rise to the vacuum energy is needed (for instance through Schwinger’s source theory), or

(b) ‘external’ in the sense that QFT (the Standard Model) is considered effectively correct as a low energy theory, but needs to be embedded in an extended framework to address the question (e.g. supersymmetry).

3.The link between GR and QFT is problematic. Once more, we see at least two

ways in which this may be the case, either the problem is

(a) ‘internal’ in the sense that the link cannot even be discussed properly due to our limited understanding of the coupling between GR and QFT (e.g. QFT in curved spacetime, and back-reaction), or

(b) ‘external’ in the sense that we due to the limited understanding of the coupling between GR and QFT ought to postpone the problem until we have a theory in which the link is embedded in an extended framework for both GR and QFT since only in such a theory will the problem be completely well posed (e.g. string theory)

Can you add others not mentioned above?