Cosmology 267
immediately enforce us into it, but we still may do it.
N. Arkani-Hamed I just want to pop onto Seiberg’s question. I think it is very
interesting that with two years to go until the LHC, the situation is dramatically
different from what it was in 1982 with two years to go until the discovery of the
W and Z-boson at CERN. I think that 10 years ago, even the phenomenologist
among us would have been a lot more confident about what to expect at the
LHC than we are now. And as I mentioned in my previous remarks, that is
associated with the fact that, quite apart from all the hints from cosmology
and the theoretical hints from the string landscape, there is a growing sense
of unease with why we have not seen evidence for new physics at the TeV
scale. By itself this is not particularly dramatic, but still, something could
easily have shown up already. So I think there are three possibilities for what
might happen at the LHC and how it might impact the way we think about
these questions. One of them is that we see evidence for a really, completely
natural theory. And within a natural theory, some nice mechanism built into
it would beautifully explain why it is that this expectation we have had for all
this time that something would have shown up, was wrong. If that happened
I would actually be given some pause and would certainly re-think possible
natural solutions to the cosmological constant problem. There is the opposite
possibility that the LHC might actually prove that the weak scale is finely
tuned. That is a possibility that we have not been contemplating at all, but it
is something that may actually happen. And if that happened, there is a variety
of models, split supersymmetry being one of the examples but there are others,
where you could really be able to prove that the weak scale is very finely tuned.
If that happened, while in itself it is not evidence for landscape and anthropic
reasoning or anything like that, it would be, I think, another big push in that
direction. Now, the most ambiguous thing that can happen, I think, is that we
might discover a natural theory and find that it is a little bit tuned. That is
possible and basically every attempt to go beyond the Standard Model, when
you look at it in detail, the theory is just tuned. Depending on how you talk
about it, at the percent level, at five percent, half a percent, it does not matter,
but there is something a little bit wrong. It could be that this is just what
it is like. In the Standard Model we have several parameters which appear to
be a little finely tuned, and that would just be another example. I think that
would be the most ambiguous possibility. The natural possibility and the tuned
natural possibility would shed no light on the cosmological constant problem,
but I think that if we find evidence for tuning of the weak scale at LHC, for
me it would be a very powerful evidence that the cosmological constant is also
finely tuned. And, whatever the explanation is, we would have to think about
it along those lines.
