Exploring the Freedom of Model Building in Non-Perturbative String Theory

[Creighton Hogg]

Since there are so many possible vacuum states in string theory, with many
different possible compactifications and configurations of background
D-branes, should (in your opinions) the "final" non-perturbative string
theory/M-theory restrict it down to a few or even
just one vacuum state or will there always be freedom in model building?

I was just wondering since my main interest is in phenomenology.

 

[Arvind Rajaraman]

On Sun, 28 Mar 2004, Creighton Hogg wrote:

> Since there are so many possible vacuum states in string theory, with many
> different possible compactifications and configurations of background
> D-branes, should (in your opinions) the "final" non-perturbative string
> theory/M-theory restrict it down to a few or even
> just one vacuum state or will there always be freedom in model building?
>
> I was just wondering since my main interest is in phenomenology.
>

It seems rather unlikely that the final theory will restrict the
number of vacua drastically; at least the highly supersymmetric vacua seem
to be completely stable. The hope is that there are only a finite number
of non-supersymmetric vacua, in which case there is still predictivity.
Mike Douglas has some papers on this problem.

 

[Urs Schreiber]

On Wed, 31 Mar 2004, Arvind Rajaraman wrote:

> On Sun, 28 Mar 2004, Creighton Hogg wrote:
>
> > Since there are so many possible vacuum states in string theory, with many
> > different possible compactifications and configurations of background
> > D-branes, should (in your opinions) the "final" non-perturbative string
> > theory/M-theory restrict it down to a few or even
> > just one vacuum state or will there always be freedom in model building?
> >
> > I was just wondering since my main interest is in phenomenology.
> >
>
> It seems rather unlikely that the final theory will restrict the
> number of vacua drastically; at least the highly supersymmetric vacua seem
> to be completely stable. The hope is that there are only a finite number
> of non-supersymmetric vacua, in which case there is still predictivity.
> Mike Douglas has some papers on this problem.Sometimes one hears some people claim that 'string theory predicts
nothing', due to the apparently non-unique vacuua. There is a nice reply
to such comments by Jacques Distler on
http://golem.ph.utexas.edu/string/archives/000330.html#c000877 .

 

[Creighton Hogg]

On Wed, 31 Mar 2004, Urs Schreiber wrote:

> ... Sometimes one hears some people claim that 'string theory predicts
> nothing', due to the apparently non-unique vacuua. There is a nice reply
> to such comments by Jacques Distler on
>
> http://golem.ph.utexas.edu/string/archives/000330.html#c000877 .

Well, I tend to view things in terms of model building, so I don't see the
non-unique vacuua as a problem. This is my personal view, but I don't see
it as being a problem anymore than the freedom to choose a lagrangian in
QFT. It seems to me that in QFT your background is assumed and your
interactions are left to choice, while in string theory your interactions
are assumed and your background is left to choice.

 

[Urs Schreiber]

On Wed, 31 Mar 2004, Creighton Hogg wrote:

> Well, I tend to view things in terms of model building, so I don't see the
> non-unique vacuua as a problem. This is my personal view, but I don't see
> it as being a problem anymore than the freedom to choose a lagrangian in
> QFT. It seems to me that in QFT your background is assumed and your
> interactions are left to choice, while in string theory your interactions
> are assumed and your background is left to choice.

If you are into model buiding, maybe you can help me with the following
question:

In many models that are being discussed it seems that one does
have very incomplete knowledge even of the _theoretical_ viability
of the model, e.g. of instabilities and anomalies. For instance
in

https://www.physicsforums.com/showpost.php?p=162692&postcount=11

"R.X." writes:

"I would say that many if not most of those more phenomenologically
oriented papers, on brane models and alike, are pretty off the track
and sometimes even outright wrong, just because they do not take
effects into account which we know from Douglas' work.

"For example, many papers assume (in the context of a given brane model),
that a brane-anti-brane pair breaks supersymmetry due to the
tachyonic mode between them. They use this tofeed some degree of
SUSY breaking into their models. But we know from Douglas' work
(via his concept of flow gradings), that if you take the quantum geometry
of those branes properly into account, then the notion of what a
brane is and what an anti-brane is, is not a universal notion but
depends on where you are in the moduli space. It generically so
happens that a naive supersymmetry-breaking brane-antibrane pair turns
into a susy preserving brane-brane pair in some other region of the
moduli space.

"In other words, from the effective action point of view, the naive
barne-anti-brane system has a non-perturbative potential with a susy
restoring minimum, somewhere in the moduli space.

"This is probably not what the unsuspecting brane model buidlers
had in mind... and they cannot know it if they didn't read Douglas'
papers.

"Summa summarum, it just doesn't makes sense to attempt any sort of
brane model building, without the knowledge of such effects.
Admittedly, this is mathematically very complicated stuff, and this is
why only few people know about it - most others go the easy way
and ignore it."

 

[Lubos Motl]

"Creighton Hogg" <wchogg@hep.wisc.edu> wrote in message
news:Pine.LNX.4.31.0403281208510.27267-100000@feynman.harvard.edu...

> Since there are so many possible vacuum states in string theory, with many
> different possible compactifications and configurations of background
> D-branes, should (in your opinions) the "final" non-perturbative string
> theory/M-theory restrict it down to a few or even
> just one vacuum state or will there always be freedom in model building?

This is, of course, one of the most important questions of superstring
phenomenology nowadays. A well-known founder of string theory (L.S.) is now
writing a book about his recent "discovery" called the "stringy landscape".
There exists a growing evidence that the number of metastable vacua in
string theory is very large, and therefore one might be forced to adopt at
least some aspects of the anthropic thinking.

The most successful industry of propaganda, that tries to argue that we know
almost for sure that the number of vacua is huge, was started by KKLT

http://arxiv.org/abs/hep-th/0301240

Of course, many of us are highly irritated by the idea that we would have to
adopt the anthropic principle. Some people are approaching these questions
scientifically, some people approach them less scientifically. Even if the
number of vacua is large, as some people argue, it might be that the allowed
cosmologies are much more constrained. Even if the number of cosmologies is
large, the predictivity does not have to be lost. Two famous physicists
(N.A-H. and S.D.) are now working on their amazing predictions for the LHC
accelerator - if this prediction is confirmed, they say, you will have to
believe that the landscape is reality.

I hope that the start of the LHC will remove a lot of unconstructive ideas
at the end. It is just not certain which ideas are constructive and which
ideas are not.