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Conceptual question

  1. Mar 28, 2004 #1
    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.
     
  2. jcsd
  3. Mar 31, 2004 #2
    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.
     
  4. Mar 31, 2004 #3
    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 apparantly 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 .
     
  5. Mar 31, 2004 #4
    On Wed, 31 Mar 2004, Urs Schreiber wrote:

    > ... Sometimes one hears some people claim that 'string theory predicts
    > nothing', due to the apparantly 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.
     
  6. Mar 31, 2004 #5
    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."
     
  7. Apr 2, 2004 #6
    "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.
     
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