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D-brane probes?

  1. Mar 26, 2004 #1
    Stupid Question #2 for today:

    I started trying to read hep-th/0403247, QED and String Theory, last night
    but I really don't understand this concept of probe D-branes.
    When they say that they're taking a probe Dp-brane in the background of a
    D9-antiD9 brane system, is the Dp-brane part of the background too or is
    it just a mathematical construct, kindof a reverse method of images, meant
    to help analyze the physics of the system. If it's part of the
    background, I don't understand why it's being called a probe, but if it's
    just a construct I don't understand why they're describing the physics on
    its worldvolume. Sorry, but I'm rather confused at this point.

    [moderator note: a probe is an object - a real object, not just a virtual
    gedanken experiment - that is meant to measure and see the properties of
    the background, and it is probe because it should be light or invisible
    enough so that it does not affect the background, or at least we can
    neglect such a "backreaction". Nevertheless, in string theory you are only
    allowed to consider probes that are allowed by the theory - not some
    fictitious angels. For example, string theory predicts that there are no
    objects that are more localized than some concrete (sub)planckian
    distance. This really means that shorter distances don't exist in the
    geometrical sense. Everyone: please feel free to give a different answer. lm]
  2. jcsd
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