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Detecting large extra dimensions via mini black holes ? 
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Dec3107, 05:00 AM

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Occasionally I come across something explaining that one of the
possible discoveries at the Large Hadron Collider might be the production of "mini black holes", which if found would demonstrate the existence of large extra dimensions. The idea, at least as I understand it, is supposed to be that gravity in an morethanfour dimensional universe could be actually much stronger than we measure it to be; but in a way that only has any effect over very small distances, because the gravitons leak out into the extra dimensions if given the chance. The "very small distances", if I'm understanding all this right, could possibly be large enough that colliding particles at a modern particle accelerator would be able to trigger the creation of microscopic, shortlived black holes. The reason I usually see given for why people are excited about this possibility is that it would provide strong experimental support for string theory, by showing one of string theory's more controversial elements extra dimensions to be not just a theoretical convenience but actually a physical fact. An example of a writing on this subject, picked at random from google, might be: http://cerncourier.com/cws/article/cern/29199 or: http://quasar9.blogspot.com/2006/08/...nsatlhc.html The thing that confuses me about this, though, is the frequent implication that this effect the effect that allows for mini black hole production in particle accelerators, that is wouldn't exist in all theories of morethanfourdimensional spacetime, or even all variations of string theory. It's usually left very vague, however, *which* theories would or wouldn't produce this behavior. This seems to make it very difficult to evaluate what the detection or non detection of these black holes at the LHC would or wouldn't be telling us. So, I would like to ask: ** What attributes would a string theory have to have, in order for the extra dimensions to be in principle detectable through black hole production in a particle accelerator? The one thing everything I find on this subject seems to agree on is that the spacetime which the strings inhabit must have more than four noncompact dimensions, but are there any *other* conditions which either the spacetime, or the string theory acting within that spacetime, must satisfy for the "mini black hole" production to be possible? ** I have a few slightly more specific versions of this question I'd also like to ask, but I unfortunately do not know very much about String Theory so I am not certain I know how to ask them correctly. So please excuse me if the following turns out to be gibberish: 1. As far as I'm aware, the preeminent variation of string theory with "large extra dimensions" would be the "brane cosmology" models, where ALL 10 or 11 dimensions are taken to be arbitrarily large, but the perceived universe is lowerdimensional because the movement of strings is restricted to the surfaces of lowerdimensional "branes". (I somehow got the impression that the string theories with compact extra dimensions can be approximated within this model by folding the branes properly, but I am not sure about this.) Within a model of braneworld cosmology, is it possible to see miniblackhole production at a particle accelerator within some individual braneworld embedded in the bulk? And if so, would the miniblackhole effect be *required* by the use of braneworld cosmology, or is it possible to design a braneworld where the effect which results in the miniblackholes does not exist? 2. If the answer to the last question is "yes, but only in a model with the correct circumstances", then is the miniblackhole effect a property of the theory which describes the branes, or is it only a property of some individual braneworld described by that theory? In other words, would it be possible for there to be a higherdimensional bulk, contained within which were BOTH braneworlds which allow the "mini black hole" production, and also braneworlds which do not? 3. The specific largeextradimensions model I seem to hear about the most is this KachruKalloshLindeTrivedi, or KKLT, construction, defined by the paper the arXiv has at hepth/0301240. My *incredibly* limited understanding of this construction is that it assumes a braneworld cosmology model (i.e. all tenish dimensions are noncompact but strings live on a lowerdimensional brane) and then describes a way of configuring branes within the bulk so that you create a nice de sitter space for the strings to live on. (I somehow got the impression that the "string landscape" you sometimes hear about specifically refers to all the different ways of configuring the KKLT construction, but I am not sure about this.) Does use of the KKLT construction allow the mini black holes effect to be present within a braneworld? Does KKLT *require* the effect be present? Thanks! 


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