sage
发表文章数: 1125
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Physics Benchmarks of String theory: D-branes
D-brane was the next major advance in the string theory. It
dramatically changed the possible applications of string theory to
physics.
J. Polchinski realized that there is a class of non-perturbative
object whose property could be studied, i.e., calculated, using open
strings. This is revolutionary since it is first time we are able to
study strings in a non-trivial background.
The D-brane break through, like all the others, does not come from
fancy mathematics at all. It started from a simple observation in the
open string spectrum.
It is the starting point of all kinds of later studies such as
dualities, blackhole entropy and so on. It also gives a very important
play ground for models of our world. It dramatically increased the
possible unification gauge groups. It provide new ways to embed chiral
fermions.
D-branes change dramatically the spacetime structure around them. This
also give rise to many more interesting possible space-time back
grounds.
It is still uncertain whether superstring string theory will ever have
anything to do with nature. However, if it does, D-branes will almost
certainly play an important role.
| 发表时间：2005-09-29, 17:01:16 |
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轩轩
发表文章数: 1352
武功等级: 易筋经
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内力值: 567/567
Re: Physics Benchmarks of String theory: D-branes
D-brane是一个2维面还是一个超曲面？？？如果是
超曲面，它是类空的吗？？？
string是不是计算2个D膜之间的casimir能量
引力是非局部的，量子力学也是非局部的。《相对论通俗演义》
i will love you till the null infinity.
| 发表时间：2005-09-29, 20:45:54 |
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sage
发表文章数: 1125
武功等级: 天山六阳掌
(第六重)
内力值: 535/535
Re: Physics Benchmarks of String theory: D-branes
>D-brane是一个2维面还是一个超曲面？？？如果是
>超曲面，它是类空的吗？？？
D brane comes with a variety of dimensions, from 1-10 in the superstring framework. Dimension of a D-brane is usually labeled by p=number of spactial dimensions. So a D3 brane usually refer to a 4 dimenisonal object with 1 time-like dimensions. There are Euclidean D-branes as well with all its dimensions space-like.
string是不是计算2个D膜之间的casimir能量
That is one of the things you can use open string partitiion fucntion to compute. There are a lot of other things, such as the bending of the D-brane, Gravitional attraction, repulsion due to RR charge, etc., that can be computed using open string worldsheet conformal field theory.
By the way, are you doing brane-world cosmology?
| 发表时间：2005-09-29, 21:49:49 |
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轩轩
发表文章数: 1352
武功等级: 易筋经
(第二重)
内力值: 567/567
Re: Physics Benchmarks of String theory: D-branes
By the way, are you doing brane-world cosmology?
yes , i did RS brane-world cosmology 。那是我的本科毕业论文，但引力的brane宇宙与string有很大的区别。 我现在已经没有碰膜宇宙了，所以只知道个大概。不过现在好象膜宇宙已经冷下来了？
引力是非局部的，量子力学也是非局部的。《相对论通俗演义》
i will love you till the null infinity.
| 发表时间：2005-09-29, 22:34:32 |
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sage
发表文章数: 1125
武功等级: 天山六阳掌
(第六重)
内力值: 535/535
Re: Physics Benchmarks of String theory: D-branes
yes , i did RS brane-world cosmology 。那是我的本科毕业论文，
但引力的brane宇宙与string有很大的区别。
they are not that different. The supergravity lagrangian used in the calculation is supposedly derived from string theory. Stringy corrections to the Lagrangian is very important to the early universe cosmology... The work of Henry Tye and his collaborators on the braneworld cosmolgy has very close connection to string theory/
我现在已经没有碰膜宇宙了，所以只知道个大概。
不过现在好象膜宇宙已经冷下来了？
No. On the contrary, it is one of the hotest area in cosmology and string theory. There is a collection of paper from stanford group: Linde, Kachru, Kallosh, and so on, trying to do inflation in the framework of braneworld cosmology. Another recent hot topic in string theory these days is flux compactification, which is also done in a braneworld setup.
| 发表时间：2005-09-29, 23:08:27 |
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轩轩
发表文章数: 1352
武功等级: 易筋经
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内力值: 567/567
Re: Physics Benchmarks of String theory: D-branes
在引力中，人们往往把brane放在ADS中。
在string里，brane是不是也喜欢放在ADS中？？？
什么叫flux紧致化？？？ 什么场的flux？？？
引力是非局部的，量子力学也是非局部的。《相对论通俗演义》
i will love you till the null infinity.
| 发表时间：2005-09-29, 23:30:45 |
作者资料
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sage
发表文章数: 1125
武功等级: 天山六阳掌
(第六重)
内力值: 535/535
Re: Physics Benchmarks of String theory: D-branes
>在引力中，人们往往把brane放在ADS中。
>在string里，brane是不是也喜欢放在ADS中？？？
---------------------------------------------------------------------------
Of course. Near horizon geomtry of a D-brane is AdS. Generically, presence of a brane changes vacuum energy. In a superrsymmetric setup, this means that you are more likely to have AdS.
什么叫flux紧致化？？？ 什么场的flux？？？
Presence of the flux changes the potential of the moduli fields. it could stablize the, say radius, to a specific value. This class of models are generically call flux compactification.
In principle, flux could be any gauge field. In particular, people recently are interested in the effects of NS-NS and RR 3-form flux.
The classical paper here is Giddings, Kachru and Polchinski.
| 发表时间：2005-09-30, 08:43:41 |
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星空与道德
发表文章数: 258
武功等级: 华山剑法
(第九重)
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Re: Physics Benchmarks of String theory: D-branes
传说用子空间来描述D-brane是一种极端简化的说法。我听说描述D-brane的正确数学语言可能是Derived Category of coherent sheaves. 如果是真的话，那就走到我研究的方向了。这也正是我花时间学String Theory的一个原因。呵呵。
痛苦的人没有悲观的权利！ ——尼采
| 发表时间：2005-10-04, 20:59:18 |
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sage
发表文章数: 1125
武功等级: 天山六阳掌
(第六重)
内力值: 535/535
Re: Physics Benchmarks of String theory: D-branes
>传说用子空间来描述D-brane是一种极端简化的说法。我听说描述D-brane
>的正确数学语言可能是Derived Category of coherent sheaves.
I am sure all those words, plus things like K-theory, morse theory, and so on will have something to do with the branes.
from a field theory point of view, D-branes is a solitonic solutiion (with central charges, and so on). Using topological language (category and so on) to it is similar to using homotopy classification to the states of solitons in D=4. It classifies the states, but contain few information about its dynamics.
what is really special about D-branes is that they have a dynamical description in terms of conformal field theory of the open strngs.
> 如果是真的话，
>那就走到我研究的方向了。这也正是我花时间学String Theory的一个原
>因。呵呵。
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| 发表时间：2005-10-04, 21:57:53 |
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星空与道德
发表文章数: 258
武功等级: 华山剑法
(第九重)
内力值: 360/360
Re: Physics Benchmarks of String theory: D-branes
真是太好了，所有的数学都派上用场了，而且都有了直观一些地解释。怪不得Singer(Atiyah-Singer)说现在的数学和物理的交叉给数学带来无限机遇，叫大家一定要珍惜！
痛苦的人没有悲观的权利！ ——尼采
| 发表时间：2005-10-06, 03:36:23 |
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小追
发表文章数: 133
武功等级: 罗汉拳
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Re: Physics Benchmarks of String theory: D-branes
这个东西写得好，我喜欢。
不竞言，不竞智，不竞巧；
无可竞者，无人能竞～
| 发表时间：2005-10-06, 08:05:07 |
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