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In | {{Cosmology}} | ||
'''Brane cosmology''' refers to several theories in [[particle physics]] and [[physical cosmology|cosmology]] related to [[string theory]], [[superstring theory]] and [[M-theory]]. | |||
==Brane and bulk== | |||
{{Main|Brane}} | |||
The central idea is that the visible, [[four-dimensional]] [[universe]] is restricted to a [[brane]] inside a [[Kaluza-Klein|higher-dimensional]] space, called the "bulk" (also known as "hyperspace"). If the additional [[dimension]]s are [[compact dimension|compact]], then the observed universe contains the extra dimensions, and then no reference to the bulk is appropriate. In the bulk model, at least some of the extra dimensions are extensive (possibly infinite), and other branes may be moving through this bulk. Interactions with the bulk, and possibly with other branes, can influence our brane and thus introduce effects not seen in more standard cosmological models. | |||
==Why gravity is weak== | |||
The model can explain the weakness of [[gravity]] relative to the other [[fundamental forces]] of nature, thus solving the so-called [[hierarchy problem]]. In the brane picture, the other three forces ([[electromagnetism]] and the [[weak interaction|weak]] and [[strong interaction|strong]] nuclear forces) are localized on the brane, but gravity has no such constraint. Much of its attractive power "leaks" into the bulk. As a consequence, the force of gravity should appear significantly stronger on small (subatomic or at least sub-millimetre) scales, where less gravitational force has "leaked". Various experiments are currently under way to test this.<ref>[http://flux.aps.org/meetings/YR04/APR04/baps/abs/S690.html Session D9 - Experimental Tests of Short Range Gravitation.]</ref> | |||
==Models of brane cosmology== | |||
One of the earliest documented attempts to apply brane cosmology as part of a conceptual theory is dated to 1983.<ref>V. A. Rubakov and M. E. Shaposhnikov,''Do we live inside a domain wall?'', [http://www.sciencedirect.com/science/article/pii/0370269383912534 Physics Letters B 125 (1983) 136–138].</ref> | |||
The authors discussed the possibility that the Universe has <math>(3+N)+1</math> dimensions, but ordinary particles are confined in a potential well which is narrow along <math>N</math> spatial directions and flat along three others, and proposed a particular five-dimensional model. | |||
In 1998/99 [[Merab Gogberashvili]] published on [[Arxiv|arXiv]] a number of articles where he showed that if the Universe is considered as a thin shell (a mathematical [[synonym]] for "brane") expanding in 5-dimensional space then there is a possibility to obtain one scale for particle theory corresponding to the 5-dimensional [[cosmological constant]] and Universe thickness, and thus to solve the [[hierarchy problem]].<ref>M. Gogberashvili, ''Hierarchy problem in the shell universe model'', [http://arxiv.org/abs/hep-ph/9812296 Arxiv:hep-ph/9812296].</ref><ref>M. Gogberashvili, ''Our world as an expanding shell'', [http://arxiv.org/abs/hep-ph/9812365 Arxiv:hep-ph/9812365].</ref><ref>M. Gogberashvili, ''Four dimensionality in noncompact Kaluza-Klein model'', [http://arxiv.org/abs/hep-ph/9904383 Arxiv:hep-ph/9904383].</ref> It was also shown that the four-dimensionality of the Universe is the result of the [[Stability theory|stability]] requirement found in mathematics since the extra component of the [[Einstein field equations]] giving the confined solution for [[matter]] fields coincides with one of the conditions of stability. | |||
In 1999 there were proposed the closely related [[Randall-Sundrum model|Randall-Sundrum]] (RS1 and RS2; see ''[[5 dimensional warped geometry theory]]'' for a nontechnical explanation of RS1) scenarios. These particular models of brane cosmology have attracted a considerable amount of attention. | |||
Later, the [[pre-big bang]], [[ekpyrotic]] and [[Cyclic Model|cyclic]] proposals appeared. The ekpyrotic theory hypothesizes that the origin of the [[observable universe]] occurred when two parallel branes collided.<ref>{{cite news|last=Musser|first=George|coauthors=Minkel, JR|title=A Recycled Universe: Crashing branes and cosmic acceleration may power an infinite cycle in which our universe is but a phase|publisher=Scientific American Inc.|date=2002-02-11|url=http://www.sciam.com/article.cfm?id=a-recycled-universe|accessdate=2008-05-03}}</ref> | |||
==Empirical tests== | |||
{{see also2|[[Large_extra_dimension#Empirical_tests|Large extra dimension, Empirical tests]]}} | |||
As of now, no experimental or observational evidence of [[large extra dimension]]s, as required by the Randall–Sundrum models, has been reported. An analysis of results from the [[Large Hadron Collider]] in December 2010 severely constrains theories with [[large extra dimensions]].<ref name="arxiv.org">CMS Collaoration, "Search for Microscopic Black Hole Signatures at the Large Hadron Collider," http://arxiv.org/abs/1012.3375</ref> | |||
==Brane-world scenario== | |||
If, as brane cosmology posits, our universe is a massive 10-brane, then there might be other branes existing in a higher dimensional space. [[Brian Greene]] illustrates this by saying that it is as if the branes are slices of bread, and a [[multiverse]] is the loaf of all the slices together. He is saying that if branes are actually universes, then this might possibly imply the existence of a multiverse, called the '''braneworld scenario.''' There is no experimental evidence for this hypothesis, nor is there any definite need for the brane multiverse in [[M-theory]] or [[string theory]]. | |||
==See also== | |||
* [[Kaluza-Klein theory]] | |||
* [[M-theory]] | |||
* [[String theory]] | |||
* [[Loop quantum cosmology]] | |||
==References== | |||
<references /> | |||
==External links== | |||
* {{cite arxiv|author=[[Philippe Brax|Brax, Philippe]]; [[Carsten van de Bruck|van de Bruck, Carsten]]|title=Cosmology and Brane Worlds: A Review|year=2003|eprint=hep-th/0303095}} – Cosmological consequences of the brane world scenario are reviewed in a pedagogical manner. | |||
* {{cite arxiv|author=[[David Langlois|Langlois, David]]|title=Brane cosmology: an introduction|year=2002|eprint=hep-th/0209261}} – These notes (32 pages) give an introductory review on brane cosmology. | |||
* {{cite arxiv|author=[[Eleftherios Papantonopoulos|Papantonopoulos, Eleftherios]]|title=Brane Cosmology|year=2002|eprint=hep-th/0202044}} – Lectures (24 pages) presented at the First Aegean Summer School on Cosmology, [[Samos]], September 2001. | |||
* [http://xstructure.inr.ac.ru/x-bin/theme3.py?level=2&index1=-197206 Brane cosmology on arxiv.org] | |||
* [http://www.sciamdigital.com/index.cfm?fa=Products.ViewIssuePreview&ARTICLEID_CHAR=9D2C5D4D-2B35-221B-6C9DB167634A6DDB Dimensional Shortcuts - evidence for sterile neutrino; (August 2007; Scientific American)] | |||
{{DEFAULTSORT:Brane Cosmology}} | |||
[[Category:Physical cosmology]] | |||
[[Category:Particle physics]] | |||
[[Category:String theory]] | |||
[[Category:Astronomical hypotheses]] | |||
Revision as of 02:48, 1 November 2013
Template:Cosmology Brane cosmology refers to several theories in particle physics and cosmology related to string theory, superstring theory and M-theory.
Brane and bulk
Mining Engineer (Excluding Oil ) Truman from Alma, loves to spend time knotting, largest property developers in singapore developers in singapore and stamp collecting. Recently had a family visit to Urnes Stave Church. The central idea is that the visible, four-dimensional universe is restricted to a brane inside a higher-dimensional space, called the "bulk" (also known as "hyperspace"). If the additional dimensions are compact, then the observed universe contains the extra dimensions, and then no reference to the bulk is appropriate. In the bulk model, at least some of the extra dimensions are extensive (possibly infinite), and other branes may be moving through this bulk. Interactions with the bulk, and possibly with other branes, can influence our brane and thus introduce effects not seen in more standard cosmological models.
Why gravity is weak
The model can explain the weakness of gravity relative to the other fundamental forces of nature, thus solving the so-called hierarchy problem. In the brane picture, the other three forces (electromagnetism and the weak and strong nuclear forces) are localized on the brane, but gravity has no such constraint. Much of its attractive power "leaks" into the bulk. As a consequence, the force of gravity should appear significantly stronger on small (subatomic or at least sub-millimetre) scales, where less gravitational force has "leaked". Various experiments are currently under way to test this.[1]
Models of brane cosmology
One of the earliest documented attempts to apply brane cosmology as part of a conceptual theory is dated to 1983.[2]
The authors discussed the possibility that the Universe has dimensions, but ordinary particles are confined in a potential well which is narrow along spatial directions and flat along three others, and proposed a particular five-dimensional model.
In 1998/99 Merab Gogberashvili published on arXiv a number of articles where he showed that if the Universe is considered as a thin shell (a mathematical synonym for "brane") expanding in 5-dimensional space then there is a possibility to obtain one scale for particle theory corresponding to the 5-dimensional cosmological constant and Universe thickness, and thus to solve the hierarchy problem.[3][4][5] It was also shown that the four-dimensionality of the Universe is the result of the stability requirement found in mathematics since the extra component of the Einstein field equations giving the confined solution for matter fields coincides with one of the conditions of stability.
In 1999 there were proposed the closely related Randall-Sundrum (RS1 and RS2; see 5 dimensional warped geometry theory for a nontechnical explanation of RS1) scenarios. These particular models of brane cosmology have attracted a considerable amount of attention.
Later, the pre-big bang, ekpyrotic and cyclic proposals appeared. The ekpyrotic theory hypothesizes that the origin of the observable universe occurred when two parallel branes collided.[6]
Empirical tests
As of now, no experimental or observational evidence of large extra dimensions, as required by the Randall–Sundrum models, has been reported. An analysis of results from the Large Hadron Collider in December 2010 severely constrains theories with large extra dimensions.[7]
Brane-world scenario
If, as brane cosmology posits, our universe is a massive 10-brane, then there might be other branes existing in a higher dimensional space. Brian Greene illustrates this by saying that it is as if the branes are slices of bread, and a multiverse is the loaf of all the slices together. He is saying that if branes are actually universes, then this might possibly imply the existence of a multiverse, called the braneworld scenario. There is no experimental evidence for this hypothesis, nor is there any definite need for the brane multiverse in M-theory or string theory.
See also
References
- ↑ Session D9 - Experimental Tests of Short Range Gravitation.
- ↑ V. A. Rubakov and M. E. Shaposhnikov,Do we live inside a domain wall?, Physics Letters B 125 (1983) 136–138.
- ↑ M. Gogberashvili, Hierarchy problem in the shell universe model, Arxiv:hep-ph/9812296.
- ↑ M. Gogberashvili, Our world as an expanding shell, Arxiv:hep-ph/9812365.
- ↑ M. Gogberashvili, Four dimensionality in noncompact Kaluza-Klein model, Arxiv:hep-ph/9904383.
- ↑ Template:Cite news
- ↑ CMS Collaoration, "Search for Microscopic Black Hole Signatures at the Large Hadron Collider," http://arxiv.org/abs/1012.3375
External links
- Template:Cite arxiv – Cosmological consequences of the brane world scenario are reviewed in a pedagogical manner.
- Template:Cite arxiv – These notes (32 pages) give an introductory review on brane cosmology.
- Template:Cite arxiv – Lectures (24 pages) presented at the First Aegean Summer School on Cosmology, Samos, September 2001.
- Brane cosmology on arxiv.org
- Dimensional Shortcuts - evidence for sterile neutrino; (August 2007; Scientific American)