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{{short description|Several theories in particle physics and cosmology related to superstring theory and M-theory}}
'''Brane cosmology''' is a ] motivated by, but not rigorously derived from, ] and ]. The idea is to solve problems in ] using speculative ] theories and in turn use cosmological observations to motivate ideas in ].
{{string theory}}
⚫ {{Cosmology}}
'''Brane cosmology''' refers to several theories in ] and ] related to ], ] and ].


==Brane and bulk==
⚫ The central idea is that our visible, four-dimensional ] is entirely restricted to a ] inside a ] space, called the bulk. The additional ]s may be taken to be ], in which case the observed universe contains the extra dimensions, and then no reference to the bulk is appropriate in this context. In the bulk model, 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.
{{Main|Brane}}
]
⚫ The central idea is that the visible, four-dimensional ] is restricted to a ] inside a ] space, called the "bulk" (also known as "hyperspace"). If the additional ]s are ], then the observed universe contains the extra dimension, 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 and the cosmological constant is small==
As one of its attractive features, the model can "explain" the weakness of ] relative to the other fundamental forces of nature. In the brane picture, the other three forces (] and the ] and ] nuclear forces) are localised on the ], but gravity has no such constraint and so much of its attractive power "leaks" into the bulk. As a consequence, the force of gravity should appear significantly stronger on small (sub-millimetre) scales, where less gravitational force has "leaked". Various experiments are currently underway to test this. For example, in a particle accelerator, if a graviton were to be discovered and then observed to suddenly disappear, it might be assumed that the graviton "leaked" into the bulk.
Some versions of brane cosmology, based on the ] idea, can explain the weakness of ] relative to the other ] of nature, thus solving the ]. In the brane picture, the ], ] and ] are localized on the brane, but gravity has no such constraint and propagates on the full spacetime, called the bulk. Much of the gravitational 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>{{Cite web |title=Session D9 - Experimental Tests of Short Range Gravitation. |url=https://flux.aps.org/meetings/YR04/APR04/baps/abs/S690.html |website=flux.aps.org}}</ref> Extensions of the large extra dimension idea with ] in the bulk appear to be promising in addressing the so-called ].<ref>{{Cite journal |last1=Aghababaie |first1=Y. |last2=Burgess |first2=C. P. |last3=Parameswaran |first3=S. L. |last4=Quevedo |first4=F. |date=March 2004 |title=Towards a naturally small cosmological constant from branes in 6-D supergravity |journal=Nucl. Phys. B |volume=680 |issue=1–3 |pages=389–414 |arxiv=hep-th/0304256 |bibcode=2004NuPhB.680..389A |doi=10.1016/j.nuclphysb.2003.12.015 |s2cid=14612396}}</ref><ref>{{Cite journal |last1=Burgess |first1=C. P. |last2=van Nierop |first2=Leo |date=March 2013 |title=Technically Natural Cosmological Constant From Supersymmetric 6D Brane Backreaction |journal=Phys. Dark Univ. |volume=2 |issue=1 |pages=1–16 |arxiv=1108.0345 |bibcode=2013PDU.....2....1B |doi=10.1016/j.dark.2012.10.001 |s2cid=92984489}}</ref><ref>{{Cite journal |last1=P. Burgess |first1=C. |last2=van Nierop |first2=L. |last3=Parameswaran |first3=S. |last4=Salvio |first4=A. |last5=Williams |first5=M. |date=February 2013 |title=Accidental SUSY: Enhanced Bulk Supersymmetry from Brane Back-reaction |url=http://inspirehep.net/record/1191922 |journal=JHEP |volume=2013 |issue=2 |page=120 |arxiv=1210.5405 |bibcode=2013JHEP...02..120B |doi=10.1007/JHEP02(2013)120 |s2cid=53667729}}</ref>


==Models of brane cosmology==
The ], ], ] and ] scenarios are particular models of brane cosmology which have attracted a considerable amount of attention.
One of the earliest documented attempts to apply brane cosmology as part of a conceptual theory is dated to 1983.<ref>{{Cite journal |last1=Rubakov |first1=V. A. |last2=Shaposhnikov |first2=M. E. |year=1983 |title=Do we live inside a domain wall? |journal=] |series=B |volume=125 |issue=2–3 |pages=136–138 |bibcode=1983PhLB..125..136R |doi=10.1016/0370-2693(83)91253-4}}</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.
The theory hypothesises that the origin of the big bang could have occurred when two parallel branes touched.

In 1998/99, ] published on ] a number of articles where he showed that if the Universe is considered as a thin shell (a mathematical ] for "brane") expanding in 5-dimensional space then there is a possibility to obtain one scale for particle theory corresponding to the 5-dimensional ] and Universe thickness, and thus to solve the ].<ref>{{Cite journal |last=Gogberashvili |first=M. |date=1998 |title=Hierarchy problem in the shell universe model |journal=International Journal of Modern Physics D |volume=11 |issue=10 |pages=1635–1638 |arxiv=hep-ph/9812296 |doi=10.1142/S0218271802002992 |s2cid=119339225}}</ref><ref>{{Cite journal |last=Gogberashvili |first=M. |year=2000 |title=Our world as an expanding shell |journal=Europhysics Letters |volume=49 |issue=3 |pages=396–399 |arxiv=hep-ph/9812365 |bibcode=2000EL.....49..396G |doi=10.1209/epl/i2000-00162-1 |s2cid=38476733}}</ref> Gogberashvili also showed that the four-dimensionality of the Universe is the result of the ] requirement found in mathematics since the extra component of the ] giving the confined solution for ] fields coincides with one of the conditions of stability.<ref>{{Cite journal |last=Gogberashvili |first=M. |date=1999 |title=Four dimensionality in noncompact Kaluza–Klein model |journal=Modern Physics Letters A |volume=14 |issue=29 |pages=2025–2031 |arxiv=hep-ph/9904383 |bibcode=1999MPLA...14.2025G |doi=10.1142/S021773239900208X |s2cid=16923959}}</ref>

In 1999, there were proposed the closely related ] scenarios, RS1 and RS2. (See '']'' for a nontechnical explanation of RS1). These particular models of brane cosmology have attracted a considerable amount of attention. For instance, the related Chung-Freese model, which has applications for ], followed in 2000.<ref>{{Cite journal |last1=Chung |first1=Daniel J. H. |last2=Freese |first2=Katherine |date=2000-08-25 |title=Can geodesics in extra dimensions solve the cosmological horizon problem? |journal=Physical Review D |volume=62 |issue=6 |pages=063513 |arxiv=hep-ph/9910235 |bibcode=2000PhRvD..62f3513C |doi=10.1103/physrevd.62.063513 |issn=0556-2821 |s2cid=119511533}}</ref>

Later, the ] and ] proposals appeared. The ekpyrotic theory hypothesizes that the origin of the ] occurred when two parallel branes collided.<ref>{{Cite news |last1=Musser |first1=George |last2=Minkel |first2=J. R. |date=2002-02-11 |title=A Recycled Universe: Crashing branes and cosmic acceleration may power an infinite cycle in which our universe is but a phase |url=http://www.sciam.com/article.cfm?id=a-recycled-universe |access-date=2008-05-03 |publisher=Scientific American Inc.}}</ref>

==Empirical tests==
{{see also|Large extra dimension#Empirical tests}}

As of now, no experimental or observational evidence of ]s, as required by the Randall–Sundrum models, has been reported. An analysis of results from the ] in December 2010 severely constrains the black holes produced in theories with large extra dimensions.<ref name="arxiv.org">{{Cite journal |year=2011 |title=Search for Microscopic Black Hole Signatures at the Large Hadron Collider |journal=Physics Letters B |volume=697 |issue=5 |pages=434–453 |arxiv=1012.3375 |bibcode=2011PhLB..697..434C |doi=10.1016/j.physletb.2011.02.032 |s2cid=118488193|last1=Khachatryan |first1=V. |last2=Sirunyan |first2=A.M. |last3=Tumasyan |first3=A. |last4=Adam |first4=W. |last5=Bergauer |first5=T. |last6=Dragicevic |first6=M. |last7=Erö |first7=J. |last8=Fabjan |first8=C. |last9=Friedl |first9=M. |last10=Frühwirth |first10=R. |last11=Ghete |first11=V.M. |last12=Hammer |first12=J. |last13=Hänsel |first13=S. |last14=Hartl |first14=C. |last15=Hoch |first15=M. |last16=Hörmann |first16=N. |last17=Hrubec |first17=J. |last18=Jeitler |first18=M. |last19=Kasieczka |first19=G. |last20=Kiesenhofer |first20=W. |last21=Krammer |first21=M. |last22=Liko |first22=D. |last23=Mikulec |first23=I. |last24=Pernicka |first24=M. |last25=Rohringer |first25=H. |last26=Schöfbeck |first26=R. |last27=Strauss |first27=J. |last28=Taurok |first28=A. |last29=Teischinger |first29=F. |last30=Waltenberger |first30=W. |display-authors=1 }}</ref> The ] has also been used to put weak limits on large extra dimensions.<ref>{{Cite journal |last1=Visinelli |first1=Luca |last2=Bolis |first2=Nadia |last3=Vagnozzi |first3=Sunny |date=March 2018 |title=Brane-world extra dimensions in light of GW170817 |journal=Phys. Rev. D |volume=97 |issue=6 |pages=064039 |arxiv=1711.06628 |bibcode=2018PhRvD..97f4039V |doi=10.1103/PhysRevD.97.064039 |s2cid=88504420}}</ref><ref>{{Cite news |last=Freeland |first=Emily |date=2018-09-21 |title=Hunting for extra dimensions with gravitational waves |publisher=The Oskar Klein Centre for Cosmoparticle Physics blog |url=https://ssl.fysik.su.se/okc/internal/blog/hunting-for-extra-dimensions-with-gravitational-waves/ |access-date=2018-11-30 |archive-date=2021-01-27 |archive-url=https://web.archive.org/web/20210127215024/https://ssl.fysik.su.se/okc/internal/blog/hunting-for-extra-dimensions-with-gravitational-waves/ |url-status=dead }}</ref>


==See also== ==See also==
⚫ *]
⚫ *]
*]
⚫ *]

*]
==References==
⚫ *]
<references />
*]


==External links== ==External links==
⚫ * .
*{{cite web
* {{Cite journal |last1=Brax |first1=Philippe |author-link=Philippe Brax |last2=van de Bruck, Carsten |author-link2=Carsten van de Bruck |year=2003 |title=Cosmology and Brane Worlds: A Review |journal=Classical and Quantum Gravity |volume=20 |issue=9 |pages=R201–R232 |arxiv=hep-th/0303095 |bibcode=2003CQGra..20R.201B |doi=10.1088/0264-9381/20/9/202 |s2cid=9623407}} – Cosmological consequences of the brane world scenario are reviewed in a pedagogical manner.
| author=]; ]
*
| title=Cosmology and Brane Worlds: A Review
* {{Cite journal |last=Langlois |first=David |author-link=David Langlois |year=2003 |title=Brane cosmology: an introduction |journal=Progress of Theoretical Physics Supplement |volume=148 |pages=181–212 |arxiv=hep-th/0209261 |bibcode=2002PThPS.148..181L |doi=10.1143/PTPS.148.181 |s2cid=9751130}} – These notes (32 pages) give an introductory review on brane cosmology.
| publisher=arXiv.org e-Print archive
* {{Cite book |last=Papantonopoulos |first=Eleftherios |title=Cosmological Crossroads |year=2002 |isbn=978-3-540-43778-9 |series=Lecture Notes in Physics |volume=592 |pages=458–477 |chapter=Brane Cosmology |bibcode=2002LNP...592..458P |doi=10.1007/3-540-48025-0_15 |author-link=Eleftherios Papantonopoulos |s2cid=3084654 |arxiv=hep-th/0202044}} – Lectures (24 pages) presented at the First Aegean Summer School on Cosmology, ], September 2001.
| year=2003

| work=
{{String theory topics |state=collapsed}}
| url=http://arxiv.org/abs/hep-th/0303095/
{{Portal bar|Physics|Astronomy|Stars|Spaceflight|Outer space|Solar System|Science}}
| accessdate=January 1
⚫ {{DEFAULTSORT:Brane Cosmology}}
| accessyear=2006
]
}} – Cosmological consequences of the brane world scenario are reviewed in a pedagogical manner.
⚫ ]
*{{cite web
]
| author=]
| title=Brane cosmology: an introduction
| publisher=arXiv.org e-Print archive
| year=2002
| work=
| url=http://arxiv.org/abs/hep-th/0209261/
| accessdate=January 1
| accessyear=2006
}} – These notes (32 pages) give an introductory review on brane cosmology.
*{{cite web
| author=]
⚫ | title=Brane Cosmology
| publisher=arXiv.org e-Print archive
| year=2002
| work=
| url=http://arxiv.org/abs/hep-th/0202044/
| accessdate=January 1
| accessyear=2006
}} – Lectures (24 pages) presented at the First Aegean Summer School on Cosmology, ], September 2001.
⚫ *
]]
]

Latest revision as of 19:51, 16 September 2024

Several theories in particle physics and cosmology related to superstring theory and M-theory
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Brane cosmology refers to several theories in particle physics and cosmology related to string theory, superstring theory and M-theory.

Brane and bulk

Main article: Brane
Animation showing multiple brane universes in the bulk

The central idea is that the visible, four-dimensional spacetime 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 dimension, 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 and the cosmological constant is small

Some versions of brane cosmology, based on the large extra dimension idea, can explain the weakness of gravity relative to the other fundamental forces of nature, thus solving the hierarchy problem. In the brane picture, the electromagnetic, weak and strong nuclear force are localized on the brane, but gravity has no such constraint and propagates on the full spacetime, called the bulk. Much of the gravitational 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. Extensions of the large extra dimension idea with supersymmetry in the bulk appear to be promising in addressing the so-called cosmological constant problem.

Models of brane cosmology

One of the earliest documented attempts to apply brane cosmology as part of a conceptual theory is dated to 1983.

The authors discussed the possibility that the Universe has ( 3 + N ) + 1 {\displaystyle (3+N)+1} dimensions, but ordinary particles are confined in a potential well which is narrow along N {\displaystyle N} 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. Gogberashvili also showed 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 scenarios, RS1 and RS2. (See Randall–Sundrum model for a nontechnical explanation of RS1). These particular models of brane cosmology have attracted a considerable amount of attention. For instance, the related Chung-Freese model, which has applications for spacetime metric engineering, followed in 2000.

Later, the ekpyrotic and cyclic proposals appeared. The ekpyrotic theory hypothesizes that the origin of the observable universe occurred when two parallel branes collided.

Empirical tests

See also: Large extra dimension § 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 the black holes produced in theories with large extra dimensions. The recent multi-messenger gravitational wave event GW170817 has also been used to put weak limits on large extra dimensions.

See also

References

  1. "Session D9 - Experimental Tests of Short Range Gravitation". flux.aps.org.
  2. Aghababaie, Y.; Burgess, C. P.; Parameswaran, S. L.; Quevedo, F. (March 2004). "Towards a naturally small cosmological constant from branes in 6-D supergravity". Nucl. Phys. B. 680 (1–3): 389–414. arXiv:hep-th/0304256. Bibcode:2004NuPhB.680..389A. doi:10.1016/j.nuclphysb.2003.12.015. S2CID 14612396.
  3. Burgess, C. P.; van Nierop, Leo (March 2013). "Technically Natural Cosmological Constant From Supersymmetric 6D Brane Backreaction". Phys. Dark Univ. 2 (1): 1–16. arXiv:1108.0345. Bibcode:2013PDU.....2....1B. doi:10.1016/j.dark.2012.10.001. S2CID 92984489.
  4. P. Burgess, C.; van Nierop, L.; Parameswaran, S.; Salvio, A.; Williams, M. (February 2013). "Accidental SUSY: Enhanced Bulk Supersymmetry from Brane Back-reaction". JHEP. 2013 (2): 120. arXiv:1210.5405. Bibcode:2013JHEP...02..120B. doi:10.1007/JHEP02(2013)120. S2CID 53667729.
  5. Rubakov, V. A.; Shaposhnikov, M. E. (1983). "Do we live inside a domain wall?". Physics Letters. B. 125 (2–3): 136–138. Bibcode:1983PhLB..125..136R. doi:10.1016/0370-2693(83)91253-4.
  6. Gogberashvili, M. (1998). "Hierarchy problem in the shell universe model". International Journal of Modern Physics D. 11 (10): 1635–1638. arXiv:hep-ph/9812296. doi:10.1142/S0218271802002992. S2CID 119339225.
  7. Gogberashvili, M. (2000). "Our world as an expanding shell". Europhysics Letters. 49 (3): 396–399. arXiv:hep-ph/9812365. Bibcode:2000EL.....49..396G. doi:10.1209/epl/i2000-00162-1. S2CID 38476733.
  8. Gogberashvili, M. (1999). "Four dimensionality in noncompact Kaluza–Klein model". Modern Physics Letters A. 14 (29): 2025–2031. arXiv:hep-ph/9904383. Bibcode:1999MPLA...14.2025G. doi:10.1142/S021773239900208X. S2CID 16923959.
  9. Chung, Daniel J. H.; Freese, Katherine (2000-08-25). "Can geodesics in extra dimensions solve the cosmological horizon problem?". Physical Review D. 62 (6): 063513. arXiv:hep-ph/9910235. Bibcode:2000PhRvD..62f3513C. doi:10.1103/physrevd.62.063513. ISSN 0556-2821. S2CID 119511533.
  10. Musser, George; Minkel, J. R. (2002-02-11). "A Recycled Universe: Crashing branes and cosmic acceleration may power an infinite cycle in which our universe is but a phase". Scientific American Inc. Retrieved 2008-05-03.
  11. Khachatryan, V.; et al. (2011). "Search for Microscopic Black Hole Signatures at the Large Hadron Collider". Physics Letters B. 697 (5): 434–453. arXiv:1012.3375. Bibcode:2011PhLB..697..434C. doi:10.1016/j.physletb.2011.02.032. S2CID 118488193.
  12. Visinelli, Luca; Bolis, Nadia; Vagnozzi, Sunny (March 2018). "Brane-world extra dimensions in light of GW170817". Phys. Rev. D. 97 (6): 064039. arXiv:1711.06628. Bibcode:2018PhRvD..97f4039V. doi:10.1103/PhysRevD.97.064039. S2CID 88504420.
  13. Freeland, Emily (2018-09-21). "Hunting for extra dimensions with gravitational waves". The Oskar Klein Centre for Cosmoparticle Physics blog. Archived from the original on 2021-01-27. Retrieved 2018-11-30.

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