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==Brane and bulk==
==Brane and bulk==
{{Main|Brane}}
{{Main|Brane}}
[[File:Brane theory.ogg|thumb|left|Animation showing multiple brane universes in the bulk]]
The central idea is that the visible, [[three-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 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.
The central idea is that the visible, four-dimensional [[spacetime]] 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 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==
==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 [[electromagnetism|electromagnetic]], [[weak interaction|weak]] and [[strong interaction|strong nuclear force]] are localized on the brane, but gravity has no such constraint and propagates on the full spacetime, called 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>[http://flux.aps.org/meetings/YR04/APR04/baps/abs/S690.html Session D9 - Experimental Tests of Short Range Gravitation.]</ref> Extensions of the large extra dimension idea with [[supersymmetry]] in the bulk appears to be promising in addressing the so-called [[cosmological constant problem]].<ref>{{cite journal |author1=Y. Aghababaie |author2=C.P. Burgess |author3=S.L. Parameswaran |author4=F. Quevedo |s2cid=14612396 |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 |date=March 2004 |arxiv=hep-th/0304256 |bibcode=2004NuPhB.680..389A |doi=10.1016/j.nuclphysb.2003.12.015}}</ref><ref>{{cite journal |author=C.P. Burgess |author2=Leo van Nierop |s2cid=92984489 |title=Technically Natural Cosmological Constant From Supersymmetric 6D Brane Backreaction |journal=Phys. Dark Univ. |volume=2 |issue=1 |date=March 2013 |pages=1–16 |arxiv=1108.0345 |bibcode=2013PDU.....2....1B |doi=10.1016/j.dark.2012.10.001}}</ref><ref>{{cite journal |author=C. P. Burgess |author2=L. van Nierop |author3=S. Parameswaran |author4=A. Salvio |author5=M. Williams |s2cid=53667729 |title=Accidental SUSY: Enhanced Bulk Supersymmetry from Brane Back-reaction |journal=JHEP |volume=2013 |issue=2 |date=February 2013 |page=120 |url=http://inspirehep.net/record/1191922 |arxiv=1210.5405 |bibcode=2013JHEP...02..120B |doi=10.1007/JHEP02(2013)120}}</ref>
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 [[electromagnetism|electromagnetic]], [[weak interaction|weak]] and [[strong interaction|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.<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 [[supersymmetry]] in the bulk appear to be promising in addressing the so-called [[cosmological constant problem]].<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==
==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>{{cite journal |first1=V. A. |last1=Rubakov |first2=M. E. |last2=Shaposhnikov |title=Do we live inside a domain wall? |journal=[[Physics Letters]] |series=B |volume=125 |year=1983 |issue=2–3 |pages=136–138 |doi=10.1016/0370-2693(83)91253-4 |bibcode=1983PhLB..125..136R }}</ref>
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=[[Physics Letters]] |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 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]] 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>{{cite journal |first=M. |last=Gogberashvili |s2cid=119339225 |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 }}</ref><ref>{{cite journal |first=M. |last=Gogberashvili |s2cid=38476733 |year=2000 |title=Our world as an expanding shell |journal= Europhysics Letters |volume=49 |issue=3 |pages=396–399 |arxiv=hep-ph/9812365 |doi=10.1209/epl/i2000-00162-1 |bibcode=2000EL.....49..396G }}</ref> Gogberashvili also showed 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.<ref>{{cite journal |first=M. |last=Gogberashvili |s2cid=16923959 |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 |doi=10.1142/S021773239900208X |bibcode=1999MPLA...14.2025G }}</ref>
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]].<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 [[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.<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 [[Randall–Sundrum model|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-Freeze model, which has applications for [[Warp-field experiments|spacetime metric engineering]], 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|doi=10.1103/physrevd.62.063513|arxiv=hep-ph/9910235|bibcode=2000PhRvD..62f3513C|s2cid=119511533|issn=0556-2821}}</ref>
In 1999, there were proposed the closely related [[Randall–Sundrum model|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 [[Warp-field experiments|spacetime metric engineering]], 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 [[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|author2=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|access-date=2008-05-03}}</ref>
Later, the [[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 |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==
==Empirical tests==
{{see also|Large extra dimension#Empirical tests}}
{{see also|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 the black holes produced in theories with large extra dimensions.<ref name="arxiv.org">{{cite journal |author=CMS Collaboration |s2cid=118488193 |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 |doi=10.1016/j.physletb.2011.02.032 |bibcode=2011PhLB..697..434C |year=2011 }}</ref> The [[GW170817|recent multi-messenger gravitational wave event GW170817]] has also been used to put weak limits on large extra dimensions.<ref>{{cite journal |author1=Luca Visinelli |author2=Nadia Bolis |author3=Sunny Vagnozzi |s2cid=88504420 |title=Brane-world extra dimensions in light of GW170817 |journal=Phys. Rev. D |volume=97 |issue=6 |pages=064039 |date=March 2018 |arxiv=1711.06628 |bibcode= 2018PhRvD..97f4039V |doi= 10.1103/PhysRevD.97.064039}}</ref><ref>{{cite news|last=Freeland|first=Emily|title=Hunting for extra dimensions with gravitational waves|publisher=The Oskar Klein Centre for Cosmoparticle Physics blog|date=2018-09-21|url=https://ssl.fysik.su.se/okc/internal/blog/hunting-for-extra-dimensions-with-gravitational-waves/}}</ref>
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 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 [[GW170817|recent multi-messenger gravitational wave event GW170817]] 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==
Line 35: Line 36:


==External links==
==External links==
⚫
* [http://xstructure.inr.ac.ru/x-bin/theme3.py?level=2&index1=-197206 Brane cosmology on arxiv.org].
* {{cite journal|author=Brax, Philippe |author2=van de Bruck, Carsten|s2cid=9623407|title=Cosmology and Brane Worlds: A Review|year=2003|arxiv=hep-th/0303095|doi=10.1088/0264-9381/20/9/202|volume=20|issue=9|journal=Classical and Quantum Gravity|pages=R201–R232|bibcode = 2003CQGra..20R.201B |author-link=Philippe Brax|author2-link=Carsten van de Bruck}} – Cosmological consequences of the brane world scenario are reviewed in a pedagogical manner.
* {{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.
⚫
* {{cite journal|author=Langlois, David|s2cid=9751130|title=Brane cosmology: an introduction|year=2003|arxiv=hep-th/0209261|doi=10.1143/PTPS.148.181|volume=148|journal=Progress of Theoretical Physics Supplement|pages=181–212|bibcode = 2002PThPS.148..181L |author-link=David Langlois}} – These notes (32 pages) give an introductory review on brane cosmology.
⚫
* [https://web.archive.org/web/20130124185355/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)]
⚫
* {{cite book|author=Papantonopoulos, Eleftherios|s2cid=3084654|title=Cosmological Crossroads|chapter=Brane Cosmology|volume=592|pages=458–477|year=2002|arxiv=hep-th/0202044|doi=10.1007/3-540-48025-0_15|bibcode=2002LNP...592..458P|series=Lecture Notes in Physics|isbn=978-3-540-43778-9|author-link=Eleftherios Papantonopoulos}} – Lectures (24 pages) presented at the First Aegean Summer School on Cosmology, [[Samos]], September 2001.
⚫
* {{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.
⚫
* [http://xstructure.inr.ac.ru/x-bin/theme3.py?level=2&index1=-197206 Brane cosmology on arxiv.org]
⚫
* {{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, [[Samos]], September 2001.
⚫
* [https://web.archive.org/web/20130124185355/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)]


{{String theory topics |state=collapsed}}
{{String theory topics |state=collapsed}}
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{{DEFAULTSORT:Brane Cosmology}}
{{DEFAULTSORT:Brane Cosmology}}
[[Category:Physical cosmology]]
[[Category:Physical cosmology]]
[[Category:Particle physics]]
[[Category:String theory]]
[[Category:String theory]]
[[Category:Astronomical hypotheses]]
[[Category:Astronomical hypotheses]]

Latest revision as of 19:51, 16 September 2024

String theory
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Phenomenology
Mathematics
Related concepts
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Part of a series on
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Scientists
Subject history

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

Brane and bulk

[edit]
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

[edit]

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.[1] Extensions of the large extra dimension idea with supersymmetry in the bulk appear to be promising in addressing the so-called cosmological constant problem.[2][3][4]

Models of brane cosmology

[edit]

One of the earliest documented attempts to apply brane cosmology as part of a conceptual theory is dated to 1983.[5]

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.[6][7] 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.[8]

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.[9]

Later, the ekpyrotic and cyclic proposals appeared. The ekpyrotic theory hypothesizes that the origin of the observable universe occurred when two parallel branes collided.[10]

Empirical tests

[edit]
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.[11] The recent multi-messenger gravitational wave event GW170817 has also been used to put weak limits on large extra dimensions.[12][13]

See also

[edit]

References

[edit]
  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.
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