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postgraduate thesis: Applications of braneworld models to the theory of gravitation
Title  Applications of braneworld models to the theory of gravitation 

Authors  
Advisors  Advisor(s):Cheng, KS 
Issue Date  2012 
Publisher  The University of Hong Kong (Pokfulam, Hong Kong) 
Citation  Wong, K. C. [王祺昌]. (2012). Applications of braneworld models to the theory of gravitation. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved from http://dx.doi.org/10.5353/th_b4832953 
Abstract  I have presented an evolving wormhole solution in braneworld model. Moreover I have shown that there are observational signatures for using braneworld to solve dark matter problem.
Braneworld assumed that four dimensional spacetime embedded into five dimensional bulk. Gravity is a five dimensional interaction and the usual four dimensional description is reproduced by geometric projection. It predicts correction terms to the Einstein equation, for instance, the higher dimensional Weyl curvature projected on the brane.
This projected Weyl curvature could make braneworld wormhole satisfies the Null Energy Condition (NEC), which is impossible in general relativity. We considered inflating braneworld wormhole that enlarge with the Universe, the wormhole is supported by the Weyl curvature so that it satisfies NEC. We demonstrated how this wormhole embedded into a five dimensional bulk and studied how it evolve with our Universe. The result is that inflating wormhole satisfying general initial condition will collapse into black hole when the scalar field oscillates.
In addition, the projected Weyl curvature introduces a new source of gravity. This Weyl fluid of geometrical origin (reducing in the spherically symmetric, static configuration to a dark radiation and dark pressure) modifies spacetime geometry around galaxies and has been used to explain the flatness of galactic rotation curves. Independent observations for discerning between the Weyl fluid and other dark matter models are necessary. Gravitational lensing could provide such a test. Therefore we study null geodesics and weak gravitational lensing in
the dark radiation dominated region of galaxies in a class of spherically symmetric braneworld metrics. We find that the lensing profile in the braneworld scenario is distinguishable from dark matter lensing, despite both the braneworld scenario and dark matter models can fit the rotation curve data. In particular, in the asymptotic regions light deflection is 18% enhanced as compared to dark matter halo predictions. For a linear equation of state of the Weyl fluid we further find a critical radius, below which braneworld effects reduce, while above it they amplify light deflection. This is in contrast to any dark matter model, which
always increases the deflection angle. 
Degree  Doctor of Philosophy 
Subject  Branes. Gravitation. 
Dept/Program  Physics 
Persistent Identifier  http://hdl.handle.net/10722/173872 
HKU Library Item ID  b4832953 
DC Field  Value  Language 

dc.contributor.advisor  Cheng, KS   
dc.contributor.author  Wong, KiCheong.   
dc.contributor.author  王祺昌.   
dc.date.issued  2012   
dc.identifier.citation  Wong, K. C. [王祺昌]. (2012). Applications of braneworld models to the theory of gravitation. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved from http://dx.doi.org/10.5353/th_b4832953   
dc.identifier.uri  http://hdl.handle.net/10722/173872   
dc.description.abstract  I have presented an evolving wormhole solution in braneworld model. Moreover I have shown that there are observational signatures for using braneworld to solve dark matter problem. Braneworld assumed that four dimensional spacetime embedded into five dimensional bulk. Gravity is a five dimensional interaction and the usual four dimensional description is reproduced by geometric projection. It predicts correction terms to the Einstein equation, for instance, the higher dimensional Weyl curvature projected on the brane. This projected Weyl curvature could make braneworld wormhole satisfies the Null Energy Condition (NEC), which is impossible in general relativity. We considered inflating braneworld wormhole that enlarge with the Universe, the wormhole is supported by the Weyl curvature so that it satisfies NEC. We demonstrated how this wormhole embedded into a five dimensional bulk and studied how it evolve with our Universe. The result is that inflating wormhole satisfying general initial condition will collapse into black hole when the scalar field oscillates. In addition, the projected Weyl curvature introduces a new source of gravity. This Weyl fluid of geometrical origin (reducing in the spherically symmetric, static configuration to a dark radiation and dark pressure) modifies spacetime geometry around galaxies and has been used to explain the flatness of galactic rotation curves. Independent observations for discerning between the Weyl fluid and other dark matter models are necessary. Gravitational lensing could provide such a test. Therefore we study null geodesics and weak gravitational lensing in the dark radiation dominated region of galaxies in a class of spherically symmetric braneworld metrics. We find that the lensing profile in the braneworld scenario is distinguishable from dark matter lensing, despite both the braneworld scenario and dark matter models can fit the rotation curve data. In particular, in the asymptotic regions light deflection is 18% enhanced as compared to dark matter halo predictions. For a linear equation of state of the Weyl fluid we further find a critical radius, below which braneworld effects reduce, while above it they amplify light deflection. This is in contrast to any dark matter model, which always increases the deflection angle.   
dc.language  eng   
dc.publisher  The University of Hong Kong (Pokfulam, Hong Kong)   
dc.relation.ispartof  HKU Theses Online (HKUTO)   
dc.rights  The author retains all proprietary rights, (such as patent rights) and the right to use in future works.   
dc.rights  This work is licensed under a Creative Commons AttributionNonCommercialNoDerivatives 4.0 International License.   
dc.source.uri  http://hub.hku.hk/bib/B48329538   
dc.subject.lcsh  Branes.   
dc.subject.lcsh  Gravitation.   
dc.title  Applications of braneworld models to the theory of gravitation   
dc.type  PG_Thesis   
dc.identifier.hkul  b4832953   
dc.description.thesisname  Doctor of Philosophy   
dc.description.thesislevel  Doctoral   
dc.description.thesisdiscipline  Physics   
dc.description.nature  published_or_final_version   
dc.identifier.doi  10.5353/th_b4832953   
dc.date.hkucongregation  2012   