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Cosmology of codimensiontwo braneworlds
 JHEP
, 2003
"... Abstract: We present a comprehensive study of the cosmological solutions of 6D braneworld models with azimuthal symmetry in the extra dimensions, moduli stabilization by flux or a bulk scalar field, and which contain at least one 3brane that could be identified with our world. We emphasize an unusu ..."
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Abstract: We present a comprehensive study of the cosmological solutions of 6D braneworld models with azimuthal symmetry in the extra dimensions, moduli stabilization by flux or a bulk scalar field, and which contain at least one 3brane that could be identified with our world. We emphasize an unusual property of these models: their expansion rate depends on the 3brane tension either not at all, or in a nonstandard way, at odds with the naive expected dimensional reduction of these systems to 4D general relativity at low energies. Unlike other braneworld attempts to find a selftuning solution to the cosmological constant problem, the apparent failure of decoupling in these models is not associated with the presence of unstabilized moduli; rather it is due to automatic cancellation of the brane tension by the curvature induced by the brane. This provides some corroboration for the hope that these models provide a distinctive step toward understanding the smallness of the observed cosmological constant. However, we point out
and gravity in warped extradimensional models, in preparation
"... Warped extra dimension claims remarkable success: solving the hierarchy problem; explaining hierarchies in particle phenomenology; yielding standard cosmology, plus interesting nonstandard scenarios. Yet it has marked shortcomings: we overrely on a single toy model, RandallSundrum; we treat matter ..."
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Warped extra dimension claims remarkable success: solving the hierarchy problem; explaining hierarchies in particle phenomenology; yielding standard cosmology, plus interesting nonstandard scenarios. Yet it has marked shortcomings: we overrely on a single toy model, RandallSundrum; we treat matter and gravity in an ad hoc, asymmetric way; and we conceptualize integrated 4D effective field theory inconsistently. I here construct sounder 4D effective field theories for matter and gravity in warped extra dimension — whether RandallSundrum or higher codimension. I track both Planck and particle scales through brane formation, beginning with fully extradimensional matter and gravity, at unified scale, in gravitationally warped backgrounds with bulk electroweak symmetrybreaking. This validates hierarchy solution, as warp generically drives 4D effective Planck and particle scales apart. It evades classic obstacles to warped confinement of matter: colocalizing particles and assuring effective charge universality. Diverse particles do fail to colocalize, generically and in discussed models; however, aggregate 4D effective field theory still holds, since hierarchy solution fixes unresolvably small extradimensional radius. Electromagnetic charge universality emerges generically, and weak charge universality in the RandallSundrum case.
A cigarlike Universe
, 2003
"... Abstract: We study the localization of gravity on a stringlike topological defect within a 6dimensional spacetime. Assuming zero cosmological constant we find complete numerical solutions to a set of firstorder, Bogomol’nyiPrasadSommeferld (BPS)like, equations for the metric and the scalar fi ..."
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Abstract: We study the localization of gravity on a stringlike topological defect within a 6dimensional spacetime. Assuming zero cosmological constant we find complete numerical solutions to a set of firstorder, Bogomol’nyiPrasadSommeferld (BPS)like, equations for the metric and the scalar field, where the dynamics of the latter are dictated by a supergravitytype potential. Our axially symmetric solutions have no deficit angle and factorize as AdS5 × S1 far from the core. They are regular everywhere, providing complete smooth cigarlike geometries. The total energy of these configurations depends only on the boundary conditions for the warp factor and it is shown to vanish.
hepth/0401085 Black Brane World from Gravitating Half σlump
, 2004
"... We study O(N +1) nonlinear σmodel in (p+1+N)dimensional curved spacetime with a negative cosmological constant, and find a new σlump solution with halfinteger winding and divergent energy. When the spatial structure of N extradimensions is determined by this global defect, a black σpbrane surr ..."
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We study O(N +1) nonlinear σmodel in (p+1+N)dimensional curved spacetime with a negative cosmological constant, and find a new σlump solution with halfinteger winding and divergent energy. When the spatial structure of N extradimensions is determined by this global defect, a black σpbrane surrounded by the degenerated horizon is formed and its nearhorizon geometry is identified as a warp geometry of a cigar type.
Casimir effect in a sixdimensional vortex scenario
, 2005
"... Recently RandjbarDaemi and Shaposhnikov put forward a 4dimensional effective QED coming from a NielsenOlesen vortex solution of the abelian Higgs model with fermions coupled to gravity in D = 6. However, exploring possible physical consequences of such an effective QED was left open. In this lett ..."
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Recently RandjbarDaemi and Shaposhnikov put forward a 4dimensional effective QED coming from a NielsenOlesen vortex solution of the abelian Higgs model with fermions coupled to gravity in D = 6. However, exploring possible physical consequences of such an effective QED was left open. In this letter we study the corresponding effective Casimir effect. We find that the extra dimensions yield a modified Casimir force which allows to set bounds to the parameters of the 6dimensional scenario in order not to be in clash with current experiments. 1 The idea that our observable 4dimensional universe may be a brane extended in some higherdimensional spacetime has been attracting interest for many years [1–3]. Roughly speaking, there exist two different approaches to implement this idea. One approach is to start with theories that incorporate gravity in a reliable manner such as string theory/Mtheory
hepth/0401207 Scalar Hair of Global Defect and Black Brane World
, 2004
"... We consider a complex scalar field in (p + 3)dimensional bulk with a negative cosmological constant and study global vortices in two extradimensions. We reexamine carefully the coupled scalar and Einstein equations, and show that the boundary value of scalar amplitude at infinity of the extradime ..."
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We consider a complex scalar field in (p + 3)dimensional bulk with a negative cosmological constant and study global vortices in two extradimensions. We reexamine carefully the coupled scalar and Einstein equations, and show that the boundary value of scalar amplitude at infinity of the extradimensions should be smaller than vacuum expectation value. The brane world has a cigarlike geometry with an exponentially decaying warp factor and a flat thick pbrane is embedded. Since a coordinate transformation identifies the obtained brane world as a black pbrane world bounded by a horizon, this strange boundary condition of the scalar amplitude is understood as existence of a short scalar hair.