Exact Scale Invariance of Composite-Field Coupling Constants

We show that the coupling constant of a quantum-induced composite field is scale invariant due to its compositeness condition. It is first demonstrated in next-to-leading order in 1/N in typical models, and then we argue that it holds exactly.Comment: 4 page

Dilatation symmetry in higher dimensions and the vanishing of the cosmological constant

A wide class of dilatation symmetric effective actions in higher dimensions leads to a vanishing four-dimensional cosmological constant. This requires no tuning of parameters and results from the absence of an allowed potential for the scalar dilaton field. The field equations admit many solutions with flat four-dimensional space and non-vanishing gauge couplings. In a more general setting, these are candidates for asymptotic states of cosmological runaway solutions, where dilatation symmetry is realized dynamically if a fixed point is approached as time goes to infinity. Dilatation anomalies during the runaway can lift the degeneracy of solutions and lead to an observable dynamical dark energy.Comment: 4 page

Fermions on the brane in 6D with nonsingular exponential scale factors

We introduce new realistic brane-solutions with exponential scale factors in the 6D-space-time. We show that for these solutions the zero modes of all bulk fields are sharply localized at different positions on the brane and have "Gaussian shape" wave-functions in the extra space. We also explicitly show that in the model there are cases when exactly three fermion generations naturally arise only through gravity. Because of localized fermion modes are also stuck at different positions in the extra space, there is possibility to provide a framework for natural explaining the fermion mass hierarchy in terms of higher dimensional geography.Comment: 6 pages, revtex4,new section added, explicit forms of wavefunctions and of source functions added,corrected typo

Muon anomalous magnetic moment due to the brane-stretching effect

We investigate the contribution of extra dimensions to the muon anomalous magnetic moment by using an ADD-type 6-dimensional model. This approach analyzes the extent of the influence of classical brane fluctuations on the magnetic moment. When we consider that the brane fluctuations are static in time, they add new potential terms to the Schr{\"o}dinger equation through the induced vierbein. This paper shows that the brane fluctuation is responsible for the brane-stretching effect. This effect would be capable of reproducing the appropriate order for recent Brookhaven National Laboratory measurements of the muon (g-2) deviation.Comment: 17 pages, 1 figure, minor changed, accepted for Phys. Rev.

Metastable Kinks in the Orbifold

We consider static configurations of bulk scalar fields in extra dimensional models in which the fifth dimension is an $S^1/Z_2$ orbifold. There may exist a finite number of such configurations, with total number depending on the size of the orbifold interval. We perform a detailed Sturm-Liouville stability analysis that demonstrates that all but the lowest-lying configurations - those with no nodes in the interval - are unstable. We also present a powerful general criterion with which to determine which of these nodeless solutions are stable. The detailed analysis underlying the results presented in this letter, and applications to specific models, are presented in a comprehensive companion paper.Comment: 4 pages, 4 figures, reference added, typo corrected, submitted to PR

Gauss-Bonnet gravity, brane world models, and non-minimal coupling

We study the case of brane world models with an additional Gauss-Bonnet term in the presence of a bulk scalar field which interacts non-minimally with gravity, via a possible interaction term of the form $-1/2 \xi R \phi^2$. The Einstein equations and the junction conditions on the brane are formulated, in the case of the bulk scalar field. Static solutions of this model are obtained by solving numerically the Einstein equations with the appropriate boundary conditions on the brane. Finally, we present graphically and comment these solutions for several values of the free parameters of the model.Comment: 13 pages,4 figures, published versio

On the stability of thick brane worlds non-minimally coupled to gravity

We analyze a class of 5D models where a 3 brane is generated by a bulk scalar field non minimally coupled to gravity. We show that perturbative stability of such branes is normally guaranteed although non minimal couplings are not innocuous in general. After the physical states are identified the linearized equations for propagating modes are evaluated into a Schroedinger form and supersymmetric quantum mechanics provides the absence of tachyons. The spectrum contains a tower of spin 2 and spin 0 fields with continuous masses starting from zero ones. For regular geometries the scalar spectrum contains a state with zero mass which is always non normalizable. The propagating massive scalar states are repelled off the brane due to a centrifugal potential.Comment: 15 page

Nambu-Jona-Lasinio Model at the Next-to-Leading Order in 1/N

We derived and solved the compositeness condition in the Nambu-Jona-Lasinio model at the next-to-leading order in 1/N, and obtained the expressions for the effective coupling constants in terms of the compositeness scale. In the NJL model with a scalar composite, the next to leading contributions are too large for N=3. In the induced gauge theory with abelian gauge symmetry, the correction term is reasonably suppressed, while, in the SU(N_c) gauge theory with N_f flavors of fermions, the correction is suppressed only for N_f>11N_c/2, complementarily to asymptotic freedom.Comment: 7 pages, latex, Invited talk presented at International Conference on Quark Lepton Nuclear Physics, Osaka, Japan, May 1997. To be published in Proceeding

Quartification On An Orbifold

We investigate quartification models in five dimensions, with the fifth dimension forming an $S^1/Z_2\times Z_2'$ orbifold. The orbifold construction is combined with a boundary Higgs sector to break the quartified gauge group directly to a group $H\subset SU(3)^4$ which is operative at the electroweak scale. We consider $H=G_{SM}\otimes SU(2)_\ell$ and $H=G_{SM}$, where $G_{SM}$ is the standard model gauge group, and find that unification occurs only when the remnant leptonic colour symmetry $SU(2)_\ell$ remains unbroken. Furthermore, the demands of a realistic low energy fermion spectrum specify a unique symmetry breaking route for the unifying case of $H=G_{SM}\otimes SU(2)_\ell$. We contrast this with four dimensional quartification models where unification may be achieved via a number of different symmetry breaking routes both with and without the remnant $SU(2)_\ell$ symmetry. The boundary Higgs sector of our model may be decoupled to achieve a Higgsless limit and we show that the electroweak Higgs doublet may be identified as the fifth component of a higher dimensional gauge field.Comment: 14 pages, misprint corrected, matches PRD versio