Renormalization and ultraviolet sensitivity of gauge vertices in universal extra dimensions

Abstract We reconsider a modification of the N-point amplitude of the Neveu-Schwarz (NS) model in which the tachyon becomes a pion by shifting its mass to zero and keeping the super-projective invariance of the integrand of the amplitude. For the scattering of four particles it reduces to the amplitude written by Lovelace and Shapiro that has Adler zeroes. We confirm that also the N-pion amplitude has Adler zeroes and show that it reduces to that of the non-linear σ-model for α′ → 0 keeping Fπ fixed. The four- and six-point flavour-ordered amplitudes satisfy tree-level unitarity since they can be derived from the correspondent amplitudes of the NS model in ten dimensions by suitably choosing the components of the momenta of the external mesons in the six extra dimensions. Negative norm states (ghosts) are shown to appear instead in higher-point amplitudes. We also discuss several amplitudes involving different external mesons.

Download Full-text

Unitarity in KK-graviton production, a case study in warped extra-dimensions

Journal of High Energy Physics ◽

10.1007/jhep04(2021)143 ◽

2021 ◽

Vol 2021 (4) ◽

Author(s):

A. de Giorgi ◽

S. Vogl

Keyword(s):

Extra Dimensions ◽

Sum Rules ◽

Effective Theory ◽

Higher Dimensional ◽

Massive Spin ◽

The Matrix ◽

Dimensional Gravity ◽

Warped Extra Dimensions ◽

Kaluza Klein

Abstract The Kaluza-Klein (KK) decomposition of higher-dimensional gravity gives rise to a tower of KK-gravitons in the effective four-dimensional (4D) theory. Such massive spin-2 fields are known to be connected with unitarity issues and easily lead to a breakdown of the effective theory well below the naive scale of the interaction. However, the breakdown of the effective 4D theory is expected to be controlled by the parameters of the 5D theory. Working in a simplified Randall-Sundrum model we study the matrix elements for matter annihilations into massive gravitons. We find that truncating the KK-tower leads to an early breakdown of perturbative unitarity. However, by considering the full tower we obtain a set of sum rules for the couplings between the different KK-fields that restore unitarity up to the scale of the 5D theory. We prove analytically that these are fulfilled in the model under consideration and present numerical tests of their convergence. This work complements earlier studies that focused on graviton self-interactions and yields additional sum rules that are required if matter fields are incorporated into warped extra-dimensions.

Download Full-text

Kinetic mixing, dark photons and extra dimensions. Part III. Brane localized dark matter

Journal of High Energy Physics ◽

10.1007/jhep03(2021)173 ◽

2021 ◽

Vol 2021 (3) ◽

Author(s):

Thomas G. Rizzo ◽

George N. Wojcik

Keyword(s):

Dark Matter ◽

Extra Dimensions ◽

Model Building ◽

New Physics ◽

Model Complexity ◽

Complex Scalar ◽

Dark Photon ◽

Complex Models ◽

The Cost ◽

D Model

Abstract Extra dimensions have proven to be a very useful tool in constructing new physics models. In earlier work, we began investigating toy models for the 5-D analog of the kinetic mixing/vector portal scenario where the interactions of dark matter, taken to be, e.g., a complex scalar, with the brane-localized fields of the Standard Model (SM) are mediated by a massive U(1)D dark photon living in the bulk. These models were shown to have many novel features differentiating them from their 4-D analogs and which, in several cases, avoided some well-known 4-D model building constraints. However, these gains were obtained at the cost of the introduction of a fair amount of model complexity, e.g., dark matter Kaluza-Klein excitations. In the present paper, we consider an alternative setup wherein the dark matter and the dark Higgs, responsible for U(1)D breaking, are both localized to the ‘dark’ brane at the opposite end of the 5-D interval from where the SM fields are located with only the dark photon now being a 5-D field. The phenomenology of such a setup is explored for both flat and warped extra dimensions and compared to the previous more complex models.

Download Full-text