Electroweak and Flavor Physics in Extensions of the Standard Model with Large Extra Dimensions
A. Delgado, A. Pomarol, M. Quiros
TL;DR
The paper investigates electroweak and flavor consequences of large extra dimensions by placing SM gauge bosons in a 5D bulk and allowing fermions/Higgs to live on branes or in the bulk. It derives the effective 4D theory after integrating out KK modes to first order in $X=\frac{\pi^2}{3}\frac{m_Z^2}{M_c^2}$, and analyzes shifts in $M_W$, $M_Z$, and fermion couplings, yielding bounds $M_c\sim 2$--$5$ TeV from electroweak precision tests, with some setups even improving the weak charge prediction $Q_W$. In softly-broken 5D SUSY, non-decoupling effects modify the low-energy theory, while nonuniversal quark localization produces tree-level flavor-violating KK-gluon interactions that push bounds up to $M_c\sim 5000$ TeV, severely constraining TeV-scale string scenarios. Overall, the work constrains the scale of extra dimensions through detailed EW and flavor analyses and highlights configurations that remain phenomenologically viable versus those that are strongly disfavored.
Abstract
We study the implications of extra dimensions of size $R\sim 1/TeV$ on electroweak and flavor physics due to the presence of Kaluza-Klein excitations of the SM gauge-bosons. We consider several scenarios with the SM fermions either living in the bulk or being localized at different points of an extra dimension. Global fits to electroweak observables provide lower bounds on 1/R, which are generically in the 2-5 TeV range. We find, however, certain models where the fit to electroweak observables is better than in the SM, because of an improvement in the prediction to the weak charge Q_W. We also consider the case of softly-broken supersymmetric theories and we find new non-decoupling effects that put new constraints on 1/R. If quarks of different families live in different points of the extra dimension, we find that the Kaluza-Klein modes of the SM gluons generate (at tree level) dangerous flavor and CP-violating interactions. The lower bounds on 1/R can increase in this case up to 5000 TeV, disfavoring these scenarios in the context of TeV-strings.