Signals from extra dimensions decoupled from the compactification scale

TL;DR

This paper demonstrates that multilocalization in a flat extra dimension decouples the light KK spectrum from the compactification scale, allowing a light vector-like quark to appear while the KK scale remains high. By constructing a 5D flavour model on $S^1/Z_2$ with order-one Yukawas, the authors reproduce SM quark masses and mixings and predict a vector-like quark with $m_Q \approx 478$ GeV (and a compactification scale $M_c \approx 85$ TeV) arising from multilocalization; heavier KK modes lie above $\sim 50$ TeV. The top sector couplings are modified by mixing with the light KK state, e.g. $W^L_{tb} \approx 0.96$ and $X^L_{tt} \approx 0.93$, while the CKM structure remains consistent with data. The scenario evades FCNC bounds and offers observable signatures at the Tevatron and LHC, illustrating a geometrical origin for fermion mass hierarchies and a realistic pathway to collider-accessible extra-dimensional effects.

Abstract

Multilocalization provides a simple way of decoupling the mass scale of new physics from the compactification scale of extra dimensions. It naturally appears, for example, when localization of fermion zero modes is used to explain the observed fermion spectrum, leaving low energy remnants of the geometrical origin of the fermion mass hierarchy. We study the phenomenology of the simplest five dimensional model with order one Yukawa couplings reproducing the standard fermion masses and mixing angles and with a light Kaluza-Klein quark Q_{2/3} saturating experimental limits on V_{tb} and m_Q, and then with observable new effects at Tevatron.

Figures (7)

• Figure 1: Values of the masses of the first KK modes as a function of the five dimensional mass in units of $1/R$. We have fixed $a=R/2$.
• Figure 2: Potential $M^2-M^\prime(y)$ of the equivalent Schrödinger equation for a multikink mass term in arbitrary units (for $a=R/2$). On the left there is no multilocalization ($MR<2/\pi$), in contrast with the potential on the right which does multilocalize ($MR>2/\pi$).
• Figure 3: Profiles of the massless zero mode $f^R_0$ and the first KK excitation $f^R_1$ with no multilocalization, $MR=-2$ (left), and with multilocalization, $MR=2$ (right).
• Figure 4: Profiles of the RH up quark zero modes for the five dimensional masses given in the text. Only $t_R$ is multilocalized.
• Figure 5: Top coupling $W^L_{tb}$ and lightest vector-like quark mass $m_Q$ as a function of the intermediate brane position $a$ and the five dimensional mass $M^u_3$. Solid (dotted) lines stand for fixed $\frac{a}{R}$ ($M^u_3R$) values, from left to right $0.53,0.51,0.49$ ($5.55,4.85,4.5$). We take as in the text $R=(85\quad \mathrm{TeV})^{-1}$. The shadowed region corresponds to the 3 standard deviation exclusion region for $R_b$.