On Direct Verification of Warped Hierarchy-and-Flavor Models

TL;DR

This paper assesses the experimental prospects of verifying warped Randall-Sundrum models at current and future colliders, concluding that only a high-energy 60 TeV collider with high luminosity can potentially detect key signatures like KK modes of SM fermions and gravitons.

Contribution

It provides a detailed analysis of the collider energies and luminosities needed to directly observe warped model signatures, highlighting the limitations of the LHC and the necessity of a 60 TeV collider.

Findings

LHC likely cannot detect bulk SM fermion KK modes or gravitons.

Discovery of KK modes requires a 60 TeV collider with high luminosity.

Establishing warped models experimentally needs future high-energy colliders.

Abstract

We consider direct experimental verification of warped models, based on the Randall-Sundrum (RS) scenario, that explain gauge and flavor hierarchies, assuming that the gauge fields and fermions of the Standard Model (SM) propagate in the 5D bulk. Most studies have focused on the bosonic Kaluza Klein (KK) signatures and indicate that discovering gauge KK modes is likely possible, yet challenging, while graviton KK modes are unlikely to be accessible at the LHC, even with a luminosity upgrade. We show that direct evidence for bulk SM fermions, {\it i.e.} their KK modes, is likely also beyond the reach of a luminosity-upgraded LHC. Thus, neither the spin-2 KK graviton, the most distinct RS signal, nor the KK SM fermions, direct evidence for bulk flavor, seem to be within the reach of the LHC. We then consider hadron colliders with $\sqrt{s} =$ 21, 28, and 60 TeV. We find that discovering the first KK modes of SM fermions and the graviton typically requires the Next Hadron Collider (NHC) with $\sqrt{s} \approx 60$ TeV and ${\cal O}(1)$ ab$^{-1}$ of integrated luminosity. If the LHC yields hints of these warped models, establishing that Nature is described by them, or their 4D CFT duals, requires an NHC-class machine in the post-LHC experimental program.