Down type iso-singlet quarks at the HL-LHC and FCC-hh Arpon Paul, Sezen Sekmen and Gokhan Unel Eur. Phys. J. C, 81 3 (2021) 214 Published online: 03 March 2021 DOI: 10.1140/epjc/s10052-021-08982-4