By Nathan Ridley Under-fire Red Bull boss Christian Horner has denied any rift with Max Verstappen and the world champion’s dad, Jos. Horner, 50, remains under investigation at Red Bull Racing amid allegations of inappropriate behaviour, understood to have been made by a female colleague, which he strongly denies. The team principal and CEO has also been subject to claims of a bust-up with the two Verstappens just three weeks before the start of the new Formula 1 season. On Thursday, Horner made his first public appearance since the investigation began to present Red Bull’s new car ahead of th…