MANCHESTER, England (AP) — England defender Luke Shaw became the world’s most expensive teenage player on Friday and Manchester United’s second signing in 24 hours following its worst English Premier League campaign. The 18-year-old left back joined United from Southampton, reportedly for more than 27 million pounds ($46 million), straight after returning from his first World Cup with England. Southampton confirmed the deal made Shaw “the most expensive teenager ever,” which would eclipse fees of around 26 million pounds ($44 million) that saw Wayne Rooney join Manchester United in 2004 and Marquinhos sign for Paris Saint-Germain last year. Shaw signed a four-year contract, with an option to extend for a further year if he continues to develop as one of the most exciting youngsters in football. “I want to continue to progress my career and joining United is the ideal place for me to do that,” Shaw said in a statement. Louis van Gaal doesn’t officially take charge at United until his World Cup campaign as Netherlands manager is over, but players are being signed ready for the Dutchman’s arrival. United paid around $50 million for Spanish midfielder Ander Herrera the day before Shaw’s arrival. The record 20-time English champions…