Once again, Europe's grandest club competition opens its doors, carrying with it the oldest of football's questions: whether excellence can be sustained, or whether the summit, once reached, inevitably recedes. Paris St-Germain enter as back-to-back champions chasing a third consecutive title — a feat modern football has made nearly mythological — while Arsenal, armed with statistical favour and a defence built for endurance, emerge as the likeliest inheritors of that prize. The competition begins this week with thirty-six clubs, four of them newcomers, each carrying the particular hope that t