$A_rx = qr{ \Q $A }x;
$w_rx = qr{ \Q $w }x;

$rx = qr{
  $A_rx \s*
  \*? \s*
  cos \s*
  (?:
    \( \s* $w_rx \s* \*? \s* t \s* \)
    | $w_rx \s* \*? \s* t \s
  ) \s*
  A
}x;