You had a bug. The alternation || is only written with *one* pipe character. The zero length pattern between each of the |s is also available so you could match anything that /^\s*$/ would match. The \Q...\E means quotemeta(). I've removed the \Q$A\E by doing quotemeta outside teh regexp. Since quotemeta has no effect on stuff like t and A, I removed it from those as well. I factored out the common parts of the expression so they aren't repeated. I also used the /x flag so I could add in as much extra whitespace as a I want - makes it easier to read. You'll notice how now everything except one branch of the alternation is followed by optional whitespace. That's to prevent "tA" from matching.

$A = quotemeta -4;
$w = quotemeta 500;

  $re =
  '/^  \s*
   $A \s*
   -? \s*
   cos \s*
   (?: \( \d+ t \)
     | \d+ t \s ) \s*
   A \s*
   $/x;
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