the left part is a character and the top part is a rule so the details depend on the font (you have given no information) and the way your pdf viewer (you have not said which) snaps rules and characters to pixel boundaries.
– David CarlisleNov 25 '23 at 20:27
5
Please check if zooming in fixes the issue -- have seen that problen over the years. Then, it is a problem with the pdf viewer which can be resolved by switching pdf viewers until the problem is resolved in the original viewer. Futhermore, while code snippets are useful in explanations, it is always best to compose a fully compilable MWE that illustrates the problem including the \documentclass and the appropriate packages so that those trying to help don't have to recreate it. In this case it would also be helpful to mention the pdf viewer.
– Peter GrillNov 25 '23 at 20:31
David and Peter already told you why this happens. In ConTeXt it is possible to use glyphs instead of rules for the bar, and then this problem usually goes away.
– mickepNov 25 '23 at 21:11
What you've encountered is a sceen resolution artefact. I won't show up in print.
– MicoNov 25 '23 at 21:26
Off-topic: Do try to ween yourself off an excessive reliance on \left and \right. For the equation at hand, the \left and \right directives do nothing useful, but do create needless code clutter.
– MicoNov 25 '23 at 21:28
\documentclassand the appropriate packages so that those trying to help don't have to recreate it. In this case it would also be helpful to mention the pdf viewer. – Peter Grill Nov 25 '23 at 20:31\leftand\right. For the equation at hand, the\leftand\rightdirectives do nothing useful, but do create needless code clutter. – Mico Nov 25 '23 at 21:28