Are lie detector tests admissible in Louisiana courts?

No. Although lie detectors seem credible, they can be often faked to produce response opposite to what you want. The lie detectors lack the hard evidence that normal court order can provide (such as blood stain, DNA analysis, etc) and relies solely on how stressed the person is. Even when you didn't commit the crime, extremely high level of stress can tick the lie detector. Similarly, even when you did commit the crime, low level of stress can fool the lie detector.

Some people say that lie detectors have a 99% chance of succeeding. It is that 1% that makes the people say "No, we don't want it."