There are still string theorists who think that string theory is incompatible with the positive vacuum energy, full stop. So despite being theoretical physics, there's room for disagreement there. Sometimes the leading candidate would be quintessence. Would be a scaler field slowly rolling down a potentiala now, i've written about quintessence back in the day. I was the first one to really emphasize the fact that if you have these quintessence fields, they should couple to other fields. They should couple to the standard model fields, and be detectable for that reason.