Task: Text Categorization
Input (English): The Montonen-Olive Duality Conjecture concerns a field theory in which these particles exist as solitons; that theory was developed by 't Hooft and Polyakov. The original hypothesis of these particles' existence requires the use of two separate vector potentials and a singularity, and was developed by Paul Dirac. Gauss's Law of Magnetism, which states that the divergence of a magnetic field is zero, implies that these particles cannot exist. For 10 points, name these hypothetical particles that can only have an isolated North or South pole.
Output (English): Science