Superpartner

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A superpartner is a particle related to a more standard particle by supersymmetry. In this physical theory, it is proposed that every fermion should have a "partner" boson (the fermion's superpartner), and vice versa. Exact unbroken supersymmetry would predict that a particle and its superpartners would have the same mass. No superpartners of the Standard Model particles have yet been found because supersymmetry is not an exact unbroken symmetry of nature. If a superpartner is found, its mass would determine the scale supersymmetry is broken.

For particles that are real scalars (such as an axion), there is a fermion superpartner and as well as a second real scalar field. For axions, these particles are often referred to as axinos and saxions.

In extended supersymmetry there may be more than one superparticle for a given particle. For instance with two copies of supersymmetry in four dimensions, a photon would have two fermion superpartners and a scalar superpartner.

In zero dimensions (often known as matrix mechanics), it is possible to have supersymmetry, but have no superpartners, but this is the only example where supersymmetry does not imply the existence of superpartners.