Trimaximal mixing (also known as threefold maximal mixing) refers to the highly symmetric, maximally CP-violating, 3 × × 3 fermion mixing configuration, characterised by a unitary matrix ( U ) having all its elements equal in modulus ( | U a i | = 1 / 3 , a , i = 1 , 2 , 3 ) as may be written, e.g.: