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Groups with faithful irreducible projective unitary representations

For a countable group G and a multiplier c on G with values in the circle, we study the property of G having a unitary projective c-representation which is both irreducible and projectively faithful. We show that this property is equivalent to G being the quotient of an appropriate group by its centre. A criterion is given in terms of the minisocle of G. Several examples are described to show the existence of various behaviours.