Probing for massive stochastic gravitational-wave background with a detector network

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In a general metric theory of gravitation in four dimensions, six polarizations of a gravitational wave are allowed: two scalar and two vector modes, in addition to two tensor modes in general relativity. Such additional polarization modes appear due to additional degrees of freedom in modified gravity theories. Also graviton mass, which could be different in each polarization, is another characteristic of modification of gravity. Thus, testing the existence of additional polarization modes and graviton mass can be a model-independent test of gravity theories. Here we extend the previous framework of correlation analysis of a gravitational-wave background to the massive case and show that a ground-based detector network can probe for massive stochastic gravitational waves with its mass around 10⁻¹⁴ eV. We also show that more than three detectors can cleanly separate the mixture of polarization modes in detector outputs and determine the graviton mass.