Null geodesics and repulsive behavior of gravity in |$(2+1)$| D massive gravity.

We study the null geodesics in a static circularly symmetric (SCS) black hole spacetime, which is a solution in the |$(2+1)$| D massive gravity proposed by Bergshoeff, Hohm, and Townsend (BHT massive gravity). We obtain analytic solutions for the null geodesic equation in the SCS black hole background and find the explicit form of deflection angles. We see that, for various values of the impact parameter, the deflection angle can be positive, negative, or even zero in this black hole spacetime. The negative deflection angle indicates the repulsive behavior of the gravity that comes from the gravitational hair parameter that is the most characteristic quantity of the BHT massive gravity. [ABSTRACT FROM AUTHOR]