Quasinormal modes of black holes in f(T) gravity
  We calculate the quasinormal modes (QNM) frequencies of a test massless
scalar field around static black holes in f(T) gravity. Focusing on quadratic
f(T) modifications, which is a good approximation for every realistic f(T)
theory, we first extract the spherically symmetric solutions using the
perturbative method, imposing two ansatze for the metric functions, which
suitably quantify the deviation from the Schwarzschild solution. Moreover, we
extract the effective potential and then we calculate the QNM frequency of the
obtained solutions. Firstly, we solve the Schrodinger-like equation numerically
using the discretization method, and we extract the frequency and the time
evolution of the dominant mode applying the function fit method. Secondly, we
perform a semi-analytical calculation by applying the third-order WKB
approximation method. We show that the results for f(T) gravity are different
comparing to General Relativity, and in particular we obtain a different slope
and period of the field decay behavior for different values of the model
parameter. Hence, under the light of gravitational-wave observations of
increasing accuracy from binary systems, the whole analysis could be used as an
additional tool in order to test General Relativity and examine whether
torsional gravitational modifications are possible.
