Decay rates of Gaussian-type I-balls and Bose-enhancement effects in 3+1
  dimensions
  I-balls/oscillons are long-lived spatially localized lumps of a scalar field
which may be formed after inflation. In the scalar field theory with monomial
potential nearly and shallower than quadratic, which is motivated by chaotic
inflationary models and supersymmetric theories, the scalar field configuration
of I-balls is approximately Gaussian. If the I-ball interacts with another
scalar field, the I-ball eventually decays into radiation. Recently, it was
pointed out that the decay rate of I-balls increases exponentially by the
effects of Bose enhancement under some conditions and a non-perturbative method
to compute the exponential growth rate has been derived. In this paper, we
apply the method to the Gaussian-type I-ball in 3+1 dimensions assuming
spherical symmetry, and calculate the partial decay rates into partial waves,
labelled by the angular momentum of daughter particles. We reveal the
conditions that the I-ball decays exponentially, which are found to depend on
the mass and angular momentum of daughter particles and also be affected by the
quantum uncertainty in the momentum of daughter particles.
