Effects of bulk viscosity on hadron spectra and the Hanbury-Brown Twiss radius by causal viscous hydrodynamics

The particle spectra and Hanbury-Brown Twiss (HBT) radius of Au+Au collisions at RHIC energy are investigated by a hydrodynamical expanding source with both shear and bulk viscosities (\zeta). With a large width of the ratio of \zeta to entropy density s, both the particle transverse momentum spectra and the ratio R_out/R_side of HBT radii in the direction of the total transverse momentum of detected two particles (R_out) and perpendicular to both this direction and the beam direction (R_side) become a little steeper.