Exact calculation of disconnected loops

We present an implementation of the disconnected diagram contributions to quantities such as the flavor-singlet pseudoscalar meson mass which are accelerated by GPGPU technology utilizing the NVIDIA CUDA platform. To enable the exact evaluation of the disconnected loops we use a $16^3 \times 32$ lattice and $N_f=2$ Wilson fermions simulated by the SESAM Collaboration. The disconnected loops are also computed using stochastic methods with several noise reduction techniques. In particular, we analyze various dilution schemes as well as the recently proposed truncated s olver method. We find consistency among the different methods used for the determination of the $η^\prime$ mass, albeit that the gauge noise for the ensemble studied is large. We also find that the effect of 'dilution' d oes not go beyond that of optimal statistical noise in many cases. It has been observed, however, that spin dilution does have a significant effect for some quantities studied.

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