The Highly Improved Staggered Quark (HISQ) action is the next-generation
improved action for calculations in lattice QCD that rely on the staggered
fermions formalism. The dominant O(a2) discretization error in current
simulations arises from the splitting of the continuum pion into several
non-degenerate "tastes" at nonzero lattice spacing. The HISQ
action significantly reduces the splitting among different pion tastes, thus
providing faster approach to the continuum limit. In this talk I review
simulations with dynamical highly improved staggered quarks (that pose some
computational challenges) and present recent results for a set of ensembles
with the light quark masses set to 1/5 of the strange quark mass and with
the strange and charm quark masses tuned to their physical values. I also
review an exploratory study of the QCD Thermodynamics with HISQ at almost
physical light quark masses.
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