The finite temperature QCD transition for physical quark masses is a
crossover. For smaller quark masses a first-order phase transition is expected.
Using Symanzik improved gauge and stout improved fermion action for 2+1 flavour
staggered QCD we give estimates/bounds for the phase line separating the
first-order region from the crossover one. The calculations are carried out on
two different lattice spacings. Our conclusion for the critical mass is m0​≲0.07⋅mphys​ for NT​=4 and m0​≲0.12⋅mphys​ for NT​=6 lattices.Comment: Talk presented at the XXV International Symposium on Lattice Field
Theory, July 30 - August 4 2007, Regensburg, Germany. 7 pages, 6 figure