The finite temperature QCD using 2+1 flavors of domain wall fermions at N_t = 8

We study the region of the QCD phase transition using 2+1 flavors of domain wall fermions (DWF) and a $16^3 \times 8$ lattice volume with a fifth dimension of $L_s = 32$. The disconnected light quark chiral susceptibility, quark number susceptibility and the Polyakov loop suggest a chiral and deconfining crossover transition lying between 155 and 185 MeV for our choice of quark mass and lattice spacing. In this region the lattice scale deduced from the Sommer parameter $r_0$ is $a^{-1} \approx 1.3$ GeV, the pion mass is $\approx 300$ MeV and the kaon mass is approximately physical. The peak in the chiral susceptibility implies a pseudo critical temperature $T_c = 171(10)(17)$ MeV where the first error is associated with determining the peak location and the second with our unphysical light quark mass and non-zero lattice spacing. The effects of residual chiral symmetry breaking on the chiral condensate and disconnected chiral susceptibility are studied using several values of the valence $L_s$.Comment: 41 pages, 10 tables, 13 figure

The QCD chiral transition, U(1)AU(1)_{A} symmetry and the Dirac spectrum using domain wall fermions

Buchoff MI, Cheng M, Christ NH, et al. The QCD chiral transition, $U(1)_{A}$ symmetry and the Dirac spectrum using domain wall fermions. Physical Review D. 2014;89(5): 054514

Biology is only part of the story …

The origins and development of human cognition constitute one of the most interesting questions to which archaeology can contribute today. In this paper, we do so by presenting an overview of the evolution of artefact technology from the maker's point of view, and linking that development to some hypotheses on the evolution of human cognitive capacity. Our main hypothesis is that these data indicate that, in the first part of the trajectory, biological limits to cognitive capacity were a major constraint that limited technology, whereas, in the second part, this biological constraint seems to have been lifted and others have come in its place. But these are modifiable by means of conceptual frameworks that facilitate concept innovation and therefore enable learning, thereby permitting acceleration in the pace of change in technology. In the last part of the paper, we elaborate on some of the consequences of that acceleration

QCD Phase Transition with Chiral Quarks and Physical Quark Masses

Bhattacharya T, Buchoff MI, Christ NH, et al. QCD Phase Transition with Chiral Quarks and Physical Quark Masses. Physical Review Letters. 2014;113(8): 82001.We report on the first lattice calculation of the QCD phase transition using chiral fermions with physical quark masses. This calculation uses 2 + 1 quark flavors, spatial volumes between (4 fm)(3) and (11 fm)(3) and temperatures between 139 and 196 MeV. Each temperature is calculated at a single lattice spacing corresponding to a temporal Euclidean extent of N-t = 8. The disconnected chiral susceptibility, chi(disc) shows a pronounced peak whose position and height depend sensitively on the quark mass. We find no metastability near the peak and a peak height which does not change when a 5 fm spatial extent is increased to 10 fm. Each result is strong evidence that the QCD "phase transition" is not first order but a continuous crossover for m(pi) = 135 MeV. The peak location determines a pseudocritical temperature T-c = 155(1)(8) MeV, in agreement with earlier staggered fermion results. However, the peak height is 50% greater than that suggested by previous staggered results. Chiral SU(2)(L) x SU(2)(R) symmetry is fully restored above 164 MeV, but anomalous U(1)A symmetry breaking is nonzero above T-c and vanishes as T is increased to 196 MeV