Thermodynamics of Lattice QCD with massless quarks and chiral 4-fermion interactions

We have simulated lattice QCD with an irrelevant 4-fermion interaction and 2 zero mass quarks. The chiral phase transition is observed to be second order and we discuss extraction of critical exponents.Comment: LATTICE98(hightemp

The finite temperature transition for 3-flavour lattice QCD at finite isospin density

We simulate 3-flavour lattice QCD with a small chemical potential $\mu_I$ for isospin, at temperatures close to the finite temperature transition. Using quark masses just above the critical mass for zero chemical potential, we determine the position of the transition from hadronic matter to a quark-gluon plasma as a function of $\mu_I$. We see evidence for a critical endpoint where the transition changes from a crossover to a first-order transition as $\mu_I$ is increased. We argue that QCD at finite $\mu_I$ and QCD at finite quark-numberchemical potential $\mu$ should behave similarly in this region.Comment: 3 pages LaTex, 2 postscript figures. Parallel talk presented at Lattice 2004 (non-zero), Fermila

Manifestations of the axial anomaly in finite temperature QCD

We compute the flavor singlet meson correlators and screening masses in quenched and $N_f=2$ QCD at $N_t=8$. The consequences of our results for the realization of the $U_A(1)$ symmetry at finite T are discussed and an interpretation of our measurements in terms of the behaviour of the low lying fermionic modes is proposed.Comment: Talk presented at LATTICE96(chirality in QCD

Consensus Views on Advance Care Planning for Dementia: A Delphi Study

yesThe uptake of advance care planning (ACP) is particularly low among people with dementia. This may reflect barriers to communication between professionals, patients and families in the face of lack of consensus about the process. This study aimed to methodically investigate consensus views of how ACP should be explained and carried out with people with dementia. A three-round Delphi study explored views of how and when ACP should be addressed, what should be covered, who should be involved and why rates of ACP are low. Seventeen participants took part comprising family members, old age psychiatrists and policy makers. Thirty-two items reached consensus. The panel agreed on 11 different areas for discussion. They concurred that ACP was best addressed after the person has come to terms with the diagnosis when the individual feels ready to do so. There was a consensus view that the process should be couched in terms of ‘certain possibilities’. Consensus items emphasised personal choice and autonomy, while also prioritising the need to discuss financial aspects and to include spouses. There was no consensus that professionals should be involved, although the panel viewed them as carrying some responsibility for low uptake. It is suggested that ACP should include general discussion of values as well as coverage of specific points. Professionals need to offer discussion and information on ACP, but also make clear that the patient has the right to choose whether to pursue ACP or not

Lattice QCD at finite isospin density at zero and finite temperature

We simulate lattice QCD with dynamical $u$ and $d$ quarks at finite chemical potential, $\mu_I$, for the third component of isospin ($I_3$), at both zero and at finite temperature. At zero temperature there is some $\mu_I$, $\mu_c$ say, above which $I_3$ and parity are spontaneously broken by a charged pion condensate. This is in qualitative agreement with the prediction of effective (chiral) Lagrangians which also predict $\mu_c=m_\pi$. This transition appears to be second order, with scaling properties consistent with the mean-field predictions of such effective Lagrangian models. We have also studied the restoration of $I_3$ symmetry at high temperature for $\mu_I > \mu_c$. For $\mu_I$ sufficiently large, this finite temperature phase transition appears to be first order. As $\mu_I$ is decreased it becomes second order connecting continuously with the zero temperature transition.Comment: 23 pages, Revtex, 9 figures. Major revision of sections 3 and 4 to include new analyses of critical scaling which we now find to be in the universality class of mean-field theor

Topology, fermionic zero modes and flavor singlet correlators in finite temperature QCD

We extend our earlier results concerning the breaking of the U_A(1) symmetry in finite temperature QCD. In particular, we use topological arguments to investigate the chiral limit.Comment: 3 pages, Talk given at LATTICE'9

Tricritical scaling at the N_t=6 chiral phase transition for 2 flavour lattice QCD with staggered quarks

We have simulated lattice QCD directly in the chiral limit of zero quark mass by adding an additional, irrelevant 4-fermion interaction to the standard action. Using lattices having temporal extent of six and spatial extents of twelve and eighteen, we find that the theory with 2 massless staggered quark flavors has a second order finite temperature phase transition. The critical exponents $\beta_{mag}$, $\delta$ and $\nu$ are measured and favour tricritical behaviour over that expected by universality arguments. The pion screening mass is consistent with zero below the transition, but is degenerate with the nonzero $\sigma(f_0)$ mass above the transition, indicating the restoration of chiral symmetry.Comment: 12 pages, 3 postscript figures Letter has been rewritten to reflect a reinterpretation of our results as indicating tricritical critical indices rather than those predicted by standard universality arguments. Some additional analysis which supports this interpretation is included. The comparison of our methods with those of others has been expande

The pseudo-Goldstone spectrum of 2-colour QCD at finite density

We examine the spectrum of 2-colour lattice QCD with 4 continuum flavours at a finite chemical potential ($\mu$) for quark-number, on a $12^3 \times 24$ lattice. First we present evidence that the system undergoes a transition to a state with a diquark condensate, which spontaneously breaks quark number at $\mu=m_\pi/2$, and that this transition is mean field in nature. We then examine the 3 states that would be Goldstone bosons at $\mu=0$ for zero Dirac and Majorana quark masses. The predictions of chiral effective Lagrangians give a good description of the behaviour of these masses for $\mu < m_\pi/2$. Except for the heaviest of these states, these predictions diverge from our measurements, once $\mu$ is significantly greater than $m_\pi/2$. However, the qualitative behaviour of these masses, indicates that the physics is very similar to that predicted by these effective Lagrangians, and there is some indication that at least part of these discrepancies is due to saturation, a lattice artifact.Comment: 32 pages LaTeX/Revtex, 8 Postscript figure

Lattice QCD at finite isospin density and/or temperature

We simulate two-flavour lattice QCD with at a finite chemical potential $\mu_I$ for isospin, and finite temperature. At small $\mu_I$, we determine the position of the crossover from hadronic matter to a quark-gluon plasma as a function of $\mu_I$. At larger $\mu_I$ we observe the phase transition from the superfluid pion-condensed phase to a quark-gluon plasma, noting its change from second order to first order as $\mu_I$ is increased. We also simulate two-flavour lattice QCD at zero quark mass, using an action which includes an additional 4-fermion interaction, at temperatures close to the chiral transition on $N_t=8$ lattices.Comment: 3 pages LaTex, 3 postscript figures. Parallel talk at Lattice2003(nonzero

Quenched QCD at finite density: g=1g=1 and g=∞g=\infty

We report on our ongoing effort to understand quenched lattice QCD at finite baryon number density. The quenched theory is sensitive to the baryon mass both at strong coupling and in the scaling region. However, we find that the quenched model is pathological for $\mu > m_\pi/2$ at $\beta= 6.0$, in agreement with past Lanczos analyses of the Dirac operator.Comment: Contribution to Lat94, 3 pages, tar-compressed uuencoded ps fil