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S. J. Hands

Publications and source records attributed to S. J. Hands.

29 records · Page 2Linked to original sources

QCD at non-zero chemical potential and temperature from the lattice

A study of QCD at non-zero chemical potential, mu, and temperature, T, is performed using the lattice technique. The transition temperature (between the confined and deconfined phases) is determined as a function of mu and is found to be in agreement with other work. In addition the variation of the pressure and energy density with mu is obtained for small positive mu. These results are of particular relevance for heavy-ion collision experiments.

hep-ph↗

Mesonic Wavefunctions in the three-dimensional Gross-Neveu model

We present results from a numerical study of bound state wavefunctions in the (2+1)-dimensional Gross-Neveu model with staggered lattice fermions at both zero and nonzero temperature. Mesonic channels with varying quantum numbers are identified and analysed. In the strongly coupled chirally broken phase at T=0 the wavefunctions expose effects due to varying the interaction strength more effectively than straightforward spectroscopy. In the weakly coupled chirally restored phase information on fermion - antifermion scattering is recovered. In the hot chirally restored phase we find evidence for a screened interaction. The T=0 chirally symmetric phase is most readily distinguished from the symmetric phase at high T via the fermion dispersion relation.

hep-lat↗

Aspects of the thermal phase transition of QCD with small chemical potential

We propose a new method to investigate the thermal properties of QCD with a small chemical potential $(μ)$. The derivatives of the phase transition point with respect to $μ$ are computed for 2 flavors of p4-improved staggered fermions. We moreover comment on the complex phase of the fermion determinant in finite-density QCD.

hep-lat↗

The (2+1)-dimensional Gross-Neveu model with a U(1) chiral symmetry at non-zero temperature

We present results from numerical simulations of the (2+1)-dimensional Gross-Neveu model with a U(1) chiral symmetry and N_f=4 fermion species at non-zero temperature. We provide evidence that there are two different chirally symmetric phases, one critical and one with finite correlation length, separated by a Berezinskii-Kosterlitz-Thouless transition. We have also identified a regime above the critical temperature in which the fermions acquire a screening mass even in the absence of chiral symmetry breaking, analogous to the pseudogap behaviour observed in cuprate superconductors.

hep-lat↗

Two-colour QCD at non-zero quark-number density

We have simulated two-colour four-flavour QCD at non-zero chemical potential $μ$ for quark number. Simulations were performed on $8^4$ and $12^3 \times 24$ lattices. Clear evidence was seen for the formation of a colourless diquark condensate which breaks quark number spontaneously, for $μ> μ_c \sim m_π/2$. The transition appears to be second order. We have measured the spectrum of scalar and pseudoscalar bosons which shows clear evidence for the expected Goldstone boson. Our results are in qualitative agreement with those from effective Lagrangians for the potential Goldstone excitations of this theory.

hep-lat↗

QED$_3$ with Dynamical Fermions in an External Magnetic Field

In this paper, we present results of numerical lattice simulations of two-flavor QED in three space-time dimensions. First, we provide evidence that chiral symmetry is spontaneously broken in the chiral and continuum limit. Next we discuss the role of an external magnetic field $B$ on the dynamically generated fermion mass. We investigate the $B$-dependence of the condensate through calculations with dynamical fermions using the non-compact formulation of the gauge field, and compare the results with those of a comparable study using the quenched approximation.

hep-lat↗

Two-colour QCD at finite fundamental quark-number density and related theories

We are simulating SU(2) Yang-Mills theory with four flavours of dynamical quarks in the fundamental representation of SU(2) `colour' at finite chemical potential, mu for quark number, as a model for QCD at finite baryon number density. In particular we observe that for mu large enough this theory undergoes a phase transition to a state with a diquark condensate which breaks quark-number symmetry. In this phase we examine the spectrum of light scalar and pseudoscalar bosons and see evidence for the Goldstone boson associated with this spontaneous symmetry breaking. This theory is closely related to QCD at finite chemical potential for isospin, a theory which we are now studying for SU(3) colour.

hep-lat↗

The Three Dimensional Thirring Model for N_f=4 and N_f=6

We present Monte Carlo simulation results for the three dimensional Thirring model for numbers of fermion flavors N_f=4 and 6. For N_f=4 we find a second order chiral symmetry breaking transition at strong coupling, corresponding to an ultra-violet fixed point of the renormalisation group defining a non-trivial continuum limit. The critical exponents extracted from a fit to a model equation of state are distinct from those found for N_f=2. For N_f=6, in contrast, we present evidence for tunnelling between chirally symmetric and broken vacua at strong coupling, implying that the phase transition is first order and no continuum limit exists. The implications for the phase diagram of the model in the plane of coupling strength and N_f are briefly discussed.

hep-lat↗

The Three Dimensional Thirring Model for Small N_f

We formulate the three dimensional Thirring model on a spacetime lattice and study it for various even numbers of fermion flavors N_f by Monte Carlo simulation. We find clear evidence for spontaneous chiral symmetry breaking at strong coupling, contradicting the predictions of the 1/N_f expansion. The critical point appears to correspond to an ultra-violet fixed point of the renormalisation group; a fit to a RG-inspired equation of state in the vicinity of the fixed point yields distinct critical exponents for N_f=2 and N_f=4, while no fit is found for N_f=6, suggesting there is a critical number N_fc<6 beyond which no chiral symmetry breaking occurs. The spectrum of the N_f=2 theory is studied; the states examined vary sharply but continuously across the transition.

hep-lat↗

Point-to-point Hadron Correlation Functions using the Sheikholeslami--Wohlert Action

We calculate correlations between hadronic current operators as a function of their spatial separation, in a quenched lattice QCD simulation at $β=6.2$ on a $24^3\times48$ lattice. The lattice fermion formulation used is that due to Sheikholeslami and Wohlert. The correlation functions are then compared with the corresponding quantities calculated in the infinite volume chiral limit of the non-interacting theory. The ratio of the two quantities contains information on the vacuum structure of QCD. Results obtained are consistent with previous studies, and with known hadron phenomenology, although certain features of the fermion action used make it impossible to probe the $r\to0$ limit directly, thus limiting the accuracy possible.

hep-lat↗

Spectroscopy, Equation Of State And Monopole Percolation In Lattice QED With Two Flavors

Non-compact lattice QED with two flavors of light dynamical quarks is simulated on $16^4$ lattices, and the chiral condensate, monopole density and susceptibility and the meson masses are measured. Data from relatively high statistics runs at relatively small bare fermion masses of 0.005, 0.01, 0.02 and 0.03 (lattice units) are presented. Three independent methods of data analysis indicate that the critical point occurs at $β=0.225(5)$ and that the monopole condensation and chiral symmetry breaking transitions are coincident. The monopole condensation data satisfies finite size scaling hypotheses with critical indices compatible with four dimensional percolation. The best chiral equation of state fit produces critical exponents ($δ=2.31$, $β_{mag}=0.763$) which deviate significantly from mean field expectations. Data for the ratio of the sigma to pion masses produces an estimate of the critical index $δ$ in good agreement with chiral condensate measurements. In the strong coupling phase the ratio of the meson masses are $M_σ^2/M_ρ^2\approx 0.35$, $M_{A_1}^2/M_ρ^2\approx 1.4$ and $M_π^2/M_ρ^2\approx 0.0$, while on the weak coupling side of the transition $M_π^2/M_ρ^2\approx 1.0$, $M_{A_1}^2/M_ρ^2\approx 1.0$, indicating the restoration of chiral symmetry.\footnote{$\,^{}$}{August 1992}

hep-lat↗