21 research outputs found
The equation of state for two flavor QCD
We improve the calculation of the equation of state for two flavor QCD by
simulating on lattices at appropriate values of the couplings for the
deconfinement/chiral symmetry restoration crossover. For the
energy density rises rapidly to approximately 1 just after the
crossover( at this point). Comparing with our previous
result for ~\cite{eos}, we find large finite corrections as
expected from free field theory on finite lattices. We also provide formulae
for extracting the speed of sound from the measured quantities.Comment: Contribution to Lattice 95 proceedings (combines talks presented by
T. Blum and L. Karkkainen). LaTeX, 8 pages, uses espcrc2.sty, postscript
figures include
Critical Behavior at the Chiral Phase Transition
Quantum chromodynamics with two zero mass flavors is expected to exhibit a
phase transition with O(4) critical behavior. Fixing the universality class is
important for phenomenology and for facilitating the extrapolation of
simulation data to physical quark mass values. At Lattice '96 the Tsukuba and
Bielefeld groups reported results from new simulations with dynamical staggered
quarks at , which suggested a departure from the expected critical
behavior. We report observations of similar deviations and discuss efforts in
progress to understand this phenomenon.Comment: 3 pp, LaTeX with 6 encapsulated Postscript figures. Lattice '97
proceeding
Thermodynamics with 3 and 2+1 Flavors of Improved Staggered Quarks
We present preliminary results from exploring the phase diagram of finite
temperature QCD with three degenerate flavors and with two light flavors and
the mass of the third held approximately at the strange quark mass. We use an
order Symanzik improved gauge action and an order
improved staggered quark action. The improved staggered
action leads to a dispersion relation with diminished lattice artifacts, and
hence better thermodynamic properties. It decreases the flavor symmetry
breaking of staggered quarks substantially, and we estimate that at the
transition temperature for an to lattice {\em all} pions will
be lighter than the lightest kaon. Preliminary results on lattices with
, 6 and 8 are presented.Comment: 3 pages, 6 figures, contribution to Lattice2001(hightemp) August
19--24, 2001, Berlin, German
NN Core Interactions and Differential Cross Sections from One Gluon Exchange
We derive nonstrange baryon-baryon scattering amplitudes in the
nonrelativistic quark model using the ``quark Born diagram" formalism. This
approach describes the scattering as a single interaction, here the
one-gluon-exchange (OGE) spin-spin term followed by constituent interchange,
with external nonrelativistic baryon wavefunctions attached to the scattering
diagrams to incorporate higher-twist wavefunction effects. The short-range
repulsive core in the NN interaction has previously been attributed to this
spin-spin interaction in the literature; we find that these perturbative
constituent-interchange diagrams do indeed predict repulsive interactions in
all I,S channels of the nucleon-nucleon system, and we compare our results for
the equivalent short-range potentials to the core potentials found by other
authors using nonperturbative methods. We also apply our perturbative
techniques to the N and systems: Some
channels are found to have attractive core potentials and may accommodate
``molecular" bound states near threshold. Finally we use our Born formalism to
calculate the NN differential cross section, which we compare with experimental
results for unpolarised proton-proton elastic scattering. We find that several
familiar features of the experimental differential cross section are reproduced
by our Born-order result.Comment: 27 pages, figures available from the authors, revtex, CEBAF-TH-93-04,
MIT-CTP-2187, ORNL-CCIP-93-0
Static hybrid quarkonium potential with improved staggered quarks
We are studying the effects of light dynamical quarks on the excitation
energies of a flux tube between a static quark and antiquark. We report
preliminary results of an analysis of the ground state potential and the
and potentials. We have measured these potentials
on closely matched ensembles of gauge configurations, generated in the quenched
approximation and with 2+1 flavors of Asqtad improved staggered quarks.Comment: Lattice2002(heavyquark
High temperature QCD with three flavors of improved staggered quarks
We present an update of our study of high temperature QCD with three flavors
of quarks, using a Symanzik improved gauge action and the Asqtad staggered
quark action. Simulations are being carried out on lattices with Nt=4, 6 and 8
for the case of three degenerate quarks with masses less than or equal to the
strange quark mass, , and on lattices with Nt=6 and 8 for degenerate up
and down quarks with masses in the range 0.2 m_s \leq m_{u,d} \leq 0.6 m_s, and
the strange quark fixed near its physical value. We also report on first
computations of quark number susceptibilities with the Asqtad action. These
susceptibilities are of interest because they can be related to event-by-event
fluctuations in heavy ion collision experiments. Use of the improved quark
action leads to a substantial reduction in lattice artifacts. This can be seen
already for free fermions and carries over into our results for QCD.Comment: Lattice2002(Non-zero temperature and density
Thermodynamics for two flavor QCD
We conclude our analysis of the N_t=6 equation of state for two flavor QCD,
first described at last year's conference. We have obtained new runs at
am_q=0.025 and improved runs at am_q=0.0125. The results are extrapolated to
m_q=0, and we extract the speed of sound as well. We also present evidence for
a restoration of the SU(2) X SU(2) chiral symmetry just above the crossover,
but not of the axial U(1) chiral symmetry.Comment: Poster presented at LATTICE96(finite temperature). 4 pages, LaTeX
plus 5 encapsulated Postscript figure
I=3/2 Scattering in the Nonrelativisitic Quark Potential Model
We study elastic scattering to Born order using
nonrelativistic quark wavefunctions in a constituent-exchange model. This
channel is ideal for the study of nonresonant meson-meson scattering amplitudes
since s-channel resonances do not contribute significantly. Standard quark
model parameters yield good agreement with the measured S- and P-wave phase
shifts and with PCAC calculations of the scattering length. The P-wave phase
shift is especially interesting because it is nonzero solely due to
symmetry breaking effects, and is found to be in good agreement with experiment
given conventional values for the strange and nonstrange constituent quark
masses.Comment: 12 pages + 2 postscript figures, Revtex, MIT-CTP-210
Kaon-Nucleon Scattering Amplitudes and Z-Enhancements from Quark Born Diagrams
We derive closed form kaon-nucleon scattering amplitudes using the ``quark
Born diagram" formalism, which describes the scattering as a single interaction
(here the OGE spin-spin term) followed by quark line rearrangement. The low
energy I=0 and I=1 S-wave KN phase shifts are in reasonably good agreement with
experiment given conventional quark model parameters. For Gev
however the I=1 elastic phase shift is larger than predicted by Gaussian
wavefunctions, and we suggest possible reasons for this discrepancy. Equivalent
low energy KN potentials for S-wave scattering are also derived. Finally we
consider OGE forces in the related channels K, KN and K,
and determine which have attractive interactions and might therefore exhibit
strong threshold enhancements or ``Z-molecule" meson-baryon bound states.
We find that the minimum-spin, minimum-isospin channels and two additional
K channels are most conducive to the formation of bound states.
Related interesting topics for future experimental and theoretical studies of
KN interactions are also discussed.Comment: 34 pages, figures available from the authors, revte
Quark Loop Effects with an Improved Staggered Action
We have been studying effects of dynamical quarks on various hadronic
observables, using our recently formulated improvement for staggered fermions.
To illustrate improvement, we show that the light hadron spectrum in the
quenched approximation gives remarkably good scaling. We highlight three new
results: (1) We find no apparent quark loop effects in the Edinburgh plot with
2+1 flavors of dynamical quarks at a = 0.14 fm. (2) We show that dynamical
quarks modify the shape of the heavy quark potential. (3) We present results
hinting at meson decay effects in light hadron spectroscopy.Comment: 5 pages, 7 figures, Lattice 2000 (Spectrum