6,183 research outputs found
Comparison of finite-size-scaling functions for 3d O(N) spin models to QCD
We calculate numerically universal finite-size-scaling functions of the
magnetization for the three-dimensional O(4) and O(2) spin models. The approach
of these functions to the infinite-volume scaling functions is studied in
detail on the critical and pseudocritical lines. For this purpose we determine
the pseudocritical line in two different ways. We find that the asymptotic form
of the finite-size-scaling functions is already reached at small values of the
scaling variable. A comparison with QCD lattice data for two flavours of
staggered fermions shows a similar finite-size behaviour which is compatible
with that of the spin models.Comment: Lattice2001(hightemp), 3 pages, 5 figures, acknowledgements
completed, minor typographical errors correcte
Block Spin Effective Action for Polyakov Loops in 4D SU(2) LGT
Using a variant of the IMCRG method of Gupta and Cordery, we explicitly
compute majority rule block spin effective actions for the signs of the
Polyakov loops in 4D SU(2) finite temperature lattice gauge theories. To the
best of our knowledge, this is the first attempt to compute numerically
effective actions for the Polyakov loop degrees of freedom in 4D SU(2). The
most important observations are: 1. The renormalization group flow at the
deconfinement transition can be nicely matched with the flow of the 3D Ising
model, thus confirming the Svetitsky-Yaffe conjecture. 2. The IMCRG simulations
of the FT SU(2) model have strongly reduced critical slowing down.Comment: Contribution to the Lattice 97 proceedings, LaTeX, 3 pages, 3
figures, uses espcrc2.sty, epsfig.st
Critical behaviour of SU(2) lattice gauge theory. A complete analysis with the -method
We determine the critical point and the ratios and
of critical exponents of the deconfinement transition in gauge theory
by applying the -method to Monte Carlo data of the modulus and the
square of the Polyakov loop. With the same technique we find from the Binder
cumulant its universal value at the critical point in the thermodynamical
limit to and for the next-to-leading exponent .
From the derivatives of the Polyakov loop dependent quantities we estimate then
. The result from the derivative of is , in
complete agreement with that of the Ising model.Comment: 11 pages, 3 Postscript figures, uses Plain Te
Specific heat and energy for the three-dimensional O(2) model
We investigate the three-dimensional O(2) model on lattices of size 8^3 to
160^3 close to the critical point at zero magnetic field. We confirm explicitly
the value of the critical coupling J_c found by Ballesteros et al. and estimate
there the universal values of g_r and xi/L. At the critical point we study the
finite size dependencies of the energy density epsilon and the specific heat C.
We find that the nonsingular part of the specific heat C_{ns} is linearly
dependent on 1/alpha. From the critical behaviour of the specific heat for T
not T_c on the largest lattices we determine the universal amplitude ratio
A+/A-. The alpha- dependence of this ratio is close to the phenomenological
relation A+/A- = 1-4alpha.Comment: Lattice2001(spin), 3 pages, 4 figure
The chiral transition of N_f=2 QCD with fundamental and adjoint fermions
We study QCD with two staggered Dirac fermions both in the fundamental (QCD)
and the adjoint representation (aQCD) near the chiral transition. The aim is to
find the universality class of the chiral transition and to verify Goldstone
effects below the transition. We investigate aQCD, because in that theory the
deconfinement and the chiral transitions occur at different temperatures
T_d<T_c. Here, we show that the scaling behaviour of the chiral condensate in
the vicinity of \beta_c is in full agreeement with that of the 3d O(2)
universality class. In the region T_d<T<T_c we confirm the quark mass
dependence of the chiral condensate which is expected due to the existence of
Goldstone modes like in 3d O(N) spin models. For fundamental QCD we use the
p4-action. Here, we find Goldstone effects below T_c like in aQCD and the 3d
O(N) spin models, however no O(2)/O(4) scaling near the chiral transition
point. The result for QCD may be a consequence of the coincidence of the
deconfinement transition with the chiral transition.Comment: 6 pages, 5 figures, poster contribution to Lattice 2005 (Nonzero
temperature and density), one reference added, figure 2 change
Scaling and Goldstone effects in a QCD with two flavours of adjoint quarks
We study QCD with two Dirac fermions in the adjoint representation at finite
temperature by Monte Carlo simulations.In such a theory the deconfinement and
chiral phase transitions occur at different temperatures. We locate the second
order chiral transition point at beta_c=5.624(2) and show that the scaling
behaviour of the chiral condensate in the vicinity of beta_c is in full
agreeement with that of the 3d O(2) universality class, and to a smaller extent
comparable to the 3d O(6) class. From the previously determined first order
deconfinement transition point beta_d=5.236(3) and the two-loop beta function
we find the ratio T_c/T_d = 7.8(2). In the region between the two phase
transitions we explicitly confirm the quark mass dependence of the chiral
condensate which is expected due to the existence of Goldstone modes like in 3d
O(N) spin models. At the deconfinement transition the condensate shows a gap,
and below beta_d, it is nearly mass-independent for fixed beta.Comment: 28 pages, 12 figures, Latex2
Non-perturbative determination of anisotropy coefficients and pressure gap at the deconfining transition of QCD
We propose a new non-perturbative method to compute derivatives of gauge
coupling constants with respect to anisotropic lattice spacings (anisotropy
coefficients). Our method is based on a precise measurement of the finite
temperature deconfining transition curve in the lattice coupling parameter
space extended to anisotropic lattices by applying the spectral density method.
We determine the anisotropy coefficients for the cases of SU(2) and SU(3) gauge
theories. A longstanding problem, when one uses the perturbative anisotropy
coefficients, is a non-vanishing pressure gap at the deconfining transition
point in the SU(3) gauge theory. Using our non-perturbative anisotropy
coefficients, we find that this problem is completely resolved.Comment: LATTICE98(hightemp
Back action of graphene charge detectors on graphene and carbon nanotube quantum dots
We report on devices based on graphene charge detectors (CDs) capacitively
coupled to graphene and carbon nanotube quantum dots (QDs). We focus on back
action effects of the CD on the probed QD. A strong influence of the bias
voltage applied to the CD on the current through the QD is observed. Depending
on the charge state of the QD the current through the QD can either strongly
increase or completely reverse as a response to the applied voltage on the CD.
To describe the observed behavior we employ two simple models based on single
electron transport in QDs with asymmetrically broadened energy distributions of
the source and the drain leads. The models successfully explain the back action
effects. The extracted distribution broadening shows a linear dependency on the
bias voltage applied to the CD. We discuss possible mechanisms mediating the
energy transfer between the CD and QD and give an explanation for the origin of
the observed asymmetry.Comment: 6 pages, 4 figure
A numerical study of Goldstone-mode effects and scaling functions of the three-dimensional O(2) model
We investigate numerically the three-dimensional O(2) model on 8^3-160^3
lattices as a function of the magnetic field H. In the low-temperature phase we
verify the H-dependence of the magnetization M induced by the Goldstone modes
and determine M in the thermodynamic limit on the coexistence line both by
extrapolation and by chiral perturbation theory. We compute two critical
amplitudes from the scaling behaviours on the coexistence line and on the
critical line. In both cases we find negative corrections to scaling. With
additional high temperature data we calculate the scaling function and show
that it has a smaller slope than that of the O(4) model. For future tests of
QCD lattice data we study as well finite-size-scaling functions.Comment: Lattice 2000 (Spin Models), minor typographic errors fixe
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