283 research outputs found
The fixed point action of the Schwinger model
We compute the fixed point action for the Schwinger model through an
expansion in the gauge field. The calculation allows a check of the locality of
the action. We test its perfection by computing the 1-loop mass gap at finite
spatial volume.Comment: 3 pages, LaTeX, 2 figures, uses styles [twoside,fleqn,espcrc2,
epsfig], talk presented at Lattice 9
Lattice renormalization of the static quark derivative operator
We give the analytical expressions and numerical values of radiative
corrections to the covariant derivative operator on the static quark line, used
for the lattice calculation of the Isgur-Wise form factors and
. Those corrections induce an enhancement of renormalized
quantities if an hypercubic blocking is applied to the Wilson line, whereas
there is a reduction without such a blocking
A measure of conductivity for lattice fermions at finite density
We study the linear response to an external electric field of a system of
fermions in a lattice at zero temperature. This allows to measure numerically
the Euclidean conductivity which turns out to be compatible with an analytical
calculation for free fermions. The numerical method is generalizable to systems
with dynamical interactions where no analytical approach is possible.Comment: version to be published in Physics Letters
The index theorem in QCD with a finite cut-off
The fixed point Dirac operator on the lattice has exact chiral zero modes on
topologically non-trivial gauge field configurations independently whether
these configurations are smooth, or coarse. The relation ,
where is the number of left (right)-handed zero modes and
is the fixed point topological charge holds not only in the continuum
limit, but also at finite cut-off values. The fixed point action, which is
determined by classical equations, is local, has no doublers and complies with
the no-go theorems by being chirally non-symmetric. The index theorem is
reproduced exactly, nevertheless. In addition, the fixed point Dirac operator
has no small real eigenvalues except those at zero, i.e. there are no
'exceptional configurations'.Comment: 9 pages, 1 figure. Minor clarifying changes are made and new
references adde
Improving the Quark Number Susceptibilities for Staggered Fermions
Quark number susceptibilities approach their ideal gas limit at sufficiently
high temperatures. As in the case of other thermodynamic quantities, this limit
itself is altered substantially on lattices with small temporal extent, N_t =
4-8, making it thus difficult to check the validity of perturbation theory.
Unlike other observables, improving susceptibilities or number densities is
subject to constraints of current conservation and absence of chemical
potential dependent divergences. We construct such an improved number density
and susceptibility for staggered fermions and show that they approximate the
continuum ideal gas limit better on small temporal lattices.Comment: Lattice2002(nonzerot), 3 pages, 3 figure
Boosting Higgs discovery - the forgotten channel
Searches for a heavy Standard Model Higgs boson focus on the 'gold plated
mode' where the Higgs decays to two leptonic Z bosons. This channel provides a
clean signature, in spite of the small leptonic branching ratios. We show that
using fat jets the semi-leptonic ZZ mode significantly increases the number of
signal events with a similar statistical significance as the leptonic mode.Comment: 12 pages, 3 figure
Heavy Dynamical Fermions in Lattice QCD
It is expected that the only effect of heavy dynamical fermions in QCD is to
renormalize the gauge coupling. We derive a simple expression for the shift in
the gauge coupling induced by flavors of heavy fermions. We compare this
formula to the shift in the gauge coupling at which the
confinement-deconfinement phase transition occurs (at fixed lattice size) from
numerical simulations as a function of quark mass and . We find remarkable
agreement with our expression down to a fairly light quark mass. However,
simulations with eight heavy flavors and two light flavors show that the eight
flavors do more than just shift the gauge coupling. We observe
confinement-deconfinement transitions at induced by a large number of
heavy quarks. We comment on the relevance of our results to contemporary
simulations of QCD which include dynamical fermions.Comment: COLO-HEP-311, 26 pages and 6 postscript figures; file is a shar file
and all macros are (hopefully) include
Solutions of the Ginsparg-Wilson Relation
We analyze general solutions of the Ginsparg-Wilson relation for lattice
Dirac operators and formulate a necessary condition for such operators to have
non-zero index in the topologically nontrivial background gauge fields.Comment: 6 pages, latex, no figures, set T to 1 in eqs. (10)--(13
Exact chiral invariance at finite density on the lattice
We propose a lattice action for the overlap Dirac matrix with nonzero
chemical potential which is shown to preserve the chiral invariance on the
lattice exactly. We further demonstrate it to arise from the Domain wall by
letting the chemical potential count only the physically relevant wall modes.Comment: 4 pages, RevTe
Finite-size scaling of the helicity modulus of the two-dimensional O(3) model
Using Monte Carlo methods, we compute the finite-size scaling function of the
helicity modulus of the two-dimensional O(3) model and compare it to
the low temperature expansion prediction. From this, we estimate the range of
validity for the leading terms of the low temperature expansion of the
finite-size scaling function and for the low temperature expansion of the
correlation length. Our results strongly suggest that a Kosterlitz-Thouless
transition at a temperature is extremely unlikely in this model.Comment: 4 pages, 3 Postscript figures, to appear in Phys. Rev. B Jan. 1997 as
a Brief Repor
- âŠ