474 research outputs found
The massless supersymmetric ladder with L rungs
We show that in the massless N=1 supersymmetric Wess-Zumino theory it is
possible to devise a computational strategy by which the x-space calculation of
the ladder 4-point correlators can be carried out without introducing any
regularization. As an application we derive a representation valid at all loop
orders in terms of conformal invariant integrals. We obtain an explicit
expression of the 3-loop ladder diagram for collinear external points.Comment: LaTeX, 17 pages, 8 figure
Parallel computing and molecular dynamics of biological membranes
In this talk I discuss the general question of the portability of Molecular
Dynamics codes for diffusive systems on parallel computers of the APE family.
The intrinsic single precision arithmetics of the today available APE platforms
does not seem to affect the numerical accuracy of the simulations, while the
absence of integer addressing from CPU to individual nodes puts strong
constraints on the possible programming strategies. Liquids can be very
satisfactorily simulated using the "systolic" method. For more complex systems,
like the biological ones at which we are ultimately interested in, the "domain
decomposition" approach is best suited to beat the quadratic growth of the
inter-molecular computational time with the number of elementary components of
the system. The promising perspectives of using this strategy for extensive
simulations of lipid bilayers are briefly reviewed.Comment: 4 pages LaTeX, 2 figures included, espcrc2.sty require
Non-perturbative renormalization in kaon decays
We discuss the application of the MPSTV non-perturbative method \cite{NPM} to
the operators relevant to kaon decays. This enables us to reappraise the
long-standing question of the rule, which involves
power-divergent subtractions that cannot be evaluated in perturbation theory.
We also study the mixing with dimension-six operators and discuss its
implications to the chiral behaviour of the parameter.Comment: Talk presented at LATTICE96(improvement), LaTeX 3 pages, uses
espcrc2, 2 postscript figure
Gauge equivalence in QCD: the Weyl and Coulomb gauges
The Weyl-gauge ( QCD Hamiltonian is unitarily transformed to a
representation in which it is expressed entirely in terms of gauge-invariant
quark and gluon fields. In a subspace of gauge-invariant states we have
constructed that implement the non-Abelian Gauss's law, this unitarily
transformed Weyl-gauge Hamiltonian can be further transformed and, under
appropriate circumstances, can be identified with the QCD Hamiltonian in the
Coulomb gauge. We demonstrate an isomorphism that materially facilitates the
application of this Hamiltonian to a variety of physical processes, including
the evaluation of -matrix elements. This isomorphism relates the
gauge-invariant representation of the Hamiltonian and the required set of
gauge-invariant states to a Hamiltonian of the same functional form but
dependent on ordinary unconstrained Weyl-gauge fields operating within a space
of ``standard'' perturbative states. The fact that the gauge-invariant
chromoelectric field is not hermitian has important implications for the
functional form of the Hamiltonian finally obtained. When this nonhermiticity
is taken into account, the ``extra'' vertices in Christ and Lee's Coulomb-gauge
Hamiltonian are natural outgrowths of the formalism. When this nonhermiticity
is neglected, the Hamiltonian used in the earlier work of Gribov and others
results.Comment: 25 page
Baryon Number Fluctuation and the Quark-Gluon Plasma
We show that or , the squared baryon or
antibaryon number fluctuation per baryon or antibaryon, is a possible signature
for the quark-gluon plasma that is expected to be created in relativistic heavy
ion collisions, as it is a factor of three smaller than in an equilibrated
hadronic matter due to the fractional baryon number of quarks. Using kinetic
equations with exact baryon number conservation, we find that their values in
an equilibrated matter are half of those expected from a Poisson distribution.
Effects due to finite acceptance and non-zero net baryon number are also
studied.Comment: discussion and references added, version to appear in PR
A 0-dimensional counter-example to rooting?
We provide an example of a 0-dimensional field theory where rooting does not
work.Comment: 3 pages; Physics Letters B (2010
The continuum limit of the quark mass step scaling function in quenched lattice QCD
The renormalisation group running of the quark mass is determined
non-perturbatively for a large range of scales, by computing the step scaling
function in the Schroedinger Functional formalism of quenched lattice QCD both
with and without O(a) improvement. A one-loop perturbative calculation of the
discretisation effects has been carried out for both the Wilson and the
Clover-improved actions and for a large number of lattice resolutions. The
non-perturbative computation yields continuum results which are regularisation
independent, thus providing convincing evidence for the uniqueness of the
continuum limit. As a byproduct, the ratio of the renormalisation group
invariant quark mass to the quark mass, renormalised at a hadronic scale, is
obtained with very high accuracy.Comment: 23 pages, 3 figures; minor changes, references adde
New results in the deformed N=4 SYM theory
We investigate various perturbative properties of the deformed N=4 SYM
theory. We carry out a three-loops calculation of the chiral matter superfield
propagator and derive the condition on the couplings for maintaining finiteness
at this order. We compute the 2-, 3- and 4-point functions of composite
operators of dimension 2 at two loops. We identify all the scalar operators
(chiral and non-chiral) of bare dimension 4 with vanishing one-loop anomalous
dimension. We compute some 2- and 3-point functions of these operators at two
loops and argue that the observed finite corrections cannot be absorbed by a
finite renormalization of the operators.Comment: LaTeX, 16 pages, 1 figure; references added; typos corrected; final
version to appear in Nucl. Phys.
Twisted-mass lattice QCD with mass non-degenerate quarks
The maximally twisted lattice QCD action of an doublet of mass
degenerate Wilson quarks gives rise to a real positive fermion determinant and
it is invariant under the product of standard parity times the change of sign
of the coefficient of the Wilson term. The existence of this spurionic symmetry
implies that O() improvement is either automatic or achieved through simple
linear combinations of quantities taken with opposite external three-momenta.
We show that in the case of maximal twist all these nice results can be
extended to the more interesting case of a mass non-degenerate quark pair.Comment: 10 pages (due to different LateX style), Latex file, based on a talk
presented by G.C. Rossi at LHP2003 - Cairns. Reasons for replacement:
Correction of the transformation properties of energies under r --> -r. Minor
changes in Appendix
- …