146 research outputs found
Fermionic Loops in Numerical Stochastic Perturbation Theory
We discuss the inclusion of fermionic loops contributions in Numerical
Stochastic Perturbation Theory for Lattice Gauge Theories. We show how the
algorithm implementation is in principle straightforward and report on the
status of the project.Comment: Lattice 2000 (Perturbation Theory), 4 pages, (misprint corrected
The n_f=2 residual mass in lattice HQET to alpha^3 order
We compute the so called residual mass in Lattice Heavy Quark Effective
Theory to alpha^3 order in the n_f=2 (unquenched) case. The control of this
additive mass renormalization is crucial for the determination of the heavy
quark mass from lattice simulations. We discuss the impact on an unquenched
determination of the b-quark mass.Comment: Lattice2004(heavy), 3 pages, 1 figur
A consistency check for Renormalons in Lattice Gauge Theory: beta^(-10) contributions to the SU(3) plaquette
We compute the perturbative expansion of the Lattice SU(3) plaquette to
beta^(-10) order. The result is found to be consistent both with the expected
renormalon behaviour and with finite size effects on top of that.Comment: 15 pages, 5 colour eps figures. Axes labels added in the figures. A
comment added in the appendi
Quantum Interactions Between Non-Perturbative Vacuum Fields
We develop an approach to investigate the non-perturbative dynamics of
quantum field theories, in which specific vacuum field fluctuations are treated
as the low-energy dynamical degrees of freedom, while all other vacuum field
configurations are explicitly integrated out from the path integral. We show
how to compute the effective interaction between the vacuum field degrees of
freedom both perturbatively (using stochastic perturbation theory) and fully
non-perturbatively (using lattice field theory simulations). The present
approach holds to all orders in the couplings and does not rely on the
semi-classical approximation.Comment: 15 pages, 4 figure
High loop renormalization constants for Wilson fermions/Symanzik improved gauge action
We present the current status of our computation of quark bilinear
renormalization constants for Wilson fermions and Symanzik improved gauge
action. Computations are performed in Numerical Stochastic Perturbation Theory.
Volumes range from 10^4 to 32^4. Renormalization conditions are those of the
RI'-MOM scheme, imposed at different values of the physical scale. Having
measurements available at several momenta, irrelevant effects are taken into
account by means of hypercubic symmetric Taylor expansions. Finite volumes
effects are assessed repeating the computations at different lattice sizes. In
this way we can extrapolate our results to the continuum limit, in infinite
volume.Comment: 8 pages, 3 figures, talk presented at the 27th International
Symposium on Lattice Field Theory (Lattice 2009), Beijing, China, 26-31 Jul
200
Quantum field theories on the Lefschetz thimble
In these proceedings, we summarize the Lefschetz thimble approach to the sign
problem of Quantum Field Theories. In particular, we review its motivations,
and we summarize the results of the application of two different algorithms to
two test models.Comment: contributions to 31st International Symposium on Lattice Field Theory
- LATTICE 2013, July 29 - August 3, 2013, Mainz, Germany and QCD-TNT-III, 2-6
September, 2013, European Centre for Theoretical Studies in Nuclear Physics
and Related Areas (ECT*), Villazzano, Trento (Italy
Non-Compact QED_3 with N_f=1 and N_f=4
We present numerical results for non-compact three-dimensional QED for
numbers of flavors N_f=1 and N_f=4.In particular, we address the issue of
whether chiral symmetry is spontaneously broken in the continuum limit, and
obtain a positive answer for N_f=1, with a dimensionless condensate estimated
to be beta^2 ~= O(10^-3), implying that the critical number of
flavors N_fc>1. We also compare the N_f=1 and N_f=4 models by analysing the
transition from strong to weak coupling behaviour using an equation of state
based on a continuous phase transition. While some qualitative differences
emerge, it appears difficult to determine whether N_f=4 lies above or below
N_fc.Comment: 19 pages, 10 figure
The residual mass in Lattice Heavy Quark Effective Theory to alpha^3 order
We determine to order alpha^3 in the quenched approximation the so-called
residual mass in the lattice regularisation of the Heavy Quark Effective
Theory. We follow a gauge-invariant strategy which exploits the fact that this
mass term dominates the exponential decrease of perturbative Wilson loops at
large perimeters. Our computational tool is Numerical Stochastic Perturbation
Theory. The new coefficient we compute is crucial to improve the determination
of the (MS bar) mass of the b-quark from lattice simulations of the Heavy Quark
Effective Theory.Comment: 11 pages, 1 figure. Axes labels added to the figure. Two references
added. Section 3.2 a bit enriched to clarify the message. A few other
comments added for the sake of clearnes
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