1,720,988 research outputs found
Four-loop lattice-regularized vacuum energy density of the three-dimensional SU(3) + adjoint Higgs theory
No full textDi Renzo F, Laine M, Schroeder Y, Torrero C. Four-loop lattice-regularized vacuum energy density of the three-dimensional SU(3) + adjoint Higgs theory. JHEP. 2008;2008(09):061.The pressure of QCD admits at high temperatures a factorization into purely perturbative contributions from "hard" thermal momenta, and slowly convergent as well as non-perturbative contributions from "soft" thermal momenta. The latter can be related to various effective gluon condensates in a dimensionally reduced effective field theory, and measured there through lattice simulations. Practical measurements of one of the relevant condensates have suffered, however, from difficulties in extrapolating convincingly to the continuum limit. In order to gain insight on this problem, we employ Numerical Stochastic Perturbation Theory to estimate the problematic condensate up to 4-loop order in lattice perturbation theory. Our results seem to confirm the presence of "large" discretization effects, going like , where is the lattice spacing. For definite conclusions, however, it would be helpful to repeat the corresponding part of our study with standard lattice perturbation theory techniques
The leading non-perturbative coefficient in the weak-coupling expansion of hot QCD pressure
No full textDi Renzo F, Laine M, Miccio V, Schroeder Y, Torrero C. The leading non-perturbative coefficient in the weak-coupling expansion of hot QCD pressure. JHEP. 2006;2006(07):026.Using Numerical Stochastic Perturbation Theory within three-dimensional pure SU(3) gauge theory, we estimate the last unknown renormalization constant that is needed for converting the vacuum energy density of this model from lattice regularization to the MS scheme. Making use of a previous non-perturbative lattice measurement of the plaquette expectation value in three dimensions, this allows us to approximate the first non-perturbative coefficient that appears in the weak-coupling expansion of hot QCD pressure
Interplay between temperature and trap effects in one-dimensional lattice systems of bosonic particles
No full textWe investigate the interplay of temperature and trap effects in cold particle
systems at their quantum critical regime, such as cold bosonic atoms in optical
lattices at the transitions between Mott-insulator and superfluid phases. The
theoretical framework is provided by the one-dimensional Bose-Hubbard model in
the presence of an external trapping potential, and the trap-size scaling
theory describing the large trap-size behavior at a quantum critical point. We
present numerical results for the low-temperature behavior of the particle
density and the density-density correlation function at the Mott transitions,
and within the gapless superfluid phase
Critical parameters from trap-size scaling in trapped particle systems
No full textWe investigate the critical behavior of trapped particle systems at the
low-temperature superfluid transition. In particular, we consider the
three-dimensional Bose-Hubbard model in the presence of a trapping harmonic
potential coupled with the particle density, which is a realistic model of cold
bosonic atoms in optical lattices. We present a numerical study based on
quantum Monte Carlo simulations, analyzed in the framework of the trap-size
scaling (TSS).
We show how the critical parameters can be derived from the trap-size
dependences of appropriate observables, matching them with TSS. This provides a
systematic scheme which is supposed to exactly converge to the critical
parameters of the transition in the large trap-size limit. Our numerical
analysis may provide a guide for experimental investigations of trapped systems
at finite-temperature and quantum transitions, showing how critical parameters
may be determined by looking at the scaling of the critical modes with respect
to the trap size, i.e. by matching the trap-size dependence of the experimental
data with the expected TSS Ansatz
High-loop perturbative renormalization constants for Lattice QCD. I. Finite constants for Wilson quark currents.
No full textWe present a high order perturbative computation of the renormalization constants Z_V, Z_A and of the ratio Z_P/Z_S for Wilson fermions. The computational setup is the one provided by the RI'-MOM scheme. Three- and four-loop expansions are made possible by Numerical Stochastic Perturbation Theory. Results are given for various numbers of flavours and/or (within a finite accuracy) for generic n_f up to three loops. For the case n_f=2 we also present four-loop results. Finite size effects are well under control and the continuum limit is taken by means of hypercubic symmetric Taylor expansions. The main indetermination comes from truncation errors, which should be assessed in connection with convergence properties of the series. The latter is best discussed in the framework of Boosted Perturbation Theory, whose impact we try to assess carefully. Final results and their uncertainties show that high-loop perturbative computations of Lattice QCD RC's are feasible and should not be viewed as a second choice. As a by-product, we discuss the perturbative expansion for the critical mass, also for which results are for generic n_f up to three loops, while a four-loop result is obtained for n_f=2
Renormalization constants for Lattice QCD: New results from Numerical Stochastic Perturbation Theory
No full text
3-d lattice SU(3) free energy to four loops
No full textDi Renzo F, Mantovi A, Miccio V, Schroeder Y, Torrero C. 3-d lattice SU(3) free energy to four loops. In: Nuclear Physics B - Proceedings Supplements. Nucl. Phys. Proc. Suppl. Vol 140. Elsevier BV; 2005: 586-588.We report on the perturbative computation of the 3d lattice Yang-Mills free energy to four loops by means of Numerical Stochastic Perturbation Theory. The known first and second orders have been correctly reproduced: the third and fourth order coefficients are new results and the known logarithmic IR divergence in the fourth order has been correctly identified. Progress is being made in switching to the gluon mass IR regularization and the related inclusion of the Faddeev-Popov determinant
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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