1,721,598 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
Thermal phase transitions in cosmology
No full textLaine M. Thermal phase transitions in cosmology. Presented at the COSMO-01, Rovaniemi, Finland
Lattice study of a magnetic contribution to heavy quark momentum diffusion
Full text linkHeavy quarks placed within a hot QCD medium undergo Brownian motion, characterized by specific transport coefficients. Their determination can be simplified by expanding them in T/M, where T is the temperature and M is a heavy quark mass. The leading term in the expansion originates from the colour-electric part of a Lorentz force, whereas the next-to-leading order involves the colour-magnetic part. We measure a colour-magnetic 2-point correlator in quenched QCD at T ∼ (1.2 − 2.0)Tc. Employing multilevel techniques and non-perturbative renormalization, a good signal is obtained, and its continuum extrapolation can be estimated. Modelling the shape of the corresponding spectral function, we subsequently extract the momentum diffusion coefficient, κ. For charm (bottom) quarks, the magnetic contribution adds ∼ 30% (10%) to the electric one. The same increases apply also to the drag coefficient, η. As an aside, the colour-magnetic spectral function is computed at NLO
What is the simplest effective approach to hot QCD thermodynamics?
No full textLaine M. What is the simplest effective approach to hot QCD thermodynamics? Presented at the SEWM 2002, Heidelberg, Germany
Finite baryon density effects on gauge field dynamics
No full textBödeker D, Laine M. Finite baryon density effects on gauge field dynamics. JHEP. 2001;109:029
Heavy quark chemical equilibration rate as a transport coefficient
No full textBödeker D, Laine M. Heavy quark chemical equilibration rate as a transport coefficient. JHEP. 2012;2012(7): 130.Motivated by indications that heavy (charm and bottom) quarks interactstrongly at temperatures generated in heavy ion collision experiments, wesuggest a non-perturbative definition of a heavy quark chemical equilibrationrate as a transport coefficient. Within leading-order perturbation theory(corresponding to 3-loop level), the definition is argued to reduce to anexpression obtained from the Boltzmann equation. Around T ~ 400 MeV, anorder-of-magnitude estimate for charm yields a rate Gamma^{-1}_{chem} > 60 fm/cwhich remains too slow to play a practical role in current experiments.However, the rate increases rapidly with T and, due to non-linear effects, alsoif the initial state contains an overabundance of heavy quarks
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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