16286511
Infrared exponents of gluon and ghost propagators from Lattice QCD
The compatibility of the pure power law infrared solution of QCD Dyson-Schwinger equations (DSE) and lattice data for the gluon and ghost propagators in Landau gauge is discussed. For the gluon propagator, the lattice data is compatible with the DSE infrared solution with an exponent $\kappa\sim0.53$, measured using a technique that suppresses finite volume effects and allows to model these corrections to the lattice data. For the ghost propagator, the lattice data does not seem to follow the infrared DSE power law solution.
118493159
Gluon screening mass at finite temperature from the Landau gauge gluon propagator in lattice QCD
We address the interpretation of the Landau gauge gluon propagator at finite temperature as a massive-type bosonic propagator. Using pure gauge SU(3) lattice simulations at a fixed lattice volume $\ensuremath{\sim}(6.5\text{ }\text{ }\mathrm{fm}{)}^{3}$, we compute the electric and magnetic form factors, extract a gluon mass from Yukawa-like fits, and study its temperature dependence. This is relevant both for the Debye screening at high temperature $T$ and for confinement at low $T$.
118792625
Some properties of two Nambu-Jona-Lasinio -type models with inputs from lattice QCD
IPNL, Universit´e de Lyon/Universit´e Lyon 1, CNRS/IN2P3, 4 rue E.Fermi,F-69622 Villeurbanne Cedex, FranceWe investigate the phase diagram of the so-called Polyakov–Nambu–Jona-Lasinio (PNJL) model at ﬁnite temperature and nonzero chemicalpotential. The calculations are performed in the light and strange quarksectors (u, d, s), which includes the ’t Hooft instanton induced interactionterm that breaks the axial symmetry, and the quarks are coupled to the(spatially constant) temporal background gauge ﬁeld. On one hand, a spe-cial attention is payed to the critical end point (CEP). The strength of theﬂavor-mixing interaction alters the CEP location, since when it becomesweaker the CEP moves to low temperatures and can even disappear. Onthe other hand, we also explore the connection between QCD, a nonlocalNambu–Jona-Lasinio type model and the Landau gauge gluon propaga-tor. Possible links between the quenched gluon propagator and low energyhadronic phenomenology are investigated.PACS numbers: 11.10.Wx, 11.30.Rd, 12.40.-y
15178500
Gauge fixing methods and Gribov copies effects in lattice QCD
We compare two Landau gauge fixing methods, aiming to find the global maximum of the gauge fixing functional. Moreover, a systematic effect of Gribov copies in the gluon and ghost propagators computed in Landau gauge is presented and discussed.
7542535
Exploring the infrared Landau gauge propagators using large asymmetric lattices
We report on the infrared limit of the quenched lattice Landau gauge gluon and ghost propagators computed from large asymmetric lattices. In particular, the compatibility of the pure power law infrared solutions of the Dyson-Schwinger equations with the lattice data is investigated and the exponent $\kappa$ is measured. The gluon lattice data favour $\kappa \sim 0.52$, which would imply a vanishing zero momentum gluon propagator. For the subset of lattices where the ghost propagator was computed, the data is not compatible with a pure power law. Our data also show a decreasing running coupling in the infrared region. Furthermore, positivity violation for the gluon propagator is also verified.
118845565
Spectral densities from the lattice
We discuss a method to extract the K\"all\'{e}n-Lehmann spectral density of a particle (be it elementary or bound state) propagator by means of 4d lattice data. We employ a linear regularization strategy, commonly known as the Tikhonov method with Morozov discrepancy principle. An important virtue over the popular maximum entropy method is the possibility to also probe unphysical spectral densities, as, for example, of a confined gluon. We apply our proposal to the SU(3) glue sector.
122619113
Infrared Finite Gluon Propagator and the Structure of Chiral Symmetry Breaking
We study the chiral symmetry breaking in QeD, using an effective potential for composite operators, with infrared finite gluon propagators that have been found by numerical calculation of the Schwinger· Dyson equations as well. as in lattice simulations. The existence of a gluon propagator that is finite at k 2 =O modifies substantially the transition between the phases with and without chiral symmetry.
51050384
Intercalibration of the barrel electromagnetic calorimeter of the CMS experiment at start-up
Calibration of the relative response of the individual channels of the barrel electromagnetic calorimeter of the CMS detector was accomplished, before installation, with cosmic ray muons and test beams. One fourth of the calorimeter was exposed to a beam of high energy electrons and the relative calibration of the channels, the intercalibration, was found to be reproducible to a precision of about 0.3%. Additionally, data were collected with cosmic rays for the entire ECAL barrel during the commissioning phase. By comparing the intercalibration constants obtained with the electron beam data with those from the cosmic ray data, it is demonstrated that the latter provide an intercalibration precision of 1.5% over most of the barrel ECAL. The best intercalibration precision is expected to come from the analysis of events collected in situ during the LHC operation. Using data collected with both electrons and pion beams, several aspects of the intercalibration procedures based on electrons or neutral pions were investigated.
1436056
Critical coupling for dynamical chiral-symmetry breaking with an infrared finite gluon propagator
Abstract We compute the critical coupling constant for the dynamical chiral-symmetry breaking in a model of quantum chromodynamics, solving numerically the quark self-energy using infrared finite gluon propagators found as solutions of the Schwinger-Dyson equation for the gluon, and one gluon propagator determined in numerical lattice simulations. The gluon mass scale screens the force responsible for the chiral breaking, and the transition occurs only for a larger critical coupling constant than the one obtained with the perturbative propagator. The critical coupling shows a great sensibility to the gluon mass scale variation, as well as to the functional form of the gluon propagator.
197509312
Jet and underlying event properties as a function of charged-particle multiplicity in proton–proton collisions at √s = 7 TeV
Characteristics of multi-particle production in proton-proton collisions at √ s = 7 TeV are studied as a function of the charged-particle multiplicity, Nch. The produced particles are separated into two classes: those belonging to jets and those belonging to the underlying event. Charged particles are measured with pseudorapidity |η| < 2.4 and transverse momentum pT > 0.25 GeV/c. Jets are reconstructed from chargedparticles only and required to have pT > 5 GeV/c. The distributions of jet pT, average pT of charged particles belonging to the underlying event or to jets, jet rates, and jet shapes are presented as functions of Nch and compared to the predictions of the PYTHIA and HERWIG event generators. Predictions without multi-parton interactions fail completely to describe the Nch-dependence observed in the data. For increasing Nch, PYTHIA systematically predicts higher jet rates and harder pT spectra than seen in the data, whereas HERWIG shows the opposite trends. At the highest multiplicity, the data–model agreement is worse for most observables, indicating the need for further tuning and/or new model ingredients. Published in the European Physical Journal C as doi:10.1140/epjc/s10052-013-2674-5. c © 2013 CERN for the benefit of the CMS Collaboration. CC-BY-3.0 license ∗See Appendix A for the list of collaboration members ar X iv :1 31 0. 45 54 v2 [ he pex ] 1 3 D ec 2 01 3 FERMILAB-PUB-13-627-CMS
118795909
Singlet Majorana fermion dark matter, DAMA, CoGeNT, and CDMS-II
We propose a model where a sterile Majorana fermion with mass in the range of 10 GeV-1 TeV can account for the whole amount of dark matter in the Universe. The model involves a right-handed singlet Majorana fermion as a weakly interacting massive particle, a charged and a neutral scalar, and all singlets by the standard model symmetry and makes use of a discrete symmetry in order to guarantee the singlet fermion stability. Also, motivated by the recent results reported by CoGeNT and CDMS-II experiments concerning excess events of the expected background, and the intriguing annual modulation observed by DAMA, we look for a possible explanation to some of these experiments. Our results show that there is a lot of room in the parameter space to make this sterile Majorana fermion a viable dark matter candidate, and, if it is realized in nature, it is also capable of explaining DAMA annual modulation signal and/or CoGeNT excess events or CDMS-II excess event candidates. Besides, a light Higgs boson is preferred in this scenario.