62820378
Glueball spectral densities from the lattice
The propagator of a physical degree of freedom ought to obey a Kallen-Lehmann spectral representation, with positive spectral density. The latter quan tity is directly related to a cross section based on the optical theorem. The spectral density is a crucial ingredient of a quantum field theory with elementary and bound states, with a direct experimental connection as the masses of the excitations reflect themselves into (continuum) δ -singularities. In usual lattice simulational approaches to the QCD spectrum the spectral density itself is not accessed. The (bound state) masses are extracted from the asymptotic exponential decay of the two-point function. Given the importance of the spectral density, each nonperturbative continuum approach to QCD should be able to adequately describe it or to take into proper account . In this work, we wish to present a first trial in extracting an estimate for the scalar glueball spectral density in SU(3) gluodynamics using lattice gauge theory.
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 $T$.
117914077
Force Gradient Integrators
We present initial results of the use of Force Gradient integ rators for lattice field theories. These promise to give significant performance improvements, espe cially for light fermions and large lattices. Our results show that this is indeed the case, indi cating a speed-up of more than a factor of two, which is expected to increase as the integration step size becomes smaller for larger lattices and smaller fermion masses.
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.
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
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.
56306636
Light composite Higgs from an effective action for technicolor
We compute an effective action for a composite Higgs boson formed by new fermions belonging to a general technicolor non-Abelian gauge theory, using a quite general expression for the fermionic self-energy that depends on a certain parameter ($\ensuremath{\alpha}$), that defines the technicolor theory from the extreme walking behavior up to the one with a standard operator product expansion behavior. We discuss the values of the trilinear and quadrilinear scalar couplings. Our calculation spans all the possible physical possibilities for mass and couplings of the composite system. In the case of extreme walking technicolor theories we verify that it is possible to have a composite Higgs boson with a mass as light as the present experimental limit, contrary to the usual expectation of a heavy mass for the composite Higgs boson. In this case we obtain an upper limit for the Higgs boson mass, (${M}_{H}\ensuremath{\le}\mathcal{O}(700)\text{ }\text{ }\mathrm{GeV}$ for $SU(2{)}_{\mathrm{TC}}$), and the experimental data on the Higgs boson mass constrain $SU(N{)}_{\mathrm{TC}}$ technicolor gauge groups to be smaller than $SU(10{)}_{\mathrm{TC}}$.
122731585
Search for $B^0_s \to \mu^+ \mu^-$ and $B^0 \to \mu^+ \mu^-$ decays
A search for the rare decays B_s to mu+ mu- and B^0 to mu^+ mu^- is performed in pp collisions at sqrt(s) = 7 TeV, with a data sample corresponding to an integrated luminosity of 5 inverse femtobarns collected by the CMS experiment at the LHC. In both decays, the number of events observed after all selection requirements is consistent with the expectation from background plus standard model signal predictions. The resulting upper limits on the branching fractions are Br(B_s to mu^+ mu^-) < 7.7E-9 and Br(B^0 to mu^+ mu^-) < 1.8E-9 at 95% confidence level.
110352212
Energy reconstruction for a hadronic calorimeter using neural networks
Abstract Often calorimeters have a non-compensating response ( e / h ≠ 1 ) . Non-compensation degrades both resolution and linearity figures. To improve on this, weighting techniques are frequently applied. These techniques normally use linear combination of the energy deposited in the calorimeter cells or longitudinal samples. For the hadronic calorimeter of ATLAS, Tilecal, the use of a neural network is proposed to perform the energy reconstruction for pions, taking into account both linearity and energy resolution. Experimental data from testbeam periods were used to perform neural reconstruction.
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.
14228967
Bounds on the simplest little Higgs model mass spectrum through Z leptonic decay
We derive the leptonic neutral current in the simplest little Higgs model and compute the contribution of the model to the decay width $Z\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}$. Using the precision electroweak data we obtain a strong lower bound $f\ensuremath{\ge}5.6\text{ }\text{ }\mathrm{TeV}$ at 95% C.L. on the characteristic energy scale of the model. It results in a lower bound for the new gauge bosons ${W}^{\ensuremath{'}\ifmmode\pm\else\textpm\fi{}}$ and ${Z}^{\ensuremath{'}}$ as being ${M}_{{W}^{\ensuremath{'}\ifmmode\pm\else\textpm\fi{}}}\ensuremath{\ge}2.6\text{ }\text{ }\mathrm{TeV}$ and ${M}_{{Z}^{\ensuremath{'}}}\ensuremath{\ge}3.1\text{ }\text{ }\mathrm{TeV}$, respectively. We also present the allowed values of the $k={f}_{1}/{f}_{2}$ which is the parameter relating the two vacuum expectation values of the scalar triplets in the model, and the $\ensuremath{\mu}$ parameter of a quadratic term, involving the triplets, necessary to provide an acceptable mass range for the standard Higgs boson.