Search results for "Reno"
showing 10 items of 1031 documents
Gauge-invariant resummation formalism for two-point correlation functions
1996
The consistent description of unstable particles, renormalons, or other Schwinger--Dyson-type of solutions within the framework of perturbative gauge field theories necessitates the definition and resummation of off-shell Green's functions, which must respect several crucial physical requirements. A formalism is presented for resummation of off-shell two-point correlation functions, which is mainly based on arguments of analyticity, unitarity, gauge invariance and renormalizability. The analytic results obtained with various methods, including the background field gauges and the pinch technique are confronted with the physical requirements imposed; to one-loop order the pinch technique appr…
Properties of Hadronic Z-decays and Test of QCD Generators
1992
Distributions are presented of event shape variables, jet roduction rates and charged particle momenta obtained from 53 000 hadronic Z decays. They are compared to the predictions of the QCD + hadronization models JETSET, ARIADNE and HERWIG, and are used to optimize several model parameters. The JETSET and ARIADNE coherent parton shower (PS) models with running alpha(s) and string fragmentation yield the best description of the data. The HERWIG parton shower model with cluster fragmentation fits the data less well. The data are in better agreement with JETSET PS than with JETSET O(alpha(s)2) matrix elements (ME) even when the renormalization scale is optimized.
New High Order Relations between Physical Observables in Perturbative QCD
1997
We exploit the fact that within massless perturbative QCD the same Green's function determines the hadronic contribution to the $\tau$ decay width and the moments of the $e^+e^-$ cross section. This allows one to obtain relations between physical observables in the two processes up to an unprecedented high order of perturbative QCD. A precision measurement of the $\tau$ decay width allows one then to predict the first few moments of the spectral density in $e^+e^-$ annihilations integrated up to $s\sim m_\tau^2$ with high accuracy. The proposed tests are in reach of present experimental capabilities.
QCD effective charges from lattice data
2010
We use recent lattice data on the gluon and ghost propagators, as well as the Kugo-Ojima function, in order to extract the non-perturbative behavior of two particular definitions of the QCD effective charge, one based on the pinch technique construction, and one obtained from the standard ghost-gluon vertex. The construction relies crucially on the definition of two dimensionful quantities, which are invariant under the renormalization group, and are built out of very particular combinations of the aforementioned Green's functions. The main non-perturbative feature of both effective charges, encoded in the infrared finiteness of the gluon propagator and ghost dressing function used in their…
Determination of 55-155-155-1in second order QCD from hadronic Z decays
1992
Distributions of event shape variables obtained from 120600 hadronic Z decays measured with the DELPHI detector are compared to the predictions of QCD based event generators. Values of the strong coupling constant αs are derived as a function of the renormalization scale from a quantitative analysis of eight hadronic distributions. The final result, αs(MZ), is based on second order perturbation theory and uses two hadronization corrections, one computed with a parton shower model and the other with a QCD matrix element model. © 1992 Springer-Verlag.
Generalized on-shell renormalization of heavy quarks
1992
A generalized on-shell (GOS) renormalization scheme of QCD is developed to evaluate the renormalization of heavy quark wave functions and currents. All large logarithms arising from the physical range of quark masses and momentum transferq 2 can be absorbed into wave function and vertex renormalization. Our results are more general than those of the heavy quark effective theory and agree with the latter only at zero recoil. The proposed GOS scheme is very suitable for the μ/m Q expansion. As an application we discuss the renormalization of the flavour changing currentsb-c, t-b andt-c.
Improving the kinetic couplings in lattice nonrelativistic QCD
2019
We improve the non-relativistic QCD (NRQCD) action by comparing the dispersion relation to that of the continuum through $\mathcal{O}(p^6)$ in perturbation theory. The one-loop matching coefficients of the $\mathcal{O}(p^4)$ kinetic operators are determined, as well as the scale at which to evaluate $\alpha_s$ in the $V$-scheme for each quantity. We utilise automated lattice perturbation theory using twisted boundary conditions as an infrared regulator. The one-loop radiative corrections to the mass renormalisation, zero-point energy and overall energy-shift of an NRQCD $b$-quark are also found. We also explore how a Fat$3$-smeared NRQCD action and changes of the stability parameter $n$ aff…
Incommensurate phases of a bosonic two-leg ladder under a flux
2016
A boson two--leg ladder in the presence of a synthetic magnetic flux is investigated by means of bosonization techniques and Density Matrix Renormalization Group (DMRG). We follow the quantum phase transition from the commensurate Meissner to the incommensurate vortex phase with increasing flux at different fillings. When the applied flux is $\rho \pi$ and close to it, where $\rho$ is the filling per rung, we find a second incommensuration in the vortex state that affects physical observables such as the momentum distribution, the rung-rung correlation function and the spin-spin and charge-charge static structure factors.
Nonequilibrium critical scaling in quantum thermodynamics
2016
The emerging field of quantum thermodynamics is contributing important results and insights into archetypal many-body problems, including quantum phase transitions. Still, the question whether out-of-equilibrium quantities, such as fluctuations of work, exhibit critical scaling after a sudden quench in a closed system has remained elusive. Here, we take a novel approach to the problem by studying a quench across an impurity quantum critical point. By performing density matrix renormalization group computations on the two-impurity Kondo model, we are able to establish that the irreversible work produced in a quench exhibits finite-size scaling at quantum criticality. This scaling faithfully …
Flavour Conservation in Two Higgs Doublet Models
2018
In extensions of the Standard Model with two Higgs doublets, flavour changing Yukawa couplings of the neutral scalars may be present at tree level. In this work we consider the most general scenario in which those flavour changing couplings are absent. We re-analyse the conditions that the Yukawa coupling matrices must obey for such \emph{general flavour conservation} (gFC), and study the one loop renormalisation group evolution of such conditions in both the quark and lepton sectors. We show that gFC in the leptonic sector is one loop stable under the Renormalization Group Evolution (RGE) and in the quark sector we present some new Cabibbo like solution also one loop RGE stable. At a pheno…