Search results for "Computer Science Application"
showing 10 items of 3998 documents
Accuracy of Rotational Parameters Predicted by High-Level Quantum-Chemical Calculations: Case Study of Sulfur-Containing Molecules of Astrochemical I…
2018
The accuracy of rotational parameters obtained from high-level quantum-chemical calculations is discussed for molecules containing second-row atoms. The main focus is on computed rotational constants for which two statistical analyses have been carried out. A first benchmark study concerns sulfur-bearing species and involves 15 molecules (for a total of 74 isotopologues). By comparing 15 different computational approaches, all of them based on the coupled-cluster singles and doubles approach (CCSD) augmented by a perturbative treatment of triple excitations, CCSD(T), we have analyzed the effects on computed rotational constants due to (i) extrapolation to the complete basis-set limit, (ii) …
Unraveling the organization of the QCD tapestry
2015
I review some key aspects of the ongoing progress in our understanding of the infrared dynamics of the QCD Green's functions, derived from the close synergy between Schwinger-Dyson equations and lattice simulations. Particular attention is dedicated to the elaborate nonperturbative mechanisms that endow the fundamental degrees of freedom (quarks and gluons) with dynamical masses. In addition, the recently established connection between the effective interaction obtained from the gauge sector of the theory and that needed for the veracious description of the ground-state properties of hadrons is briefly presented.
Gluon mass and freezing of the QCD coupling
2007
Infrared finite solutions for the gluon propagator of pure QCD are obtained from the gauge-invariant non-linear Schwinger-Dyson equation formulated in the Feynman gauge of the background field method. These solutions may be fitted using a massive propagator, with the special characteristic that the effective mass employed drops asymptotically as the inverse square of the momentum transfer, in agreement with general operator-product expansion arguments. Due to the presence of the dynamical gluon mass the strong effective charge extracted from these solutions freezes at a finite value, giving rise to an infrared fixed point for QCD.
Parity violating electron scattering at MAMI
2012
The investigation of the structure of the nucleon can help to understand the non-pertubative regime of the QCD. In the viewpoint of QCD, the nucleon is made up of constituent quarks, sea quarks and gluons. The nucleon structure can be described by the electromagnetic form factors. Parity violating electron scattering offers a tool to investigate the strange quark contribution to the nucleon form factors. Such measurements are carried out at the electron accelerator facility MAMI at Mainz. Recent results are presented here.
Constraining nonstandard neutrino-quark interactions with solar, reactor and accelerator data
2009
We present a reanalysis of nonstandard neutrino-down-quark interactions of electron and tau neutrinos using solar, reactor and accelerator data. In addition updating the analysis by including new solar data from SNO phase III and Borexino, as well as new KamLAND data and solar fluxes, a key role is played in our analysis by the combination of these results with the CHARM data. The latter allows us to better constrain the axial and axial-vector electron and tau-neutrino nonstandard interaction parameters characterizing the deviations from the Standard Model predictions.
Light-front transverse charge densities
2010
We discuss the recent interpretation of quark-distribution functions in the plane transverse to the light-cone direction. Such a mapping is model independent and allows one to build up multidimensional pictures of the hadron and to develop a semi-classical interpretation of the quark dynamics. We comment briefly the results obtained from the form factors of the nucleon. We show that a generalization to a target with arbitrary spin leads to a set of preferred values for the electromagnetic coupling characterizing structureless particles. Finally, we present the Wigner distribution for an unpolarized quark in an unpolarized proton and we propose an interpretation of the observed distortion as…
Kl3form factor withNf= 2 +1 dynamical domain wall fermions
2008
We present the latest results from the UKQCD/RBC collaborations for the Kl3 form factor from simulations with 2 + 1 flavours of dynamical domain wall quarks. Simulations are performed on lattices with two different volumes and four values of the light quark mass, allowing for an extrapolation to the chiral limit. The analysis includes a thorough investigation into the sources of systematic error in our fits. After interpolating to zero momentum transfer, we obtain f+(0) = 0.964(5) (or ?f = -0.013(5)) which, when combined with the latest experimental results for Kl3 decays, leads to |Vus| = 0.2249(14).
Isospin-breaking contributions to ε ′ / ε
2020
Abstract We present an updated analysis of isospin-violating corrections to ε ′/ε in the framework of chiral perturbation theory, taking advantage of the currently improved knowledge on quark masses and nonperturbative parameters. The role of the different ingredients entering into the analysis is carefully assessed. Our final result is Ω eff = 0.110 − 0.088 + 0.090 [1].
Vector-like quarks and New Physics in the flavour sector
2013
We present a detailed analysis of recent flavour data in the framework of a simple extension of the Standard Model, where a Q = 2/3 vector-like isosinglet quark is added to the spectrum. Constraints from all the relevant quark flavour sectors are used. Important deviations from Standard Model expectations in different observables such as the semileptonic asymmetry in Bd decays, AdSL, the time-dependent CP asymmetry in Bs ? J/??, and rare decays such as K+ ? ?+? can be obtained.
Flavour Symmetries and SUSY Soft Breaking in the LHC Era
2007
The so-called supersymmetric flavour problem does not exist in isolation to the Standard Model flavour problem. We show that a realistic flavour symmetry can simultaneously solve both problems without ad hoc modifications of the SUSY model. Furthermore, departures from the SM expectations in these models can be used to discriminate among different possibilities. In particular we present the expected values for the electron EDM in a flavour model solving the supersymmetric flavour and CP problems.