Elisabetta Pallante

Light hadrons from lattice QCD with light (u, d), strange and charm dynamical quarks

We present results of lattice QCD simulations with mass-degenerate up and down and mass-split strange and charm (Nf = 2 + 1 + 1) dynamical quarks using Wilson twisted mass fermions at maximal twist. The tuning of the strange and charm quark masses is performed at two values of the lattice spacing a ≈ 0:078 fm and a ≈ 0:086 fm with lattice sizes ranging from L ≈ 1:9 fm to L ≈ 2:8 fm. We measure with high statistical precision the light pseudoscalar mass mPS and decay constant fPS in a range 270 ≲ mPS ≲ 510 MeV and determine the low energy parameters f0 and

QCD and strongly coupled gauge theories: challenges and perspectives

{\bar{l}_{3,4}}

Comment on the pion pole part of the light-by-light contribution to the muon g − 2

of SU(2) chiral perturbation theory. We use the two values of the lattice spacing, several lattice sizes as well as different values of the light, strange and charm quark masses to explore the systematic effects. A first study of discretisation effects in light-quark observables and a comparison to Nf = 2 results are performed.

Analysis of the hadronic light-by-light contributions to the muon g - 2

We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.

Evidence for a conformal phase in SU(N) gauge theories

We comment on the recent calculations of the pion pole part of the light-by-light contribution to the muon anomalous magnetic moment and we point out where the analysis in our previous work was mistaken.

The physics of eight flavours

We calculate the hadronic light-by-light contributions to the muon g - 2. We use both 1/Nc and chiral counting to organize the calculation. Then we calculate the leading and next-to-leading order in the 1/Nc expansion low energy contributions using the Extended Nambu-Jona-Lasinio model as hadronic model. We do that to all orders in the external momenta and quark masses expansion. Although the hadronic light-by-light contributions to muon g - 2 are not saturated by these low energy contributions we estimate them conservatively. A detailed analysis of the different hadronic light-by-light contributions to muon g - 2 is done. The dominant contribution light-by-light is the twice anomalous pseudoscalar exchange diagram. The final result we get is aµlight-by-light = (-9.2±3.2) A— 10-10. This is between two and three times the expected experimental uncertainty at the forthcoming BNL muon g - 2 experiment.

Hyperon–nucleon scattering from fully-dynamical lattice QCD

We discuss the existence of a conformal phase in SU(N) gauge theories in four dimensions. In this lattice study, we explore the model in the bare parameter space, varying the lattice coupling and bare mass. Simulations are carried out with three colors and 12 flavors of dynamical staggered fermions in the fundamental representation. The analysis of the chiral order parameter and the mass spectrum of the theory indicates the restoration of chiral symmetry at zero temperature and the presence of a Coulomb-like phase, depicting a scenario compatible with the existence of an infrared stable fixed point at nonzero coupling. Our analysis supports the conclusion that the onset of the conformal window for QCD-like theories is smaller than N(f) = 12, before the loss of asymptotic freedom at 16 and 1/ 2 flavors. We discuss open questions and future directions.

Computing K and D meson masses with N_f = 2+1+1 twisted mass lattice QCD

Abstract We study Quantum Chromodynamics with eight flavours by use of lattice simulations and present evidence that the theory still breaks chiral symmetry in the zero temperature, continuum limit. This confirms that the lower end of the conformal window of QCD lies above N f = 8 .

Light hadrons from Nf=2+1+1 dynamical twisted mass fermions

Abstract We present results of the first fully-dynamical lattice QCD determination of hyperon–nucleon scattering. One s-wave phase shift was determined for nΛ scattering in both spin-channels at pion masses of 350, 490 and 590 MeV, and for n Σ − scattering in both spin channels at pion masses of 490 and 590 MeV. The calculations were performed with domain-wall valence quarks on dynamical, staggered gauge configurations with a lattice spacing of b ∼ 0.125 fm .

Computing K and D meson masses with N-f=2+1+1 twisted mass lattice QCD

We discuss the computation of the mass of the K and D mesons within the framework of N-f = 2 + 1 + 1 twisted mass lattice QCD from a technical point of view. These quantities are essential, already at the level of generating gauge configurations, being obvious candidates to tune the strange and charm quark masses to their physical values. In particular, we address the problems related to the twisted mass flavor and parity symmetry breaking, which arise when considering a non-degenerate (c, s) doublet. We propose and verify the consistency of three methods to extract the K and D meson masses in this framework. (c) 2010 Elsevier By. All rights reserved.