Search results for "Qcd"
showing 10 items of 614 documents
Progress in three-particle scattering from LQCD
2017
We present the status of our formalism for extracting three-particle scattering observables from lattice QCD (LQCD). The method relies on relating the discrete finite-volume spectrum of a quantum field theory with its scattering amplitudes. As the finite-volume spectrum can be directly determined in LQCD, this provides a method for determining scattering observables, and associated resonance properties, from the underlying theory. In a pair of papers published over the last two years, two of us have extended this approach to apply to relativistic three-particle scattering states. In this talk we summarize recent progress in checking and further extending this result. We describe an extensio…
Strongly interacting matter under external magnetic fields within nonlocal NJL-type models
2017
We study the behavior of strongly interacting matter under an external magnetic field in the context of nonlocal Nambu-Jona-Lasinio (NJL) -like models. We find that at zero temperature the condensates display the well-known Magnetic Catalysis effect, showing a good quantitative agreement with lattice QCD (LQCD) results. Moreover, when extended to finite temperature we find that (contrary to what happens in the local NJL model) the Inverse Magnetic Catalysis (IMC) effect is naturally incorporated. We also analyze the magnetic susceptibility of the QCD vacuum in the limit of small magnetic field, considering two different model parametrizations, and compare our numerical results to those obta…
Form factors for semileptonic B -> pi and D -> pi decays from the Omnes representation
2000
We use the Omnes representation to obtain the q-squared dependence of the form factors f+ and f0 for semileptonic H -> pi decays from the elastic pi H -> pi H scattering amplitudes, where H denotes a B or D meson. The scattering amplitudes used satisfy elastic unitarity and are calculated from two-particle irreducible amplitudes obtained using tree-level heavy meson chiral perturbation theory (HMChPT). The q-squared dependences for the form factors agree with lattice QCD results when the HMChPT coupling constant, g, takes values smaller than 0.32, and confirm the milder dependence of f0 on q-squared found in sumrule calculations.
Vector screening masses in the quark–gluon plasma and their physical significance
2014
Static and non-static thermal screening states that couple to the conserved vector current are investigated in the high-temperature phase of QCD. Their masses and couplings to the current are determined at weak coupling, as well as using two-flavor lattice QCD simulations. A consistent picture emerges from the comparison, providing evidence that non-static Matsubara modes can indeed be treated perturbatively. We elaborate on the physical significance of the screening masses.
The spin-dependent structure function g1(x) of the deuteron from polarized deep-inelastic muon scattering
1997
We present a new measurement of the spin-dependent structure function $g_{1}^{\rm d}$ of the deuteron from deep inelastic scattering of 190 GeV polarized muons on polarized deuterons. The results are combined with our previous measurements of $g_{1}^{\rm d}$. A perturbative QCD evolution in next-to-leading order is used to compute $g_{1}^{\rm d}(x)$ at a constant $Q^{2}$. At $Q^{2} = 10$ GeV$^{2}$, we obtain a first moment $\Gamma_{1}^{\rm d} = \int_{0}^{1} g_{1}^{\rm d}{\rm d}x = 0.041 \pm 0.008$, a flavour-singlet axial charge of the nucleon $a_{0} = 0.30 \pm 0.08$, and an axial charge of the strange quark $a_{s} = -0.09 \pm 0.03$. Using our earlier determination of $\Gamma_{1}^{\rm p}$, …
Lattice quantum hadrodynamics
1992
Quantum corrections to the mean-field equation of state for nuclear matter are estimated in a lattice simulation of quantum hadrodynamics. In contrast with the standard coordinate-space methods used in lattice QCD, the calculations are carried out here in momentum space and on nonhypercubic (irregular) lattices. The quantum corrections to the known mean-field equation of state were found to be considerable.
K --> pi pi matrix elements beyond the leading-order chiral expansion
2002
We propose an approach for calculating $K\to\pi\pi$ decays to the next-to-leading order in chiral expansion. A detailed numerical study of this approach is being performed.
Relativistic, model-independent, multichannel $2\to2$ transition amplitudes in a finite volume
2016
We derive formalism for determining $\textbf{2} + \mathcal J \to \textbf{2}$ infinite-volume transition amplitudes from finite-volume matrix elements. Specifically, we present a relativistic, model-independent relation between finite-volume matrix elements of external currents and the physically observable infinite-volume matrix elements involving two-particle asymptotic states. The result presented holds for states composed of two scalar bosons. These can be identical or non-identical and, in the latter case, can be either degenerate or non-degenerate. We further accommodate any number of strongly-coupled two-scalar channels. This formalism will, for example, allow future lattice QCD calcu…
Extracting three-body observables from finite-volume quantities
2015
Scattering and transition amplitudes with three-hadron final states play an important role in nuclear and particle physics. However, predicting such quantities using numerical Lattice QCD is very difficult, in part because of the effects of Euclidean time and finite volume. In this review we highlight recent formal developments that work towards overcoming these issues. We organize the presentation into three parts: large volume expansions, non-relativistic nonperturbative analyses, and nonperturbative studies based in relativistic field theory. In the first part we discuss results for ground state energies and matrix elements given by expanding in inverse box length, $1/L$. We describe com…
Two- and Three-Pion Finite-Volume Spectra at Maximal Isospin from Lattice QCD.
2019
We present the three-pion spectrum with maximal isospin in a finite volume determined from lattice QCD, including excited states in addition to the ground states across various irreducible representations at zero and nonzero total momentum. The required correlation functions, from which the spectrum is extracted, are computed using a newly implemented algorithm which speeds up the computation by more than an order of magnitude. On a subset of the data we extract a nonzero value of the three-pion threshold scattering amplitude using the $1/L$ expansion of the three-particle quantization condition, which consistently describes all states at zero total momentum. The finite-volume spectrum is p…