Hadron-Hadron Interactions from Nf=2+1+1N_f=2+1+1 Lattice QCD: isospin-1 KKKK scattering length

We present results for the interaction of two kaons at maximal isospin. The calculation is based on $N_f=2+1+1$ flavour gauge configurations generated by the European Twisted Mass Collaboration with pion masses ranging from about $230$ to $450\,\textrm{MeV}$ at three values of the lattice spacing. The elastic scattering length $a_0^{I=1}$ is calculated at several values of the bare strange and light quark masses. We find $M_K a_0 = -0.385(16)_{\textrm{stat}} (^{+0}_{-12})_{m_s}(^{+0}_{-5})_{Z_P}(4)_{r_f}$ as the result of a combined extrapolation to the continuum and to the physical point, where the first error is statistical, and the three following are systematical. This translates to $a_0 = -0.154(6)_{\textrm{stat}}(^{+0}_{-5})_{m_s} (^{+0}_{-2})_{Z_P}(2)_{r_f}\,\textrm{fm}$.Comment: 28 pages, 18 tables, 14 figure

Recent developments in the tmLQCD software suite

We present an overview of recent developments in the tmLQCD software suite. We summarise the features of the code, including actions and operators implemented. In particular, we discuss the optimisation efforts for modern architectures using the Blue Gene/Q system as an example.Comment: presented at the 31st International Symposium on Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013, Mainz, German

Meson-meson scattering lengths at maximum isospin from lattice QCD

We summarize our lattice QCD determinations of the pion-pion, pion-kaon and kaon-kaon s-wave scattering lengths at maximal isospin with a particular focus on the extrapolation to the physical point and the usage of next-to-leading order chiral perturbation theory to do so. We employ data at three values of the lattice spacing and pion masses ranging from around 230 MeV to around 450 MeV, applying Luescher's finite volume method to compute the scattering lengths. We find that leading order chiral perturbation theory is surprisingly close to our data even in the kaon-kaon case for our entire range of pion masses.Comment: 10 pages, 8 figures, Presented at the 9th International Workshop on Chiral Dynamics, Sept. 17-21, 2018, Duke University, Durham, NC, USA , submitted to PoS, (C18-09-17.6). Funding acknowledgements added in v2 replacement, comma added in abstract. In v3 replacement, corrected typo in equation 6.2 which was referring to the pion-kaon reduced mass instead of the pion mas

Hadron-Hadron Interactions from Nf=2+1+1N_f=2+1+1 Lattice QCD: I=3/2I=3/2 πK\pi K Scattering Length

In this paper we report on results for the s-wave scattering length of the $\pi$-$K$ system in the $I=3/2$ channel from $N_f=2+1+1$ Lattice QCD. The calculation is based on gauge configurations generated by the European Twisted Mass Collaboration with pion masses ranging from about $230$ to $450\,\text{MeV}$ at three values of the lattice spacing. Our main result reads $M_{\pi}\,a_0^{3/2,\text{phys}} = -0.059(2)$. Using chiral perturbation theory we are also able to estimate $M_{\pi}\,a_0^{1/2,\text{phys}} = 0.163(3)$. The error includes statistical and systematic uncertainties, and for the latter in particular errors from the chiral and continuum extrapolations.Comment: 30 pages, 6 figures, 15 table

The η′\eta^\prime meson at the physical point with Nf=2N_f=2 Wilson twisted mass fermions

We present results for the eta prime meson and the topological susceptibility in two flavour lattice QCD. The results are obtained using Wilson twisted mass fermions at maximal twist with pion masses ranging from 340 MeV down to the physical point. A comparison to literature values is performed giving a handle on discretisation effects.Comment: Lattice 2017 proceeding contributio

Scattering of two and three physical pions at maximal isospin from lattice QCD

We present the first direct $N_f=2$ lattice QCD computation of two- and three-$\pi^+$ scattering quantities that includes an ensemble at the physical point. We study the quark mass dependence of the two-pion phase shift, and the three-particle interaction parameters. We also compare to phenomenology and chiral perturbation theory (ChPT). In the two-particle sector, we observe good agreement to the phenomenological fits in $s$- and $d$-wave, and obtain $M_\pi a_0 = -0.0481(86)$ at the physical point from a direct computation. In the three-particle sector, we observe reasonable agreement at threshold to the leading order chiral expansion, i.e.\@ a mildly attractive three-particle contact term. In contrast, we observe that the energy-dependent part of the three-particle quasilocal scattering quantity is not well described by leading order ChPT.Comment: Major reformatting. Increased number of configurations in one ensembl

Role of gadolinium-based contrast agents in neurological disorders

Gadolinium-based contrast agents (GBCAs) are widely used in magnetic resonance imaging (MRI) to help with the diagnostic and monitoring processes of many diseases, including neurological disorders. Initially, it was assumed that GBCAs carry minimal risk, are safe and well tolerated. But recent reports of GBCA-associated deposition in many body tissues have raised concerns about the broader health impacts of gadolinium exposure. The aim of this review was to summarise knowledge regarding gadolinium deposition, primarily in the brain structures, and of potential GBCA-associated toxicity. Moreover, we discuss the current recommendations on the use of GBCAs, as well as alternative contrast agents and imaging techniques

Dynamical Generation of Elementary Fermion Mass: First Lattice Evidence

Using lattice simulations we demonstrate from first principles the existence of a non-perturbative mechanism for elementary particle mass generation in models with gauge fields, fermions and scalars, if an exact invariance forbids power divergent fermion masses and fermionic chiral symmetries broken at UV scale are maximally restored. We show that in the Nambu-Goldstone phase a fermion mass term, unrelated to the Yukawa operator, is dynamically generated. In models with electro-weak interactions weak boson masses are also generated opening new scenarios for beyond the Standard Model physics.Comment: 24 pages, 17 figure

On the generalised eigenvalue method and its relation to Prony and generalised pencil of function methods

We discuss the relation of three methods to determine energy levels in lattice QCD simulations: the generalised eigenvalue, the Prony and the generalised pencil of function methods. All three can be understood as special cases of a generalised eigenvalue problem. We show analytically that the leading corrections to an energy $E_l$ in all three methods due to unresolved states decay asymptotically exponentially like $\exp(-(E_{n}-E_l)t)$. Using synthetic data we show that these corrections behave as expected also in practice. We propose a novel combination of the generalised eigenvalue and the Prony method, denoted as GEVM/PGEVM, which helps to increase the energy gap $E_{n}-E_l$. We illustrate its usage and performance using lattice QCD examples