Claudio Bonati

Axion phenomenology and θ-dependence from N f = 2 + 1 lattice QCD

A bstractWe investigate the topological properties of Nf = 2 + 1 QCD with physical quark masses, both at zero and finite temperature. We adopt stout improved staggered fermions and explore a range of lattice spacings a ∼ 0.05 − 0.12 fm. At zero temperature we estimate both finite size and finite cut-off effects, comparing our continuum extrapolated results for the topological susceptibility χ with predictions from chiral perturbation theory. At finite temperature, we explore a region going from Tc up to around 4 Tc, where we provide continuum extrapolated results for the topological susceptibility and for the fourth moment of the topological charge distribution. While the latter converges to the dilute instanton gas prediction the former differs strongly both in the size and in the temperature dependence. This results in a shift of the axion dark matter window of almost one order of magnitude with respect to the instanton computation.

QCD simulations with staggered fermions on GPUs

Abstract We report on our implementation of the RHMC algorithm for the simulation of lattice QCD with two staggered flavors on Graphics Processing Units, using the NVIDIA CUDA programming language. The main feature of our code is that the GPU is not used just as an accelerator, but instead the whole Molecular Dynamics trajectory is performed on it. After pointing out the main bottlenecks and how to circumvent them, we discuss the obtained performances. We present some preliminary results regarding OpenCL and multiGPU extensions of our code and discuss future perspectives.

Topology and θ dependence in finite temperature G 2 lattice gauge theory

A bstractIn this work we study the topological properties of the G2 lattice gauge theory by means of Monte Carlo simulations. We focus on the behaviour of topological quantities across the deconfinement transition and investigate observables related to the θ dependence of the free energy. As in SU(N) gauge theories, an abrupt change happens at deconfinement and an instanton gas behaviour rapidly sets in for T > Tc.

High-performance solution of the transport problem in a graphene armchair structure with a generic potential.

We propose an efficient numerical method to study the transport properties of armchair graphene ribbons in the presence of a generic external potential. The method is based on a continuum envelope-function description with physical boundary conditions. The envelope functions are computed in the reciprocal space, and the transmission is then obtained with a recursive scattering matrix approach. This allows a significant reduction of the computational time with respect to finite difference simulations.

Finite temperature effective string corrections in (3+1)D SU(2) lattice gauge theory

Abstract We study the effective string corrections to the inter-quark potential at finite temperature by simulating the SU ( 2 ) lattice gauge theory in four dimensions. We provide the first numerical evidence that the logarithmic correction to the potential, which was recently proposed to be a signature of the effective string at finite temperature, is universal also in ( 3 + 1 ) D gauge theory, thus extending previous results limited to the ( 2 + 1 ) D case.

Recent progress on QCD inputs for axion phenomenology

The properties of the QCD axion are strictly related to the dependence of strong interactions on the topological parameter theta. We present a determination of the topological properties of QCD for temperatures up to around 600 MeV, obtained by lattice QCD simulations with 2+1 flavors and physical quark masses. Numerical results for the topological susceptibility, when compared to instanton gas computations, differ both in size and in the temperature dependence. We discuss the implications of such findings for axion phenomenology, also in comparison to similar studies in the literature, and the prospects for future investigations.

Roberge-Weiss endpoint at the physical point of N f = 2 + 1 QCD

We study the phase diagram of

Three-dimensional, three-state Potts model in a negative external field

{N}_{f}=2+1

The Peierls argument for higher dimensional Ising models

QCD in the

Variations in the Magnetic Torque Acting on a Wire.

Tensuremath{-}{ensuremath{mu}}_{B}