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Abstract: The Prokof’ev–Svistunov worm algorithm was originally developed for models with nearest neighbor interactions that in a high temperature expansion are mapped to systems of closed loops. In this work we present the surface worm algorithm (SWA) which is a generalization of the worm algorithm concept to abelian Gauge–Higgs models on a lattice which can be mapped to systems of surfaces and loops (dual representation). Using Gauge–Higgs models with gauge groups and U(1) we compare the SWA to the conventional approach and to a local update in the dual representation. For the case we also consider finite chemical potential where the conventional representation has a sign problem which is overcome in the dual representation. For a wide range of parameters we find that the SWA clearly outperforms the local update. [Copyright &y& Elsevier]

We investigate the distribution of instanton sizes in the framework of a simplified model for ensembles of instantons. This model takes into account the non-diluteness of instantons. The infrared problem for the integration over instanton sizes is dealt with in a self-consistent manner by approximating instanton interactions by a repulsive hard core potential. This leads to a dynamical suppression of large instantons. The characteristic features of the instanton size distribution are studied by means of analytic and Monte Carlo methods. In one dimension exact results can be derived. In any dimension we find a power law behaviour for small sizes, consistent with the semiclassical results. At large instanton sizes the distribution decays exponentially. The results are compared with those from lattice simulations. [Copyright &y& Elsevier]

We present the first public version of Caravel , a C++17 framework for the computation of multi-loop scattering amplitudes in quantum field theory, based on the numerical unitarity method. Caravel is composed of modules for the D -dimensional decomposition of integrands of scattering amplitudes into master and surface terms, the computation of tree-level amplitudes in floating point or finite-field arithmetic, the numerical computation of one- and two-loop amplitudes in QCD and Einstein gravity, and functional reconstruction tools. We provide programs that showcase Caravel 's main functionalities and allow to compute selected one- and two-loop amplitudes. Program Title: Caravel CPC Library link to program files: https://doi.org/10.17632/rfjrxrb3rk.1 Developer's repository link: https://gitlab.com/caravel-public/caravel.git Licensing provisions: GPLv3 Programming language: C++ External dependencies: • Required: Python3 [1], meson [2] • Optional: Doxygen [3], Eigen [4], GiNaC [5], GMP [6], Lapack [7], MPFR [8], MPI [9], PentagonLibrary [10, 11], QD [12] Nature of problem: The computation of multi-loop multi-particle scattering amplitudes in quantum field theory Solution method: The multi-loop numerical unitarity method, functional reconstruction algorithms Additional comments including restrictions and unusual features: Current version includes tools employed in previous calculations, with the aim of showcasing details of the algorithms employed. Computations are organized by provided data files. [1] http://www.python.org/ [2] https://mesonbuild.com/ [3] http://www.doxygen.nl/ [4] http://eigen.tuxfamily.org/ [5] https://ginac.de/ [6] https://gmplib.org/ [7] http://www.netlib.org/lapack/ [8] https://www.mpfr.org/ [9] https://www.open-mpi.org/ [10] T. Gehrmann, J. M. Henn and N. A. Lo Presti, JHEP 1810 (2018) 103, arXiv:1807.09812 [hep-ph] [11] https://gitlab.com/caravel-public/pentagon-library [12] QD: A double-double and quad-double package for Fortran and C++, https://www.davidhbailey.com/dhbsoftware/ [ABSTRACT FROM AUTHOR]