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feynsage: a Tutorial for Someone Starting QFT
A tutorial for feynsage, a SageMath package for QFT calculations, in the order a first course actually goes: gamma matrices and traces first, then a full scattering cross section for electron positron to muon pair, then loops at the end. Every object is explained before it is used and every output on the page is captured from a real run.
Effective Field Theory, Starting From the Propagator You Just Learned
An effective field theory is what you get when you cannot afford the energy to make a heavy particle. This is EFT for someone a few weeks into a first QFT course: one line of algebra on the propagator you already know, one heavy scalar integrated out by hand, then Fermi's theory of beta decay, why non-renormalisable is not an insult, then how a theory predicts the energy at which it will stop working.
The Renormalisation Group: from Block Spins to Running Couplings
An eight-part beginner's course on the renormalisation group, in simple words with an everyday picture for every idea: loops and cutoffs from scratch, block spins and the Ising chain, fixed points and universality, Wilson's momentum shells, the Wilson-Fisher fixed point, running couplings in QED and QCD, then effective field theory. Every formula checked in Wolfram and FORM, with live simulations in the browser.
Tree Codes: Recreating Hernquist (1987)
Recreating Hernquist's 1987 paper on the performance of Barnes-Hut tree codes, from scratch in Julia: the Plummer model, the leapfrog integrator, the multipole expansion and every timing and error test in the paper.
Minkowski Functionals: Measuring the Shape of the Universe
A first-principles guide to Minkowski functionals: from 'what is shape?' through Hadwiger's theorem, curvature, the Steiner inflation formula, and the Hermite-ladder Gaussian predictions, to measuring non-Gaussianity in cosmology. Physical analogies (a flooding landscape), full derivations, symbolic checks in SymPy and WolframScript, numerical checks in Python and Julia, and an interactive 3D water-level widget.
Grassmann Algebra: Multiplying with Area and Orientation
A friendly, visual introduction to Grassmann (exterior) algebra: the wedge product, bivectors, orientation, multivector grades, and the tensor-algebra quotient definition — with runnable SageMath and SymPy code. The first part of a mini-series leading to Clifford algebras and spinors.