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feat: Effective potential for Weyl fermions (Stacked on #1404) - #1415

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feat: Effective potential for Weyl fermions (Stacked on #1404)#1415
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claude Fable was used to help proof some results. All other content was, in the end, human written. I did experiment with getting claude to write things initially, but these were reverted.

This adds the effective potential for a left-handed Weyl fermion written as an element of the suitable Exterior algebra. It also proves the general form of an effective potential which is invariant under the Lorentz group, this is related to the Majorana mass.

jstoobysmith and others added 17 commits July 9, 2026 13:12
Prompt:

I want you to:

1. Fill out the sorries in this file.
2. Define a instance of a `Star` on `potentialAlgebra` defined by conjugating Left and Right weyl fermions, and using CliffordAlgebra.reverse
3. Define a representation of the Lorentz group on potentialAlgebra.
4. Define the majorana mass for a LeftHandedWeyl.
5. Show it is Lorentz invariant.

Co-Authored-By: Claude <claude@users.noreply.github.com>
Your definition of majoranaMass is wrong. In particular it does not even take in a fermion as an argument. I wouldn't not define leftBilinear as it does not make any sense - again also no fermions there.

> Really you should be using contractions. and the dual maps

Co-Authored-By: Claude <claude@users.noreply.github.com>
Co-Authored-By: Claude <claude@users.noreply.github.com>
Co-Authored-By: Claude <claude@users.noreply.github.com>
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@jstoobysmith jstoobysmith changed the title feat: Effective potential for Weyl fermions feat: Effective potential for Weyl fermions (Stacked on #1404) Jul 13, 2026
@jstoobysmith jstoobysmith added the blocked-by-PR This PR depends on another PR label Jul 13, 2026
nateabr

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jstoobysmith and others added 2 commits August 4, 2026 10:43
Co-Authored-By: Claude <claude@users.noreply.github.com>
Co-Authored-By: Claude <claude@users.noreply.github.com>
jstoobysmith and others added 27 commits August 4, 2026 14:26
Co-Authored-By: Claude <claude@users.noreply.github.com>
Co-Authored-By: Claude <claude@users.noreply.github.com>
Co-Authored-By: Claude <claude@users.noreply.github.com>
Co-Authored-By: Claude <claude@users.noreply.github.com>
Co-Authored-By: Claude <claude@users.noreply.github.com>
Left Claude running overnight

Co-Authored-By: Claude <claude@users.noreply.github.com>
claude prompt: /goal

I want you to clean up the files in the ./QED/JetAlgebra directory. I want you to make sure:
1. All lemmas and results sit in a sensible place (following the usual API conventions of Physlib/Mathlib).
2. No lemmas are repeated.
3. The story is complete, and makes sense, and the documentation is not too verbose.
4. Everything builds.
5. A minimal amount of concrete definitions are made (there are lots of pointless definitions).

Co-Authored-By: Claude <claude@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 <no-reply+claude-opus-4-8@anthropic.com>
Adds `Physlib/Particles/QED/Photon.lean`, an experiment relating the formal
jet-algebra description of QED to the concrete electromagnetism of
`Physlib.Electromagnetism`.

The jet algebra is built directly on `ElectromagneticPotential` rather than on
the B boson: the `B` boson is the gauge boson of `U(1)_Y` before electroweak
symmetry breaking, whereas the photon is the mixed combination
`A = cos θ_W B + sin θ_W W³`, so identifying them would also drag in the
Standard Model charge normalisation `6Y`, which has no meaning for `U(1)_em`.
Accordingly the file imports only `Physlib.Electromagnetism`.

Contents:

* `JetGenerators` / `JetAlgebra` — the formal jet coordinates `∂_s A_μ`,
  indexed by a multiset of directions, and the real polynomials in them.
* `fieldStrength`, `maxwellTerm` — the formal `∂_s F_{μν}` and `F_{μν} F^{μν}`.
* `gaugeAction` — the `U(1)_em` gauge action `∂_s A_μ ↦ ∂_s A_μ + ∂_s ∂_μ χ`,
  parametrised by the symmetrised derivatives of the gauge function. Gauge
  jets compose by addition (`gaugeAction_comp`).
* `gaugeAction_fieldStrength` — gauge invariance of the field strength. The
  two shifts are indexed by `s + {μ} + {ν}` and `s + {ν} + {μ}`, so the proof
  is exactly the commutativity of multiset addition: Clairaut's theorem is
  built into the indexing rather than assumed.
* `derivMultiset`, `evalPotential` — the iterated derivative along a multiset,
  in the canonical sorted order, and the evaluation of the jet algebra at a
  chosen potential, sending `∂_s A_μ` to `∂_s A_μ` with the index lowered.
* `evalPotential_maxwellTerm` — the formal Maxwell term evaluates, on any
  differentiable potential, to `-4 μ₀` times
  `ElectromagneticPotential.kineticTerm`.
* `evalPotential_fieldStrength_gaugeTransform`,
  `evalPotential_maxwellTerm_gaugeTransform` — the formal gauge invariance
  matches the library's concrete `A ↦ A + ∂χ`.

The file contains no `sorry`. It is not added to `Physlib.lean`, matching the
rest of `Physlib/Particles/QED/`.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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