Imports
/- Copyright (c) 2026 Joseph Tooby-Smith. All rights reserved. Released under Apache 2.0 license as described in the file LICENSE. Authors: Joseph Tooby-Smith -/ module public import Physlib.Particles.StandardModel.HiggsBoson.Basic public import Mathlib.RingTheory.MvPolynomial.Homogeneous

The effective potential of the Higgs field

We define a general effective potential for the Higgs field. For this we define two properties of the potential: invariance under the gauge group, and a maximum mass dimension.

Given these, we prove that the potential can be expressed as a polynomial in the norm of the Higgs field.

@[expose] public section

A general potential of the Higgs field.

abbrev EffectivePotential : Type := HiggsVec → ℝ

A. The invariance of the general potential under the gauge group

The proposition that the general potential is invariant under the global action of the gauge group.

def IsInvariant (V : EffectivePotential) : Prop := ∀ (g : GaugeGroupI), ∀ (φ : HiggsVec), V (HiggsVec.repGaugeGroupI g φ) = V φ

An invariant potential is equal on gauge orbits.

lemma eq_on_orbits {φ1 φ2 : HiggsVec} {V : EffectivePotential} (h : IsInvariant V) (hφ : ∃ g : GaugeGroupI, HiggsVec.repGaugeGroupI g φ2 = φ1) : V φ1 = V φ2 := φ1:HiggsVecφ2:HiggsVecV:EffectivePotentialh:V.IsInvarianthφ:∃ g, (HiggsVec.repGaugeGroupI g) φ2 = φ1⊢ V φ1 = V φ2 φ2:HiggsVecV:EffectivePotentialh:V.IsInvariantg:GaugeGroupI⊢ V ((HiggsVec.repGaugeGroupI g) φ2) = V φ2 All goals completed! 🐙

An invariant potential is equal on Higgs vectors with identical norms.

lemma eq_of_norm_eq {φ1 φ2 : HiggsVec} {V : EffectivePotential} (h : IsInvariant V) (hφ : ‖φ1‖ = ‖φ2‖) : V φ1 = V φ2 := h.eq_on_orbits <| (HiggsVec.exists_repGaugeGroupI_eq_iff_norm_eq φ2 φ1).mpr hφ
lemma factors_through_norm {V : EffectivePotential} (h : IsInvariant V) : ∃ (f : ℝ → ℝ), V = f ∘ norm := V:EffectivePotentialh:V.IsInvariant⊢ ∃ f, V = f ∘ norm V:EffectivePotentialh:V.IsInvariant⊢ V = (fun a => V !₂[↑a, 0]) ∘ norm V:EffectivePotentialh:V.IsInvariantφ:HiggsVec⊢ V φ = ((fun a => V !₂[↑a, 0]) ∘ norm) φ V:EffectivePotentialh:V.IsInvariantφ:HiggsVec⊢ ‖φ‖ = ‖!₂[↑‖φ‖, 0]‖ conv_rhs => V:EffectivePotentialh:V.IsInvariantφ:HiggsVec| √(∑ i, ‖!₂[↑‖φ‖, 0].ofLp i‖ ^ 2) All goals completed! 🐙

B. Maximum mass dimension

The proposition that the potential V has a maximum mass dimension less then or equal to n - also implying it is a polynomial.

def HasMaxMassDimLE (V : EffectivePotential) (n : ℕ) : Prop := ∃ p : MvPolynomial (Fin 4) ℝ, (∀ φ : HiggsVec, V φ = p.eval φ.toRealScalars) ∧ p.totalDegree ≤ n

The polynomial associated to a potential V with a maximum mass dimension less than or equal to n.

def polynomial (V : EffectivePotential) {n : ℕ} (h : HasMaxMassDimLE V n) : MvPolynomial (Fin 4) ℝ := Classical.choose h
lemma polynomial_totalDegree {V : EffectivePotential} {n : ℕ} (h : HasMaxMassDimLE V n) : (polynomial V h).totalDegree ≤ n := (Classical.choose_spec h).2lemma apply_eq_polynomial {V : EffectivePotential} {n : ℕ} (h : HasMaxMassDimLE V n) (φ : HiggsVec) : V φ = (polynomial V h).eval φ.toRealScalars := (Classical.choose_spec h).1 φ

C. Terms of a given mass dimension

The part of a potential at a given mass-dimension.

def termOfMassDim (V : EffectivePotential) {n : ℕ} (h : HasMaxMassDimLE V n) (m : ℕ) : HiggsVec → ℝ := fun φ => ((polynomial V h).homogeneousComponent m).eval φ.toRealScalars
All goals completed! 🐙V:EffectivePotentialn:ℕh:V.HasMaxMassDimLE nm:ℕφ:HiggsVect:ℝd:Fin 4 →₀ ℕhd:d ∈ ((MvPolynomial.homogeneousComponent m) (V.polynomial h)).supporthdeg:∑ i, d i = m⊢ MvPolynomial.coeff d ((MvPolynomial.homogeneousComponent m) (V.polynomial h)) * ∏ i, (t • HiggsVec.toRealScalars φ) i ^ d i = t ^ m * (MvPolynomial.coeff d ((MvPolynomial.homogeneousComponent m) (V.polynomial h)) * ∏ i, HiggsVec.toRealScalars φ i ^ d i) V:EffectivePotentialn:ℕh:V.HasMaxMassDimLE nm:ℕφ:HiggsVect:ℝd:Fin 4 →₀ ℕhd:d ∈ ((MvPolynomial.homogeneousComponent m) (V.polynomial h)).supporthdeg:∑ i, d i = m⊢ MvPolynomial.coeff d ((MvPolynomial.homogeneousComponent m) (V.polynomial h)) * (t ^ m * ∏ x, HiggsVec.toRealScalars φ x ^ d x) = t ^ m * (MvPolynomial.coeff d ((MvPolynomial.homogeneousComponent m) (V.polynomial h)) * ∏ i, HiggsVec.toRealScalars φ i ^ d i) All goals completed! 🐙All goals completed! 🐙 V:EffectivePotentialn:ℕh:V.HasMaxMassDimLE nφ:HiggsVec⊢ (V.polynomial h).totalDegree + 1 ≤ n + 1 All goals completed! 🐙V:EffectivePotentialn:ℕh:V.HasMaxMassDimLE nφ:HiggsVect:ℝ⊢ ∑ m ∈ Finset.range (n + 1), V.termOfMassDim h m (t • φ) = ∑ m ∈ Finset.range (n + 1), t ^ m * V.termOfMassDim h m φ All goals completed! 🐙All goals completed! 🐙V:EffectivePotentialn:ℕh:V.HasMaxMassDimLE nm:ℕhV:V.IsInvariantφ:HiggsVec⊢ ‖φ‖ ^ m * V.termOfMassDim h m !₂[1, 0] = V.termOfMassDim h m !₂[1, 0] * ‖φ‖ ^ m All goals completed! 🐙V:EffectivePotentialn:ℕh:V.HasMaxMassDimLE nm:ℕhV:V.IsInvariantφ:HiggsVechodd:Odd mh1:V.termOfMassDim h m φ = -1 * V.termOfMassDim h m φ⊢ V.termOfMassDim h m φ = 0 All goals completed! 🐙

D. Potential in terms of the norm of the Higgs field

All goals completed! 🐙All goals completed! 🐙

The potential is equal to the sum of norms to even powers.

V:EffectivePotentialn:ℕh:V.HasMaxMassDimLE nhV:V.IsInvariantφ:HiggsVec⊢ ∑ m, V.termOfMassDim h (2 * ↑m) φ = ∑ m, (fun m' => Classical.choose ⋯) m • ‖φ‖ ^ (2 * ↑m) V:EffectivePotentialn:ℕh:V.HasMaxMassDimLE nhV:V.IsInvariantφ:HiggsVecm:Fin (n / 2 + 1)x✝:m ∈ Finset.univ⊢ V.termOfMassDim h (2 * ↑m) φ = (fun m' => Classical.choose ⋯) m • ‖φ‖ ^ (2 * ↑m) All goals completed! 🐙