feat: Add Wick terms

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jstoobysmith 2025-02-05 08:52:14 +00:00
parent 7d9e6af80c
commit 2e82f842a2
12 changed files with 634 additions and 553 deletions

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@ -6,6 +6,8 @@ Authors: Joseph Tooby-Smith
import HepLean.PerturbationTheory.WickContraction.TimeContract
import HepLean.PerturbationTheory.WickContraction.Sign.InsertNone
import HepLean.PerturbationTheory.WickContraction.Sign.InsertSome
import HepLean.PerturbationTheory.FieldOpAlgebra.NormalOrder.WickContractions
import HepLean.PerturbationTheory.FieldOpAlgebra.WickTerm
import HepLean.Meta.Remark.Basic
/-!
@ -28,289 +30,10 @@ open FieldStatistic
/-!
## Normal order of uncontracted terms within proto-algebra.
-/
/--
Let `c` be a Wick Contraction for `φs := φ₀φ₁…φₙ`.
We have (roughly) `𝓝ᶠ([φsΛ ↩Λ φ i none]ᵘᶜ) = s • 𝓝ᶠ(φ :: [φsΛ]ᵘᶜ)`
Where `s` is the exchange sign for `φ` and the uncontracted fields in `φ₀φ₁…φᵢ₋₁`.
-/
lemma normalOrder_uncontracted_none (φ : 𝓕.FieldOp) (φs : List 𝓕.FieldOp)
(i : Fin φs.length.succ) (φsΛ : WickContraction φs.length) :
𝓝(ofFieldOpList [φsΛ ↩Λ φ i none]ᵘᶜ)
= 𝓢(𝓕 |>ₛ φ, 𝓕 |>ₛ ⟨φs.get, φsΛ.uncontracted.filter (fun x => i.succAbove x < i)⟩) •
𝓝(ofFieldOpList (φ :: [φsΛ]ᵘᶜ)) := by
simp only [Nat.succ_eq_add_one, instCommGroup.eq_1]
rw [ofFieldOpList_normalOrder_insert φ [φsΛ]ᵘᶜ
⟨(φsΛ.uncontractedListOrderPos i), by simp [uncontractedListGet]⟩, smul_smul]
trans (1 : ) • (𝓝(ofFieldOpList [φsΛ ↩Λ φ i none]ᵘᶜ))
· simp
congr 1
simp only [instCommGroup.eq_1, uncontractedListGet]
rw [← List.map_take, take_uncontractedListOrderPos_eq_filter]
have h1 : (𝓕 |>ₛ List.map φs.get (List.filter (fun x => decide (↑x < i.1)) φsΛ.uncontractedList))
= 𝓕 |>ₛ ⟨φs.get, (φsΛ.uncontracted.filter (fun x => x.val < i.1))⟩ := by
simp only [Nat.succ_eq_add_one, ofFinset]
congr
rw [uncontractedList_eq_sort]
have hdup : (List.filter (fun x => decide (x.1 < i.1))
(Finset.sort (fun x1 x2 => x1 ≤ x2) φsΛ.uncontracted)).Nodup := by
exact List.Nodup.filter _ (Finset.sort_nodup (fun x1 x2 => x1 ≤ x2) φsΛ.uncontracted)
have hsort : (List.filter (fun x => decide (x.1 < i.1))
(Finset.sort (fun x1 x2 => x1 ≤ x2) φsΛ.uncontracted)).Sorted (· ≤ ·) := by
exact List.Sorted.filter _ (Finset.sort_sorted (fun x1 x2 => x1 ≤ x2) φsΛ.uncontracted)
rw [← (List.toFinset_sort (· ≤ ·) hdup).mpr hsort]
congr
ext a
simp
rw [h1]
simp only [Nat.succ_eq_add_one]
have h2 : (Finset.filter (fun x => x.1 < i.1) φsΛ.uncontracted) =
(Finset.filter (fun x => i.succAbove x < i) φsΛ.uncontracted) := by
ext a
simp only [Nat.succ_eq_add_one, Finset.mem_filter, and_congr_right_iff]
intro ha
simp only [Fin.succAbove]
split
· apply Iff.intro
· intro h
omega
· intro h
rename_i h
rw [Fin.lt_def] at h
simp only [Fin.coe_castSucc] at h
omega
· apply Iff.intro
· intro h
rename_i h'
rw [Fin.lt_def]
simp only [Fin.val_succ]
rw [Fin.lt_def] at h'
simp only [Fin.coe_castSucc, not_lt] at h'
omega
· intro h
rename_i h
rw [Fin.lt_def] at h
simp only [Fin.val_succ] at h
omega
rw [h2]
simp only [exchangeSign_mul_self]
congr
simp only [Nat.succ_eq_add_one]
rw [insertAndContract_uncontractedList_none_map]
/--
Let `c` be a Wick Contraction for `φ₀φ₁…φₙ`.
We have (roughly) `N(c ↩Λ φ i k).uncontractedList`
is equal to `N((c.uncontractedList).eraseIdx k')`
where `k'` is the position in `c.uncontractedList` corresponding to `k`.
-/
lemma normalOrder_uncontracted_some (φ : 𝓕.FieldOp) (φs : List 𝓕.FieldOp)
(i : Fin φs.length.succ) (φsΛ : WickContraction φs.length) (k : φsΛ.uncontracted) :
𝓝(ofFieldOpList [φsΛ ↩Λ φ i (some k)]ᵘᶜ)
= 𝓝(ofFieldOpList (optionEraseZ [φsΛ]ᵘᶜ φ ((uncontractedFieldOpEquiv φs φsΛ) k))) := by
simp only [Nat.succ_eq_add_one, insertAndContract, optionEraseZ, uncontractedFieldOpEquiv,
Equiv.optionCongr_apply, Equiv.coe_trans, Option.map_some', Function.comp_apply, finCongr_apply,
Fin.coe_cast, uncontractedListGet]
congr
rw [congr_uncontractedList]
erw [uncontractedList_extractEquiv_symm_some]
simp only [Fin.coe_succAboveEmb, List.map_eraseIdx, List.map_map]
congr
conv_rhs => rw [get_eq_insertIdx_succAbove φ φs i]
/-!
## Wick terms
-/
remark wick_term_terminology := "
Let `φsΛ` be a Wick contraction. We informally call the term
`(φsΛ.sign • φsΛ.timeContract 𝓞) * 𝓞.crAnF 𝓝ᶠ([φsΛ]ᵘᶜ)` the Wick term
associated with `φsΛ`. We do not make this a fully-fledge definition, as
in most cases we want to consider slight modifications of this term."
/--
Let `φsΛ` be a Wick Contraction for `φs = φ₀φ₁…φₙ`. Then the wick-term of ` (φsΛ ↩Λ φ i none)`
```(φsΛ ↩Λ φ i none).sign • (φsΛ ↩Λ φ i none).timeContract 𝓞 * 𝓞.crAnF 𝓝ᶠ([φsΛ ↩Λ φ i none]ᵘᶜ)```
is equal to
`s • (φsΛ.sign • φsΛ.timeContract 𝓞 * 𝓞.crAnF 𝓝ᶠ(φ :: [φsΛ]ᵘᶜ))`
where `s` is the exchange sign of `φ` and the uncontracted fields in `φ₀φ₁…φᵢ₋₁`.
The proof of this result relies primarily on:
- `normalOrderF_uncontracted_none` which replaces `𝓝ᶠ([φsΛ ↩Λ φ i none]ᵘᶜ)` with
`𝓝ᶠ(φ :: [φsΛ]ᵘᶜ)` up to a sign.
- `timeContract_insertAndContract_none` which replaces `(φsΛ ↩Λ φ i none).timeContract 𝓞` with
`φsΛ.timeContract 𝓞`.
- `sign_insert_none` and `signInsertNone_eq_filterset` which are used to take account of
signs.
-/
lemma wick_term_none_eq_wick_term_cons (φ : 𝓕.FieldOp) (φs : List 𝓕.FieldOp)
(i : Fin φs.length.succ) (φsΛ : WickContraction φs.length) :
(φsΛ ↩Λ φ i none).sign • (φsΛ ↩Λ φ i none).timeContract
* 𝓝(ofFieldOpList [φsΛ ↩Λ φ i none]ᵘᶜ) =
𝓢(𝓕 |>ₛ φ, 𝓕 |>ₛ ⟨φs.get, (Finset.univ.filter (fun k => i.succAbove k < i))⟩)
• (φsΛ.sign • φsΛ.timeContract * 𝓝(ofFieldOpList (φ :: [φsΛ]ᵘᶜ))) := by
by_cases hg : GradingCompliant φs φsΛ
· rw [normalOrder_uncontracted_none, sign_insert_none]
simp only [Nat.succ_eq_add_one, timeContract_insertAndContract_none, instCommGroup.eq_1,
Algebra.mul_smul_comm, Algebra.smul_mul_assoc, smul_smul]
congr 1
rw [← mul_assoc]
congr 1
rw [signInsertNone_eq_filterset _ _ _ _ hg, ← map_mul]
congr
rw [ofFinset_union]
congr
ext a
simp only [Finset.mem_sdiff, Finset.mem_union, Finset.mem_filter, Finset.mem_univ, true_and,
Finset.mem_inter, not_and, not_lt, and_imp]
apply Iff.intro
· intro ha
have ha1 := ha.1
rcases ha1 with ha1 | ha1
· exact ha1.2
· exact ha1.2
· intro ha
simp only [uncontracted, Finset.mem_filter, Finset.mem_univ, true_and, ha, and_true,
forall_const]
have hx : φsΛ.getDual? a = none ↔ ¬ (φsΛ.getDual? a).isSome := by
simp
rw [hx]
simp only [Bool.not_eq_true, Bool.eq_false_or_eq_true_self, true_and]
intro h1 h2
simp_all
· simp only [Nat.succ_eq_add_one, timeContract_insertAndContract_none, Algebra.smul_mul_assoc,
instCommGroup.eq_1]
rw [timeContract_of_not_gradingCompliant]
simp only [ZeroMemClass.coe_zero, zero_mul, smul_zero]
exact hg
/--
Let `c` be a Wick Contraction for `φ₀φ₁…φₙ`.
This lemma states that
`(c.sign • c.timeContract 𝓞) * N(c.uncontracted)`
for `c` equal to `c ↩Λ φ i (some k)` is equal to that for just `c`
mulitiplied by the exchange sign of `φ` and `φ₀φ₁…φᵢ₋₁`.
-/
lemma wick_term_some_eq_wick_term_optionEraseZ (φ : 𝓕.FieldOp) (φs : List 𝓕.FieldOp)
(i : Fin φs.length.succ) (φsΛ : WickContraction φs.length) (k : φsΛ.uncontracted)
(hlt : ∀ (k : Fin φs.length), timeOrderRel φ φs[k])
(hn : ∀ (k : Fin φs.length), i.succAbove k < i → ¬ timeOrderRel φs[k] φ) :
(φsΛ ↩Λ φ i (some k)).sign • (φsΛ ↩Λ φ i (some k)).timeContract
* 𝓝(ofFieldOpList [φsΛ ↩Λ φ i (some k)]ᵘᶜ) =
𝓢(𝓕 |>ₛ φ, 𝓕 |>ₛ ⟨φs.get, (Finset.univ.filter (fun x => i.succAbove x < i))⟩)
• (φsΛ.sign • (contractStateAtIndex φ [φsΛ]ᵘᶜ
((uncontractedFieldOpEquiv φs φsΛ) (some k)) * φsΛ.timeContract)
* 𝓝(ofFieldOpList (optionEraseZ [φsΛ]ᵘᶜ φ (uncontractedFieldOpEquiv φs φsΛ k)))) := by
by_cases hg : GradingCompliant φs φsΛ ∧ (𝓕 |>ₛ φ) = (𝓕 |>ₛ φs[k.1])
· by_cases hk : i.succAbove k < i
· rw [WickContraction.timeConract_insertAndContract_some_eq_mul_contractStateAtIndex_not_lt]
swap
· exact hn _ hk
rw [normalOrder_uncontracted_some, sign_insert_some]
simp only [instCommGroup.eq_1, smul_smul, Algebra.smul_mul_assoc]
congr 1
rw [mul_assoc, mul_comm (sign φs φsΛ), ← mul_assoc]
congr 1
exact signInsertSome_mul_filter_contracted_of_lt φ φs φsΛ i k hk hg
· omega
· have hik : i.succAbove ↑k ≠ i := Fin.succAbove_ne i ↑k
rw [WickContraction.timeConract_insertAndContract_some_eq_mul_contractStateAtIndex_lt]
swap
· exact hlt _
rw [normalOrder_uncontracted_some]
rw [sign_insert_some]
simp only [instCommGroup.eq_1, smul_smul, Algebra.smul_mul_assoc]
congr 1
rw [mul_assoc, mul_comm (sign φs φsΛ), ← mul_assoc]
congr 1
exact signInsertSome_mul_filter_contracted_of_not_lt φ φs φsΛ i k hk hg
· omega
· rw [timeConract_insertAndContract_some]
simp only [Fin.getElem_fin, not_and] at hg
by_cases hg' : GradingCompliant φs φsΛ
· have hg := hg hg'
simp only [Nat.succ_eq_add_one, Fin.getElem_fin, ite_mul, Algebra.smul_mul_assoc,
instCommGroup.eq_1, contractStateAtIndex, uncontractedFieldOpEquiv, Equiv.optionCongr_apply,
Equiv.coe_trans, Option.map_some', Function.comp_apply, finCongr_apply, Fin.coe_cast,
List.getElem_map, uncontractedList_getElem_uncontractedIndexEquiv_symm, List.get_eq_getElem,
uncontractedListGet]
by_cases h1 : i < i.succAbove ↑k
· simp only [h1, ↓reduceIte, MulMemClass.coe_mul]
rw [timeContract_zero_of_diff_grade]
simp only [zero_mul, smul_zero]
rw [superCommute_anPart_ofFieldOpF_diff_grade_zero]
simp only [zero_mul, smul_zero]
exact hg
exact hg
· simp only [h1, ↓reduceIte, MulMemClass.coe_mul]
rw [timeContract_zero_of_diff_grade]
simp only [zero_mul, smul_zero]
rw [superCommute_anPart_ofFieldOpF_diff_grade_zero]
simp only [zero_mul, smul_zero]
exact hg
exact fun a => hg (id (Eq.symm a))
· rw [timeContract_of_not_gradingCompliant]
simp only [Nat.succ_eq_add_one, Fin.getElem_fin, mul_zero, ZeroMemClass.coe_zero, smul_zero,
zero_mul, instCommGroup.eq_1]
exact hg'
/--
Given a Wick contraction `φsΛ` of `φs = φ₀φ₁…φₙ` and an `i`, we have that
`(φsΛ.sign • φsΛ.timeContract 𝓞) * 𝓞.crAnF (φ * 𝓝ᶠ([φsΛ]ᵘᶜ))`
is equal to the product of
- the exchange sign of `φ` and `φ₀φ₁…φᵢ₋₁`,
- the sum of `((φsΛ ↩Λ φ i k).sign • (φsΛ ↩Λ φ i k).timeContract 𝓞) * 𝓞.crAnF 𝓝ᶠ([φsΛ ↩Λ φ i k]ᵘᶜ)`
over all `k` in `Option φsΛ.uncontracted`.
The proof of this result primarily depends on
- `crAnF_ofFieldOpF_mul_normalOrderF_ofFieldOpFsList_eq_sum` to rewrite `𝓞.crAnF (φ * 𝓝ᶠ([φsΛ]ᵘᶜ))`
- `wick_term_none_eq_wick_term_cons`
- `wick_term_some_eq_wick_term_optionEraseZ`
-/
lemma wick_term_cons_eq_sum_wick_term (φ : 𝓕.FieldOp) (φs : List 𝓕.FieldOp) (i : Fin φs.length.succ)
(φsΛ : WickContraction φs.length) (hlt : ∀ (k : Fin φs.length), timeOrderRel φ φs[k])
(hn : ∀ (k : Fin φs.length), i.succAbove k < i → ¬timeOrderRel φs[k] φ) :
(φsΛ.sign • φsΛ.timeContract) * ((ofFieldOp φ) * 𝓝(ofFieldOpList [φsΛ]ᵘᶜ)) =
𝓢(𝓕 |>ₛ φ, 𝓕 |>ₛ ⟨φs.get, (Finset.univ.filter (fun x => i.succAbove x < i))⟩) •
∑ (k : Option φsΛ.uncontracted), ((φsΛ ↩Λ φ i k).sign •
(φsΛ ↩Λ φ i k).timeContract * (𝓝(ofFieldOpList [φsΛ ↩Λ φ i k]ᵘᶜ))) := by
rw [ofFieldOp_mul_normalOrder_ofFieldOpList_eq_sum, Finset.mul_sum,
uncontractedFieldOpEquiv_list_sum, Finset.smul_sum]
simp only [instCommGroup.eq_1, Nat.succ_eq_add_one]
congr 1
funext n
match n with
| none =>
rw [wick_term_none_eq_wick_term_cons]
simp only [contractStateAtIndex, uncontractedFieldOpEquiv, Equiv.optionCongr_apply,
Equiv.coe_trans, Option.map_none', one_mul, Algebra.smul_mul_assoc, instCommGroup.eq_1,
smul_smul]
congr 1
rw [← mul_assoc, exchangeSign_mul_self]
simp
| some n =>
rw [wick_term_some_eq_wick_term_optionEraseZ _ _ _ _ _
(fun k => hlt k) (fun k a => hn k a)]
simp only [uncontractedFieldOpEquiv, Equiv.optionCongr_apply, Equiv.coe_trans, Option.map_some',
Function.comp_apply, finCongr_apply, Algebra.smul_mul_assoc, instCommGroup.eq_1, smul_smul]
congr 1
· rw [← mul_assoc, exchangeSign_mul_self]
rw [one_mul]
· rw [← mul_assoc]
congr 1
have ht := (WickContraction.timeContract φsΛ).prop
rw [@Subalgebra.mem_center_iff] at ht
rw [ht]
/-!
## Wick's theorem
@ -335,9 +58,8 @@ lemma wicks_theorem_nil :
rfl
lemma wicks_theorem_congr {φs φs' : List 𝓕.FieldOp} (h : φs = φs') :
∑ (φsΛ : WickContraction φs.length), (φsΛ.sign • φsΛ.timeContract) * 𝓝(ofFieldOpList [φsΛ]ᵘᶜ)
= ∑ (φs'Λ : WickContraction φs'.length), (φs'Λ.sign • φs'Λ.timeContract) *
𝓝(ofFieldOpList [φs'Λ]ᵘᶜ) := by
∑ (φsΛ : WickContraction φs.length), φsΛ.wickTerm
= ∑ (φs'Λ : WickContraction φs'.length), φs'Λ.wickTerm := by
subst h
simp
@ -356,17 +78,21 @@ remark wicks_theorem_context := "
The statement of these theorems for bosons is simplier then when fermions are involved, since
one does not have to worry about the minus-signs picked up on exchanging fields."
/-- Wick's theorem for time-ordered products of bosonic and fermionic fields.
The time ordered product `T(φ₀φ₁…φₙ)` is equal to the sum of terms,
for all possible Wick contractions `c` of the list of fields `φs := φ₀φ₁…φₙ`, given by
the multiple of:
- The sign corresponding to the number of fermionic-fermionic exchanges one must do
to put elements in contracted pairs of `c` next to each other.
- The product of time-contractions of the contracted pairs of `c`.
- The normal-ordering of the uncontracted fields in `c`.
/-- Wick's theorem states that for a list of fields `φs = φ₀…φₙ`
`𝓣(φs) = ∑ φsΛ, (φsΛ.sign • φsΛ.timeContract) * 𝓝([φsΛ]ᵘᶜ)`
where the sum is over all Wick contractions `φsΛ` of `φs`.
The proof is via induction on `φs`. The base case `φs = []` is handled by `wicks_theorem_nil`.
The inductive step works as follows:
- The lemma `timeOrder_eq_maxTimeField_mul_finset` is used to write
`𝓣(φ₀…φₙ)` as ` 𝓢(φᵢ,φ₀…φᵢ₋₁) • φᵢ * 𝓣(φ₀…φᵢ₋₁φᵢ₊₁φₙ)` where `φᵢ` is
the maximal time field in `φ₀…φₙ`.
- The induction hypothesis is used to expand `𝓣(φ₀…φᵢ₋₁φᵢ₊₁φₙ)` as a sum over Wick contractions of
`φ₀…φᵢ₋₁φᵢ₊₁φₙ`.
- Further the lemmas `wick_term_cons_eq_sum_wick_term` and `insertLift_sum` are used.
-/
theorem wicks_theorem : (φs : List 𝓕.FieldOp) → 𝓣(ofFieldOpList φs) =
∑ (φsΛ : WickContraction φs.length), (φsΛ.sign • φsΛ.timeContract) * 𝓝(ofFieldOpList [φsΛ]ᵘᶜ)
∑ (φsΛ : WickContraction φs.length), φsΛ.wickTerm
| [] => wicks_theorem_nil
| φ :: φs => by
have ih := wicks_theorem (eraseMaxTimeField φ φs)
@ -380,18 +106,10 @@ theorem wicks_theorem : (φs : List 𝓕.FieldOp) → 𝓣(ofFieldOpList φs) =
conv_rhs => rw [insertLift_sum]
apply Finset.sum_congr rfl
intro c _
have ht := Subalgebra.mem_center_iff.mp (Subalgebra.smul_mem (Subalgebra.center _)
(WickContraction.timeContract c).2 (sign (eraseMaxTimeField φ φs) c))
rw [Algebra.smul_mul_assoc, ← mul_assoc, ht, mul_assoc]
rw [wick_term_cons_eq_sum_wick_term
rw [Algebra.smul_mul_assoc, wickTerm_cons_eq_sum_wick_term
(maxTimeField φ φs) (eraseMaxTimeField φ φs) (maxTimeFieldPosFin φ φs) c]
trans (1 : ) • ∑ k : Option { x // x ∈ c.uncontracted }, sign
(List.insertIdx (↑(maxTimeFieldPosFin φ φs)) (maxTimeField φ φs) (eraseMaxTimeField φ φs))
(c ↩Λ (maxTimeField φ φs) (maxTimeFieldPosFin φ φs) k) •
↑((c ↩Λ (maxTimeField φ φs) (maxTimeFieldPosFin φ φs) k).timeContract) *
𝓝(ofFieldOpList (List.map (List.insertIdx (↑(maxTimeFieldPosFin φ φs))
(maxTimeField φ φs) (eraseMaxTimeField φ φs)).get
(c ↩Λ (maxTimeField φ φs) (maxTimeFieldPosFin φ φs) k).uncontractedList))
trans (1 : ) • ∑ k : Option { x // x ∈ c.uncontracted },
(c ↩Λ (maxTimeField φ φs) (maxTimeFieldPosFin φ φs) k).wickTerm
swap
· simp [uncontractedListGet]
rw [smul_smul]