Brownian Motion in AdS/CFT - ggcyzha.github.io
Transcript of Brownian Motion in AdS/CFT - ggcyzha.github.io
Jilin University (via Zoom)
Masaki Shigemori
February 4, 2021
Based on work with Tatsuki Nakajima (Nagoya) and Hirano Shinji (Wits), arxiv:2012.03972
What is 𝑇𝑇?
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𝒪𝑇𝑇 ≡ 𝑇𝑇 − Θ2
Various other expressions:
𝑇 = 𝑇 , 𝑇 = 𝑇 , Θ = 𝑇
𝒪𝑇𝑇 =18(𝑇 𝑇 − 𝑇 𝑇 )
= −14det 𝑇 = −
18𝜖 𝜖 𝑇 𝑇
In 2D QFT, the 𝑇𝑇 operator is defined by
𝑧 = 𝑥1 + 𝑖𝑥2
What is 𝑇𝑇?
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Nice properties:[Zamolodchikov 2004]
lim→
𝑇 𝑧 𝑇 𝑧 − Θ 𝑧 Θ z = 𝒪𝑇𝑇(𝑧 ) + (derivatives)
𝒪𝑇𝑇 = ⟨𝑇⟩⟨𝑇⟩ − ⟨Θ⟩2 Å Not just for |0⟩ but for |𝑛⟩
𝑇𝑇 deformation
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` Non-renormalizable ( 𝜇 = mass−2 = length2).
` Still, surprisingly predictable
` Energy spectrum of a theory on a circle of radius 𝑅
𝐸 𝑅, 𝜇 = 𝑅 1 − 1 − 2𝐶𝑅𝜇 , 𝐶 = + −𝑐/12
𝑅
` Integrable
` Thermodynamics (𝜇 < 0: Hagedorn)
` Deformed theory with (𝑔, 𝑇) ∼ undeformed theory with (𝑔 , 𝑇 )
[Smirnov-Zamolodchikov ’16][Cavaglia, Negro, Szecsenyi, Tateo ’16]
𝑆de ormed = 𝑆 + 𝜇∫ 𝒪𝑇𝑇 (roughly)
Cf. [Haruna, Ishii, Kawai, Sakai, Yoshida ’20]
non-unitary
Holography
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` 𝑇𝑇: irrelevant in IR, relevant in UV
Æ Non-normalizable in AdS
Æ Change AdS asymptotics?
𝜌 = 0
AdS AdS
?
∼ 𝜇
“Undo decoupling”?
deformBoundary
𝜌 𝜌
Holography: moving field theory into bulk
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The deformed theory corresponds to placingthe field theory at 𝜌𝑐 ∼ 𝜇 of the bulk(𝜌: radial coordinate in Fefferman-Graham coordinates)
[McGough, Mezei, Verlinde ’16][Guica-Monten ’19][Caputa-Datta-Jiang-Kraus ’20]
` 𝑇𝑇 deformation makes the bndy cond be naturally given at 𝜌𝑐
` CFT living at 𝜌 = 0 is “equivalent” to deformed theory at 𝜌𝑐 ∼ 𝜇
𝑆 = 𝑆de ormed + 𝑆ann lar
` Valid only in pure gravity without matter (so far)
𝜌 = 0 𝜌
CFT lives here
Deformed theory
lives here
𝜌𝑐~𝜇
“annular region”
𝑇𝑇 and width of particles [Cardy-Doyon ’20] [Jiang ’20]
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Deformation makes particles have “width” 𝜇
` 𝑇𝑇 deformation dynamically changes the metric
` 𝑇𝑇 deforming free scalars Æ Nambu-Goto with tension −𝜇[Cavaglia, Negro, Szecsenyi, Tateo ’16]
A lot more to explore about 𝑇𝑇 deformation!
“Random geometry” by Cardy
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Idea: rewrite 𝑇𝑇 using Hubbard-Stratonovich transformation
[Cardy ’18]
exp −𝜇∫ 𝑇2 ∼ ∫ [𝑑ℎ] exp 1 ∫ ℎ2 − ∫ ℎ𝑇
This talk:` Apply this to compute 𝑇𝑇-deformed 𝑇 correlators
` Previous results: 2pt func at 𝒪(𝜇2), 3pt func at 𝒪(𝜇)
` Develop a new method to compute 𝑇-correlators
` We computed 4pt func at 𝒪(𝜇)
` Result is applicable to any deformed CFT
deformation of backgnd geometry
(because 𝑇 ∼ 𝑆𝑔
)
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What we do:
` Compute 𝒪 𝜇 correction to Liouville-Polyakov anomaly action
≡ 𝑆 =0[𝑔] → 𝑆 [𝑔]
` Vary backgnd metric 𝑔 → 𝑔 + ℎ to compute 𝑇-correlators (explicit computations at 𝒪(𝜇))
Plan
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1. Introduction
2. 𝑇𝑇 deformation as random geometries
3. 𝑇𝑇-deformed Liouville action
4. Stress tensor correlators (technical!)
5. 𝑇𝑇-deformed OPEs
6. Discussions
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𝑇𝑇 deformation
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` 𝑇𝑇-deformed theory is defined incrementally by:
𝑇 : stress-energy tensor of the 𝜇-deformed theory
𝑆 𝜇 + 𝛿𝜇 − 𝑆 𝜇 =𝛿𝜇𝜋2
𝑑2𝑥 𝑔 𝒪𝑇𝑇 ≡ 𝛿𝑆
* Our convention for 𝑇 :
` 𝑇𝑇-deformed theory with finite 𝜇 is obtained by iteration
` We will often suppress 𝑑2𝑥 𝑔
𝛿𝑔𝑆 =14𝜋
𝑇 𝛿𝑔
𝑇𝑇 = random geometries
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` HS transformation:
𝑒− 𝑆 = 𝑒8 ∫ 𝑑 𝑔 𝑇 𝑇
Saddle point: ℎ∗ = − 𝜖 𝜖 𝑇 = 𝒪(𝛿𝜇)
Change in backgnd metric𝑔 → 𝑔 + ℎ
“Master formula”
Gaussian integral over ℎ
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𝑇𝑇-deformed theory with 𝑔, 𝑇
Undeformed theory with 𝑔 , 𝑇′=
(up to the HS action)
𝜇
𝑔, 𝑇
deformedCFT
Equivalent theories
In saddle-pt approximation,
Cf. bulk picture
Parametrizing ℎ
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ℎ = ∇ 𝛼 + ∇ 𝛼 + 2𝑔 Φ
In 2D, any ℎ = diff + Weyl
𝑥 → 𝑥 + 𝛼 𝑑𝑠2 → 𝑒2Φ𝑑𝑠2
Useful to write Φ = 𝜙 − 12∇ 𝛼
“Master formula”
Summary so far
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ℎ = ∇ 𝛼 + ∇ 𝛼 + 2𝑔 𝜙 − 12∇ ⋅ 𝛼
` 𝑇𝑇 = random geometries
` “Master formula”
Liouville-Polyakov action (1)
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` Dependence of CFT2 on backgnd metric 𝑔 (𝑥) is determined by conformal anomaly [Polyakov ’81]:
= 1 for flat ℝ2
Cf. For general fiducial metric 𝑔,
Conformal gauge 𝑑𝑠2 = 𝑒2Ω𝑑𝑧 𝑑 𝑧
𝑆0 𝑒2Ω𝑔 = −24 ∫𝑑2𝑥 𝑔 𝑔 𝜕 Ω𝜕 Ω + 𝑅Ω + 𝑆0 𝑔
But note that we are not doing Liouville field theory
Liouville (-Polyakov) action
conformal-gauge Liouville action
Liouville-Polyakov action (2)
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` Valid for any CFT
` We can compute correlators ⟨𝑇𝑇… ⟩ by varying 𝑔 → 𝑔 + ℎ and taking derivatives of 𝑆0 with respect to ℎ
` The conformal form 𝑆0[𝑒2Ω𝛿] contains the same information as 𝑆0[𝑔]
Æ Can also use 𝑆0 𝑒2 𝛿 to compute ⟨𝑇𝑇… ⟩
(We will come back to this point later)
𝑇𝑇-deforming Liouville action (1)
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` We could expand 𝑆0[𝑔 + ℎ] in ℎ
` But we take a different approach
𝑒− 𝑆 [𝑔]+ 𝑆[𝑔] ∼ 𝑑𝛼 𝑑𝜙 𝑒−1
8 ∫ ℎℎ−𝑆 [𝑔+ℎ]
` Let’s consider how Liouville action 𝑆0[𝑔] is 𝑇𝑇-deformed (at 𝒪(𝛿𝜇))
From the deformed action 𝛿𝑆 𝑔 , we can compute any ⟨𝑇𝑇… ⟩for any 𝑇𝑇-deformed CFT
Possible approaches:
Need to evaluate 𝑆0[𝑔 + ℎ]
𝑇𝑇-deforming Liouville action (2)
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` In 2D, we can bring 𝑔 + ℎ back to original metric via diff, up to Weyl rescaling
𝑔 (𝑥) + ℎ (𝑥) 𝑑𝑥 𝑑𝑥 = 𝑒2Ψ 𝑔 𝑥 𝑑𝑥 𝑑𝑥
𝑥 = 𝑥 + 𝐴 (𝑥) For some 𝐴 𝑥 ,Ψ(𝑥)
This is possible even for finite ℎ = ∇ α + ∇ α + 2𝑔 Φ
Æ easy to evaluateÆ 𝑆0 𝑔(𝑥) + ℎ(𝑥) = 𝑆0[𝑒2Ψ 𝑔 𝑥 ]
𝐴 2 ,Ψ(2), … are complicated (nonlocal)
Our approach:
𝑇𝑇-deforming Liouville action (3)
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For 𝑒2Ψ 𝑔 𝑥 ≡ 𝑔 𝑥 ,
Æ Using the master formula and carrying outGaussian integration, we can get 𝛿𝑆
𝑇𝑇-deforming Liouville action (4)
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𝛿𝑆[𝑔] = 𝛿𝑆saddle[𝑔] + 𝛿𝑆 l t[𝑔]
` Exact at 𝒪 𝛿𝜇
` Nonlocal (expected of 𝑇𝑇-deformed theory, but so was original LP action...)
` 𝛿𝑆 l t is fluctuation term coming from Gaussian integral.
` Contains contribution from Ψ(2). Very complicated and divergent. Depends on measure.
` Vanishes after regularization (this can be shown using conformal pert theory)
` Non-vanishing at 𝒪(𝛿𝜇2) [Kraus-Liu-Marolf ’18]
` Can be dropped at large 𝑐 (𝛿𝑆saddle ∼ 𝑐 +1𝛿𝜇 ), which is relevant for holography
𝑇𝑇-deforming Liouville action (5)
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𝛿𝑆 is very simple in conformal gauge:
` “Local” in Ω but it’s really nonlocal (just like the CFT Liouville action)
` We will use this to compute 𝑇 correlators
Higher order
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` The same procedure gives a differential equation to determine the effective action 𝑆 [𝑒2Ω𝛿] at finite deformation 𝜇:
` We ignored fluctuation (i.e., it’s valid at large 𝑐)
` Recursive relation:
where 𝑆 = ∑!𝐒
` No longer “local” in Ω at 𝒪(𝜇2)
Summary so far
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Polyakov-Liouville action
Deformed action at 𝒪 𝛿𝜇
Was useful: ℎ = ∇ α + ∇ α + 2𝑔 Φ
diff Weyl
Getting 𝑇 correlators (1)
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` We can get ⟨𝑇𝑇… ⟩ by varying 𝑔 → 𝑔 + ℎ,expanding 𝑍 𝑔 + ℎ = 𝑒−𝑆 [𝑔+ℎ] in ℎ,and reading off coefficients.
We know this.CFT: Liouville action 𝑆0deformed: 𝛿𝑆 we just computed
Getting 𝑇 correlators (2)
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` Flat background: 𝑔 = 𝛿, 𝑑𝑠2 = 𝑑𝑧𝑑 𝑧.
Coeff of 𝜕𝛼
Coeff of ��𝛼
Coeff of 𝜙
𝑇 = 𝑇
𝑇 = 𝑇
Θ = 𝑇
e.g.
→ 𝑇𝑇 ∼ 1−
𝑆𝑒 𝛿 + ℎ ⊃ ∬ −
ℎ = 𝜕 α + 𝜕 α + 2𝑔 Φ
Using conformal-gauge action
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` Can use conformal-gauge action 𝑆e 𝑒2Ω𝛿 instead of 𝑆e [𝑔] to compute 𝑇 correlators
1. Start with flat backgnd, 𝑑𝑠2 = 𝑑𝑧 𝑑 𝑧
2. Vary 𝛿 → 𝛿 + ℎ. 𝑑𝑠 2 = 𝑑𝑧 𝑑 𝑧 + 2 𝜕𝛼 𝑑𝑧2 + ��𝛼 𝑑 𝑧2 + 𝜙 𝑑𝑧 𝑑 𝑧 .(Here 𝛼, 𝜙 are finite.)
3. Find diff 𝑥 → 𝑥 = 𝑥 + 𝐴(𝑥) that brings metric into conformal gauge:
𝑑𝑠 2 = 𝑒2Ψ( , )𝑑�� 𝑑 ��
4. Compute 𝑆e 𝑒2Ψ𝛿 = 𝑆e 𝛿 + ℎ
5. Read off correlator from expansion
Similar to what we did when we computed deformed Liouville action. But here we need 𝐴,Ψ to higher order to compute higher correlator 𝑇𝑇𝑇… .
Check: the case of CFT
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To check that this method works, let’s apply it to some CFT correlators.
Conformal-gauge action:
𝑆e = 𝑆0 𝑒2Ω𝛿 = −𝑐
12𝜋𝑑2𝑧 𝜕Ω ��Ω
Let’s reproduce the known expressions
𝑇1𝑇2 =𝑐
2𝑧124
𝑇1𝑇2𝑇3 =𝑐
𝑧122 𝑧132 𝑧232
2pt:
3pt:
CFT 2pt func (1)
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To see how it goes, let’s carry out this procedure for CFT.
�� = 𝑧 + 𝐴(1) + 𝐴 2 + ⋯ ,
Varied action:
𝑆0 𝑒2Ψ( , )𝛿 = −𝑐
12𝜋𝑑2�� 𝜕 Ψ 𝜕zΨ
𝐴(1) = 𝛼
Ψ = Ψ 1 + Ψ 2 +⋯ , Ψ 1 = Φ = 𝜙 − (𝜕𝛼 + ��𝛼)
Want ⟨𝑇𝑇⟩Æ Extract coeff of ��𝛼 ��𝛼
= −𝑐
12𝜋𝑑2𝑧 𝜕 𝜙 − 𝜕𝛼 + ��𝛼 �� 𝜙 − 𝜕𝛼 + ��𝛼 + (higher)
= −𝑐
12𝜋𝑑2𝑧 𝜕Ψ ��Ψ + (higher)
CFT 2pt func (2)
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𝑆0 𝑒2Ψ( , )𝛿 ⊃ −𝑐
12𝜋 𝑑2𝑧 𝜕2𝛼 𝜕��𝛼
��1𝑧= 2𝜋𝛿2(𝑧)
=𝑐
12𝜋 𝑑2𝑧 𝜕3𝛼 ��𝛼
=𝑐
12𝜋 𝑑2𝑧 𝜕31����𝛼 ��𝛼
1��=
12𝜋
𝑑2𝑧𝑧 − 𝑧′ 𝜕3
1��=−3𝜋
𝑑2𝑧𝑧 − 𝑧 4
(above) =−𝑐4𝜋 𝑑2𝑧
��𝛼 𝑧 ��𝛼 𝑧𝑧 − 𝑧 4
⟨𝑇𝑇 ⟩ =𝑐
2 𝑧 − 𝑧 4
Here
Therefore
3
Also,Cf. Θ = − 1
48𝑅
(“created” ��𝛼)
CFT 3pt func
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Conformal-gauge action 𝑆0[𝑒2Ω𝛿] is quadratic. How can we get ⟨𝑇𝑇𝑇⟩?
1. Need to rewrite ��, �� in 𝑆0[𝑒2Ψ , 𝛿] in terms of 𝑧, 𝑧
2. Ψ = Ψ 1 + Ψ 2 +⋯
𝑆0 𝑒2Ψ( , )𝛿 = − 𝑐12 ∫ 𝑑2�� 𝜕 Ψ(𝑥) 𝜕 Ψ(𝑥)
𝒪(ℎ) 𝒪(ℎ2)
𝜕 ��, ��𝜕 𝑧, 𝑧
𝑑2𝑧𝜕𝑧𝜕�� 𝜕 +
𝜕 𝑧𝜕�� ��
𝜕𝑧𝜕 ��
𝜕 +𝜕 𝑧𝜕 ��
��
𝑇1𝑇2𝑇3 = 𝑐` By similar manipulations, can check
𝑥 + 𝐴(𝑥)
` All contributions are needed to reproduce the correct result
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Explicit forms of second-order terms:
Deformed 𝑇-correlators (1)
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We just reproduced CFT correlators.
Now consider deformed ones.
𝛿𝑆 𝑒2Ω𝛿 =
= −2(𝜕Ω)(��Ω)(𝜕��Ω) + 𝒪(Ω4)
What’s known in the literature at 𝒪(𝛿𝜇):` 3pt functions (based on conformal pert theory [Kraus-Liu-Marolf ’18],
and random geom and WT id [Aharony-Vaknin ’18])
` No 4pt functions
Deformed 3pt functions
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Deformed 3pt func is just like CFT 2pt func;Simply set Ω → Ψ ∼ Φ = 𝜙 − (𝜕𝛼 + ��𝛼) and also 𝑥 ∼ 𝑥
𝛿𝑆 𝑒2Ω𝛿 ⊃
Straightforward to read off
Reproduces known results
Deformed 4pt functions
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Deformed 4pt func is similar to CFT 3pt func.
We have to take into account 𝑥 = 𝑥 + 𝐴(𝑥) and correction Ψ 2 .Also, 𝛿𝑆 has quartic terms 𝒪(Ω4) as well.
All contributions are needed for final results
Deformed OPEs?
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Can understand these from deformed OPEs?
OPEs from 3pt funcs (1)
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` 3pt func is reproduced
` Consistent with the flow equation Θ = − 𝑇𝑇
OPEs from 3pt funcs (2)
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More interesting:
= −2𝑐 𝛿𝜇𝜋
1𝑧 − 𝑤
𝑑𝑧′ 𝑇(𝑧′) + (𝑧 ↔ 𝑤)
` Can be regarded as coming from field-dependent diff[Conti, Negro, Tateo ’18,’19] [Cardy ’19]
𝑇 𝑧 → 𝑇 𝑧 + 𝜖 = 𝑇 + 𝜕𝑇 𝜖, 𝜖 =𝛿𝜇𝜋 𝑑𝑧 𝑇 𝑧
𝑇 𝑧 𝑇 𝑤 → 𝑇 𝑧 ��𝑇 𝑤 𝜖 ∼ − 2𝑐−
𝜖
` Non-local OPE
OPEs from 3pt funcs (3)
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Different pair in the same 3pt func:
` Again, comes from field-dependent diff
𝑇 𝑧 → 𝑇 𝑧 + 𝜖 = 𝑇 + 𝜕𝑇 𝜖, 𝜖 =𝛿𝜇𝜋 𝑑𝑧 𝑇 𝑧
𝑇 𝑧 𝑇 𝑤 → 𝑇 𝑧 𝜖 ��𝑇 𝑤 ∼ 𝑇 𝑧 ∫ 𝑑𝑧 𝑇 𝑧 ��𝑇 𝑤 → (above)
Consistency check with 4pt funcs
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Check OPEs derived above using 4pt funcs:
−2𝑐 𝛿𝜇𝜋 𝑧34
𝑑𝑧 ⟨𝑇 𝑧1 𝑇(𝑧2)𝑇 𝑧 ⟩ + (𝑧3 ↔ 𝑧4)
Å 𝑇𝑇 OPE at 𝒪(𝛿𝜇0)
Å 𝑇𝑇 OPE at 𝒪(𝛿𝜇)
Agrees with the 𝑧34 → 0 expansion of the 4pt func
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Summary:` Studied the stress-energy sector of 𝑇𝑇-deformed theories using random
geometry approach
` Found 𝑇𝑇-deformed Liouville-Polyakov action exactly at 𝒪(𝛿𝜇)
` Derived equation to determine deformed action for finite 𝜇
` Developed technique to compute 𝑇-correlators
Correlators at 𝒪(𝛿𝜇) is computable also by conformal perturbation theory. Random geometry approach seems to allow straightforward generalization to higher order, at least formally
` Deformed OPEs show sign of non-locality
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Future directions:` Go to higher order in 𝛿𝜇
` Solve the differential equation for 𝑆 [𝑔]? Large 𝑐 (dual to classical gravity)?
` All-order correlators, such as 𝐺Θ 𝑧12 ≡ ⟨Θ(𝑧1)Θ(𝑧2)⟩ ?Expectation: 𝐺Θ < 0 at short distances (negative norm)cf. [Haruna-Ishii-Kawai-Skai-Yoshida ’20]
` Better understand the fluctuation part 𝑆 l t
` Why does it vanish at 𝒪 𝛿𝜇 , as indicated by conf pert theory?
` Use vanishing of it at 𝒪 𝛿𝜇 to regularize 𝑆 l t
` More
` Compute physically interesting quantities
` Inclusion of matter Æ modify the 𝑇𝑇 operator?
` Position-dependent coupling cf. [Chandra et al., 2101.01185]