Hamiltonian formulation of Carrollian Maxwell theory in Deformed Light-cone Kaluza-Klein-like Null reduction
Pith reviewed 2026-06-26 11:44 UTC · model grok-4.3
The pith
Kaluza-Klein-like null reduction of a complex Maxwell field in a Bargmann deformed light-cone background produces both magnetic and electric Carrollian Maxwell theories while preserving gauge symmetry.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Performing Kaluza-Klein-like null reduction of a complex Maxwell field in a Bargmann deformed light-cone background with manifest gauge symmetry yields both magnetic and electric Carrollian Maxwell theories. The procedure preserves a first-class U(1) Gauss constraint throughout the Carrollian limit, so gauge invariance is maintained in the Hamiltonian formulation. By choosing different scalings one obtains the standard magnetic Carrollian theory and the electric Carrollian theory; in addition a scalar field can appear in the resulting theory in a coupled or decoupled way.
What carries the argument
The Kaluza-Klein-like null reduction applied to a complex Maxwell field inside a Bargmann deformed light-cone background, with scalings chosen so that the U(1) Gauss constraint stays first-class.
If this is right
- Gauge invariance remains intact in the Hamiltonian formulation of the obtained Carrollian theories.
- A scalar field can enter the Carrollian theory either coupled to the Maxwell sector or decoupled from it.
- The same reduction procedure can generate both the magnetic and the electric Carrollian Maxwell theories from one starting setup.
- The method supplies an explicit working example for applying the deformed light-cone null reduction to gauge theories.
Where Pith is reading between the lines
- The same background and scaling technique could be tried on non-Abelian gauge fields to produce Carrollian Yang-Mills theories.
- The decoupled scalar that appears for some scalings may correspond to a new degree of freedom whose Carrollian dynamics has not yet been explored in the literature.
- Varying the deformation parameter of the light-cone background might produce still other Carrollian limits that interpolate between magnetic and electric regimes.
Load-bearing premise
The chosen Bargmann deformed light-cone background together with the selected field scalings keep the U(1) Gauss constraint first-class and produce consistent Carrollian theories without extra inconsistencies.
What would settle it
An explicit reduction calculation that shows the Gauss constraint becoming second-class or that the resulting equations fail to match the known Carrollian Maxwell dynamics under the stated scalings would falsify the construction.
Figures
read the original abstract
We construct magnetic and electric Carrollian Maxwell theories by performing Kaluza-Klein-like null reduction of a complex Maxwell field in a Bargmann deformed light-cone background with manifest gauge symmetry. The procedure preserves a first-class U(1) Gauss constraint throughout the Carrollian limit. Gauge invariance is therefore maintained in our Hamiltonian formulation. By choosing different scalings, we obtain standard magnetic Carrollian theory and electric Carrollian theory. However, a scalar field could appear in the Carrollian theory in a coupled or decoupled way, which has not been found by previous methods. This result fully reveals the diversity of Carrollian theories accessible through the deformed light-cone Kaluza-Klein-like null reduction method. Furthermore, our work provides an explicit example of the correct application of this approach, thereby broadening the scope of its applicability to gauge theories.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript constructs magnetic and electric Carrollian Maxwell theories via a Kaluza-Klein-like null reduction of a complex Maxwell field on a Bargmann-deformed light-cone background. It asserts that the reduction preserves a first-class U(1) Gauss constraint and manifest gauge invariance in the Hamiltonian formulation; different scalings are stated to recover the standard magnetic and electric Carrollian theories, with optional scalar coupling that prior methods did not produce.
Significance. If the explicit reduction steps and constraint algebra are verified, the work supplies a concrete example of applying the deformed light-cone null-reduction technique to gauge theories, thereby extending its reach and revealing additional Carrollian models not previously obtained.
major comments (1)
- [Abstract] Abstract: the central claim that the chosen Bargmann-deformed light-cone background and scalings preserve the first-class nature of the U(1) Gauss constraint throughout the Carrollian limit is asserted without any displayed reduction ansatz, Poisson-bracket calculation, or verification that no second-class constraints arise. This verification is load-bearing for the construction and must be supplied explicitly (e.g., in the section deriving the reduced Hamiltonian and constraints).
Simulated Author's Rebuttal
We thank the referee for their detailed reading and for identifying the need to strengthen the presentation of the constraint analysis. We address the major comment below and will revise the manuscript to incorporate the requested explicit verification.
read point-by-point responses
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Referee: [Abstract] Abstract: the central claim that the chosen Bargmann-deformed light-cone background and scalings preserve the first-class nature of the U(1) Gauss constraint throughout the Carrollian limit is asserted without any displayed reduction ansatz, Poisson-bracket calculation, or verification that no second-class constraints arise. This verification is load-bearing for the construction and must be supplied explicitly (e.g., in the section deriving the reduced Hamiltonian and constraints).
Authors: We agree that the explicit verification is essential for substantiating the central claim. The manuscript asserts preservation of the first-class Gauss constraint but does not display the full reduction ansatz, Poisson-bracket computations, or explicit check against second-class constraints. In the revised manuscript we will add these calculations in the section on the reduced Hamiltonian and constraints, including the ansatz for the fields and momenta, the computation of the relevant Poisson brackets, and the demonstration that the Gauss constraint remains first-class with no second-class constraints generated by the reduction. revision: yes
Circularity Check
No significant circularity identified
full rationale
The paper presents an explicit constructive procedure: Kaluza-Klein-like null reduction of a complex Maxwell field on a Bargmann-deformed light-cone background, with different scalings yielding magnetic/electric Carrollian theories while preserving the first-class U(1) Gauss constraint. No fitted parameters are renamed as predictions, no self-definitional loops appear in the reduction ansatz, and no load-bearing self-citations or uniqueness theorems imported from prior author work are invoked to force the result. The derivation chain is self-contained as a direct reduction from the higher-dimensional setup; the central claim (constraint preservation and theory diversity) follows from the stated procedure without reducing to its own inputs by construction.
Axiom & Free-Parameter Ledger
free parameters (1)
- scaling parameters for magnetic vs electric limits
axioms (1)
- domain assumption The Bargmann deformed light-cone background preserves the first-class U(1) Gauss constraint in the Carrollian limit.
Reference graph
Works this paper leans on
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[1]
The kinetic terms must remain finite, and the Gauss-multiplier term should also survive to enforce the constraint
Standard contraction For the magnetic contraction we wish to keep the mag- netic energy ∝ |F ′ ij|2 while suppressing the electric energy ∝ |Π′i|2. The kinetic terms must remain finite, and the Gauss-multiplier term should also survive to enforce the constraint. Examining Table I, a consistent choice of exponents is γA =−1, γ Π = 0, α A =−2, αΠ = 1, β A =...
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[2]
If one wishes to avoid introducingm, a viable choice is γA =−1, γ Π = 0, α A =−2, αΠ = 1, β A =−1, β Π = 0, µ=−3
Contraction induces decoupling with the scalar sector It should be noted that in (3.4), A− is no longer present, which of course stems from our choice of scaling exponents. If one wishes to avoid introducingm, a viable choice is γA =−1, γ Π = 0, α A =−2, αΠ = 1, β A =−1, β Π = 0, µ=−3. (3.14) And the action reads S(1) mag = Z dτ d⃗ x Πi∂τ Ai + Πτ ∂τ Aτ − ...
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[3]
It cannot propagate and does not carry energy in the Carrollian sense
Thus A− describes a frozen, non-dynamical scalar field. It cannot propagate and does not carry energy in the Carrollian sense. What’s more, the transverse gauge fields Ai, Πi and the Gauss constraint are completely decoupled from the scalar sector. And the residual U(1) gauge symmetry acts only onA i andA τ, whileA − is gauge invariant. In standard magnet...
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[4]
The lowest -order mixing term between the transverse momentum and the scalar is c2+γΠ+βA Re Π′i ∂iA′ −
No Contraction induces coupling with the scalar sector In the magnetic Carrollian theory, the survival of the transverse kinetic term and the magnetic energy forces the scaling exponents γA = −1 and γΠ = 0, completely fixing the scaling of the gauge sector. The lowest -order mixing term between the transverse momentum and the scalar is c2+γΠ+βA Re Π′i ∂iA...
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[5]
(3.17) Thec→0 limit yields the real action: Selec = Z dτ d⃗ x h Πi∂τ Ai +(Πτ ∂τ Aτ) − 1 2ΠiΠi +A τ ∂iΠi −uΠ τ i
Standard contraction To preserve the electric energy ∝ ΠiΠi while discarding the magnetic energy, γA = 0, γ Π =−1, α A =−1, αΠ = 0, β A = 0, β Π = 0, µ=−2. (3.17) Thec→0 limit yields the real action: Selec = Z dτ d⃗ x h Πi∂τ Ai +(Πτ ∂τ Aτ) − 1 2ΠiΠi +A τ ∂iΠi −uΠ τ i . (3.18) Varying action (3.17) yields several equations of motion: •Variation with respec...
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[6]
(3.27) The new equations of motion are ∂τ A− = Π−, ∂ τΠ− = 0⇒∂ 2 τ A− = 0
Contraction induces decoupling with the scalar sector If we choose the following scaling: γA = 0, γ Π =−1, α A =−1, αΠ = 0, β A = 0, β Π =−1, µ=−2, (3.26) we can preserve scalar sector A− but in a decoupled way: S(1) elec = Z dτ d⃗ x h Πi∂τ Ai + Πτ ∂τ Aτ + Π−∂τ A− −1 2ΠiΠi − 1 2Π−Π− +A τ ∂iΠi −uΠ τ i . (3.27) The new equations of motion are ∂τ A− = Π−, ∂ ...
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[7]
(3.33) The equations of motion are δΠi :∂ τ Ai = Πi +∂ iA−, δAi :−∂ τΠi = 0, δΠ− :∂ τ A− = 0, δA− :−∂ τΠ− +∂ 2 i A− +∂ iΠi = 0
Contraction induces coupling with the scalar sector We choose the following scaling: γA = 0, γ Π =−1, α A = 0, αΠ = 0, β A =−1, β Π = 0, µ= 0, (3.32) to obtain the action preserving scalar sector A− but in a coupled way: S(3) elec = Z dτ d⃗ x h Πi∂τ Ai + Π−∂τ A− − 1 2ΠiΠi −1 2(∂iA−)(∂iA−)−Π i∂iA− i . (3.33) The equations of motion are δΠi :∂ τ Ai = Πi +∂ ...
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[8]
performed a similar reduction for a complex vector theory. However, surprisingly, the resulting Carrollian theory turned out to be a collection of free complex scalar fields lacking gauge symmetry, with an increased number of physical degrees of freedom due to the loss of symmetry constraints. Based on a framework involving independent scaling of differen...
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[9]
However, it is worth emphasizing that the resulting Carrollian theory depends on the specific choice of scaling
We have already illustrated this for Maxwell theory in Section II and III. However, it is worth emphasizing that the resulting Carrollian theory depends on the specific choice of scaling. Although this approach effectively preserves the phase space structure, it sacrifices the convenience of dynam- ically realizing Carrollian conformal symmetry. In any ca...
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[10]
The multipliers appear only linearly: −uΠτ and −wΠσ
Integratinguandw. The multipliers appear only linearly: −uΠτ and −wΠσ. Functional integration over u and w yields delta-functionals that impose the primary con- straints: Z Du e i ℏ R −uΠτ ∝δ[Π τ], Z Dw e i ℏ R −wΠσ ∝δ[Π σ]. (B.2) Hence we can set Π τ = 0 and Π σ = 0 in the remain- ing integral. 8
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[11]
With Πτ = 0, the term Π τ ∂τ Aτ disappears and the Aτ dependence reduces to Aτ ∂iΠi
IntegratingA τ andσ. With Πτ = 0, the term Π τ ∂τ Aτ disappears and the Aτ dependence reduces to Aτ ∂iΠi. The functional integral overA τ gives Z DAτ exp i ℏ Z Aτ ∂iΠi =δ[∂ iΠi].(B.3) This enforces the Gauss constraint ∂iΠi = 0. Simi- larly, with Π σ = 0, the term involving σ becomes −σ ∂2 i A−. Integrating overσyields Z Dσexp i ℏ Z −σ ∂2 i A− =δ[∂ 2 i A−...
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[12]
After this step, the generating functional reads Z∝ Z DAi DΠi DA− DΠ− δ[∂iΠi]δ[∂ 2 i A−] ×exp i ℏ Z dτ d⃗ x Πi∂τ Ai + Π−∂τ A− ×exp − i ℏ Z dτ d⃗ x 1 4 FijF ij + 1 2(∂iA−)(∂iA−) . (B.5)
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[13]
The functional integral over Π − then produces δ[∂τ A−], enforcing ∂τ A− = 0
Freezing the scalar sector. The functional integral over Π − then produces δ[∂τ A−], enforcing ∂τ A− = 0. Together with ∂2 i A− = 0 one obtains, for well -behaved bound- ary conditions, A− = constant (or zero). The scalar sector is thus completely frozen and contributes only an irrelevant constant factor to the generating functional
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[14]
After the previous steps the path integral reduces to Z∝ Z DAi DΠi δ[∂iΠi] exp i ℏ Z dτ d⃗ x Πi∂τ Ai − 1 4 FijF ij
Gauge fixing and transverse decomposition. After the previous steps the path integral reduces to Z∝ Z DAi DΠi δ[∂iΠi] exp i ℏ Z dτ d⃗ x Πi∂τ Ai − 1 4 FijF ij . (B.6) The remaining Gauss constraint ∂iΠi = 0 is still first-class and generates the U(1) gauge transforma- tions δAi = ∂iϵ. To eliminate the gauge redundancy we choose the Coulomb gauge χ≡∂ iAi = ...
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[15]
Substituting the decomposition into the action (B.7), the magnetic term simplifies because the lon- gitudinal parts drop out
Two point correlation function. Substituting the decomposition into the action (B.7), the magnetic term simplifies because the lon- gitudinal parts drop out. the generating functional reduces to Z∝ Z DA⊥ i DΠi⊥ exp h i ℏ Z dτ d⃗ x Πi⊥∂τ A⊥ i − 1 2(∂iA⊥ j )(∂iAj⊥ ) i . (B.7) Because of Z DΠi⊥ exp i ℏ Z Πi⊥∂τ A⊥ i ∝δ[∂ τ A⊥ i ], the transverse field have to...
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