REVIEW
Regularization by Dimensional Reduction: Consistency, Quantum Action Principle, and Supersymmetry
High Energy Physics - Phenomenology · Submitted 14 Mar 2005 · 25 references
Pith's verdict: A careful, honest attempt to put DRED on a firm footing; the construction is checkable and the QAP transfer is justified, with the gamma-counting rules the main place where detail is thin.
T0 · AI review
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Referee report
The paper
The paper claims
Dimensional reduction, the regularization most loop calculations in supersymmetric theories rely on, is given an explicit consistent construction, and the quantum action principle is shown to hold in it.
The reading
What carries the argument
The quasi-four-dimensional space $Q_4S$, built as the direct sum of a formally $D$-dimensional and a formally $(4-D)$-dimensional infinite-dimensional space, with metric tensors satisfying $g^{mn} = g^{mn} + g^{mn}$, $g^{mn}g_{mn} = D$, $g^{mn}g_{mn} = 4-D$, and $g^{mn}g_{mn} = 0$. It is what allows the $D$-dimensional momentum space to sit inside the four-dimensional one, so that $p p = p^2$ and the Dirac propagator $(p+m)/(p^2-m^2)$ really inverts $(p-m)$ — the property the whole consistency argument rests on. On top of it, the quantum action principle converts a statement about symmetry breaking into a statement about inserting a specific operator into 1PI Green functions, and the paper reduces the question of whether a given Slavnov-Taylor identity holds to counting how many gamma matrices can survive in the closed fermion line of the relevant diagrams.
Extended reading notes
Core claim
The paper makes two claims and then uses the second to do physics. First, dimensional reduction can be given a mathematically consistent formulation: the space in which the four-dimensional objects live is not four-dimensional but a quasi-four-dimensional space $Q_4S = Q_DS + Q_4S$, the direct sum of two infinite-dimensional spaces carrying metric tensors $g^{mn}$ and $g^{mn}$ with $g^{mn}g_{mn} = D$ and $g^{mn}g_{mn} = 4-D$. Appendix A gives explicit gamma matrices, an anticommuting $g_5$, a charge conjugation matrix, and a trace definition in this space, so that index counting fails (five Lorentz indices can all be different) while the Dirac algebra, hermiticity, and the usual charge-conjugation rearrangements still hold. The practical cost is that Fierz identities are not available. Second, in this formulation the quantum action principle holds at all orders: $i d <T f_1...f_n> = <T f_1...f_n D>$, where $D$ is the integrated variation of the Lagrangian. The proof is the one known for dimensional regularization, and it turns on two facts that the construction preserves: the free propagator is genuinely the inverse of the kinetic operator, $D_ij P_jk = i d_ik$, and scaleless integrals vanish. Applied to the Slavnov-Taylor identity of a general supersymmetric gauge theory, this yields a master equation $S(G_DRED) = i[S(G_cl)] · G_DRED$, and the author evaluates $S(G_cl)$ explicitly: it is a sum of four-fermion operators, all of which vanish in strictly four dimensions where Fierz rearrangements are allowed, and none of which vanish identically in the quasi-four-dimensional space.
Load-bearing premise
The proof that the quantum action principle holds in dimensional regularization is taken over to the new space without being re-derived step by step; that transfer needs the free propagator to remain the exact inverse of the kinetic operator inside the infinite-dimensional construction.
Editorial extensions
If this is right
- Dimensional reduction can be used without the internal contradiction that made it hard to prove general statements about it; the calculational rules of Section 2 are self-consistent, with the single exception that Fierz identities may not be used.
- The supersymmetry Slavnov-Taylor identity relating the scalar and fermion propagators of a chiral multiplet holds in dimensional reduction up to the two-loop level, because the closed fermion line in the relevant diagrams can carry at most three gamma matrices.
- The identity governing the loop-corrected supersymmetry transformations of the scalar and fermion holds up to two loops by the same counting argument.
- The Slavnov-Taylor identity that fixes the quartic scalar coupling in terms of gauge and superpotential couplings — the relation behind the tree-level Higgs mass bound — holds at one loop in dimensional reduction, a case not previously checked.
- If a totally anticommuting $g_5$ is used, the breaking terms are purely four-fermion operators; if instead a strictly four-dimensional $g_5$ is used, even the simplest one-loop propagator identities fail, just as in dimensional regularization.
- The counting rules indicate where violations could first appear at higher orders, so supersymmetry-restoring counterterms, if needed, would be needed only in a much narrower class of diagrams than in dimensional regularization.
Reading between the lines
- The paper's counting criterion — how many gamma matrices can survive in the closed fermion loop after loop-momentum integration — is a practical diagnostic that could be applied diagram-by-diagram in real calculations to decide in advance whether a given Green function is safe in dimensional reduction.
- Because the construction replaces four-dimensional index counting with an infinite-dimensional space, any calculation that silently relies on identities valid only for a finite number of dimensions (Fierz being the named example) becomes suspect; this suggests auditing existing dimensional-reduction results for hidden Fierz use rather than re-deriving them wholesale.
- The same master-equation technique should transfer to other symmetries with equal ease, since the machinery only needs the classical action and the variation of the Lagrangian; gauge and translational Ward identities are the obvious next targets.
- The explicit two-loop violation channel the author flags for the quartic-coupling identity — an exchanged vector boson supplying an extra covariant to the fermion line — is concrete enough to be checked directly, and would be the natural first place to look for a genuine breakdown.
Original abstract
It is proven by explicit construction that regularization by dimensional reduction can be formulated in a mathematically consistent way. In this formulation the quantum action principle is shown to hold. This provides an intuitive and elegant relation between the D-dimensional Lagrangian and Ward or Slavnov-Taylor identities, and it can be used in particular to study to what extent dimensional reduction preserves supersymmetry. We give several examples of previously unchecked cases.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
It is proven by explicit construction that regularization by dimensional reduction can be formulated in a mathematically consistent way. In this formulation the quantum action principle is shown to hold. This provides an intuitive and elegant relation between the D-dimensional Lagrangian and Ward or Slavnov-Taylor identities, and it can be used in particular to study to what extent dimensional reduction preserves supersymmetry. We give several examples of previously unchecked cases.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | It is proven by explicit construction that regularization by dimensional reduction can be formulated in a mathematically consistent way. | result 0.95 | 0.88 | 0.78 | asserted 1.00 |
| s1 | In this formulation the quantum action principle is shown to hold. | result 0.99 | 0.91 | 0.14 | asserted 1.00 |
| s2 | This provides an intuitive and elegant relation between the D-dimensional Lagrangian and Ward or Slavnov-Taylor identities, and it can be used in particular to study to what extent dimensional reduction preserves supersymmetry. | interpretation 0.95 | 0.77 | 0.20 | asserted 0.70 |
| s3 | We give several examples of previously unchecked cases. | contribution 0.93 | 0.90 | 0.03 | asserted 0.91 |
What was examined, and what was not
- arXiv listing abstract v3
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- relations to other papers
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Figures
Figures reproduced from arXiv:hep-ph/0503129 by the authors.
References
How later papers used it
62 later papers cite it
2 later papers by other authors are listed below: 2 used its method or tool.
Uses its method or tool 2 of 10 papers with this label
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Chose to work in the dimensional reduction scheme of this paper, which preserves supersymmetry.
CP violation at one loop in the polarization-independent chargino production in e+e- collisions (2007) · 0.84 · paraphrased: the licence does not allow quoting
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Used dimensional reduction, which preserves supersymmetry, to regularize one-loop integrals, citing this paper.
One-loop corrections to three-body leptonic chargino decays (2007) · 0.94 · paraphrased: the licence does not allow quoting
How the literature uses it
56 arXiv papers cite this in 74 sentences
Papers citing it · 56 sentences without a confident label
Contests it 1 paper
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We note that there are inconsistencies in Siegel's RDR scheme which have been pointed out by several authors including Siegel himself [ref] .
${\cal N}=4$ supersymmetric Yang-Mills thermodynamics to order $\lambda^2$ · Introduction · contest 0.81
Builds on it 1 paper
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Beyond the extensions shown in Table [ref], we also supplement the operators provided in Refs. [ref] by a set of operators that are needed when matching a UV model regularised using dimensional reduction (), as introduced in Refs. [ref] , to an EFT regularised using dimensional regularisation (), introduced in Ref. [ref] .
One Formula To Match Them All: The Bispinor Universal One-Loop Effective Action · Introduction · 0.88
Uses its method or tool 8 papers
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These diagrams are regulated dimensionally in $D=4-2ε$ dimensions within the supersymmetry preserving four-dimensional helicity scheme [ref] so that UV and IR divergences appear as poles of the form $ε^-1$ and $ε^-2$.
Radiative corrections to stop-antistop annihilation into gluons and light quarks · Virtual corrections and renormalization · 1.00
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As regularization scheme we have used constrained differential regularization [ref] , which has been shown to be equivalent to dimensional reduction [ref] at the level [ref] , thus preserving supersymmetry [ref] .
The Charged Higgs Boson Mass of the MSSM in the Feynman-Diagrammatic Approach · One-loop corrections · 0.93
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The loop integrals are regularised via dimensional reduction [ref] , which ensures that SUSY is preserved, via the implementation described in Refs. [ref] .
Consistent on shell renormalisation of electroweakinos in the complex MSSM: LHC and LC predictions · NLO predictions at the LHC and the LC · 1.00
Cites it as support 3 papers
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It is also a convenient choice regarding the non-breaking of supersymmetry [ref] .
$\gamma_{5}$ in FDH · FDH and DRED · 0.96
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However, it has been shown [ref] that such inconsistencies become active only in the higher orders of perturbation theory, when, for example, traces over at least ten $γ$-matrices and anti-symmetrization over five indices are involved.
Precision Calculations in Supersymmetric Theories · Framework · 0.96
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Thus the employed regularization scheme preserves SUSY [ref] and guarantees that the SUSY relations are kept intact, that the gauge couplings of the SM vertices and the Yukawa couplings of the corresponding SUSY vertices also coincide to order in the SUSY limit.
Chargino and Neutralino Production at e+e- Colliders in the Complex MSSM: A Full One-Loop Analysis · Ultraviolet, infrared and collinear divergences · 0.97
Cites it as background 4 papers
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This quasi-$4$-dimensional space is decomposed as $Q4S=QdS⊕QϵS$, where $QdS$ is an infinite dimensional space that is formally $d$-dimensional and $QϵS$ is its complement, formally of dimension $ϵ=4-d$ [ref] .
Extending the Universal One-Loop Effective Action by Regularization Scheme Translating Operators · Epsilon scalars in dimensional reduction · 0.92
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The problem has been known since a long time [ref] , yet the precision required to confront with experiments in order to assess evidence of indirect signals of new Beyond-the-Standard-Model (BSM) physics calls for the development of efficient tools in order to ensure the fulfillment of the relevant symmetries of the model and consequently the consistency of the inserted finite counter-terms.
Gauge-Invariant Quantum Fields · Introduction · 0.81
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Among them are the Conventional Dimensional Regularisation (CDR, introduced in [ref]), the `t Hooft and Veltman (HV) scheme [ref] , the Four-Dimensional Helicity scheme (FDH) [ref] and Dimensional Reduction (DRED) [ref] .
Four-dimensional representation of scattering amplitudes and physical observables through the application of the Loop-Tree Duality theorem · A brief review of other regularisation methods · 0.99
Discussion
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