Recent theorems

13T1 Theorem
Replacing fields with the solutions of their field equations preserves the master equation 
12T1 Theorem
Procedure to convert the functional integral to the conventional form 
06T1 Theorem
Terms quadratically proportional to the field equations and field redefinitions 
05T1 Theorem
Maximum poles of Feynman diagrams
Recent Papers

18A2 Damiano Anselmi and Marco Piva
The ultraviolet behavior of quantum gravityA theory of quantum gravity has been recently proposed by means of a novel quantization prescription, which is able to turn the poles of the ... (read more)

18A1 Damiano Anselmi
Fakeons and LeeWick modelsThe “fakeon” is a fake degree of freedom, i.e. a degree of freedom that does not belong to the physical spectrum, but propagates inside the ... (read more)

17A3 Damiano Anselmi
On the quantum field theory of the gravitational interactionsWe study the main options for a unitary and renormalizable, local quantum field theory of the gravitational interactions. The first model is a LeeWick superrenormalizable ... (read more)

17A2 Damiano Anselmi and Marco Piva
Perturbative unitarity of LeeWick quantum field theoryWe study the perturbative unitarity of the LeeWick models, formulated as nonanalytically Wick rotated Euclidean theories. The complex energy plane is divided into disconnected regions ... (read more)

17A1 Damiano Anselmi and Marco Piva
A new formulation of LeeWick quantum field theoryThe LeeWick models are higherderivative theories that are claimed to be unitary thanks to a peculiar cancelation mechanism. In this paper, we provide a new ... (read more)

16A3 Damiano Anselmi
Algebraic cutting equationsWe prove a set of polynomial identities for complex numbers associated with Feynman diagrams. The equations are at the core of perturbative unitarity in quantum ... (read more)

16A2 Ugo G. Aglietti and Damiano Anselmi
Inconsistency of Minkowski higherderivative theoriesWe show that Minkowski higherderivative quantum field theories are generically inconsistent, because they generate nonlocal, nonHermitian ultraviolet divergences, which cannot be removed by means of ... (read more)

16A1 Damiano Anselmi
Aspects of perturbative unitarityWe reconsider perturbative unitarity in quantum field theory and upgrade several arguments and results. The minimum assumptions that lead to the largest time equation, the ... (read more)

15A4 Damiano Anselmi
Background field method and the cohomology of renormalizationUsing the background field method and the BatalinVilkovisky formalism, we prove a key theorem on the cohomology of perturbatively local functionals of arbitrary ghost numbers, ... (read more)

15A3 Damiano Anselmi
Some reference formulas for the generating functions of canonical transformationsWe study some properties of the canonical transformations in classical mechanics and quantum field theory and give a number of practical formulas concerning their generating ... (read more)

15A2 Damiano Anselmi
AdlerBardeen theorem and cancellation of gauge anomalies to all orders in nonrenormalizable theoriesWe prove the AdlerBardeen theorem in a large class of general gauge theories, including nonrenormalizable ones. We assume that the gauge symmetries are general covariance, ... (read more)

15A1 Damiano Anselmi
Ward identities and gauge independence in general chiral gauge theoriesUsing the BatalinVilkovisky formalism, we study the Ward identities and the equations of gauge dependence in potentially anomalous general gauge theories, renormalizable or not. A ... (read more)

14A2 D. Anselmi
Weighted power counting and chiral dimensional regularizationWe define a modified dimensionalregularization technique that overcomes several difficulties of the ordinary technique, and is specially designed to work efficiently in chiral and parity ... (read more)

14A1 D. Anselmi
AdlerBardeen theorem and manifest anomaly cancellation to all orders in gauge theoriesWe reconsider the AdlerBardeen theorem for the cancellation of gauge anomalies to all orders, when they vanish at one loop. Using the BatalinVilkovisky formalism and ... (read more)

13A3 D. Anselmi
Background field method, BatalinVilkovisky formalism and parametric completeness of renormalizationWe investigate the background field method with the BatalinVilkovisky formalism, to generalize known results, study parametric completeness and achieve a better understanding of several properties. ... (read more)
Papers
Here are all papers published on Renormalization.COM
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15A2 Damiano Anselmi
AdlerBardeen theorem and cancellation of gauge anomalies to all orders in nonrenormalizable theories
We prove the AdlerBardeen theorem in a large class of general gauge theories, including nonrenormalizable ones. We assume that the gauge symmetries are general covariance, local Lorentz symmetry and Abelian and nonAbelian YangMills symmetries, and that the local functionals of vanishing ghost numbers satisfy a variant of the KlubergStern–Zuber conjecture. We show that if the gauge anomalies are trivial at one loop, for every truncation of the theory there exists a subtraction scheme where they manifestly vanish to all orders, within the truncation. Outside the truncation the cancellation of gauge anomalies can be enforced by finetuning local counterterms. The framework of the proof is worked out by combining a recently formulated chiral dimensional regularization with a gauge invariant higherderivative regularization. If the higherderivative regularizing terms are placed well beyond the truncation, and the energy scale $\Lambda $ associated with them is kept fixed, the theory is superrenormalizable and has the property that, once the gauge anomalies are canceled at one loop, they manifestly vanish from two loops onwards by simple power counting. When the $\Lambda $ divergences are subtracted away and $\Lambda $ is sent to infinity, the anomaly cancellation survives in a manifest form within the truncation and in a nonmanifest form outside. The standard model coupled to quantum gravity satisfies all the assumptions, so it is free of gauge anomalies to all orders.
Phys. Rev. D 91 (2015) 105016  DOI: 10.1103/PhysRevD.91.105016
15A1 Damiano Anselmi
Ward identities and gauge independence in general chiral gauge theories
Using the BatalinVilkovisky formalism, we study the Ward identities and the equations of gauge dependence in potentially anomalous general gauge theories, renormalizable or not. A crucial new term, absent in manifestly nonanomalous theories, is responsible for interesting effects. We prove that gauge invariance always implies gauge independence, which in turn ensures perturbative unitarity. Precisely, we consider potentially anomalous theories that are actually free of gauge anomalies thanks to the AdlerBardeen theorem. We show that when we make a canonical transformation on the treelevel action, it is always possible to rerenormalize the divergences and refinetune the finite local counterterms, so that the renormalized $\Gamma $ functional of the transformed theory is also free of gauge anomalies, and is related to the renormalized $\Gamma $ functional of the starting theory by a canonical transformation. An unexpected consequence of our results is that the beta functions of the couplings may depend on the gaugefixing parameters, although the physical quantities remain gauge independent. We discuss nontrivial checks of highorder calculations based on gauge independence and determine how powerful they are.
Phys. Rev. D 92 (2015) 025027  DOI: 10.1103/PhysRevD.92.025027
We define a modified dimensionalregularization technique that overcomes several difficulties of the ordinary technique, and is specially designed to work efficiently in chiral and parity violating quantum field theories, in arbitrary dimensions greater than 2. When the dimension of spacetime is continued to complex values, spinors, vectors and tensors keep the components they have in the physical dimension, therefore the $\gamma $ matrices are the standard ones. Propagators are regularized with the help of evanescent higherderivative kinetic terms, which are of the Majorana type in the case of chiral fermions. If the new terms are organized in a clever way, weighted power counting provides an efficient control on the renormalization of the theory, and allows us to show that the resulting chiral dimensional regularization is consistent to all orders. The new technique considerably simplifies the proofs of properties that hold to all orders, and makes them suitable to be generalized to wider classes of models. Typical examples are the renormalizability of chiral gauge theories and the AdlerBardeen theorem. The difficulty of explicit computations, on the other hand, may increase.
Phys. Rev. D 89 (2014) 125024  DOI: 10.1103/PhysRevD.89.125024
14A1 D. Anselmi
AdlerBardeen theorem and manifest anomaly cancellation to all orders in gauge theories
We reconsider the AdlerBardeen theorem for the cancellation of gauge anomalies to all orders, when they vanish at one loop. Using the BatalinVilkovisky formalism and combining the dimensionalregularization technique with the higherderivative gauge invariant regularization, we prove the theorem in the most general perturbatively unitary renormalizable gauge theories coupled to matter in four dimensions, and identify the subtraction scheme where anomaly cancellation to all orders is manifest, namely no subtractions of finite local counterterms are required from two loops onwards. Our approach is based on an orderbyorder analysis of renormalization, and, differently from most derivations existing in the literature, does not make use of arguments based on the properties of the renormalization group. As a consequence, the proof we give also applies to conformal field theories and finite theories.
Eur. Phys. J. C 74 (2014) 3083  DOI: 10.1140/epjc/s1005201430830
13A3 D. Anselmi
Background field method, BatalinVilkovisky formalism and parametric completeness of renormalization
We investigate the background field method with the BatalinVilkovisky formalism, to generalize known results, study parametric completeness and achieve a better understanding of several properties. In particular, we study renormalization and gauge dependence to all orders. Switching between the background field approach and the usual approach by means of canonical transformations, we prove parametric completeness without making use of cohomological theorems, namely show that if the starting classical action is sufficiently general all divergences can be subtracted by means of parameter redefinitions and canonical transformations. Our approach applies to renormalizable and nonrenormalizable theories that are manifestly free of gauge anomalies and satisfy the following assumptions: the gauge algebra is irreducible and closes off shell, the gauge transformations are linear functions of the fields, and closure is fieldindependent. YangMills theories and quantum gravity in arbitrary dimensions are included, as well as effective and higherderivative versions of them, but several other theories, such as supergravity, are left out.
Phys. Rev. D 89 (2014) 045004  DOI: 10.1103/PhysRevD.89.045004
The classical action of quantum gravity, determined by renormalization, contains infinitely many independent couplings and can be expressed in different perturbatively equivalent ways. We organize it in a convenient form, which is based on invariants constructed with the Weyl tensor. We show that the FLRW metrics are exact solutions of the field equations in arbitrary dimensions, and so are all locally conformally flat solutions of the Einstein equations. Moreover, expanding the metric tensor around locally conformally flat backgrounds the quadratic part of the action is free of higher derivatives. Blackhole solutions of Schwarzschild and Kerr type are modified in a nontrivial way. We work out the first corrections to their metrics and study their properties.
JHEP 1305 (2013) 028  DOI: 10.1007/JHEP05(2013)028
13A1 D. Anselmi
Renormalization of gauge theories without cohomology
We investigate the renormalization of gauge theories without assuming cohomological properties. We define a renormalization algorithm that preserves the BatalinVilkovisky master equation at each step and automatically extends the classical action till it contains sufficiently many independent parameters to reabsorb all divergences into parameterredefinitions and canonical transformations. The construction is then generalized to the master functional and the fieldcovariant proper formalism for gauge theories. Our results hold in all manifestly anomalyfree gauge theories, powercounting renormalizable or not. The extension algorithm allows us to solve a quadratic problem, such as finding a sufficiently general solution of the master equation, even when it is not possible to reduce it to a linear (cohomological) problem.
Eur. Phys. J. C 73 (2013) 2508  DOI: 10.1140/epjc/s1005201325085
We develop a general fieldcovariant approach to quantum gauge theories. Extending the usual set of integrated fields and external sources to “proper” fields and sources, which include partners of the composite fields, we define the master functional $\Omega$, which collects oneparticle irreducible diagrams and upgrades the usual $\Gamma$functional in several respects. The functional $\Omega$ is determined from its classical limit applying the usual diagrammatic rules to the proper fields. Moreover, it behaves as a scalar under the most general perturbative field redefinitions, which can be expressed as linear transformations of the proper fields. We extend the BatalinVilkovisky formalism and the master equation. The master functional satisfies the extended master equation and behaves as a scalar under canonical transformations. The most general perturbative field redefinitions and changes of gaugefixing can be encoded in proper canonical transformations, which are linear and do not mix integrated fields and external sources. Therefore, they can be applied as true changes of variables in the functional integral, instead of mere replacements of integrands. This property overcomes a major difficulty of the functional $\Gamma$. Finally, the new approach allows us to prove the renormalizability of gauge theories in a general fieldcovariant setting. We generalize known cohomological theorems to the master functional and show that when there are no gauge anomalies all divergences can be subtracted by means of parameter redefinitions and proper canonical transformations.
Eur. Phys. J. C 73 (2013) 2363  DOI: 10.1140/epjc/s1005201323634
We study a new generating functional of oneparticle irreducible diagrams in quantum field theory, called master functional, which is invariant under the most general perturbative changes of field variables. The functional $\Gamma$ does not transform as a scalar under the transformation law inherited from its very definition, although it does transform as a scalar under an unusual transformation law. The master functional, on the other hand, is the Legendre transform of an improved functional W = ln Z with respect to the sources coupled to both elementary and composite fields. The inclusion of certain improvement terms in W and Z is necessary to make this transform well defined. The master functional behaves as a scalar under the transformation law inherited from its very definition. Moreover, it admits a proper formulation, obtained extending the set of integrated fields to the socalled proper fields, which allows us to work without passing through Z, W or $\Gamma$. In the proper formulation the classical action coincides with the classical limit of the master functional, and correlation functions and renormalization are calculated applying the usual diagrammatic rules to the proper fields. Finally, the most general change of field variables, including the map relating bare and renormalized fields, is a linear redefinition of the proper fields.
Eur. Phys. J. C 73 (2013) 2385  DOI: 10.1140/epjc/s100520132385y
In all nontrivial cases renormalization, as it is usually formulated, is not a change of integration variables in the functional integral, plus parameter redefinitions, but a set of replacements, of actions and/or field variables and parameters. Because of this, we cannot write simple identities relating bare and renormalized generating functionals, or generating functionals before and after nonlinear changes of field variables. In this paper we investigate this issue and work out a general fieldcovariant approach to quantum field theory, which allows us to treat all perturbative changes of field variables, including the relation between bare and renormalized fields, as true changes of variables in the functional integral, under which the functionals Z and W = ln Z behave as scalars. We investigate the relation between composite fields and changes of field variables, and show that, if J are the sources coupled to the elementary fields, all changes of field variables can be expressed as Jdependent redefinitions of the sources L coupled to the composite fields. We also work out the relation between the renormalization of variablechanges and the renormalization of composite fields. Using our transformation rules it is possible to derive the renormalization of a theory in a new variable frame from the renormalization in the old variable frame, without having to calculate it anew. We define several approaches, useful for different purposes, in particular a linear approach where all variable changes are described as linear source redefinitions. We include a number of explicit examples.
Eur. Phys. J. C 73 (2013) 2338  DOI: 10.1140/epjc/s1005201323385
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Book
14B1 D. Anselmi
Renormalization
Last update: May 9th 2015, 230 pages
Contents: Preface  1. Functional integral  2. Renormalization  3. Renormalization group  4. Gauge symmetry  5. Canonical formalism  6. Quantum electrodynamics  7. NonAbelian gauge field theories  Notation and useful formulas  References
Course on renormalization, taught in Pisa in 2015. (More chapters will be added later.)
Sections
 Unitarity of quantum field theory (7)
 Fakeons (2)
 Renormalization of general gauge theories (14)
 Fieldcovariant quantum field theory (4)
 AdlerBardeen theorem (5)
 Quantum gravity (16)
 Lorentz violating quantum field theory (8)
 Background field method (3)
 Infinite reduction of couplings (4)
 Renormalization group (14)
 Regularization (5)
 Conformal field theory (20)
 Topological field theory (5)
 Instantons (4)
 Field redefinitions (4)
 Dimensional regularization (5)
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