Course

19S1 D. Anselmi
Theories of gravitation

Program

PDF

Book

D. Anselmi
From Physics To Life

A journey to the infinitesimally small and back

In English and Italian

Available on Amazon:
US: book | ebook  (in EN)
IT: book | ebook  (in IT)




Recent Papers




Recent papers and theorems

24A2 Damiano Anselmi
Quantum gravity with purely virtual particles from asymptotically local quantum field theory

We investigate the local limits of various classes of unitary, nonlocal quantum field theories. While it is easy to build nonlocal models with well-behaved asymptotics in Euclidean space, the Minkowskian correlation functions typically exhibit singular behaviors. We introduce "asymptotically local" quantum field theory (AL-QFT) as the class that encompasses unitary, ... [more]

24A1 Damiano Anselmi
Cosmological inhomogeneities, primordial black holes, and a hypothesis on the death of the universe

We study the impact of the expansion of the universe on a broad class of objects, including black holes, neutron stars, white dwarfs, and others. Using metrics that incorporate primordial inhomogeneities, the effects of a hypothetical "center of the universe" on inflation are calculated. Dynamic coordinates for black holes that ... [more]

23A3 Damiano Anselmi
Gauge theories and quantum gravity in a finite interval of time, on a compact space manifold

We study gauge theories and quantum gravity in a finite interval of time $ \tau $, on a compact space manifold $\Omega $. The initial, final and boundary conditions are formulated in gauge invariant and general covariant ways by means of purely virtual extensions of the theories, which allow us ... [more]

23A2 Damiano Anselmi
Propagators and widths of physical and purely virtual particles in a finite interval of time

We study the free and dressed propagators of physical and purely virtual particles in a finite interval of time $τ$ and on a compact space manifold $Ω$, using coherent states. In the free-field limit, the propagators are described by the entire function $(e^{z}-1-z)/z^{2}$, whose shape on the real axis is ... [more]

23A1 Damiano Anselmi
Quantum field theory of physical and purely virtual particles in a finite interval of time on a compact space manifold: diagrams, amplitudes and unitarity

We provide a diagrammatic formulation of perturbative quantum field theory in a finite interval of time $τ$, on a compact space manifold $Ω$. We explain how to compute the evolution operator $U(t_{\text{f}},t_{\text{i}})$ between the initial time $t_{\text{i}}$ and the final time $t_{\text{f}}=t_{\text{i}}+τ$, study unitarity and renormalizability, and show how to ... [more]

22A5 Damiano Anselmi
A new quantization principle from a minimally non time-ordered product

We formulate a new quantization principle for perturbative quantum field theory, based on a minimally non time-ordered product, and show that it gives the theories of physical particles and purely virtual particles. Given a classical Lagrangian, the quantization proceeds as usual, guided by the time-ordered product, up to the common ... [more]

22A4 Damiano Anselmi
Purely virtual extension of quantum field theory for gauge invariant fields: quantum gravity

Quantum gravity is extended to include purely virtual "cloud sectors", which allow us to define a complete set of point-dependent observables, including a gauge invariant metric and gauge invariant matter fields, and calculate their off-shell correlation functions perturbatively. The ordinary on-shell correlation functions and the $S$ matrix elements are unaffected. ... [more]

22A3 Damiano Anselmi
Purely virtual extension of quantum field theory for gauge invariant fields: Yang-Mills theory

We extend quantum field theory by including purely virtual "cloud" sectors, to define physical off-shell correlation functions of gauge invariant quark and gluon fields, without affecting the $S$ matrix amplitudes. The extension is made of certain cloud bosons, plus their anticommuting partners. Both are quantized as purely virtual, to ensure ... [more]

22R2 Damiano Anselmi
A hope for particle physics – ERC Advanced Grant application (VIRTUAL)

The physics of fundamental interactions is going through a concerning, prolonged period of stagnation. The incredible success of the standard model of particle physics and the lack of new experimental data have frustrated our hopes in the future. On top of that, the scientific community shattered into a large number ... [more]

22R1 Damiano Anselmi
Purely virtual particles in quantum gravity, inflationary cosmology and collider physics

We review the concept of purely virtual particle and its uses in quantum gravity, primordial cosmology and collider physics. The fake particle, or “fakeon”, which mediates interactions without appearing among the incoming and outgoing states, can be introduced by means of a new diagrammatics. The renormalization coincides with one of ... [more]

22A2 Damiano Anselmi
Purely virtual particles versus Lee-Wick ghosts: physical Pauli-Villars fields, finite QED and quantum gravity

We reconsider the Lee-Wick (LW) models and compare their properties to the properties of the models that contain purely virtual particles. We argue against the LW premise that unstable particles can be removed from the sets of incoming and outgoing states in scattering processes. The removal leads to a non-Hermitian ... [more]

22A1 Damiano Anselmi
Dressed propagators, fakeon self-energy and peak uncertainty

We study the resummation of self-energy diagrams into dressed propagators in the case of purely virtual particles and compare the results with those obtained for physical particles and ghosts. The three geometric series differ by infinitely many contact terms, which do not admit well-defined sums. The peak region, which is ... [more]

21A5 Damiano Anselmi
Diagrammar of physical and fake particles and spectral optical theorem

We prove spectral optical identities in quantum field theories of physical particles (defined by the Feynman $i\epsilon $ prescription) and purely virtual particles (defined by the fakeon prescription). The identities are derived by means of purely algebraic operations and hold for every (multi)threshold separately and for arbitrary frequencies. Their major ... [more]

21A4 Damiano Anselmi, Kristjan Kannike, Carlo Marzo, Luca Marzola, Aurora Melis, Kristjan Müürsepp, Marco Piva and Martti Raidal
A fake doublet solution to the muon anomalous magnetic moment

Extensions to the Standard Model that use strictly off-shell degrees of freedom - the fakeons - allow for new measurable interactions at energy scales usually precluded by the constraints that target the on-shell propagation of new particles. Here we employ the interactions between a new fake scalar doublet and the ... [more]

21A3 Damiano Anselmi, Kristjan Kannike, Carlo Marzo, Luca Marzola, Aurora Melis, Kristjan Müürsepp, Marco Piva, Martti Raidal
Phenomenology of a Fake Inert Doublet Model

We introduce a new way of modeling the physics beyond the Standard Model by considering fake, strictly off-shell degrees of freedom: the fakeons. To demonstrate the approach and exemplify its reach, we re-analyze the phenomenology of the Inert Doublet Model under the assumption that the second doublet is a fakeon. ... [more]

We investigate the background field method with the Batalin-Vilkovisky 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 non-renormalizable 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 field-independent. Yang-Mills theories and quantum gravity in arbitrary dimensions are included, as well as effective and higher-derivative versions of them, but several other theories, such as supergravity, are left out.

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Phys. Rev. D 89 (2014) 045004 | DOI: 10.1103/PhysRevD.89.045004

arXiv: 1311.2704 [hep-th]


Let $S(\Phi,U,K,K_{U})$ denote the solution of the master equation $(S,S)=0$, where $\{\Phi ^{A},U\}$ are the fields and $\{K_{A},K_{U}\}$ are the sources coupled to the $\Phi ^{A}$- and $U$-gauge transformations. If we replace $U$ with the solution $U^{*}(\Phi ,K,K_{U})$ of the $U$-field equations
\begin{equation}
\frac{\delta _{r}S}{\delta U}=0,
\end{equation}
then the action
\begin{equation}
S^{*}(\Phi ,K,K_{U})=S(\Phi ,U^{*}(\Phi ,K,K_{U}),K,K_{U})
\end{equation}
satisfies the master equation $(S^{*},S^{*})=0$ in the reduced set of fields and sources $\Phi,K$.

Read the proof →

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. Black-hole solutions of Schwarzschild and Kerr type are modified in a non-trivial way. We work out the first corrections to their metrics and study their properties.

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JHEP 1305 (2013) 028 | DOI: 10.1007/JHEP05(2013)028

arXiv:1302.7100 [gr-qc]

We investigate the renormalization of gauge theories without assuming cohomological properties. We define a renormalization algorithm that preserves the Batalin-Vilkovisky master equation at each step and automatically extends the classical action till it contains sufficiently many independent parameters to reabsorb all divergences into parameter-redefinitions and canonical transformations. The construction is then generalized to the master functional and the field-covariant proper formalism for gauge theories. Our results hold in all manifestly anomaly-free gauge theories, power-counting 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.

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Eur. Phys. J. C 73 (2013) 2508 | DOI: 10.1140/epjc/s10052-013-2508-5

arXiv:1301.7577 [hep-th]

Welcome to RENORMALIZATION.COM

Here you can read papers, theorems and books about renormalization and quantum field theory in general, as well as discuss about open problems, address new projects and ideas. More details here

For queries and suggestions send an email to r enor mal ize@r enor mal izat ion.c om

We develop a general field-covariant 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 one-particle 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 Batalin-Vilkovisky 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 gauge-fixing 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 field-covariant 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.

PDF

Eur. Phys. J. C 73 (2013) 2363 | DOI: 10.1140/epjc/s10052-013-2363-4

arXiv:1205.3862 [hep-th]

We study a new generating functional of one-particle 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 so-called 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.

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Eur. Phys. J. C 73 (2013) 2385 | DOI: 10.1140/epjc/s10052-013-2385-y

arXiv:1205.3584 [hep-th]


Consider a functional integral
\[
\mathcal{I}=\int [\mathrm{d}\varphi ]\hspace{0.02in}\exp \left( -S(\varphi)+\int J\left( \varphi -bU\right) \right) ,
\]
where $U(\varphi ,bJ)$ is a local function of $\varphi$ and $J$, and $b$ is a constant. Then there exists a perturbatively local change of variables
\[
\varphi =\varphi (\varphi ^{\prime },b,bJ)=\varphi ^{\prime }+\mathcal{O}(b),
\]
expressed as a series expansion in $b$, such that
\[
\mathcal{I}=\int [\mathrm{d}\varphi ^{\prime }]\hspace{0.02in}\exp \left(
-S^{\prime }(\varphi ^{\prime },b)+\int J\varphi ^{\prime }\right) ,
\]
where $S^{\prime }(\varphi ^{\prime },b)=S(\varphi (\varphi^{\prime },b,0))$.

Read the proof →

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 field-covariant 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 J-dependent redefinitions of the sources L coupled to the composite fields. We also work out the relation between the renormalization of variable-changes 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.

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Eur. Phys. J. C 73 (2013) 2338 | DOI: 10.1140/epjc/s10052-013-2338-5

arXiv:1205.3279 [hep-th]

The idea to create this website came while completing a book about renormalization, which will be freely readable at this page once ready. I realized that the best way to disseminate knowledge, nowadays, is not to write a book. One must at least make the book “alive”, which is possible, for example, with the help of a website. I figured out that since a website is much more versatile than a book, it allows me to provide a much richer service.

Why renormalization? Because it is the main interest of my research, and because I think it has a lot to teach us, in a broad sense.

Renormalization is one of the deepest aspects of quantum field theory, and quantum field theory is one of the greatest successes of theoretical physics, certainly the most advanced achievement of high-energy particle physics.

In recent years several aspects of quantum field theory have been neglected, and the attention of theoretical physicists has been effectively diverted towards model building and other, more “horizontal”, approaches. Renormalization and several other important topics have been buried under a huge number of scientific papers on topics of questionable relevance. Existing repositories and archives do not even offer efficient searching tools. They do not allow visitors to single out papers about renormalization or other topics that are worth of special attention.

Nowadays technology allows us to copy, and save, and backup. This gives us the impression that no knowledge is at risk to be lost.  In a variety of unfortunate circumstances, several times in the past huge amounts of knowledge have been lost or buried underground and forgot there for a long time. Sometimes the lost knowledge was uncovered centuries later, some other times it was lost forever. We know that this cannot happen today, in principle.

Till a decade ago, I was convinced that I did not need to insert the words “in principle” at the end of this sentence. However, on second thought, burying something underground is not very different from drowning it under the huge amount of questionable “information” that is normally produced and circulates on the internet. In both cases knowledge is still there, in both cases it needs to be discovered again, otherwise it is lost forever. In this respect, search engines are totally useless, since they mostly point to what is popular and liked by people, but they have no way to identify what is relevant.

These observations tell us that science is all but safe today. If knowledge can be forgot, it is easy to enter the path that leads to regress.  We do not just risk to loose knowledge, actually, we also risk to forget the method to make progress and generate further knowledge. Very much like life, knowledge can be preserved only producing new knowledge. What new knowledge is produced today in theoretical physics? How many people can claim that theoretical physics is in good shape? And physics in general? and science?

One of the claims of this site is that, actually, the decline started long ago. We can reasonably say that the new era began around the early 1970s, when progress in theoretical physics reached its apex, then unexpectedly slowed down and eventually stopped. Since then theoretical problems have become more and more challenging. Partially because of this, but not only, wrong methods have been adopted to guide the scientific research, as well as wrong criteria to select and hire new people. Little by little the involution contaminated more and wider areas of research. For many reasons, it does not sound incorrect to dubb the era we have entered in “The New Middle Ages“. Probably becoming aware of this situation will not be enough to stop the decline, but it is the only hope we have.

So, I have enriched the initial project with more ambitious goals, to understand what it going on, discuss about the present situation and search for wayouts. If yuo feel you have ideas, you can help

If you wish to donate money for the maintenance of this site just buy the ebook or printed versions of the book Renormalization, as soon as it will be available.

For queries and comments about this site: r enor mal ize@r enor mal izat ion.c om

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Book

14B1 D. Anselmi
Renormalization

Course on renormalization, taught in 2015.

Last update: September 15th 2023, 242 pages

The final (2023) edition is vaibable on Amazon:

US  IT  DE  FR  ES  UK  JP  CA


Contents:
Preface
1. Functional integral
2. Renormalization
3. Renormalization group
4. Gauge symmetry
5. Canonical formalism
6. Quantum electrodynamics
7. Non-Abelian gauge field theories
Notation and useful formulas
References


The pdf file of the 2015 Edition is available here: PDF