### Course

19R1 D. Anselmi
Theories of gravitation

Program

PDF

### Recent papers and theorems

19R4 Damiano Anselmi
Fakeons and quantum gravity

Talk given at the conference PAFT 2019 - Current problems in theoretical physics. Aspects of nonperturbative QFT, foundations of quantum theory, quantum spacetime. XXV edition, Vietri sul Mare (Salerno, Italy), April 13-17, 2019 A new quantization prescription is able to endow quantum field theory with a new type of "particle", the ... [more]

19R2 Damiano Anselmi
Fakeons, quantum gravity and the classical limit

Talk given at the Conference "Scale invariance in particle physics and cosmology", CERN, on January 29th, 2019 A new quantization prescription is able to endow quantum field theory with a new type of "particle", the fakeon (fake particle), which mediates interactions, but cannot be observed. A massive fakeon of spin 2 ... [more]

19A1 Damiano Anselmi
Fakeons and the classicization of quantum gravity: the FLRW metric

Under certain assumptions, it is possible to make sense of higher derivative theories by quantizing the unwanted degrees of freedom as fakeons, which are later projected away. Then the true classical limit is obtained by classicizing the quantum theory. Since quantum field theory is formulated perturbatively, the classicization is also ... [more]

19R1 Damiano Anselmi
Theories of gravitation

Program Differential geometry topological spaces, manifolds, differential manifolds, derivations, vector fields, differential forms, tangent space, cotangent space, tangent bundle, cotangent bundle, Lie derivative, metric, covariant derivative, torsion, curvature, metric compatibility, tetrad, spin connection, Christoffel symbols, Riemann tensor, Ricci tensor, Ricci scalar, Bianchi identities. General relativity Hilbert action, Palatini formulation, field equations. Coupling of gravity to ... [more]

18R2 Damiano Anselmi
From fakeons to quantum gravity

Talk given at the Department of Physics and Astronomy of Southampton University, UK, on Nov 16th, 2018 I introduce the concept of fake particle and study how it is used to formulate a consistent theory of quantum gravity. Fakeons arise from a new quantization prescription, alternative to the Feynman one, for ... [more]

18A7 Damiano Anselmi
On the nature of the Higgs boson

Several particles are not observed directly, but only through their decay products. We consider the possibility that they might be fakeons, i.e. fake particles, which mediate interactions but are not asymptotic states. A crucial role to determine the true nature of a particle is played by the imaginary parts of ... [more]

18A6 Damiano Anselmi
Let the dice play God

We define life as the amplification of quantum uncertainty up to macroscopic scales. A living being is any amplifier that achieves this goal. We argue that everything we know about life can be explained from this idea. We study a ladder mechanism to estimate the probability that the amplification occurs ... [more]

18R1 Damiano Anselmi
The correspondence principle in quantum field theory and quantum gravity

Talk given at the conference Progress and Visions in Quantum Theory in View of Gravity: Bridging foundations of physics and mathematics Max Planck Institute for Mathematics in the Sciences, Leipzig October 04, 2018 I claim that the best correspondence principle for quantum field theory and quantum gravity is made of unitarity, locality and proper ... [more]

18A5 Damiano Anselmi
The correspondence principle in quantum field theory and quantum gravity

We discuss the fate of the correspondence principle beyond quantum mechanics, specifically in quantum field theory and quantum gravity, in connection with the intrinsic limitations of the human ability to observe the external world. We conclude that the best correspondence principle is made of unitarity, locality, proper renormalizability (a refinement ... [more]

18A4 Damiano Anselmi
Fakeons, microcausality and the classical limit of quantum gravity

We elaborate on the idea of fake particle and study its physical consequences. When a theory contains fakeons, the true classical limit is determined by the quantization and a subsequent process of "classicization". One of the major predictions due to the fake particles is the violation of microcausality, which survives ... [more]

18A3 Damiano Anselmi and Marco Piva
Quantum gravity, fakeons and microcausality

We investigate the properties of fakeons in quantum gravity at one loop. The theory is described by a graviton multiplet, which contains the fluctuation $h_{\mu \nu }$ of the metric, a massive scalar $\phi$ and the spin-2 fakeon $\chi _{\mu \nu }$. The fields $\phi$ and $\chi _{\mu ... [more] 18A2 Damiano Anselmi and Marco Piva The ultraviolet behavior of quantum gravity A theory of quantum gravity has been recently proposed by means of a novel quantization prescription, which is able to turn the poles of the free propagators that are due to the higher derivatives into fakeons. The classical Lagrangian contains the cosmological term, the Hilbert term,$ \sqrt{-g}R_{\mu \nu }R^{\mu \nu ... [more]

18A1 Damiano Anselmi
Fakeons and Lee-Wick models

The "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 Feynman diagrams. Fakeons can be used to make higher-derivative theories unitary. Moreover, they help us clarify how the Lee-Wick models work. In this paper we ... [more]

17A3 Damiano Anselmi
On the quantum field theory of the gravitational interactions

We study the main options for a unitary and renormalizable, local quantum field theory of the gravitational interactions. The first model is a Lee-Wick superrenormalizable higher-derivative gravity, formulated as a nonanalytically Wick rotated Euclidean theory. We show that, under certain conditions, the $S$ matrix is unitary when the cosmological constant ... [more]

17A2 Damiano Anselmi and Marco Piva
Perturbative unitarity of Lee-Wick quantum field theory

We study the perturbative unitarity of the Lee-Wick models, formulated as nonanalytically Wick rotated Euclidean theories. The complex energy plane is divided into disconnected regions and the values of a loop integral in the various regions are related to one another by a nonanalytic procedure. We show that the one-loop ... [more]

A new quantization prescription is able to endow quantum field theory with a new type of “particle”, the fakeon (fake particle), which mediates interactions, but cannot be observed. A massive fakeon of spin 2 (together with a scalar field) allows us to build a theory of quantum gravity that is both renormalizable and unitary, and to some extent unique. After presenting the general properties of this theory, I discuss its classical limit, which carries important remnants of the fakeon quantization prescription and reveals unforeseen features.

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Presentazione per il pubblico alla conferenza “Tantrismo e Metafisica quantica” per il ciclo “One World University: incontri tra Oriente e Occidente”, a cura di Gloria Germani, presso in Cinema Odeon di Firenze, 21/3/2019

PDF

Talk given at the Conference “Scale invariance in particle physics and cosmology“, CERN, on January 29th, 2019

A new quantization prescription is able to endow quantum field theory with a new type of “particle”, the fakeon (fake particle), which mediates interactions, but cannot be observed. A massive fakeon of spin 2 (together with a scalar field) allows us to build a theory of quantum gravity that is both renormalizable and unitary, and to some extent unique. After presenting the general properties of this theory, I discuss its classical limit, which carries important remnants of the fakeon quantization prescription.

PDF

Watch talk from the CERN Document Server

Under certain assumptions, it is possible to make sense of higher derivative theories by quantizing the unwanted degrees of freedom as fakeons, which are later projected away. Then the true classical limit is obtained by classicizing the quantum theory. Since quantum field theory is formulated perturbatively, the classicization is also perturbative. After deriving a number of properties in a general setting, we consider the theory of quantum gravity that emerges from the fakeon idea and study its classicization, focusing on the FLRW metric. We point out cases where the fakeon projection can be handled exactly, which include radiation, the vacuum energy density and the combination of the two, and cases where it cannot, which include dust. Generically, the classical limit shares many features with the quantum theory it comes from, including the impossibility to write down complete, “exact” field equations, to the extent that asymptotic series and nonperturbative effects come into play.

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J. High Energy Phys. 04 (2019) 61 | DOI: 10.1007/JHEP04(2019)061

arXiv: 1901.09273 [gr-qc]

Program

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Talk given at the Department of Physics and Astronomy of Southampton University, UK, on Nov 16th, 2018

I introduce the concept of fake particle and study how it is used to formulate a consistent theory of quantum gravity. Fakeons arise from a new quantization prescription, alternative to the Feynman one, for the poles of higher-derivative theories, which avoids the problem of ghosts. The fake particles mediate interactions and simulate true particles in many situations. Nevertheless, they are not asymptotic states and cannot be detected directly. The Wick rotation and the S matrix are regionwise analytic and the amplitudes can be calculated in all regions starting from the Euclidean one by means of an unambiguous, but nonanalytic operation. By reconciling renormalizability and unitarity in higher-derivative theories, the models containing both true and fake particles are good candidates to explain quantum gravity. In pole position is the unique theory that is strictly renormalizable. One of the major physical predictions due to the fakeons is the violation of microcausality. I discuss the classical limit of the theory and the acausal corrections to the Einstein equations.

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Several particles are not observed directly, but only through their decay products. We consider the possibility that they might be fakeons, i.e. fake particles, which mediate interactions but are not asymptotic states. A crucial role to determine the true nature of a particle is played by the imaginary parts of the one-loop radiative corrections, which are affected in nontrivial ways by the presence of fakeons in the loop. The knowledge we have today is sufficient to prove that most non directly observed particles are true physical particles. However, in the case of the Higgs boson the possibility that it might be a fakeon remains open. The issue can be resolved by means of precision measurements in existing and future accelerators.

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Mod. Phys. Lett. A 33 (2019) 1950123 | DOI: 10.1142/S0217732319501232

arXiv: 1811.02600 [hep-ph]

hal-01911950

We define life as the amplification of quantum uncertainty up to macroscopic scales. A living being is any amplifier that achieves this goal. We argue that everything we know about life can be explained from this idea. We study a ladder mechanism to estimate the probability that the amplification occurs spontaneously in nature. The amplification mechanism is so sensitive to small variations of its own parameters that it acts as a bifurcation itself, i.e. it implies that the universe is either everywhere dead or alive wherever possible. Since the first option is excluded by the existence of life on earth, we infer that the universe hosts a huge number of inhabited planets (possibly one per star on average). We also investigate models of conscious and unconscious learning processes, as well as the structure of the brain and evolution. Finally, we address the problem of creating artificial life.

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hal-01911993

Talk given at the conference

Progress and Visions in Quantum Theory in View of Gravity: Bridging foundations of physics and mathematics

Max Planck Institute for Mathematics in the Sciences, Leipzig

October 04, 2018

I claim that the best correspondence principle for quantum field theory and quantum gravity is made of unitarity, locality and proper renormalizability (which is a refinement of strict renormalizability), combined with fundamental local symmetries and the requirement of having a finite number of fields. Quantum gravity is identified in an essentially unique way. It emerges from a new quantization prescription, which introduces the notion of fake particle, or “fakeon”, and uses it to resolve the long-standing problem of the higher-derivative ghosts. I discuss the major physical prediction of the theory, which is the violation of causality at small distances. The correspondence principle identifies the gauge interactions uniquely in form, but does not predict the gauge group. On the other hand, the matter sector remains almost completely unrestricted.

PDF

We discuss the fate of the correspondence principle beyond quantum mechanics, specifically in quantum field theory and quantum gravity, in connection with the intrinsic limitations of the human ability to observe the external world. We conclude that the best correspondence principle is made of unitarity, locality, proper renormalizability (a refinement of strict renormalizability), combined with fundamental local symmetries and the requirement of having a finite number of fields. Quantum gravity is identified in an essentially unique way. The gauge interactions are uniquely identified in form. Instead, the matter sector remains basically unrestricted. The major prediction is the violation of causality at small distances.

PDF

hal-01900207

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### Book

14B1 D. Anselmi
Renormalization

PDF

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. Non-Abelian gauge field theories
Notation and useful formulas
References

Course on renormalization, taught in Pisa in 2015. (More chapters will be added later.)