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

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Recent Papers

Recent papers and theorems

20S3 Damiano Anselmi
Quantum gravity with purely virtual particles: from quantum field theory to primordial cosmology

Talk at NICPB, Tallinn, Estonia, Oct 14th, 2020 Abstract: I introduce the concept of purely virtual particle, or fakeon, and show how to use to make sense of quantum gravity as a quantum field theory. Then I discuss novel features of the classical limit and derive predictions in inflationary cosmology that ... [more]

20A5 Damiano Anselmi
High-order corrections to inflationary perturbation spectra in quantum gravity

We compute the inflationary perturbation spectra and the quantity $r+8n_{T}$ to the next-to-next-to-leading log order in quantum gravity with purely virtual particles (which means the theory $R+R^{2}+C^{2}$ with the fakeon prescription/projection for $C^{2}$). The spectra are functions of the inflationary running coupling $\alpha (1/k)$ and satisfy the cosmic renormalization-group flow ... [more]

20A4 Damiano Anselmi
Cosmic inflation as a renormalization-group flow: the running of power spectra in quantum gravity

We study the running of power spectra in inflationary cosmology as a renormalization-group flow from the de Sitter fixed point. The beta function is provided by the equations of the background metric. The spectra of the scalar and tensor fluctuations obey RG evolution equations with vanishing anomalous dimensions. By organizing ... [more]

20S2 Marco Piva
Predictions in inflationary cosmology from quantum gravity with purely virtual quanta

Testable predictions of quantum gravity with fakeons on the spectra of the CMB radiation Based on the paper 20A3 Renorm (arXiv: 2006.01163 [hep-th]) Talk given online by M. Piva for the Tokyo Institute of Technology, on Jun 16th, 2020 Talk given online by Marco Piva for the University of Sussex, on July 20th, ... [more]

20S1 Marco Piva
Predictions in inflationary cosmology from quantum gravity with purely virtual quanta

Testable predictions of quantum gravity with fakeons on the spectra of the CMB radiation Talk given by M. Piva at the National Institute of Chemical Physics and Biophysics, Tallinn, Estonia, on Jun 9th, 2020 Based on the paper 20A3 Renorm (arXiv: 2006.01163 ... [more]

20A3 Damiano Anselmi
Quantum field theories of arbitrary-spin massive multiplets and Palatini quantum gravity

We formulate quantum field theories of massive fields of arbitrary spins. The presence of both physical and fake particles, organized into multiplets, makes it possible to fulfill the requirements of locality, unitarity and renormalizability at the same time. The theories admit cubic and quartic self-interactions and can be coupled to ... [more]

20A2 Damiano Anselmi, Eugenio Bianchi and Marco Piva
Predictions of quantum gravity in inflationary cosmology: effects of the Weyl-squared term

We derive the predictions of quantum gravity with fakeons on the amplitudes and spectral indices of the scalar and tensor fluctuations in inflationary cosmology. The action is $R+R^{2}$ plus the Weyl-squared term. The ghost is eliminated by turning it into a fakeon, that is to say a purely virtual particle. ... [more]

20A1 Damiano Anselmi
The quest for purely virtual quanta: fakeons versus Feynman-Wheeler particles

The search for purely virtual quanta has attracted interest in the past. We consider various proposals and compare them to the concept of fake particle, or "fakeon". In particular, the Feynman-Wheeler propagator, which amounts to using the Cauchy principal value inside Feynman diagrams, violates renormalizability, unitarity and stability, due to ... [more]

19S13 Damiano Anselmi
A predictive theory of quantum gravity from fake particles

Talk given at Penn State University, Dec 17, 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 ... [more]

19S12 Damiano Anselmi
Quantum gravity al pub (in Italian)

Conferenza pubblica al pub "Lo spaventapasseri" di Pisa, il 28/11/2019 alle ore 20.00, sul tema della gravità ... [more]

19R2 Damiano Anselmi
Fakeons, quantum gravity and the correspondence principle

The correspondence principle made of unitarity, locality and renormalizability has been very successful in quantum field theory. Among the other things, it helped us build the standard model. However, it also showed important limitations. For example, it failed to restrict the gauge group and the matter sector in a powerful ... [more]

19S11 Damiano Anselmi
A predictive theory of quantum gravity from fake particles

Talk given at the conference "Quantum Gravity and Quantum Geometry", Nijmegen Oct 29 - Nov 1, 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]

19A3 Damiano Anselmi and Antonio Marino
Fakeons and microcausality: light cones, gravitational waves and the Hubble constant

The concept of fake particle, or "fakeon", allows us to make sense of quantum gravity as an ultraviolet complete theory, by renouncing causality at very small distances. We investigate whether the violation of microcausality can be amplified or detected in the most common settings. We show that it is actually ... [more]

19A2 Damiano Anselmi
Fakeons, unitarity, massive gravitons and the cosmological constant

We give a simple proof of perturbative unitarity in gauge theories and quantum gravity using a special gauge that allows us to separate the physical poles of the free propagators, which are quantized by means of the Feynman prescription, from the poles that belong to the gauge-trivial sector, which are ... [more]

19S10 Marco Piva
One-loop effective action of quantum gravity with fakeons and its phenomenology

Talk given by Marco Piva at the conference "Avenues of quantum field theory in curved spacetime", Modena, Sept 9th, ... [more]

Talk at NICPB, Tallinn, Estonia, Oct 14th, 2020

Abstract: I introduce the concept of purely virtual particle, or fakeon, and show how to use to make sense of quantum gravity as a quantum field theory. Then I discuss novel features of the classical limit and derive predictions in inflationary cosmology that could be tested in the forthcoming years, paying special attention to the effects of fakeons on perturbation spectra

PDF

We compute the inflationary perturbation spectra and the quantity $r+8n_{T}$ to the next-to-next-to-leading log order in quantum gravity with purely virtual particles (which means the theory $R+R^{2}+C^{2}$ with the fakeon prescription/projection for $C^{2}$). The spectra are functions of the inflationary running coupling $\alpha (1/k)$ and satisfy the cosmic renormalization-group flow equations, which determine the tilts and the running coefficients. The tensor fluctuations receive contributions from the spin-2 fakeon $\chi _{\mu \nu }$ at every order of the expansion in powers of $\alpha \sim 1/115$. The dependence of the scalar spectrum on the $\chi
_{\mu \nu }$ mass $m_{\chi }$, on the other hand, starts from the $\alpha^{2}$ corrections, which are handled perturbatively in the ratio $m_{\phi}/m_{\chi }$, where $m_{\phi }$ is the inflaton mass. The predictions have theoretical errors ranging from $\alpha ^{4}\sim 10^{-8}$ to $\alpha^{3}\sim 10^{-6}$. Nontrivial issues concerning the fakeon projection at higher orders are addressed.

PDF

arXiv: 2010.04739 [hep-th]

We study the running of power spectra in inflationary cosmology as a renormalization-group flow from the de Sitter fixed point. The beta function is provided by the equations of the background metric. The spectra of the scalar and tensor fluctuations obey RG evolution equations with vanishing anomalous dimensions. By organizing the perturbative expansion in terms of leading and subleading logs, we calculate the spectral indices, their runnings, the runnings of the runnings, etc., to the next-to-leading log order in quantum gravity with fakeons (i.e., the theory $R+R^2+C^2$ with the fakeon prescription/projection for $C^2$). We show that these quantities are related to the spectra in a universal way. We also compute the first correction to the relation $r=−8n_T$ and provide a number of quantum gravity predictions that can be hopefully tested in the forthcoming future.

PDF

arXiv: 2007.15023 [hep-th]

The Youtube Channel Quantum Gravity has just crossed the threshold of 200 subscribers. Its URL address is http://youtube.com/c/QuantumGravityTheory.

Quick statistics up to date, at 1.5 years since creation:

Total number of views: 15564
Total watched time: 1721 hours
Number of subscribers: 200
Number of videos: 75

Most watched videos:

Quantum gravity from fakeons – Catania 2019: 2393 views, 21 likes
Theories of Gravitation Lecture 1: 1283 views, 13 likes
A predictive theory of quantum gravity from fake particles: 782 views, 11 likes
Quantum gravity from fakeons – Marseille: 635 views, 5 likes
Quantum gravity al pub: 599 views, 11 likes
La fisica e la vita – Viaggio nell’infinitamente piccolo, e ritorno: 587 views, 7 likes
The corr. principle in quantum field th. and quantum grav.: 428 views, 2 likes

Let the dice play God: 344 views, 2 like
From fakeons to quantum gravity: 339 views, 5 likes

Number of visits to this website since creation (2013): 43448

Download count for the papers posted on archives other than arXiv (which does not allow download count):

18A5 The corr. principle in q. field th. and q. grav.: 1162 downloads (5 archives)
17A3 On the quantum field theory of the grav. interactions: 436 downloads (2 archives)
18A6 Let the dice play God: 355 downloads (4 archives)
18A7 On The Nature of the Higgs Boson: 278 downloads (4 archives)

Last update: 24/07/2020

Testable predictions of quantum gravity with fakeons on the spectra of the CMB radiation

Based on the paper 20A3 Renorm (arXiv: 2006.01163 [hep-th])

Talk given online by M. Piva for the Tokyo Institute of Technology, on Jun 16th, 2020

Talk given online by Marco Piva for the University of Sussex, on July 20th, 2020

PDF

Testable predictions of quantum gravity with fakeons on the spectra of the CMB radiation

Talk given by M. Piva at the National Institute of Chemical Physics and Biophysics, Tallinn, Estonia, on Jun 9th, 2020

Based on the paper 20A3 Renorm (arXiv: 2006.01163 [hep-th])

PDF

We formulate quantum field theories of massive fields of arbitrary spins. The presence of both physical and fake particles, organized into multiplets, makes it possible to fulfill the requirements of locality, unitarity and renormalizability at the same time. The theories admit cubic and quartic self-interactions and can be coupled to quantum gravity and gauge fields. The simplest irreducible bosonic and fermionic multiplets are made of towers of alternating physical and fake particles. Their mass spectrum is constrained by RG invariant relations and depends on just one or two masses. The fixed points of the renormalization-group flow are scale invariant, but not necessarily conformal invariant. The Palatini version of quantum gravity with fakeons is equivalent to the non-Palatini one coupled to a peculiar multiplet of order 3. As a consequence, it is equally renormalizable and unitary.

PDF

J. High Energy Phys. 07 (2020) 176 | DOI: 10.1007/JHEP07(2020)176

arXiv: 2006.01163 [hep-th]

We derive the predictions of quantum gravity with fakeons on the amplitudes and spectral indices of the scalar and tensor fluctuations in inflationary cosmology. The action is $R+R^{2}$ plus the Weyl-squared term. The ghost is eliminated by turning it into a fakeon, that is to say a purely virtual particle. We work to the next-to-leading order of the expansion around the de Sitter background. The consistency of the approach puts a lower bound ($m_{\chi }>m_{\phi }/4$) on the mass $m_{\chi }$ of the fakeon with respect to the mass $m_{\phi }$ of the inflaton. The tensor-to-scalar ratio $r$ is predicted within less than an order of magnitude ($4/3 < N^{2}r<12$ to the leading order in the number of $e$-foldings $N$). Moreover, the relation $r\simeq -8n_{T}$ is not affected by the Weyl-squared term. No vector and no other scalar/tensor degree of freedom is present.

PDF

J. High Energy Phys. 07 (2020) 211 | DOI: 10.1007/JHEP07(2020)211

arXiv: 2005.10293 [hep-th]

The search for purely virtual quanta has attracted interest in the past. We consider various proposals and compare them to the concept of fake particle, or “fakeon”. In particular, the Feynman-Wheeler propagator, which amounts to using the Cauchy principal value inside Feynman diagrams, violates renormalizability, unitarity and stability, due to the coexistence of the prescriptions $\pm i\epsilon $. We contrast the Feynman, fakeon and Feynman-Wheeler prescriptions in ordinary as well as cut diagrams. The fakeon does not have the problems of the Feynman-Wheeler propagator and emerges as the correct concept of purely virtual quantum. It allows us to make sense of quantum gravity at the fundamental level, and places it on an equal footing with the standard model. The resulting theory of quantum gravity is perturbative up to an incredibly high energy.

PDF

J. High Energ. Phys. 03 (2020) 142 | DOI: 10.1007/JHEP03(2020)142

arXiv: 2001.01942 [hep-th]

Talk given at Penn State University, Dec 17, 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. The theory predicts that causality is lost at sufficiently small distances, where time makes no longer sense. After presenting the general formulation of the theory, I explain its nontrivial classical limit, the modifications of the FLRW metric and the role of the cosmological constant. Finally, I discuss the possibility that the Higgs boson might be a fakeon.

PDF

Book

14B1 D. Anselmi
Renormalization

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

Last update: May 9th 2015, 230 pages

Avaibable on Amazon:

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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


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