Roberto Percacci
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Detection and Monitoring of Volcanic Islands in Tonga from Sentinel-2 Data Open
This work presents an automated method for detecting and monitoring volcanic islands in the Tonga archipelago using Sentinel-2 satellite imagery. The method is able to detect newly created islands, as well as an increase in island size, a …
View article: Visions in quantum gravity
Visions in quantum gravity Open
To deepen our understanding of Quantum Gravity and its connections with black holes and cosmology, building a common language and exchanging ideas across different approaches is crucial. The Nordita Program “Quantum Gravity: From gravitati…
Massive spin 3 and Metric-Affine Gravity Open
Symmetric Metric-Affine Gravity is a theory of gravity with an independent non-metric connection, and zero torsion. It can be thought of as ordinary metric gravity coupled to a rank-three tensor Q, symmetric in one pair of indices. This fi…
Quantum Fields and the Cosmological Constant Open
It has been shown that if one solves self-consistently the semiclassical Einstein equations in the presence of a quantum scalar field, with a cutoff on the number of modes, spacetime become flatter when the cutoff increases. Here, we exten…
Some simple theories of gravity with propagating nonmetricity Open
We investigate symmetric metric-affine theories of gravity with a Lagrangian containing all operators of dimension up to four that are relevant to free propagation in flat space. Complementing recent work in the antisymmetric case, we deri…
Quantum fields and the cosmological constant Open
It has been shown that if one solves self-consistently the semiclassical Einstein equations in the presence of a quantum scalar field, with a cutoff on the number of modes, spacetime become flatter when the cutoff increases. Here we extend…
Renormalization and running in the 2D CP (1) model Open
A bstract We calculate the scattering amplitude in the two dimensional CP (1) model in a regularization scheme independent way. When using cutoff regularization, a new Feynman rule from the path integral measure is required if one is to pr…
The Starobinsky model of inflation and Renormalizability Open
The Starobinsky model was born in a cosmological scenario where conformally coupled matter quantum field fluctuations on the vacuum drive a non trivial semiclassical energy momentum tensor quadratic in curvature. The presence of an unstabl…
View article: Visions in Quantum Gravity
Visions in Quantum Gravity Open
To deepen our understanding of Quantum Gravity and its connections with black holes and cosmology, building a common language and exchanging ideas across different approaches is crucial. The Nordita Program "Quantum Gravity: from gravitati…
Non-Perturbative Quantum Field Theory Open
This book presents in a systematic fashion a number of quantum field theoretic phenomena that have a topological underpinning. The systematics is provided by the homotopy groups of the configuration space: solitons and instantons are relat…
The cosmological constant problem and the effective potential of a gravity-coupled scalar Open
A bstract We consider a quantum scalar field in a classical (Euclidean) De Sitter background, whose radius is fixed dynamically by Einstein’s equations. In the case of a free scalar, it has been shown by Becker and Reuter that if one regul…
Renormalization and running in the 2D $CP(1)$ model Open
We calculate the scattering amplitude in the two dimensional $CP(1)$ model in a regularization scheme independent way. When using cutoff regularization, a new Feynman rule from the path integral measure is required if one is to preserve th…
Physical Running of Couplings in Quadratic Gravity Open
We argue that the well-known beta functions of quadratic gravity do not correspond to the physical dependence of scattering amplitudes on external momenta, and derive the correct physical beta functions. Asymptotic freedom turns out to be …
Some simple theories of gravity with propagating torsion Open
We consider antisymmetric metric-affine theories of gravity with a Lagrangian containing the most general terms up to dimension four and search for theories that are ghost- and tachyon-free when expanded around flat space. We find new exam…
The cosmological constant problem and the effective potential of a gravity-coupled scalar Open
We consider a quantum scalar field in a classical (Euclidean) De Sitter background, whose radius is fixed dynamically by Einstein's equations. In the case of a free scalar, it has been shown by Becker and Reuter that if one regulates the q…
On the renormalization of Poincaré gauge theories Open
A bstract Poincaré Gauge Theories are a class of Metric-Affine Gravity theories with a metric-compatible (i.e. Lorentz) connection and with an action quadratic in curvature and torsion. We perform an explicit one-loop calculation starting …
Physical running of couplings in quadratic gravity Open
We argue that the well-known beta functions of quadratic gravity do not correspond to the physical dependence of scattering amplitudes on external momenta, and derive the correct physical beta functions. Asymptotic freedom turns out to be …
Amplitudes and renormalization group techniques: A case study Open
We explore the properties of a simple renormalizable shift-symmetric model with a higher-derivative kinetic energy and quartic-derivative coupling that can serve as a toy model for higher-derivative theories of gravity. The scattering ampl…
Some simple theories of gravity with propagating nonmetricity Open
We investigate symmetric Metric-Affine Theories of Gravity with a Lagrangian containing all operators of dimension up to four that are relevant to free propagation in flat space. Complementing recent work in the antisymmetric case, we deri…
Some simple theories of gravity with propagating torsion Open
We consider antisymmetric Metric-Affine Theories of Gravity with a Lagrangian containing the most general terms up to dimension four and search for theories that are ghost- and tachyon-free when expanded around flat space. We find new exam…
On the renormalization of Poincaré gauge theories Open
Poincaré Gauge Theories are a class of Metric-Affine Gravity theories with a metric-compatible (i.e. Lorentz) connection and with an action quadratic in curvature and torsion. We perform an explicit one-loop calculation starting with a sin…
Amplitudes and Renormalization Group Techniques: A Case Study Open
We explore the properties of a simple renormalizable shift symmetric model with a higher derivative kinetic energy and quartic derivative coupling, that can serve as a toy model for higher derivative theories of gravity. The scattering amp…
Gravity as a Quantum Field Theory Open
Classical gravity is understood as the geometry of spacetime, and it seems very different from the other known interactions. In this review, I will instead stress the analogies: Like strong interactions, the low energy effective field theo…
Renormalization group flows between Gaussian fixed points Open
A bstract A scalar theory can have many Gaussian (free) fixed points, corresponding to Lagrangians of the form ϕ □ n ϕ . We use the non-perturbative RG to study examples of flows between such fixed points. We show that the anomalous dimens…
Renormalization Group flows between Gaussian Fixed Points Open
A scalar theory can have many Gaussian (free) fixed points, corresponding to Lagrangians of the form $ϕ\,\Box^kϕ$. We use the non-perturbative RG to study examples of flows between such fixed points. We show that the anomalous dimension ch…
Limit of vanishing regulator in the functional renormalization group Open
The non-perturbative functional renormalization group equation depends on the\nchoice of a regulator function, whose main properties are a "coarse-graining\nscale" $k$ and an overall dimensionless amplitude $a$. In this paper we shall\ndis…