A5051381011- Cosmology and Gravitation Theories
- Black Holes and Theoretical Physics
- Geophysics and Gravity Measurements
- Pulsars and Gravitational Waves Research
- Quantum Electrodynamics and Casimir Effect
- Advanced Differential Geometry Research
- Geomagnetism and Paleomagnetism Studies
- Astronomy and Astrophysical Research
- Noncommutative and Quantum Gravity Theories
- High-Energy Particle Collisions Research
- Galaxies: Formation, Evolution, Phenomena
- Nuclear physics research studies
- Relativity and Gravitational Theory
- Quantum Chromodynamics and Particle Interactions
- High-pressure geophysics and materials
Scuola Superiore Meridionale
2021-2024
Istituto Nazionale di Fisica Nucleare, Sezione di Napoli
2022-2024
Istituto Nazionale di Fisica Nucleare
2024
University of Naples Federico II
2017-2022
Abstract The elusive physical nature of Horndeski gravity is elucidated in a new approach depicting this class theories as dissipative effective fluid. Requiring the constitutive equations latter to be those Newtonian fluid restricts theory only two disconnected subclasses “viable” gravity. Therefore, stress-energy tensor fluid, linear first derivatives fluid’s 4-velocity, sufficient condition for gravitational waves propagate at light speed. All other correspond exotic non-Newtonian fluids....
We delve into the first-order thermodynamics of Horndeski gravity, focusing on spatially flat, homogeneous, and isotropic cosmologies. Our exploration begins with a comprehensive review effective fluid representation within viable gravity. Notably, we uncover surprising alignment between constitutive relations governing ``Horndeski fluid'' those Eckart's thermodynamics. Narrowing our focus, specialize discussion to flat Friedmann-Lema\^{\i}tre-Robertson-Walker spacetimes. Within this...
Abstract This study explores the feasibility of an effective Friedmann equation in removing classical Big Bang initial singularity and replacing it with a non-singular bounce occurring at critical energy density value. In spatially flat, homogeneous, isotropic universe, theory is obtained by introducing function parametrically dependent on density. measures deviation from benchmark theory, which recovered as approaches infinity. Focusing covariant single-field formulation viable Horndeski...
Abstract We apply to tensor-multi-scalar gravity the effective fluid analysis based on representation of gravitational scalar field as a dissipative fluid. This generalization poses new challenges is now complicated mixture individual fluids mutually coupled each other, and many reference frames are possible for its description. They all legitimate, although not convenient specific problems, they give rise different physical interpretations. Two these highlighted, implications cosmology pointed out.
We investigate McVittie and generalized solutions for Horndeski gravity with a spatially homogeneous gravitational scalar field, which is stealth at small scales near the central object but, large scales, sources Friedmann--Lema\^{\i}tre--Robertson--Walker universe in inhomogeneity embedded. Unlike previous studies, we include matter obtain extended cuscuton model. The possible configurations are classified according to time dependence of coupling, radial energy flow, accretion rate onto...
Abstract We explore Noether symmetries of Horndeski gravity, extending the classification general scalar–tensor theories. Starting from minimally coupled scalar field and first-generation discussion is generalised to kinetic gravity braiding gravity. highlight main findings by focusing on non-minimally Gauss–Bonnet term extended cuscuton model. Finally, we discuss how presence matter can influence symmetries. It turns out that selected functions are unchanged with respect vacuum case.
Loop Quantum Cosmology (LQC) is a theory which renders the Big Bang initial singularity into quantum bounce, by means of short range repulsive effects at Planck scale. In this work, we are interested in reproducing effective Friedmann equation LQC, considering generic $f(R,P,Q)$ gravity, where $R=g^{\mu\nu}R_{\mu\nu}$ Ricci scalar, $P=R_{\mu\nu}R^{\mu\nu}$, and $Q=R_{\alpha\beta\mu\nu}R^{\alpha\beta\mu\nu}$ Kretschmann scalar. An order reduction technique allows us to work theories...
The Big Bang initial singularity problem can be solved by means of bouncing solutions. In the context extended theories gravity, we will look for covariant effective actions whose field equations contain up to fourth-order derivatives metric tensor. finding such solutions, make use an order reduction technique based on a perturbative approach. Reducing second-order, are able find solutions which perturbatively close General Relativity. We build resulting reduced theories.
We delve into the first-order thermodynamics of Horndeski gravity, focusing on spatially flat, homogeneous, and isotropic cosmologies. Our exploration begins with a comprehensive review effective fluid representation within viable gravity. Notably, we uncover surprising alignment between constitutive relations governing "Horndeski fluid" those Eckart's thermodynamics. Narrowing our focus, specialize discussion to flat Friedmann-Lema{\^i}tre-Robertson-Walker spacetimes. Within this specific...
This study explores the feasibility of an effective Friedmann equation in removing classical initial Big Bang singularity, replaced by a bounce occurring at critical energy density value. In spatially flat, homogeneous, and isotropic universe, theory is obtained introducing function parametrically dependent on density. It measures deviation from benchmark characterising asymptotic behaviour as approaches infinity. Focusing covariant single-field formulation viable Horndeski gravity, our...
We explore alternative formulations of the analogy between viable Horndeski gravity and Eckart's first-order thermodynamics. single out a class identifications for effective stress-energy tensor scalar field fluid that, upon performing imperfect decomposition, yields constitutive relations that can be mapped onto theory. then investigate how different couplings to Einstein's gravity, at level equations, affect thermodynamic formalism overall. Lastly, we specialise discussion case...
The Tolman-Ehrenfest criterion of thermal equilibrium for a static fluid in spacetime is generalized to stationary heat conduction, the approximation which backreaction negligible. Applying this Hawking radiation Schwarzschild-de Sitter geometry shows that two horizons (which act as thermostats) remain equilibrium. temperature interpolates between temperatures at horizons, with analytic profile given explicitly.
The elusive physical nature of Horndeski gravity is elucidated in a new approach depicting this class theories as dissipative effective fluid. Requiring the constitutive equations latter to be those Newtonian fluid restricts theory only two disconnected subclasses "viable" gravity. Therefore, stress-energy tensor fluid, linear first derivatives fluid's 4-velocity, sufficient condition for gravitational waves propagate at light speed. All other correspond exotic non-Newtonian fluids.
We apply to tensor-multi-scalar gravity the effective fluid analysis based on representation of gravitational scalar field as a dissipative fluid. This generalization poses new challenges is now complicated mixture individual fluids mutually coupled each other and many reference frames are possible for its description. They all legitimate, although not convenient specific problems, they give rise different physical interpretations. Two these highlighted.