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41 results on '"Felice, Antonio De"'

5. Baryon Physics and Tight Coupling Approximation in Boltzmann Code

Author

Pookkillath, Masroor Chandhanapparambil, Mukohyama, Shinji, and Felice, Antonio De

Subjects
astronomy_astrophysics
Abstract

Boltzmann codes are essential tools for studying cosmology. Most of the codes are based on a seminal work by Ma and Bertschinger. We found that the formalism employed in those codes has at least three possible problems which need to be understood. i) The equation of motion for baryons are gauge incompatible, ii) they break the Bianchi identity, and iii) it is not clear from the equations of motion which physical system is considered. In this work we revisit the baryon physics and address all the above mentioned issues, based solely on conservation of stress-energy tensor, resulting in taking into account a correction that is usually neglected and that is numerically small. We also study the tight coupling approximation up to the second order without choosing any gauge. We implement the improved baryon equations in a Boltzmann code and investigate the change in the estimate of cosmological parameters by performing an MCMC analysis. While in this paper we study the Lambda-CDM model only, our baryon equations can be easily implemented in other models and various modified gravity theories.

Published
2019

6. Dark energy in multifractional spacetimes

Author

Japan Society for the Promotion of Science, Ministerio de Ciencia, Innovación y Universidades (España), European Cooperation in Science and Technology, Kyoto University, Calcagni, Gianluca, Felice, Antonio de, Japan Society for the Promotion of Science, Ministerio de Ciencia, Innovación y Universidades (España), European Cooperation in Science and Technology, Kyoto University, Calcagni, Gianluca, and Felice, Antonio de

Abstract

We study the possibility to obtain cosmological late-time acceleration from a geometry changing with the scale, in particular, in the so-called multifractional theories with q-derivatives and with weighted derivatives. In the theory with q-derivatives, the luminosity distance is the same as in general relativity and, therefore, geometry cannot act as dark energy. In the theory with weighted derivatives, geometry alone is able to sustain a late-time acceleration phase without fine tuning, while being compatible with structure-formation and big-bang nucleosynthesis bounds. This suggests to extend the theory, in a natural way, from just small-scale to also large-scale modifications of gravity. Surprisingly, the Hausdorff dimension of spacetime is constrained to be close to the topological dimension 4. After arguing that this finding might not be a numerical coincidence, we conclude that present-day acceleration could be regarded as the effect of a new restoration law for spacetime geometry.

Published
2020

14. Testing general relativity with present and future astrophysical observations

Author

Berti, Emanuele, primary, Barausse, Enrico, additional, Cardoso, Vitor, additional, Gualtieri, Leonardo, additional, Pani, Paolo, additional, Sperhake, Ulrich, additional, Stein, Leo C, additional, Wex, Norbert, additional, Yagi, Kent, additional, Baker, Tessa, additional, Burgess, C P, additional, Coelho, Flávio S, additional, Doneva, Daniela, additional, Felice, Antonio De, additional, Ferreira, Pedro G, additional, Freire, Paulo C C, additional, Healy, James, additional, Herdeiro, Carlos, additional, Horbatsch, Michael, additional, Kleihaus, Burkhard, additional, Klein, Antoine, additional, Kokkotas, Kostas, additional, Kunz, Jutta, additional, Laguna, Pablo, additional, Lang, Ryan N, additional, Li, Tjonnie G F, additional, Littenberg, Tyson, additional, Matas, Andrew, additional, Mirshekari, Saeed, additional, Okawa, Hirotada, additional, Radu, Eugen, additional, O’Shaughnessy, Richard, additional, Sathyaprakash, Bangalore S, additional, Broeck, Chris Van Den, additional, Winther, Hans A, additional, Witek, Helvi, additional, Aghili, Mir Emad, additional, Alsing, Justin, additional, Bolen, Brett, additional, Bombelli, Luca, additional, Caudill, Sarah, additional, Chen, Liang, additional, Degollado, Juan Carlos, additional, Fujita, Ryuichi, additional, Gao, Caixia, additional, Gerosa, Davide, additional, Kamali, Saeed, additional, Silva, Hector O, additional, Rosa, João G, additional, Sadeghian, Laleh, additional, Sampaio, Marco, additional, Sotani, Hajime, additional, and Zilhao, Miguel, additional

Published
2015
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34. On the cosmology of massive gravity.

Author

Felice, Antonio De, Gümrükçüoğlu, A Emir, Lin, Chunshan, and Mukohyama, Shinji

Subjects
*METAPHYSICAL cosmology, *GRAVITY, *NONLINEAR theories, *PARAMETER estimation, *GENERAL relativity (Physics), *MATHEMATICAL models
Abstract

We present a review of cosmological solutions in nonlinear massive gravity, focusing on the stability of perturbations. Although homogeneous and isotropic solutions have been found, these are now known to suffer from either the Higuchi ghost or a new nonlinear ghost instability. We discuss two approaches to alleviate this issue. By relaxing the symmetry of the background by e.g. breaking isotropy in the hidden sector, it is possible to accommodate a stable cosmological solution. Alternatively, extending the theory to allow for new dynamical degrees of freedom can also remove the conditions which lead to the instability. As examples for this case, we study the stability of self-accelerating solutions in the quasi-dilatonic extension and generic cosmological solutions in the varying mass extension. While the quasi-dilaton case turns out to be unstable, the varying mass case allows stable regimes of parameters. Viable self-accelerating solutions in the varying mass theory yet remain to be found. [ABSTRACT FROM AUTHOR]

Published
2013
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35. Stability of the 3-form field during inflation.

Author

Felice, Antonio De, Karwan, Khamphee, and Wongjun, Pitayuth

Subjects
*FIELD theory (Physics), *INFLATIONARY universe, *COUPLED mode theory (Wave-motion), *PLASMA instabilities, *POTENTIAL theory (Physics), *QUANTUM perturbations, *SCALAR field theory
Abstract

We consider the minimally coupled 3-form field, which has been considered as a candidate for realizing inflation. We have studied the conditions to avoid ghosts and Laplacian instabilities and found that some classes of potentials, e.g., the Mexican-hat, will in general be unstable. We then propose other classes of potentials which are instead free from any instability, drive a long enough slow-roll regime followed by an oscillatory epoch, and as a consequence, can provide successful inflation. Finally, we also provide stable potentials that lead to a small enough propagation speed for the scalar perturbations, making it possible for these models to produce non-Gaussianities. [ABSTRACT FROM AUTHOR]

Published
2012
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39. Effective gravitational couplings for cosmological perturbations in generalized Proca theories.

Author

Felice, Antonio De, Heisenberg, Lavinia, Ryotaro Kase, Shinji Mukohyama, Shinji Tsujikawa, and Ying-li Zhang

Subjects
*LAGRANGE equations, *GRAVITATIONAL constant, *DARK energy
Abstract

We consider the finite interactions of the generalized Proca theory including the sixth-order Lagrangian and derive the full linear perturbation equations of motion on the flat Friedmann-Lemaître-Robertson-Walker background in the presence of a matter perfect fluid. By construction, the propagating degrees of freedom (besides the matter perfect fluid) are two transverse vector perturbations, one longitudinal scalar, and two tensor polarizations. The Lagrangians associated with intrinsic vector modes neither affect the background equations of motion nor the second-order action of tensor perturbations, but they do give rise to nontrivial modifications to the no-ghost condition of vector perturbations and to the propagation speeds of vector and scalar perturbations. We derive the effective gravitational coupling Geff with matter density perturbations under a quasistatic approximation on scales deep inside the sound horizon. We find that the existence of intrinsic vector modes allows a possibility for reducing Geff. In fact, within the parameter space, Geff can be even smaller than the Newton gravitational constant G at the late cosmological epoch, with a peculiar phantom dark energy equation of state (without ghosts). The modifications to the slip parameter η and the evolution of the growth rate fσ8 are discussed as well. Thus, dark energy models in the framework of generalized Proca theories can be observationally distinguished from the ΛCDM model according to both cosmic growth and expansion history. Furthermore, we study the evolution of vector perturbations and show that outside the vector sound horizon the perturbations are nearly frozen and start to decay with oscillations after the horizon entry. [ABSTRACT FROM AUTHOR]

Published
2016
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40. Cosmological Perturbations in General Modified Gravity Theories

Author

Tsujikawa, Shinji, Felice, Antonio De, and Mukohyama, Shinji

Abstract

We derive the equations of linear cosmological perturbations for the general Lagrangian density f (R,ϕ, X)/2 + Lc, where R is a Ricci scalar, ϕ is a scalar field, and X = -∂µ ϕ∂µ ϕ/2 is a field kinetic energy. We take into account a nonlinear self-interaction term Lc = ξ(ϕ) □ϕ(∂µ ϕ∂µ ϕ), which keeps the field equations at second order. Taking into account a scalar-field mass explicitly, the equations of matter density perturbations and gravitational potentials are obtained under a quasi-static approximation on sub-horizon scales. We also derive conditions for the avoidance of ghosts and Laplacian instabilities associated with propagation speeds.

Published
2013
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41. IL REGIME FISCALE DEL TERZO SETTORE

Author

giovanni girelli, Cristina Amato, Elisabetta Bani, Massimo Bianca, Francesco Bosetti, Flavia De Felice, Antonio De Mauro, Giovanni Di Pierdomenico, Raffaele Di Raimo, Antonio Fici, Giovanni Girelli, Marilena Gorgoni, Fernando Greco, Simona Marchetti, Agostino Meale, Maria Paola Monaco, Andrea Nervi, Stefano Pardini, Dianora Poletti, Giulio Ponzanelli, Paolo Sanna, Gorgoni, Marilena, Girelli, Giovanni, and Marilena Gorgoni

Subjects
Terzo settore, ente non commerciale, agevolazione, imposta, terzo settore, imposte sui redditi, agevolazioni, impresa sociale
Abstract

Il contributo analizza in veste critica la disciplina tributaria prevista per gli enti del Terzo settore

Published
2018

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