Article
Astronomy & Astrophysics
Bita Farsi, Ahmad Sheykhi
Summary: This study reveals the effects of an extra longitudinal degree of freedom on the evolution of perturbations in the context of mimetic gravity. By analyzing linear perturbations, it is found that the mimetic potential can act as dark energy and influence the dynamics of matter perturbations and cosmological parameters.
Article
Multidisciplinary Sciences
Adam Z. Kaczmarek, Dominik Szczesniak
Summary: The study examines the f(R, R-μνR-μν) gravity theory within the mimetic approach, involving field equations, cosmological models, and inflation consistency. Reconstruction schemes are used to derive specific models and discuss dark energy density, indicating the potential of mimetic extension in describing diverse cosmological scenarios.
SCIENTIFIC REPORTS
(2021)
Article
Physics, Mathematical
E. H. Baffou, M. J. S. Houndjo, I. G. Salako, L. D. Gbetoho
Summary: In this work, we investigate the inflationary scenario in viscous f(R, T) gravity with mimetic potential and Lagrange multiplier. By considering a perfect fluid, a dark energy, and a bulk viscous fluid in our universe, we derive a main differential equation for the cosmological evolution in viscous mimetic f(R, T) gravity using modified Friedmann equations. Numerical results for inflationary parameters, such as the tensor-to-scalar ratio r and the scalar spectral index ns, are presented for a specific choice of the model and two forms of bulk viscosity coefficient. Comparisons with observational data demonstrate that our model can describe the accelerated expansion of the universe.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2023)
Article
Astronomy & Astrophysics
Sahazada Aziz, Sohan Kumar Jha, Anisur Rahaman
Summary: This study investigates a specific f(R) model with multiple higher-order terms in the cosmic inflation scenario, finding that under certain conditions, it leads to a viable inflationary model which aligns well with recent Planck results.
CLASSICAL AND QUANTUM GRAVITY
(2021)
Article
Astronomy & Astrophysics
Mahmoud AlHallak, Amer AlRakik, Nidal Chamoun, Moustafa Sayem El-Daher
Summary: This study investigates the application of Palatini f(R) theory, characterized by an alpha R2 term, in a scenario driven by a temporal variation of strong coupling constant. The findings suggest that a quadratic kinetic energy can be obtained without dropping this term, leading to a kinematically-induced inflationary paradigm. The study also reveals that fitting the Planck 2018 data requires fine tuning for the alpha >> 1 case, known as k-inflation, with nonvanishing nonminimal coupling to gravity parameter xi, while the alpha << 1 case, studied in the constant-roll regime, can fit the data for vanishing xi. Additionally, the varying strong coupling inflation scenario remains viable when implemented through a warm inflation scenario with or without f(R) gravity.
Article
Astronomy & Astrophysics
G. G. L. Nashed, Shin'ichi Nojiri
Summary: New classes of black hole solutions are constructed within the mimetic Euler-Heisenberg theory, exhibiting different properties compared to standard gravitational theories. These solutions violate energy conditions and show stronger singularities, with satisfactory thermodynamic properties and stability conditions analyzed. Additionally, multihorizon black hole solutions are derived and studied in this framework for the first time.
Article
Physics, Multidisciplinary
A. I. Keskin
Summary: This study investigates the inflationary era of the Universe in the context of f(R) gravity, considering scalar perturbation equations and assuming specific parameter values to achieve inflation. The findings suggest that this inflation scenario for the early universe is possible, as observed parameters align with latest observational data.
EUROPEAN PHYSICAL JOURNAL PLUS
(2021)
Article
Astronomy & Astrophysics
Kota Numajiri, Yong -Xiang Cui, Taishi Katsuragawa, Shin'ichi Nojiri
Summary: We reexamine the static and spherical symmetric compact star configuration in the R2 model of the F(R) gravity theory. With asymptotic solutions for the additional scalar degrees of freedom, we refine analysis on the external geometry and settle the scalar-hair problem argued in previous works. Performing the numerical integration of the modified Tolman-Oppenheimer-Volkoff equations as a two-boundaries-value problem, we further discuss the scalar-field distribution inside the compact stars and its influence on the mass-radius relation. We show that the chameleon potential plays an essential role in determining the scalar field inside the star. The scalar field often behaves as a quintessential field that effectively decreases the mass of compact stars with lower central energy density.
Article
Physics, Particles & Fields
Pawan Joshi, Sukanta Panda
Summary: A Hamiltonian for the nonlocal F(R) theory is constructed in this work, revealing the nature of the ghost degrees of freedom. Finally, conditions that lead to ghost-free theories are found.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Physics, Multidisciplinary
J. A. Astorga-Moreno, E. A. Mena-Barboza
Summary: Modified gravity theories have gained significant attention in the past decade. This study utilizes deformed phase space in f(R) gravity to derive the Wheeler-DeWitt equation in the Quantum Cosmology scenario for a Friedmann-Lemaitre-Robertson-Walker model. Furthermore, a function f(R) that corresponds to the -Cold Dark Matter model is also considered.
Article
Astronomy & Astrophysics
Junior D. Toniato, Davi C. Rodrigues
Summary: This paper reviews the differences between the PPN gamma parameter and the gravitational slip, emphasizing the usefulness of a gamma-like parameter introduced by Berry and Gair. It discusses the application of these concepts to well-known cases like massive Brans-Dicke gravity and f(R) gravity, highlighting potential conflicting results. The study reveals that Palatini f(R) theories always have gamma = 1, while metric f(R) theories can only have values of either 1 or 1/2. Additionally, it explores the implications of the findings for gamma inferences at external galaxies.
Article
Physics, Multidisciplinary
S. Noori Gashti, J. Sadeghi, S. Upadhyay, M. R. Alipour
Summary: In this paper, the authors study a gravity theory called mimetic f(R, T) in the presence of the swampland dS conjecture. They introduce several inflation solutions and calculate various quantities to analyze the stability and compatibility of the inflationary model with the latest observational data.
COMMUNICATIONS IN THEORETICAL PHYSICS
(2022)
Article
Astronomy & Astrophysics
J. Bezerra-Sobrinho, L. G. Medeiros
Summary: In the context of effective theories of gravity, this paper proposes a minimalist bottom-up approach that considers 1-loop quantum corrections. It introduces four extra terms in the Einstein-Hilbert action to ensure renormalizability and accounts for the integration of massless/light matter fields. The focus is on analyzing the impact of the nonlocal term R ln (square) R on Starobinsky inflation, where it is treated as a small correction to the R-2 term. The model is shown to behave like a local model in this context, with a canonical scalar field minimally coupled to general relativity in the approximate Einstein frame. The inflationary regime of the model is studied and its free parameters are constrained through observations of CMB anisotropies.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Joao C. Lobato, Isabela S. Matos, Mauricio O. Calvao, Ioav Waga
Summary: The study introduces an alternative choice of variables for treating f(R) models in their Palatini formulation, leading to the derivation of general results and a complete description of the phase space for exponential gravity. It is shown that Palatini exponential gravity theories have a final attractor critical point with specific effective equation of state parameters. Comparison of analytical results with numerical solutions of the field equations is also conducted.
Article
Astronomy & Astrophysics
Jafar Sadeghi, Behnam Pourhassan, Saeed Noori Gashti, Elaheh Naghd Mezerji, Antonio Pasqua
Summary: In this study, the inflationary scenario in logarithmic f (R) gravity is examined, with a focus on the constant-roll rate of inflation. The cosmic evolution of the logarithmic f (R) gravity is investigated using constant-roll conditions, and numerical and graphical analyses are presented. The resulting potential satisfying the constant-roll conditions is obtained and tested against the refined swampland conjecture and the latest observable data.
Article
Astronomy & Astrophysics
Fulvio Ferlito, Sunny Vagnozzi, David F. Mota, Marco Baldi
Summary: In this study, we investigate the non-linear effects of scattering between dark energy and baryons on the formation of cosmic structures. Using large N-body simulations, we find that the signatures of this scattering in the non-linear regime are significantly larger than in the linear regime, and could potentially be constrained through a combination of observables.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Isabelle Tanseri, Steffen Hagstotz, Sunny Vagnozzi, Elena Giusarma, Katherine Freese
Summary: This study revisits cosmological constraints on the sum of the neutrino masses and improves upon previous research by combining BOSS galaxy clustering and Planck CMB data. The results provide an upper limit on the sum of the neutrino masses when combining these measurements with the Planck CMB data. The study also discusses the comparable information content between the full-shape information and the geometrical information of the BAO peaks in the galaxy clustering data, and performs robustness tests on bias and shot noise parameters.
JOURNAL OF HIGH ENERGY ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
Sunny Vagnozzi, Fabio Pacucci, Abraham Loeb
Summary: We use the ages of old astrophysical objects as tests of cosmic expansion history and find a disagreement between the upper limit on the Hubble constant derived from these ages and local measurements. This suggests the need for new physics to reconcile cosmic ages with early-time and local Hubble constant measurements.
JOURNAL OF HIGH ENERGY ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
Sunny Vagnozzi, Abraham Loeb
Summary: Recent debates on the testability of the inflationary paradigm raise the question of how to distinguish it from other scenarios in a model-independent manner. We argue that the detection of cosmic graviton background (CGB), radiation left over from gravitons during the Planck time, would invalidate the inflationary paradigm as it would be diluted to an unobservable level in realistic inflation models. The contribution of CGB to the effective number of relativistic species is within the range of detection for next-generation cosmological probes. Detecting the high-frequency stochastic gravitational wave background associated with CGB would be challenging but potentially feasible. Alternative theories such as bouncing cosmologies and emergent scenarios are also briefly discussed.
ASTROPHYSICAL JOURNAL LETTERS
(2022)
Article
Astronomy & Astrophysics
Alexander Reeves, Laura Herold, Sunny Vagnozzi, Blake D. Sherwin, Elisa G. M. Ferreira
Summary: The study investigates whether freeing the total neutrino mass can improve the fit of the early dark energy (EDE) model to galaxy clustering data. Bayesian and frequentist profile likelihood analyses using Planck CMB and BOSS galaxy clustering data show that freeing the total neutrino mass does not significantly improve the fit to galaxy clustering. The worsening fit is mainly caused by background modifications to the late-time expansion rate due to massive neutrinos which affect the measurements of the BAO scale.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Misba Afrin, Sunny Vagnozzi, Sushant G. Ghosh
Summary: The collaboration of the Event Horizon Telescope (EHT) has captured the first direct evidence of the supermassive black hole Sgr A* at the center of our galaxy. The size and shape of Sgr A*'s shadow provide valuable information for analyzing gravity in the strong-field regime and testing loop quantum gravity (LQG). The observational results of EHT also help constrain the metrics of LQG-inspired rotating black hole models.
ASTROPHYSICAL JOURNAL
(2023)
Article
Astronomy & Astrophysics
Sunny Vagnozzi, Rittick Roy, Yu-Dai Tsai, Luca Visinelli, Misba Afrin, Alireza Allahyari, Parth Bambhaniya, Dipanjan Dey, Sushant G. Ghosh, Pankaj S. Joshi, Kimet Jusufi, Mohsen Khodadi, Rahul Kumar Walia, Ali Ovgun, Cosimo Bambi
Summary: Horizon-scale images of black holes provide the opportunity to test gravity and fundamental physics in the strong-field regime. Using observations from the Event Horizon Telescope, we have narrowed down the possible deviations from classical general relativity solutions for black holes.
CLASSICAL AND QUANTUM GRAVITY
(2023)
Article
Astronomy & Astrophysics
Yu-Dai Tsai, Youjia Wu, Sunny Vagnozzi, Luca Visinelli
Summary: We investigate the possibility of using asteroid astrometric data to probe long-range fifth forces through the fifth force-induced orbital precession. Our study focuses on nine Near-Earth Object (NEO) asteroids with accurately determined orbital trajectories. We estimate the sensitivity reach for the fifth force coupling strength and mediator mass in the mass range near the fuzzy dark matter region. Our findings suggest potential to exceed current limits from equivalence principle tests in a specific mass range.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Shahnawaz A. Adil, Upala Mukhopadhyay, Anjan A. Sen, Sunny Vagnozzi
Summary: Early data from the JWST has revealed the existence of a large population of massive galaxies at high redshift, which challenges the standard cosmology. This study investigates whether the JWST observations point to more complex dynamics in the dark energy sector. The results suggest that a scenario inspired by string theory, with a negative cosmological constant and an evolving component, can explain the observed galaxies and alter the growth of structure compared to the standard model.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Sunny Vagnozzi
Summary: Various pulsar timing array experiments recently reported evidence of excess red common-spectrum signals, suggesting a stochastic gravitational wave background origin. The NANOGrav signal supports an inflationary gravitational wave background explanation, but requires a very blue tensor spectrum and a low reheating scale. However, well-motivated inflationary models struggle to achieve such a blue tilt without predicting non-Gaussianities. Ekpyrotic models predict a gravitational wave background with a spectral index of 2, but the amplitude is too small to explain the signal detected by pulsar timing array experiments.
JOURNAL OF HIGH ENERGY ASTROPHYSICS
(2023)
Article
Astronomy & Astrophysics
Sunny Vagnozzi
Summary: The Hubble tension has reached a significant level and requires a combination of early- and late-time new physics, as well as local new physics, to be solved.
Article
Astronomy & Astrophysics
Yifan Chen, Rittick Roy, Sunny Vagnozzi, Luca Visinelli
Summary: Ultralight bosons can affect the dynamics of spinning black holes through superradiant instability, leading to time evolution of supermassive black hole shadows. We introduce two observables, shadow drift and azimuthal angle lapse variation, which are sensitive to shadow time evolution and complementary depending on the observer's inclination angle. For the supermassive object Sgr A*, we show that these observables can vary significantly over a few years and can be observed and used to probe ultralight bosons in the mass range of approximately 10-17 eV, with the help of the Event Horizon Telescope.
Article
Astronomy & Astrophysics
Rafael C. Nunes, Sunny Vagnozzi, Suresh Kumar, Eleonora Di Valentino, Olga Mena
Summary: In this study, we explore the role of redshift-space galaxy clustering data in constraining nongravitational interactions between dark energy (DE) and dark matter (DM). By combining the data from galaxy power spectrum and Baryon Acoustic Oscillation (BAO) measurements with Cosmic Microwave Background (CMB) data, we obtain one of the strongest limits on the DM-DE coupling strength. Contrary to previous observations, we find that the combination of CMB and full-shape (FS) galaxy power spectrum returns tighter constraints compared to the combination of CMB and BAO, indicating valuable additional information in the broadband of the power spectrum. Our results highlight the critical role of redshift-space galaxy clustering measurements in precision cosmology.
Article
Astronomy & Astrophysics
Rittick Roy, Sunny Vagnozzi, Luca Visinelli
Summary: This study reconsiders the evolution of black hole shadows induced by superradiance and investigates the case of two ultralight bosons. The study finds that gas accretion and gravitational wave radiation have a negligible effect on the results, and the inclusion of an additional ultralight boson does not shorten the shadow evolution time scale.
Article
Astronomy & Astrophysics
Micol Benetti, Leila L. Graef, Sunny Vagnozzi
Summary: This study revisits the possibility that the stochastic common-spectrum process detected by the NANOGrav pulsar timing array experiment could be due to primordial gravitational waves. By considering a broken power-law parametrization for the stochastic gravitational wave background (SGWB) spectrum, the authors find that this phenomenological model is able to explain the NANOGrav signal while remaining consistent with a variety of cosmological and gravitational wave observations. Further exploration of connections to specific well-motivated early-Universe models is warranted.
