scholarly journals Minimally modified gravity fitting Planck data better than $$\Lambda $$ CDM

2020 ◽  
Vol 80 (8) ◽  
Author(s):  
Katsuki Aoki ◽  
Antonio De Felice ◽  
Shinji Mukohyama ◽  
Karim Noui ◽  
Michele Oliosi ◽  
...  
Keyword(s):  
Modified Gravity ◽  
Parameter Family ◽  
Hamiltonian Constraint ◽  
Planck Data ◽  
Matter Coupling ◽  
Modified Gravity Theories ◽  
General Relativistic ◽  
Free Function ◽  
Intermediate Redshifts ◽  
Better Than

Abstract We study the phenomenology of a class of minimally modified gravity theories called $$f(\mathcal {H})$$ f ( H ) theories, in which the usual general relativistic Hamiltonian constraint is replaced by a free function of it. After reviewing the construction of the theory and a consistent matter coupling, we analyze the dynamics of cosmology at the levels of both background and perturbations, and present a concrete example of the theory with a 3-parameter family of the function f. Finally, we compare this example model to Planck data as well as some later-time probes, showing that such a realization of $$f(\mathcal {H})$$ f ( H ) theories fits the data significantly better than the standard $$\Lambda $$ Λ CDM model, in particular by modifying gravity at intermediate redshifts, $$z\simeq 743$$ z ≃ 743 .

Minimally Modified Gravity Fitting Planck Data Better Than ΛCDM

2021 ◽  
Vol 65 (10) ◽  
pp. 1021-1025
Author(s):  
M. C. Pookkillath
Keyword(s):  
Modified Gravity ◽  
Planck Data ◽  
Better Than

scholarly journals Testing dispersion of gravitational waves from eccentric extreme-mass-ratio inspirals

2019 ◽  
Vol 28 (15) ◽  
pp. 1950166
Author(s):  
Shu-Cheng Yang ◽  
Wen-Biao Han ◽  
Shuo Xin ◽  
Chen Zhang
Keyword(s):  
General Relativity ◽  
Gravitational Waves ◽  
Modified Gravity ◽  
Arrival Time ◽  
Graviton Mass ◽  
Mass Ratio ◽  
Dispersion Effect ◽  
Intermediate Mass ◽  
Modified Gravity Theories ◽  
Better Than

In general relativity, there is no dispersion in gravitational waves, while some modified gravity theories predict dispersion phenomena in the propagation of gravitational waves. In this paper, we demonstrate that this dispersion will induce an observable deviation of waveforms if the orbits have large eccentricities. The mechanism is that the waveform modes with different frequencies will be emitted at the same time due to the existence of eccentricity. During the propagation, because of the dispersion, the arrival time of different modes will be different, then produce the deviation and dephasing of waveforms compared with general relativity. This kind of dispersion phenomena related with extreme-mass-ratio inspirals could be observed by space-borne detectors, and the constraint on the graviton mass could be improved. Moreover, we find that the dispersion effect may also be constrained by ground detectors better than the current result if a highly eccentric intermediate-mass-ratio inspirals be observed.

scholarly journals Scalar field dark energy with a minimal coupling in a spherically symmetric background

2017 ◽  
Vol 27 (01) ◽  
pp. 1750173 ◽  
Author(s):  
Jiro Matsumoto
Keyword(s):  
Dark Energy ◽  
Solar System ◽  
Modified Gravity ◽  
Spherically Symmetric ◽  
Field Equations ◽  
Minimal Coupling ◽  
Matter Coupling ◽  
Energy Models ◽  
Modified Gravity Theories ◽  
Quintessence Model

Dark energy models and modified gravity theories have been actively studied and the behaviors in the solar system have been also carefully investigated in a part of the models. However, the isotropic solutions of the field equations in the simple models of dark energy, e.g. quintessence model without matter coupling, have not been well investigated. One of the reason would be the nonlinearity of the field equations. In this paper, a method to evaluate the solution of the field equations is constructed, and it is shown that there is a model that can easily pass the solar system tests, whereas, there is also a model that is constrained from the solar system tests.

scholarly journals Does the Cosmological Expansion Change Local Dynamics?

Symmetry ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 1417
Author(s):  
Marcelo Schiffer
Keyword(s):  
Dark Matter ◽  
Modified Gravity ◽  
Hubble Constant ◽  
Matter Content ◽  
Matter Distribution ◽  
Present Value ◽  
Field Equations ◽  
Local Dynamics ◽  
Cosmological Expansion ◽  
Modified Gravity Theories

It is a well-known fact that the Newtonian description of dynamics within Galaxies for its known matter content is in disagreement with the observations as the acceleration approaches a0≈1.2×10−10 m/s2 (slighter larger for clusters). Both the Dark Matter scenario and Modified Gravity Theories (MGT) fail to explain the existence of such an acceleration scale. Motivated by the closeness of the acceleration scale and the Hubble constant cH0≈10−9 h m/s2, we are led to analyze whether this coincidence might have a Cosmological origin for scalar-tensor and spinor-tensor theories by performing detailed calculations for perturbations that represent the local matter distribution on the top of the cosmological background. Then, we solve the field equations for these perturbations in a power series in the present value of the Hubble constant. As we shall see, for both theories, the power expansion contains only even powers in the Hubble constant, a fact that renders the cosmological expansion irrelevant for the local dynamics.

scholarly journals A logarithmic correction in the entropy functional formalism

2016 ◽  
Vol 25 (07) ◽  
pp. 1650080 ◽  
Author(s):  
Fayçal Hammad ◽  
Mir Faizal
Keyword(s):  
Quantum Gravity ◽  
Modified Gravity ◽  
Correction Term ◽  
Modified Theories Of Gravity ◽  
Logarithmic Correction ◽  
Functional Formalism ◽  
Entropy Formula ◽  
Entropy Functional ◽  
Modified Gravity Theories ◽  
Theories Of Gravity

The entropy functional formalism allows one to recover general relativity, modified gravity theories, as well as the Bekenstein–Hawking entropy formula. In most approaches to quantum gravity, the Bekenstein–Hawking’s entropy formula acquires a logarithmic correction term. As such terms occur almost universally in most approaches to quantum gravity, we analyze the effect of such terms on the entropy functional formalism. We demonstrate that the leading correction to the micro-canonical entropy in the entropy functional formalism can be used to recover modified theories of gravity already obtained with an uncorrected micro-canonical entropy. Furthermore, since the entropy functional formalism reproduces modified gravity, the rise of gravity-dependent logarithmic corrections turns out to be one way to impose constraints on these theories of modified gravity. The constraints found here for the simple case of an [Formula: see text]-gravity are the same as those obtained in the literature from cosmological considerations.

scholarly journals Dark matter in logarithmic F(R) gravity

2019 ◽  
Vol 28 (12) ◽  
pp. 1950157 ◽  
Author(s):  
Tomohiro Inagaki ◽  
Yamato Matsuo ◽  
Hiroki Sakamoto
Keyword(s):  
General Relativity ◽  
Dark Matter ◽  
Modified Gravity ◽  
Field Method ◽  
Quantum Corrections ◽  
Prototype Model ◽  
Wide Range ◽  
Modified Gravity Theories ◽  
Primordial Inflation ◽  
Cmb Fluctuations

The logarithmic [Formula: see text]-corrected [Formula: see text] gravity is investigated as a prototype model of modified gravity theories with quantum corrections. By using the auxiliary field method, the model is described by the general relativity with a scalaron field. The scalaron field can be identified as an inflaton at the primordial inflation era. It is also one of the dark matter candidates in the dark energy (DE) era. It is found that a wide range of the parameters is consistent with the current observations of CMB fluctuations, DE and dark matter.

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