scholarly journals The radial acceleration relation and its emergent nature

2019 ◽  
Vol 15 (S359) ◽  
pp. 457-459
Author(s):  
Davi C. Rodrigues ◽  
Valerio Marra
Keyword(s):  
Dark Matter ◽  
Modified Gravity ◽  
Recent Analysis ◽  
Radial Acceleration ◽  
Modified Gravity Theories ◽  
Bayesian Test ◽  
Gravity Theories

AbstractWe review some of our recent results about the Radial Acceleration Relation (RAR) and its interpretation as either a fundamental or an emergent law. The former interpretation is in agreement with a class of modified gravity theories that dismiss the need for dark matter in galaxies (MOND in particular). Our most recent analysis, which includes refinements on the priors and the Bayesian test for compatibility between the posteriors, confirms that the hypothesis of a fundamental RAR is rejected at more than 5σ from the very same data that was used to infer the RAR.

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 The weak lensing radial acceleration relation: Constraining modified gravity and cold dark matter theories with KiDS-1000

2021 ◽  
Vol 650 ◽  
pp. A113
Author(s):  
Margot M. Brouwer ◽  
Kyle A. Oman ◽  
Edwin A. Valentijn ◽  
Maciej Bilicki ◽  
Catherine Heymans ◽  
...  
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Modified Gravity ◽  
Cold Dark Matter ◽  
Weak Lensing ◽  
Mass Relation ◽  
Gravitational Acceleration ◽  
Radial Acceleration ◽  
The Galaxy ◽  
The Difference

We present measurements of the radial gravitational acceleration around isolated galaxies, comparing the expected gravitational acceleration given the baryonic matter (gbar) with the observed gravitational acceleration (gobs), using weak lensing measurements from the fourth data release of the Kilo-Degree Survey (KiDS-1000). These measurements extend the radial acceleration relation (RAR), traditionally measured using galaxy rotation curves, by 2 decades in gobs into the low-acceleration regime beyond the outskirts of the observable galaxy. We compare our RAR measurements to the predictions of two modified gravity (MG) theories: modified Newtonian dynamics and Verlinde’s emergent gravity (EG). We find that the measured relation between gobs and gbar agrees well with the MG predictions. In addition, we find a difference of at least 6σ between the RARs of early- and late-type galaxies (split by Sérsic index and u − r colour) with the same stellar mass. Current MG theories involve a gravity modification that is independent of other galaxy properties, which would be unable to explain this behaviour, although the EG theory is still limited to spherically symmetric static mass models. The difference might be explained if only the early-type galaxies have significant (Mgas ≈ M⋆) circumgalactic gaseous haloes. The observed behaviour is also expected in Λ-cold dark matter (ΛCDM) models where the galaxy-to-halo mass relation depends on the galaxy formation history. We find that MICE, a ΛCDM simulation with hybrid halo occupation distribution modelling and abundance matching, reproduces the observed RAR but significantly differs from BAHAMAS, a hydrodynamical cosmological galaxy formation simulation. Our results are sensitive to the amount of circumgalactic gas; current observational constraints indicate that the resulting corrections are likely moderate. Measurements of the lensing RAR with future cosmological surveys (such as Euclid) will be able to further distinguish between MG and ΛCDM models if systematic uncertainties in the baryonic mass distribution around galaxies are reduced.

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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