Evolving Newton’s constant, extended gravity theories, and SnIa data analysis

2006 ◽  
Vol 73 (10) ◽  
Author(s):  
S. Nesseris ◽  
L. Perivolaropoulos
Keyword(s):  
Data Analysis ◽  
Extended Gravity ◽  
Gravity Theories

scholarly journals Light bending in F[g(□)R] extended gravity theories

2018 ◽  
Vol 780 ◽  
pp. 54-60 ◽  
Author(s):  
Breno L. Giacchini ◽  
Ilya L. Shapiro
Keyword(s):  
Extended Gravity ◽  
Light Bending ◽  
Gravity Theories

Causality of 3D extended gravity theories

2019 ◽  
Vol 34 (16) ◽  
pp. 1950122
Author(s):  
Meguru Komada
Keyword(s):  
Shock Wave ◽  
Three Dimensional ◽  
Massive Gravity ◽  
Gravity Theory ◽  
Delay Effect ◽  
Fundamental Physics ◽  
Extended Gravity ◽  
3D Gravity ◽  
Gravity Theories ◽  
Time Delay Effect

Causality is one of the most important properties to understand gravity theories. It gives us not only a method to confirm that the gravity theories are really consistent, but also gives implications about the properties which unknown fundamental physics should obey. We investigate the causality of three-dimensional (3D) gravity theories, which are considered to be important, by using the Shapiro time delay effect in the Shock wave geometry. One of such gravity theories is the Zwei-Dreibein Gravity (ZDG) theory, which is a consistent 3D gravity theory. In ZDG theory, the serious problems can be removed that have appeared in another important gravity theory called New Massive Gravity (NMG). We study whether the ZDG theory could preserve the causality without losing the above good properties and how the causality structure is related to the structure of the NMG theory.

scholarly journals Extended gravity theories from dynamical noncommutativity

2012 ◽  
Vol 45 (2) ◽  
pp. 411-426 ◽  
Author(s):  
Paolo Aschieri ◽  
Leonardo Castellani
Keyword(s):  
Extended Gravity ◽  
Gravity Theories

scholarly journals Barred spiral galaxies in modified gravity theories

2021 ◽  
Vol 503 (2) ◽  
pp. 2833-2860 ◽  
Author(s):  
Mahmood Roshan ◽  
Indranil Banik ◽  
Neda Ghafourian ◽  
Ingo Thies ◽  
Benoit Famaey ◽  
...  
Keyword(s):  
Galaxy Formation ◽  
Gravity Models ◽  
Dynamical Friction ◽  
Extended Gravity ◽  
Corotation Radius ◽  
Cosmological Context ◽  
Gravity Theories ◽  
Barred Spiral Galaxies ◽  
Pattern Speeds ◽  
Almost All

ABSTRACT When bars form within galaxy formation simulations in the standard cosmological context, dynamical friction with dark matter (DM) causes them to rotate rather slowly. However, almost all observed galactic bars are fast in terms of the ratio between corotation radius and bar length. Here, we explicitly display an 8σ tension between the observed distribution of this ratio and that in the EAGLE simulation at redshift 0. We also compare the evolution of Newtonian galactic discs embedded in DM haloes to their evolution in three extended gravity theories: Milgromian Dynamics (MOND), a model of non-local gravity, and a scalar–tensor–vector gravity theory (MOG). Although our models start with the same initial baryonic distribution and rotation curve, the long-term evolution is different. The bar instability happens more violently in MOND compared to the other models. There are some common features between the extended gravity models, in particular the negligible role played by dynamical friction − which plays a key role in the DM model. Partly for this reason, all extended gravity models predict weaker bars and faster bar pattern speeds compared to the DM case. Although the absence of strong bars in our idealized, isolated extended gravity simulations is in tension with observations, they reproduce the strong observational preference for ‘fast’ bar pattern speeds, which we could not do with DM. We confirm previous findings that apparently ‘ultrafast’ bars can be due to bar-spiral arm alignment leading to an overestimated bar length, especially in extended gravity scenarios where the bar is already fast.

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