A VARIATIONAL APPROACH TO THE COMPUTATION OF THE COSMOLOGICAL CONSTANT IN A MODIFIED GRAVITY THEORY

Author(s):  
R. GARATTINI
Symmetry ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 1528 ◽  
Author(s):  
Sergei V. Ketov

We review a possible origin of cosmological inflation from higher ( D ) spacetime dimensions in the context of modified gravity theory. It is demonstrated that it requires a spontaneous warped compactification of higher ( D ) spacetime dimensions together with the stabilization of extra ( D − 4 ) dimensions by Freund–Rubin mechanism. The relevant tools include an extra gauge ( D / 2 − 1 ) -form field with a non-vanishing flux in compact dimensions and a positive cosmological constant in D dimensions. Those features are illustrated on the specific example in eight spacetime dimensions compactified on a four-sphere with a warped factor and a flux, which leads to a viable Starobinsky-like inflationary model in four (non-compact) spacetime dimensions.


2019 ◽  
Vol 71 (3) ◽  
pp. 312 ◽  
Author(s):  
Metin Gürses ◽  
Çetin Şentürk

2012 ◽  
Vol 21 (02) ◽  
pp. 1250012
Author(s):  
PRIYADARSHI MAJUMDAR

We formulate a modified gravity theory that eliminates the need for dark energy and is stable for a Lagrangian containing R, R2 as well as 1/R terms (i.e. nonlinear contributions of the Ricci curvature with a non-analytic model of f(R) at R = 0) without considering any matter-dominated era. The terms with positive powers (1, 2) of the curvature support the inflationary epoch while the terms with negative power (-1) serves as effective dark energy, supporting current cosmic acceleration. We present a few analytical solutions of evolution equation for the deceleration parameter q as a function of Hubble parameter H and time t; specially in one solution, the universe evolves continuously from q = 1 (a radiation-dominated epoch) to q = -1/2 (dark-energy-dominated late-time accelerating phase) when the universe is sufficiently old. The solution is supported by numerical results. The transition from the decelerated (q > 0) to the accelerated phase (q < 0) of expansion takes place smoothly without having to resort to a study of asymptotic behavior.


2010 ◽  
Vol 25 (31) ◽  
pp. 2655-2666
Author(s):  
KOHKICHI KONNO ◽  
TOYOKI MATSUYAMA ◽  
SATOSHI TANDA

We consider relativistic fluid flow under Chern–Simons modified Maxwell theory and under Chern–Simons modified gravity theory. We take account of the effects of Chern–Simons corrections on the quantities of fluid flow that is conserved without the Chern–Simons corrections. We find that the conservations of several quantities are generally broken by the Chern–Simons corrections.


Author(s):  
Jacob D. Bekenstein

The impressive success of the standard cosmological model has suggested to many that its ingredients are all that one needs to explain galaxies and their systems. I summarize a number of known problems with this programme. They might signal the failure of standard gravity theory on galaxy scales. The requisite hints as to the alternative gravity theory may lie with the modified Newtonian dynamics (MOND) paradigm, which has proved to be an effective summary of galaxy phenomenology. A simple nonlinear modified gravity theory does justice to MOND at the non-relativistic level, but cannot be consistently promoted to relativistic status. The obstacles were first side-stepped with the formulation of tensor–vector–scalar theory (T e V e  S), a covariant-modified gravity theory. I review its structure, its MOND and Newtonian limits, and its performance in the face of galaxy phenomenology. I also summarize features of T e V e  S cosmology and describe the confrontation with data from strong and weak gravitational lensing.


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