De Sitter Space Solutions Research Articles

Renormalizable, asymptotically free gravity without ghosts or tachyons

We analyse scale invariant quadratic quantum gravity incorporating non-minimal coupling to a multiplet of scalar fields in a gauge theory, with particular emphasis on the consequences for its interpretation resulting from a transformation from the Jordan frame to the Einstein frame. The result is the natural emergence of a de Sitter space solution which, depending the gauge theory and region of parameter space chosen, can be free of ghosts and tachyons, and completely asymptotically free. In the case of an SO(10) model, we present a detailed account of the spontaneous symmetry breaking, and we calculate the leading (two-loop) contribution to the dilaton mass.

Comment on “Covariant version of Verlinde’s emergent gravity”

Following recent Verlinde's heuristic construction or emergent gravity, Hossenfelder wrote down the Lagrangian capturing some aspects of this theory. We point out that there is an error in calculations whose consequence is that a cosmological de Sitter space solution is not recovered from this Lagrangian. We correct this error in order to obtain the desired solution. We also show that small perturbations around de Sitter space grow, which implies that this state is not stable. However, the presence of matter and radiation might in principle provide stability.

Stability analysis for new theories of massive spin-two particle and black hole entropy of new bigravity

In Phys.\ Rev.\ D 90 043006 (2014), we proposed a new ghost-free massive spin-two model in flat spacetime. Furthermore, as some extension, we couple the new model with a non-dynamical curved background in Phys.\ Rev.\ D 90 123013 (2014) and constructed new interaction terms without appearance of an extra mode. The characteristic property of the new model is the existence of nonlinear potential terms which give the nontrivial vacua. The presence of the nontrivial vacua, however, does not mean that the particle can be defined around all vacua. Therefore, in this paper, we discuss the condition for the new model to have stable vacua in flat spacetime and curved spacetime. Then, we couple this spin-two theory with a dynamical background and obtain the solutions. Moreover, we investigate the effect of this new spin-two model to the Einstein gravity by calculating the black hole entropy since the gravity coupled massive spin-two theory admits a black hole solution in addition to (anti-) de Sitter space solution.

Is the future universe singular: Dark matter versus modified gravity?

The fundamental problem of the occurrence/removal of finite-time future singularity in the universe evolution for coupled Dark Energy (DE) is addressed. It is demonstrated the existence of the (instable or local minimum) de Sitter space solution which may cure the Type II or Type IV future singularity for DE coupled with DM as the result of tuning the initial conditions. In case of phantom DE, the corresponding coupling may help to resolve the coincidence problem but not the Big Rip (Type I) singularity issue. We show that modified gravity of special form or inhomogeneous DE fluid may offer the universal scenario to cure the Type I, II, III or IV future singularity of coupled (fluid or scalar) DE evolution.

One-loop effective action for non-local modified Gauss–Bonnet gravity in de Sitter space

We discuss the classical and quantum properties of non-local modified Gauss–Bonnet gravity in de Sitter space, using its equivalent representation via string-inspired local scalar-Gauss–Bonnet gravity with a scalar potential. A classical, multiple de Sitter universe solution is found where one of the de Sitter phases corresponds to the primordial inflationary epoch, while the other de Sitter space solution—the one with the smallest Hubble rate—describes the late-time acceleration of our universe. A Chameleon scenario for the theory under investigation is developed, and it is successfully used to show that the theory complies with gravitational tests. An explicit expression for the one-loop effective action for this non-local modified Gauss–Bonnet gravity in the de Sitter space is obtained. It is argued that this effective action might be an important step towards the solution of the cosmological constant problem.

(Non-)Abelian-gauged supergravities in nine dimensions

We construct five massive deformations of the unique nine-dimensional N = 2 supergravity, each with two parameters. All these deformations have a higher-dimensional origin via Scherk–Schwarz reduction and correspond to gauged supergravities. The gauge groups we encounter are SO(2), SO(1, 1)+, ℝ, ℝ+ and the two-dimensional non-Abelian Lie group A(1), which consists of scalings and translations in one dimension.We make a systematic search for (non-supersymmetric) de Sitter space solutions. Furthermore, we discuss which of the D = 9 gauged supergravities can be considered as candidate low-energy limits of compactified superstring theory.

(Non-)Abelian gauged supergravities in nine dimensions

We construct five massive deformations of the unique nine-dimensional N = 2 supergravity, each with two parameters. All of these deformations have a higher-dimensional origin via Scherk-Schwarz reduction and correspond to gauged supergravities. The gauge group we encounter are SO(2), SO(1,1) +, R , R + and the unique two-dimensional non-Abelian Lie group C R 1, which consists of scalings and translations in one dimension. We make a systematic search for two classes of vacuum solutions: maximally symmetric solutions with constant scalars and half-supersymmetric domain wall solutions. In the first category we find explicit solutions in the form of (non-supersymmetric) de Sitter space solutions. In the second category we find precisely the three classes of domain wall solutions that were given in an earlier work.

Inflation with blowing-up solution of cosmological constant problem

The cosmological constant problem is how one chooses, without fine-tuning, one singular point $\Lambda_{eff}=0$ for the 4D cosmological constant. We argue that some recently discovered {\it weak self-tuning} solutions can be viewed as blowing-up this one point into a band of some parameter. These weak self-tuning solutions may have a virtue that only de Sitter space solutions are allowed outside this band, allowing an inflationary period. We adopt the hybrid inflation at the brane to exit from this inflationary phase and to enter into the standard Big Bang cosmology.

(Non-)Abelian Gauged Supergravities in Nine Dimensions

We construct five different two-parameter massive deformations of the unique nine-dimensional N=2 supergravity. All of these deformations have a higher-dimensional origin via Scherk-Schwarz reduction and correspond to gauged supergravities. The gauge groups we encounter are SO(2), SO(1,1)^+, R, R^+ and the two-dimensional non-Abelian Lie group A(1), which consists of scalings and translations in one dimension. We make a systematic search for half-supersymmetric domain walls and non-supersymmetric de Sitter space solutions. Furthermore, we discuss in which sense the supergravities we have constructed can be considered as low-energy limits of compactified superstring theory.

Self-tuning solution of the cosmological constant problem with antisymmetric tensor field

We present a self-tuning solution of the cosmological constant problem with one extra dimension which is curved with a warp factor. To separate out the extra dimension and to have a self-tuning solution, a three index antisymmetric tensor field is introduced with the 1/ H 2 term in the Lagrangian. The standard model fields are located at the y=0 brane. The existence [1] of the self-tuning solution (which results without any fine tuning among parameters in the Lagrangian) is crucial to obtain a vanishing cosmological constant in a 4D effective theory. The de-Sitter and anti-de-Sitter space solutions are possible. The de-Sitter space solutions have horizons. Restricting to the spaces which contain the y=0 brane, the vanishing cosmological constant is chosen in the most probable universe. For this interpretation to be valid, the existence of the self-tuning solution is crucial in view of the phase transitions. In this paper, we show explicitly a solution in case the brane tension shifts from one to another value. We also discuss the case with the H 2 term which leads to one-fine-tuning solutions at most.