Narrow Results

Cosmological particle production within the framework of induced gravity is investigated at the phenomenological level. It turns out that the conformal invariance of the “creation law” imposes quite strict restrictions on the possible types of sources. It is shown that terms with the particle number density in the “creation law” can be interpreted as dark matter. The action under consideration is reduced to the Einstein–Hilbert action with the classical scalar field for a certain gauge, which in turn reduces to $f(R)$-gravity with $f(R)\propto R^{\frac{3}{2}}$.

In this paper, we investigate Einstein’s gravity induced from higher-derivative scalar field theories. We develop an approach utilizing an effective theory of multiple fields for the higher-derivative theory. The expressions for induced cosmological constant and the induced gravitational constant are obtained in the present scenario of induced gravity in $D$ dimensions. We also show that finite values for the induced constants can be extracted in certain infinite-derivative theories.

A UV/IR complete theory of cosmological inflation is constructed in a braneworld setup that the inflaton field evolves on a DGP brane and the curvature effect is incorporated via the Gauss–Bonnet term in the bulk action. While the Induced Gravity on the DGP brane is a manifestation of the IR limit, the stringy Gauss–Bonnet effect in the bulk action realizes the UV sector of the scenario. This scenario generally supports a red power spectrum of perturbations, and for a large field regime requires a smaller number of e-folds than other braneworld inflation scenarios given the same assumptions. For the tensor-to-scalar ratio, this inflation scenario gives a better fit to observation than alternative scenarios.

We propose a topological model of induced gravity (pregeometry) where both Newton’s coupling constant and the cosmological constant appear as integration constants in solving field equations. The matter sector of a scalar field is also considered, and by solving field equations it is shown that various types of cosmological solutions in the Friedmann–Robertson–Walker (FRW) universe can be obtained. A detailed analysis is given of the meaning of the BRST transformations, which make the induced gravity be a topological field theory, by means of the canonical quantization analysis, and the physical reason why such BRST transformations are needed in the present formalism is clarified. Finally, we propose a dynamical mechanism for fixing the Lagrange multiplier fields by following the Higgs mechanism. The present study clearly indicates that the induced gravity can be constructed at the classical level without recourse to quantum fluctuations of matter and suggests an interesting relationship between the induced gravity and the topological quantum-field theory (TQFT).

Here, we concisely review the nonminimal coupling dynamics of a single scalar field in the context of purely affine gravity and extend the study to multifield dynamics. The coupling is performed via an affine connection and its associated curvature without referring to any metric tensor. The latter arises a posteriori and it may gain an emergent character like the scale of gravity. What is remarkable in affine gravity is the transition from nonminimal to minimal couplings which is realized by only field redefinition of the scalar fields. Consequently, the inflationary models gain a unique description in this context where the observed parameters, like the scalar tilt and the tensor-to-scalar ratio, are invariant under field reparametrization. Overall, gravity in its affine approach is expected to reveal interesting and rich phenomenology in cosmology and astroparticle physics.

We investigate the observational constraints on inflationary parameters in the context of a holographic cosmology with an induced gravity correction. We consider two situations where a universe is first filled with a scalar field and second with a tachyon field. Both cases are investigated in a slow-roll regime. We adopt a quadratic potential and an exponential potential for the scalar and the tachyon inflation, respectively. In this regard, the standard background and perturbative parameters characterizing the inflationary era are modified by correction terms. We show a good agreement between theoretical model parameters and Planck2018 observational data for both scalar and tachyon fields.

In this paper, we present a model for the late-time evolution of the universe where a dark energy-dark matter interaction is invoked. Dark energy is modeled through an holographic Ricci dark energy component. The model is embedded within an induced gravity braneworld model. For suitable choices of the interaction coupling, the big rip and little rip induced by the holographic Ricci dark energy, in a relativistic model and in an induced gravity braneworld model, are removed. In this scenario, the holographic dark energy will have a phantom like behavior even though the brane is asymptotically de Sitter.

In this paper, we discuss whether black hole entropy counts short or long-range microstates in quantum gravity. In brick wall and induced gravity models, the entropy arises due to short distance correlations across the event horizon cut off at the Planck length. However, the energy of these short range degrees of freedom is too high compared to the black hole energy. We argue that the long string phenomenon, which naturally appears in matrix quantum mechanics, resolves this issue by lowering the excitation energy per degree of freedom. This mechanism also reduces the total number of microscopic degrees of freedom in a given volume, leading to a correct estimate of the Bekenstein–Hawking formula for black hole entropy.