Related papers: Weinberg's theorem, phantom crossing and screening
The statistical tension between early and late universe measurements of the Hubble constant ($H_0$) suggests that the dark sector is dynamical rather than static. We propose that this dynamics arises from a fundamental symmetry principle:…
We review the interpretation of gauge invariance as a mathematical redundancy required in a relativistic description of forces mediated by massless spin-1 and spin-2 particles. In this context we also review the Weinberg-Witten theorem and…
The acceleration of the expansion of the Universe has led to the construction of Dark Energy models where a light scalar field may have a range reaching up to cosmological scales. Screening mechanisms allow these models to evade the tight…
We review the equation of state for dark energy in modified gravity theories. In particular, we summarize the generic feature of the phantom divide crossing in the past and future in viable $f(R)$ gravity models.
We consider a scenario of modified gravity, which is generic to late-time acceleration, namely, acceleration in the Jordan frame and no acceleration in the Einstein frame. The possibility is realized by assuming an interaction between dark…
We investigate the cosmological evolution of a two-field model of dark energy where one is a dilaton field with canonical kinetic energy and the other is a phantom field with a negative kinetic energy term. A phase-plane analysis shows that…
Phantom fields with negative kinetic energy are often plagued by the vacuum quantum instability in the ultraviolet region. We present a Lorentz-violating dark energy model free from this problem and show that the crossing of the…
We consider the implications of the swampland conjectures on scalar-tensor theories defined in the Einstein frame in which the scalar interaction is screened. We show that chameleon models are not in the swampland provided the coupling to…
We study the equation of state for dark energy and explicitly demonstrate that the future crossings of the phantom divide line $w_{\mathrm{DE}}=-1$ are the generic feature in the existing viable $f(R)$ gravity models. We also explore the…
The phenomenon of the dark energy transition between the quintessence regime ($w > -1$) and the phantom regime ($w < -1$), also known as the cosmological constant boundary crossing, is analyzed in terms of the dark energy equation of state.…
We consider a scenario of large-scale modification of gravity that does not invoke extra degrees of freedom but includes coupling between baryonic matter and dark matter in the Einstein frame. The total matter energy density follows the…
The exact symmetry induced by the global shift of energy scale for the cosmological constant in the action of matter fields is spontaneously broken by setting the density of real vacuum energy and explicitly broken by the gravity that means…
Dark energy constraints have forced viable alternatives that differ substantially from a cosmological constant Lambda to have an equation of state w that evolves across the phantom divide set by Lambda. Naively, crossing this divide makes…
We complement investigations of the gauge structure of general relativity with an analysis of the physical consequences of the spontaneous breaking of diffeomorphism invariance which manifests itself in e.g. the socalled Einstein hole…
One of the clear predictions of string theory is the presence of a dynamical scalar partner of the spin-2 graviton, known as the dilaton. This will violate the Einstein Equivalence Principle, leading to a plethora of possibly observable…
It is known that scalar-tensor theory of gravity admits regular crossing of the phantom divide line $w_{\DE}=-1$ for dark energy, and existing viable models of present dark energy for its particular case -- $f(R)$ gravity -- possess one…
We establish constraints on $f(T)$ gravity by considering the possibility of a scenario that supports a phantom crossing of the equation of state parameter $\omega_{DE}$. After determining the viable parameter space of the model, while…
We study possible crossing of the phantom divided barrier in a Lorentz invariance violating dark energy model. Lorentz invariance violation which is achieved by introducing a vector field in the action, incorporates directly in the dynamics…
We study a scenario in which the dilaton, a pseudo-Goldstone boson of the spontaneous breaking of conformal symmetry, provides a portal between dark matter and the visible sector. We consider the low-energy description of the theory in…
Chameleon, environmentally dependent dilaton, and symmetron gravity are three models of modified gravity in which the effects of the additional scalar degree of freedom are screened in dense environments. They have been extensively studied…