Related papers: Towards Ghost-Free Gravity and Standard Model
We propose a new solution to the cosmological constant problem building on a nonperturbative quantum theory of gravity with torsional instantons. These pseudoparticles, which were recently found to exist in a first order formulation of…
Adopting the q-theory approach to the cosmological constant problem, a simple field-theoretic model is presented which generates an effective cosmological constant (remnant vacuum energy density) of the observed order of magnitude,…
Recently modified gravitational theories which mimic the behaviour of dark matter, the so-called "Mimetic Dark Matter", have been proposed. We study the consistency of such theories with respect to the absence of ghost instability and…
In 3+1 space-time dimensions, fourth order derivative gravity is perturbatively renormalizable. Here it is shown that it describes a unitary theory of gravitons (with/without an additional scalar) in a limited coupling parameter space which…
We reconstruct $f(R,T)$ theory (where $R$ is the scalar curvature and $T$ is the trace of energy-momentum tensor) in the framework of QCD ghost dark energy models. In this study, we concentrate on particular models of $f(R,T)$ gravity which…
We study the creation and evolution of cosmological perturbations in renormalizable quadratic gravity with a Weyl term. We adopt a prescription that implies the stability of the vacuum at the price of introducing a massive spin-two ghost…
We propose a new class of four-dimensional theories for natural electroweak symmetry breaking, relying neither on supersymmetry nor on strong dynamics at the TeV scale. The new TeV physics is perturbative, and radiative corrections to the…
We argue that the Standard Model is accompanied by a new pseudo-scalar degree of freedom, $\eta_{\rm w}$-meson, which cancels the topological susceptibility of the electroweak vacuum and gets its mass from this effect. The prediction is…
Out of the four components of the electromagnetic field, Maxwell's theory only contains two physical degrees of freedom. However, in an expanding universe, consistently eliminating one of the "unphysical" states in the covariant…
Although equivalent to general relativity, teleparallel gravity is conceptually speaking a completely different theory. In this theory, the gravitational field is described by torsion, not by curvature. By working in this context, a new…
At the quantum level, the polynomial models of gravity with six and eight derivatives are superrenormalizable, but suffer from higher derivative ghost and/or tachyonic ghost states. On the other hand, these models may have advantages in the…
Numerous claims in the literature suggest that gravity induced on a higher co-dimensional surface violates unitarity in the weak coupling regime. However, it remained unclear, why a conserved source localized on this surface and giving rise…
A form of infinite derivative gravity is free from ghost-like instabilities with improved small scale behavior. In this theory, we calculate the tree-level scattering amplitude and the corresponding weak field potential energy between two…
Theories with infinite volume extra dimensions open exciting opportunities for particle physics. We argued recently that along with attractive features there are phenomenological difficulties in this class of models. In fact, there is no…
We study the possibility of decoupling gravity from the vacuum energy. This is effectively equivalent to promoting Newton's constant to a high-pass filter that degravitates sources of characteristic wavelength larger than a certain…
To explain the currently observed accelerated expansion of the universe, a large number of different theoretical models are presently being discussed. In one way or another, all of these contain `new physics', though at different levels.…
We show that the problem of ghosts in critical gravity and its higher dimensional extensions can be resolved by giving dynamics to the symmetric rank two auxiliary field existing in the action of these theories. These New Bi-Gravities, at…
There are many theories of quantum gravity, depending on asymptotic boundary conditions, and the amount of supersymmetry. The cosmological constant is one of the fundamental parameters that characterize different theories. If it is…
We present the construction of a gravitational action including an infinite series of higher derivative terms. The outcome is a classically consistent completion of a well-studied quadratic curvature theory. The closed form for the full…
In order to explore some general features of modified theories of gravity which involve higher derivatives and spontaneous Lorentz and/or diffeomorphism symmetry breaking, we study the recently proposed new version of covariant…