Related papers: Fifth-Force Screening around Extremely Compact Sou…
Extending general relativity by adding extra degrees of freedom is a popular approach for explaining the accelerated expansion of the Universe and to build high energy completions of the theory of gravity. The presence of such new degrees…
A coupling between a scalar field (representing the dark energy) and dark matter could produce rich phenomena in cosmology. It affects cosmic structure formation mainly through the fifth force, a velocity-dependent force that acts parallel…
Chameleon particles, which could explain dark energy, are in many ways similar to axions, suggesting that an axion helioscope can be used for chameleon detection. The distinguishing property of chameleon particles is that, unlike Standard…
We study the effects of coupling a cosmologically rolling scalar field to higher order curvature terms. We show that when the strong coupling scale of the theory is on the 10^{-3}-10^{-1}eV range, the model passes all experimental bounds on…
Modifications of general relativity often involve coupling additional scalar fields to the Ricci scalar, leading to scalar-tensor theories of Brans-Dicke type. If the additional scalar fields are light, they can give rise to long-range…
We present the most recent results of both aspects of the GammeV experiment. The first aspect is a search for axion-like particles using a variable baseline, "light-shining-through-a-wall" technique. This search excludes the particle…
The spherical collapse model is often used to follow the evolution of overdensities into the nonlinear regime. We describe the correct approach to be used in coupled dark energy cosmologies, where a fifth force, different from gravity and…
We carry out a suite of cosmological simulations of modified action f(R) models where cosmic acceleration arises from an alteration of gravity instead of dark energy. These models introduce an extra scalar degree of freedom which enhances…
Scalar-tensor theories with the shift symmetries required by light scalars are well-explored modifications to GR. For these, two-derivative scalar self-interactions usually dominate at low energies and interestingly compete with the…
Dark energy models, such as the chameleon, where the acceleration of the expansion of the universe results from the dynamics of a scalar field coupled to matter, suffer from the potential existence of a fifth force. Three known mechanisms…
In the symmetron mechanism, the fifth force mediated by a coupled scalar field (the symmetron) is suppressed in high-density regions due to the restoration of symmetry in the symmetron potential. In this paper we study the background…
Nearly massless axion-like particles are of interest for astrophysical observations, and some constraints on their parameter space do exist in the literature. Here, we propose to put new constraints on these particles using polarisation…
The physical origin of the dark energy that causes the accelerated expansion rate of the universe is one of the major open questions of cosmology. One set of theories postulates the existence of a self-interacting scalar field for dark…
Chameleon mechanism appearing in massive tensor-scalar theory of gravity can effectively reduce locally the non-minimal coupling between the scalar field and matter. This mechanism is invoked to reconcile large-scale departures from general…
We revisit the possibility that the Planck mass is spontaneously generated in scale invariant scalar-tensor theories of gravity, typically leading to a "dilaton." The fifth force, arising from the dilaton, is severely constrained by…
We consider a fifth force to be an interaction that couples to matter with a strength that grows with the number of atoms. In addition to competing with the strength of gravity a fifth force can give rise to violations of the equivalence…
In this work, we derive novel constraints on scalar-tensor theories from neutrino physics. Spatial variations of the background scalar field effectively generate density and position-dependent Standard Model masses, including neutrinos.…
We study the matter and velocity divergence power spectra in a f(R) gravity theory and their time evolution measured from several large-volume N-body simulations with varying box sizes and resolution. We find that accurate prediction of the…
We study numerically the scalar wave emission by a non-spherical oscillation of neutron stars in a scalar-tensor theory of gravity with kinetic screening, considering both the monopole and quadrupole mode emission. In agreement with…
We consider static, spherically symmetric equilibrium configurations consisting of fermionic dark matter nonminimally coupled to dark energy in the form of a quintessence scalar field. With the scalar field coupling function, the form of…