30 research outputs found
Observational Constraints on Kinetic Gravity Braiding from the Integrated Sachs-Wolfe Effect
The cross-correlation between the integrated Sachs-Wolfe (ISW) effect and the
large scale structure (LSS) is a powerful tool to constrain dark energy and
alternative theories of gravity. In this paper, we obtain observational
constraints on kinetic gravity braiding from the ISW-LSS cross-correlation. We
find that the late-time ISW effect in the kinetic gravity braiding model
anti-correlates with large scale structures in a wide range of parameters,
which clearly demonstrates how one can distinguish modified gravity theories
from the LCDM model using the ISW effect. In addition to the analysis based on
a concrete model, we investigate a future prospect of the ISW-LSS
cross-correlation by using a phenomenological parameterization of modified
gravity models.Comment: 7 pages, 3 figures, accepted for publication in Physical Review
Constraint on ghost-free bigravity from gravitational Cherenkov radiation
We investigate gravitational Cherenkov radiation in a healthy branch of
background solutions in the ghost-free bigravity model. In this model, because
of the modification of dispersion relations, each polarization mode can possess
subluminal phase velocities, and the gravitational Cherenkov radiation could be
potentially emitted from a relativistic particle. In the present paper, we
derive conditions for the process of the gravitational Cherenkov radiation to
occur and estimate the energy emission rate for each polarization mode. We
found that the gravitational Cherenkov radiation emitted even from an ultrahigh
energy cosmic ray is sufficiently suppressed for the graviton's effective mass
less than , and the bigravity model with dark matter coupled to
the hidden metric is therefore consistent with observations of high energy
cosmic rays.Comment: 13 pages, 2 figures; v