1,064 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
Quantum Larmor radiation in conformally flat universe
We investigate the quantum effect on the Larmor radiation from a moving
charge in an expanding universe based on the framework of the scalar quantum
electrodynamics (SQED). A theoretical formula for the radiation energy is
derived at the lowest order of the perturbation theory with respect to the
coupling constant of the SQED. We evaluate the radiation energy on the
background universe so that the Minkowski spacetime transits to the Milne
universe, in which the equation of motion for the mode function of the free
complex scalar field can be exactly solved in an analytic way. Then, the result
is compared with the WKB approach, in which the equation of motion of the mode
function is constructed with the WKB approximation which is valid as long as
the Compton wavelength is shorter than the Hubble horizon length. This
demonstrates that the quantum effect on the Larmor radiation of the order
e^2\hbar is determined by a non-local integration in time depending on the
background expansion. We also compare our result with a recent work by Higuchi
and Walker [Phys. Rev. D80 105019 (2009)], which investigated the quantum
correction to the Larmor radiation from a charged particle in a
non-relativistic motion in a homogeneous electric field.Comment: 12 pages, 4 figure, accepted for publication in Physical Review
Reflection-Symmetry Protected Antiferromagnetic Topological Insulator in Three-Dimensional Heavy-Fermion Systems
We study the topological properties of an antiferromagnetic phase with
reflection symmetry in three-dimensional heavy-fermion systems. We here propose
a reflection-symmetric topological state in the three-dimensional
antiferromagnetic phase and demonstrate how the paramagnetic phase changes into
the antiferromagnetic topological phase of f -electron materials such as SmB6.Comment: 6pages, 2figure
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