226 research outputs found
The most general second-order field equations of bi-scalar-tensor theory in four dimensions
The Horndeski theory is known as the most general scalar-tensor theory with
second-order field equations. In this paper, we explore the bi-scalar extension
of the Horndeski theory. Following Horndeski's approach, we determine all the
possible terms appearing in the second-order field equations of the
bi-scalar-tensor theory. We compare the field equations with those of the
generalized multi-Galileons, and confirm that our theory contains new terms
that are not included in the latter theory. We also discuss the construction of
the Lagrangian leading to our most general field equations.Comment: 21 page
Time variation of proton-electron mass ratio and fine structure constant with runaway dilaton
Recent astrophysical observations indicate that the proton-electron mass
ratio and the fine structure constant have gone through nontrivial time
evolution. We discuss their time variation in the context of a dilaton runaway
scenario with gauge coupling unification at the string scale . We
show that the choice of adjustable parameters allows them to fit the same order
magnitude of both variations and their (opposite) signs in such a scenario.Comment: 16 pages, 1 figure, to appear in Phys. Rev.
Full bispectra from primordial scalar and tensor perturbations in the most general single-field inflation model
We compute the full bispectra, namely both auto- and cross- bispectra, of
primordial curvature and tensor perturbations in the most general single-field
inflation model whose scalar and gravitational equations of motion are of
second order. The formulae in the limits of k-inflation and potential-driven
inflation are also given. These expressions are useful for estimating the full
bispectra of temperature and polarization anisotropies of the cosmic microwave
background radiation.Comment: 20 pages, 5 figures, accepted to PTE
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