50 research outputs found
Following the density perturbations through a bounce with AdS/CFT Correspondence
A bounce universe model, known as the coupled-scalar-tachyon bounce (CSTB)
universe, has been shown to solve the Horizon, Flatness and Homogeneity
problems as well as the Big Bang Singularity problem. Furthermore a scale
invariant spectrum of primordial density perturbations generated from the phase
of pre-bounce contraction is shown to be stable against time evolution. In this
work we study the detailed dynamics of the bounce and its imprints on the scale
invariance of the spectrum. The dynamics of the gravitational interactions near
the bounce point may be strongly coupled as the spatial curvature becomes big.
There is no a prior reason to expect the spectral index of the primordial
perturbations of matter density can be preserved. By encoding the bounce
dynamics holographically onto the dynamics of dual Yang-Mills system while the
latter is weakly coupled, via the AdS/CFT correspondence, we can safely evolve
the spectrum of the cosmic perturbations with full control. In this way we can
compare the post-bounce spectrum with the pre-bounce one: in the CSTB model we
explicitly show that the spectrum of primordial density perturbations generated
in the contraction phase preserves its stability as well as scale invariance
throughout the bounce process.Comment: 19 pages, 4 figure
On-Shell Gauge Invariant Three-Point Amplitudes
Assuming locality, Lorentz invariance and parity conservation we obtain a set
of differential equations governing the 3-point interactions of massless
bosons, which in turn determines the polynomial ring of these amplitudes. We
derive all possible 3-point interactions for tensor fields with polarisations
that have total symmetry and mixed symmetry under permutations of Lorentz
indices. Constraints on the existence of gauge-invariant cubic vertices for
totally symmetric fields are obtained in general spacetime dimensions and are
compared with existing results obtained in the covariant and light-cone
approaches. Expressing our results in spinor helicity formalism we reproduce
the perhaps mysterious mismatch between the covariant approach and the light
cone approach in 4 dimensions. Our analysis also shows that there exists a
mismatch, in the 3-point gauge invariant amplitudes corresponding to cubic
self-interactions, between a scalar field and an antisymmetric rank-2
tensor field . Despite the well-known fact that in 4 dimensions
rank-2 anti-symmetric fields are dual to scalar fields in free theories, such
duality does not extend to interacting theories.Comment: significantly revised, final version published in JHE