6,136 research outputs found
Consistency relations in multi-field inflation
We study the consequences of spatial coordinate transformation in multi-field
inflation. Among the spontaneously broken de Sitter isometries, only dilatation
in the comoving gauge preserves the form of the metric and thus results in
quantum-protected Slavnov-Taylor identities. We derive the corresponding
consistency relations between correlation functions of cosmological
perturbations in two different ways, by the connected and
one-particle-irreducible Green's functions. The lowest-order consistency
relations are explicitly given, and we find that even in multi-field inflation
the consistency relations in the soft limit are independent of the detail of
the matter sector.Comment: 24 pages, version to appear in JCA
Quantum non-linear evolution of inflationary tensor perturbations
We study the quantum mechanical evolution of the tensor perturbations during
inflation with non-linear tensor interactions. We first obtain the Lindblad
terms generated by non-linear interactions by tracing out unobservable
sub-horizon modes. Then we calculate explicitly the reduced density matrix for
the super-horizon modes, and show that the probability of maintaining the
unitarity of the squeezed state decreases in time. The decreased probability is
transferred to other elements of the reduced density matrix including
off-diagonal ones, so the evolution of the reduced density matrix describes the
quantum-to-classical transition of the tensor perturbations. This is different
from the classicality accomplished by the squeezed state, the suppression of
the non-commutative effect, which is originated from the quadratic, linear
interaction, and also maintains the unitarity. The quantum-to-classical
transition occurs within 5 - 10 e-folds, faster than the curvature
perturbation.Comment: (v1) 39 pages, (v2) typos corrected, to be published in Journal of
High Energy Physic
Large non-Gaussianity in non-minimal inflation
We consider a simple inflation model with a complex scalar field coupled to
gravity non-minimally. Both the modulus and the angular directions of the
complex scalar are slowly rolling, leading to two-field inflation. The modulus
direction becomes flat due to the non-minimal coupling, and the angular
direction becomes a pseudo-Goldstone boson from a small breaking of the global
U(1) symmetry. We show that large non-Gaussianity can be produced during
slow-roll inflation under a reasonable assumption on the initial condition of
the angular direction. This scenario may be realized in particle physics models
such as the Standard Model with two Higgs doublets.Comment: (v1) 14 pages, 2 figures, 1 table; (v2) 15 pages, discussions and
references added, to appear in Journal of Cosmology and Astroparticle Physic
Features and stability analysis of non-Schwarzschild black hole in quadratic gravity
Black holes are found to exist in gravitational theories with the presence of
quadratic curvature terms and behave differently from the Schwarzschild
solution. We present an exhaustive analysis for determining the quasinormal
modes of a test scalar field propagating in a new class of black hole
backgrounds in the case of pure Einstein-Weyl gravity. Our result shows that
the field decay of quasinormal modes in such a non-Schwarzschild black hole
behaves similarly to the Schwarzschild one, but the decay slope becomes much
smoother due to the appearance of the Weyl tensor square in the background
theory. We also analyze the frequencies of the quasinormal modes in order to
characterize the properties of new back holes, and thus, if these modes can be
the source of gravitational waves, the underlying theories may be testable in
future gravitational wave experiments. We briefly comment on the issue of
quantum (in)stability in this theory at linear order.Comment: 18 pages, 4 figures, 1 table, several references added, version
published on JHE
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