116 research outputs found
Perturbations in higher derivative gravity beyond maximally symmetric spacetimes
We study (covariant) scalar-vector-tensor (SVT) perturbations of infinite
derivative gravity (IDG), at the quadratic level of the action, around
conformally-flat, covariantly constant curvature backgrounds which are not
maximally symmetric spacetimes (MSS). This extends a previous analysis of
perturbations done around MSS, which were shown to be ghost-free. We motivate
our choice of backgrounds which arise as solutions of IDG in the UV, avoiding
big bang and black hole singularities. Contrary to MSS, in this paper we show
that, generically, all SVT modes are coupled to each other at the quadratic
level of the action. We consider simple examples of the full IDG action, and
illustrate this mixing and also a case where the action can be diagonalized and
ghost-free solutions constructed. Our study is widely applicable for both
non-singular cosmology and black hole physics where backgrounds depart from
MSS. In appendices, we provide SVT perturbations around conformally-flat and
arbitrary backgrounds which can serve as a compendium of useful results when
studying SVT perturbations of various higher derivative gravity models.Comment: 36 pages, 1 figur
inflation to probe non-perturbative quantum gravity
It is natural to expect a consistent inflationary model of the very early
Universe to be an effective theory of quantum gravity, at least at energies
much less than the Planck one. For the moment, , or shortly ,
inflation is the most successful in accounting for the latest CMB data from the
PLANCK satellite and other experiments. Moreover, recently it was shown to be
ultra-violet (UV) complete via an embedding into an analytic infinite
derivative (AID) non-local gravity. In this paper, we derive a most general
theory of gravity that contributes to perturbed linear equations of motion
around maximally symmetric space-times. We show that such a theory is quadratic
in the Ricci scalar and the Weyl tensor with AID operators along with the
Einstein-Hilbert term and possibly a cosmological constant. We explicitly
demonstrate that introduction of the Ricci tensor squared term is redundant.
Working in this quadratic AID gravity framework without a cosmological term we
prove that for a specified class of space homogeneous space-times, a space of
solutions to the equations of motion is identical to the space of backgrounds
in a local model. We further compute the full second order perturbed
action around any background belonging to that class. We proceed by extracting
the key inflationary parameters of our model such as a spectral index (),
a tensor-to-scalar ratio () and a tensor tilt (). It appears that
remains the same as in the local inflation in the leading slow-roll
approximation, while and get modified due to modification of the
tensor power spectrum. This class of models allows for any value of
with a modified consistency relation which can be fixed by future observations
of primordial -modes of the CMB polarization. This makes the UV complete
gravity a natural target for future CMB probes.Comment: 37 page
Towards a unitary formulation of quantum field theory in curved space-time II: the case of Schwarzschild black hole
We argue that the origin of unitarity violation and information loss paradox
in our understanding of black holes (BH) lies in the standard way of doing
quantum field theory in curved space-time (QFTCS), which is heavily biased on
intuition borrowed from classical General Relativity. In this paper, with the
quantum first approach, we formulate a so-called direct sum QFT (DQFT) in BH
space-time based on a novel formulation of discrete space-time transformations
in gravity that potentially restores unitarity. By invoking the quantum effects
associated with the gravitational backreaction, we show that the Hawking quanta
emerging outside of the Schwarzschild radius () cannot be independent
of the quanta that continue to be inside . This enables the information to
be carried by Hawking quanta, but in the BH DQFT formalism, we do not get any
firewalls. Furthermore, BH DQFT does not create any entanglement between
interior and exterior Hawking quanta which implies there is no entanglement
entropy and the BH evaporation happens involving only pure states. Finally, we
discuss the ways our framework leaves important clues for formulating a
scattering matrix and probing the nature of quantum gravity.Comment: 31 pages, 4 figures. Any comments are welcom
Dark matter and Standard Model reheating from conformal GUT inflation
Spontaneous breaking of conformal symmetry has been widely exploited in
successful model building of both inflationary cosmology and particle physics
phenomenology. Conformal Grand Unified Theory (CGUT) inflation provides the
same scalar tilt and tensor-to-scalar ratio as of Starobinsky and Higgs
inflation. Moreover, it predicts a proton life time compatible with the current
experimental bound. In this paper, we extend CGUT to account for the production
of dark matter and the reheating of the Standard Model. To this end, we
introduce a hidden sector directly coupled to the inflaton, whereas the
reheating of the visible sector is realized through a portal coupling between
the dark particles and the Higgs boson. The masses and interactions of the dark
particles and the Higgs boson are determined by the form of the conformal
potential and the non-vanishing VEV of the inflaton. We provide benchmark
points in the parameter space of the model that give the observed dark matter
relic density and reheating temperatures compatible with the Big Bang
nucleosynthesis.Comment: 38 pages, 9 figures, matches published versio
Gravitational waves in attractors
We study inflation in the attractor model under a non-slow-roll
dynamics with an ansatz proposed by Gong \& Sasaki \cite{Gong:2015ypa} of
assuming . Under this approach, we construct a class of
local shapes of inflaton potential that are different from the T-models. We
find this type of inflationary scenario predicts an attractor at
and . In our approach, the non-slow-roll
inflaton dynamics are related to the parameter which is the curvature
of K\"ahler geometry in the SUGRA embedding of this model.Comment: 6 pages, 2 figures. Contribution to the proceedings of "The
Fourtheenth Marcel Grossmann Meeting on General Relativity", University of
Rome "La Sapienza", Rome, July 12-18, 2015, based on a talk delivered at the
ST4 parallel sessio
Non-slow-roll dynamics in attractors
In this paper we consider the attractor model and study inflation
under a non-slow-roll dynamics. More precisely, we follow the approach recently
proposed by Gong and Sasaki \cite{Gong:2015ypa} by means of assuming
. Within this framework we obtain a family of functions
describing the local shape of the potential during inflation. We study a
specific model and find an inflationary scenario predicting an attractor at
and . We further show that
considering a non-slow-roll dynamics, the attractor model can be
broaden to a wider class of models that remain compatible with value of
. We further explore the model parameter space with respect to large and
small field inflation and conclude that the inflaton dynamics is connected to
the parameter, which is also related to the K\"ahler manifold
curvature in the supergravity (SUGRA) embedding of this model. We also comment
on the stabilization of the inflaton's trajectory.Comment: 17 pages, 6 figures, version accepted in JCA
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