981 research outputs found
constant-roll inflation
The previously introduced class of two-parametric phenomenological
inflationary models in General Relativity in which the slow-roll assumption is
replaced by the more general, constant-roll condition is generalized to the
case of gravity. A simple constant-roll condition is defined in the
original Jordan frame, and exact expressions for a scalaron potential in the
Einstein frame, for a function (in the parametric form) and for
inflationary dynamics are obtained. The region of the model parameters
permitted by the latest observational constraints on the scalar spectral index
and the tensor-to-scalar ratio of primordial metric perturbations generated
during inflation is determined.Comment: 8 pages, 3 figures; added Fig. 2 and Appendix, matches published
versio
Constant-roll inflation: confrontation with recent observational data
The previously proposed class of phenomenological inflationary models in
which the assumption of inflaton slow-roll is replaced by the more general,
constant-roll condition is compared with the most recent cosmological
observational data, mainly the Planck ones. Models in this two-parametric class
which remain viable appear to be close to the slow-roll ones, and their
inflaton potentials are close to (but still different from) that of the natural
inflation model. Permitted regions for the two model parameters are presented.Comment: 4 pages, 1 figure; published versio
Matter power spectrum in f(R) gravity with massive neutrinos
The effect of massive neutrinos on matter power spectrum is discussed in the
context of gravity. It is shown that the anomalous growth of density
fluctuations on small scales due to the scalaron force can be compensated by
free streaming of neutrinos. As a result, models which predict observable
deviation of the equation-of-state parameter w_\DE from w_\DE=-1 can be
reconciled with observations of matter clustering if the total neutrino mass is
O(0.5 \eV).Comment: 8 pages, 6 figures; Discussion expanded, references added, results
unchanged, matches the version to be published in PT
Cosmology Based on f(R) Gravity Admits 1 eV Sterile Neutrinos
It is shown that the tension between recent neutrino oscillation experiments,
favoring sterile neutrinos with masses of the order of 1 eV, and cosmological
data which impose stringent constraints on neutrino masses from the free
streaming suppression of density fluctuations, can be resolved in models of the
present accelerated expansion of the Universe based on f(R) gravity.Comment: 5 pages, 3 figures, matches the published version in Phys. Rev. Let
Black hole perturbation in the most general scalar-tensor theory with second-order field equations I: The odd-parity sector
We perform a fully relativistic analysis of odd-type linear perturbations
around a static and spherically symmetric solution in the most general
scalar-tensor theory with second-order field equations in four-dimensional
spacetime. It is shown that, as in the case of general relativity, the
quadratic action for the perturbations reduces to the one having only a single
dynamical variable, from which concise formulas for no-ghost and no-gradient
instability conditions are derived. Our result is applicable to all the
theories of gravity with an extra scalar degree of freedom. We demonstrate how
the generic formulas can be applied to some particular examples such as the
Brans-Dicke theory, models, and Galileon gravity.Comment: 10 pages; v2. matches the published version in Phys. Rev. D; v3.
typos in Eqs. (A1), (A3)--(A5) fixed, results unchanged; v4. a typo in Eq.
(24) fixed, results unchanged; v5. a typo in Eq. (14) fixed, results
unchange
Black hole perturbation in nondynamical and dynamical Chern-Simons gravity
Chern-Simons gravitational theories are extensions of general relativity in
which the parity is violated due to the Chern-Simons term. We study linear
perturbations on the static and spherically symmetric background spacetime both
for nondynamical and dynamical Chern-Simons theories. We do not make an
assumption that the background Chern-Simons scalar field vanishes, which has
been adopted in the literature. By eliminating nondynamical variables using
their constraint equations, we derive the reduced second order action from
which a set of closed evolution equations containing only dynamical variables
are immediately obtained and therefore the number of propagating degrees of
freedom as well. It is found that ghost is present both for the nondynamical
case and for the dynamical case unless the background Chern-Simons scalar field
vanishes. It is also found that if the background scalar field vanishes, ghost
degrees of freedom are killed and all the modes propagate at the speed of
light.Comment: 18 pages; matches the published version in Phys. Rev.
Detecting Multiple Communities Using Quantum Annealing on the D-Wave System
A very important problem in combinatorial optimization is partitioning a
network into communities of densely connected nodes; where the connectivity
between nodes inside a particular community is large compared to the
connectivity between nodes belonging to different ones. This problem is known
as community detection, and has become very important in various fields of
science including chemistry, biology and social sciences. The problem of
community detection is a twofold problem that consists of determining the
number of communities and, at the same time, finding those communities. This
drastically increases the solution space for heuristics to work on, compared to
traditional graph partitioning problems. In many of the scientific domains in
which graphs are used, there is the need to have the ability to partition a
graph into communities with the ``highest quality'' possible since the presence
of even small isolated communities can become crucial to explain a particular
phenomenon. We have explored community detection using the power of quantum
annealers, and in particular the D-Wave 2X and 2000Q machines. It turns out
that the problem of detecting at most two communities naturally fits into the
architecture of a quantum annealer with almost no need of reformulation. This
paper addresses a systematic study of detecting two or more communities in a
network using a quantum annealer
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