179 research outputs found
Gravitational Waves in New General Relativity
The models of New General Relativity have recently got attention of research
community, and there are some works studying their dynamical properties. The
formal aspects of this investigation have been mostly restricted to the primary
constraints in the Hamiltonian analysis. However, it is by far not enough for
counting their degrees of freedom or judging whether they are any good and
viable. In this paper we study linearised equations in vacuum around the
trivial Minkowski tetrad. By taking the approach of cosmological perturbation
theory we show that the numbers of primary constraints are very easily seen
without any need of genuine Hamiltonian techniques, and give the full count of
linearised degrees of freedom in the weak field limit of each and every version
of New General Relativity without matter.Comment: 14 page
Crystal structures of [Cu2(2,2′-bipyridine-N,N′)2(H2O)2(μ2-OH)2](barbiturate)2·2H2O and [Cu(2,2′-bipyridine-N,N′)(H2O)(barbiturate-O)Cl]·2H2O
Initial Conditions for Vector Inflation
Recently, a model of inflation using non-minimally coupled massive vector
fields has been proposed. For a particular choice of non-minimal coupling
parameter and for a flat FRW model, the model is reduced to the model of
chaotic inflation with massive scalar field. We study the effect of non-zero
curvature of the universe on the onset of vector inflation. We find that in a
curved universe the dynamics of vector inflation can be different from chaotic
inflation, and the fraction of the initial conditions leading to inflationary
solutions is reduced compared with the chaotic inflation case.Comment: 12 pages, 5 figures, version to be published in JCA
Anisotropic Inflation with Non-Abelian Gauge Kinetic Function
We study an anisotropic inflation model with a gauge kinetic function for a
non-abelian gauge field. We find that, in contrast to abelian models, the
anisotropy can be either a prolate or an oblate type, which could lead to a
different prediction from abelian models for the statistical anisotropy in the
power spectrum of cosmological fluctuations. During a reheating phase, we find
chaotic behaviour of the non-abelian gauge field which is caused by the
nonlinear self-coupling of the gauge field. We compute a Lyapunov exponent of
the chaos which turns out to be uncorrelated with the anisotropy.Comment: 16 pages, 4 figure
Gauge-flation and Cosmic No-Hair Conjecture
Gauge-flation, inflation from non-Abelian gauge fields, was introduced in
[1,2]. In this work, we study the cosmic no-hair conjecture in gauge-flation.
Starting from Bianchi-type I cosmology and through analytic and numeric studies
we demonstrate that the isotropic FLRW inflation is an attractor of the
dynamics of the theory and that the anisotropies are damped within a few
e-folds, in accord with the cosmic no-hair conjecture.Comment: 24 pages, 18 figure
Interacting Spin-2 Fields
We construct consistent theories of multiple interacting spin-2 fields in
arbitrary spacetime dimensions using a vielbein formulation. We show that these
theories have the additional primary constraints needed to eliminate potential
ghosts, to all orders in the fields, and to all orders beyond any decoupling
limit. We postulate that the number of spin-2 fields interacting at a single
vertex is limited by the number of spacetime dimensions. We then show that, for
the case of two spin-2 fields, the vielbein theory is equivalent to the
recently proposed theories of ghost-free massive gravity and bi-metric gravity.
The vielbein formulation greatly simplifies the proof that these theories have
an extra primary constraint which eliminates the Boulware-Deser ghost.Comment: 42 pages, 3 figures. v3 alternative argument using constrained
spatial vielbeins has been removed (see footnote 3
Uncertainty relations in curved spaces
Uncertainty relations for particle motion in curved spaces are discussed. The
relations are shown to be topologically invariant. New coordinate system on a
sphere appropriate to the problem is proposed. The case of a sphere is
considered in details. The investigation can be of interest for string and
brane theory, solid state physics (quantum wires) and quantum optics.Comment: published version; phase space structure discussion adde
Perturbations and non-Gaussianities in three-form inflationary magnetogenesis
We reconsider magnetogenesis in the context of three-form inflation, and its
backreaction. In particular, we focus on first order perturbation theory during
inflation and subsequent radiation era: we discuss the consistency of the
perturbative approach, and elaborate on the possible non-Gaussian signatures of
the model.Comment: 29 pages and 8 figure
Non-canonical generalizations of slow-roll inflation models
We consider non-canonical generalizations of two classes of simple
single-field inflation models. First, we study the non-canonical version of
"ultra-slow roll" inflation, which is a class of inflation models for which
quantum modes do not freeze at horizon crossing, but instead evolve rapidly on
superhorizon scales. Second, we consider the non-canonical generalization of
the simplest "chaotic" inflation scenario, with a potential dominated by a
quartic (mass) term for the inflaton. We find a class of related non-canonical
solutions with polynomial potentials, but with varying speed of sound. These
solutions are characterized by a constant field velocity, and we dub such
models {\it isokinetic} inflation. As in the canonical limit, isokinetic
inflation has a slightly red-tilted power spectrum, consistent with current
data. Unlike the canonical case, however, these models can have an arbitrarily
small tensor/scalar ratio. Of particular interest is that isokinetic inflation
is marked by a correlation between the tensor/scalar ratio and the amplitude of
non-Gaussianity such that parameter regimes with small tensor/scalar ratio have
{\it large} associated non-Gaussianity, which is a distinct observational
signature.Comment: 12 pages, 3 figures, LaTeX; V2: version submitted to JCAP. References
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