35 research outputs found
Tensor to scalar ratio of perturbation amplitudes and inflaton dynamics
For the inflaton perturbations it is shown that the evolution of the
difference between the spectral indices can be translated into information on
the scale dependence of the tensor to scalar amplitudes ratio, , and how the
scalar field potential can be derived from that information. Examples are given
where converges to a constant value during inflation but dynamics are
rather different from the power--law model. Cases are presented where a
constant is not characteristic of the inflationary dynamics though the
resulting perturbation spectra are consistent with the CMB and LSS data.
The inflaton potential corresponding to given by a n--th order polynomial
of the e--folds number is derived in quadratures expressions. Since the
observable difference between the spectral indices evaluated at a pivot scale
yields information about the linear term of that polynomial, the first order
case is explicitly written down. The solutions show features beyond the
exponential form corresponding to power--law inflation and can be matched with
current observational data.Comment: 5 two-columns pages, two figures, RevTex4. Minor modifications. Two
references adde
Turbulence and Chaos in Anti-de-Sitter Gravity
Due to the AdS/CFT correspondence the question of instability of
Anti-de-Sitter spacetimes sits in the intersection of mathematical and
numerical relativity, string theory, field theory and condensed matter physics.
In this essay we revisit that important question emphasizing the power of
spectral methods and highlighting the effectiveness of standard techniques for
studying nonlinear dynamical systems. In particular we display explicitly how
the problem can be modeled as a system on nonlinearly coupled harmonic
oscillators. We highlight some of the many open questions that stem from this
result and point out that a full understanding will necessarily required the
interdisciplinary cooperation of various communities.Comment: 6 pages, 12 figures. Essay awarded honorable mention in the Gravity
Research Foundation essay competition 201
Higher order corrections to primordial spectra from cosmological inflation
We calculate power spectra of cosmological perturbations at high accuracy for
two classes of inflation models. We classify the models according to the
behaviour of the Hubble distance during inflation. Our approximation works if
the Hubble distance can be approximated either to be a constant or to grow
linearly with cosmic time. Many popular inflationary models can be described in
this way, e.g., chaotic inflation with a monomial potential, power-law
inflation and inflation at a maximum. Our scheme of approximation does not rely
on a slow-roll expansion. Thus we can make accurate predictions for some of the
models with large slow-roll parameters.Comment: 13 pages, 1 figure; section on consistency relations of inflation
added; accepted by Physics Letters
Inflation with a constant ratio of scalar and tensor perturbation amplitudes
The single scalar field inflationary models that lead to scalar and tensor
perturbation spectra with amplitudes varying in direct proportion to one
another are reconstructed by solving the Stewart-Lyth inverse problem to
next-to-leading order in the slow-roll approximation.
The potentials asymptote at high energies to an exponential form,
corresponding to power law inflation, but diverge from this model at low
energies, indicating that power law inflation is a repellor in this case. This
feature implies that a fine-tuning of initial conditions is required if such
models are to reproduce the observations. The required initial conditions might
be set through the eternal inflation mechanism.
If this is the case, it will imply that the spectral indices must be nearly
constant, making the underlying model observationally indistinguishable from
power law inflation.Comment: 20 pages, 7 figures. Major changes to the Introduction following
referee's comments. One figure added. Some other minor changes. No conclusion
was modifie
Black Holes with Varying Flux: A Numerical Approach
We present a numerical study of type IIB supergravity solutions with varying
Ramond-Ramond flux. We construct solutions that have a regular horizon and
contain nontrivial five- and three-form fluxes. These solutions are
holographically dual to the deconfined phase of confining field theories at
finite temperature. As a calibration of the numerical method we first
numerically reproduce various analytically known solutions including singular
and regular nonextremal D3 branes, the Klebanov-Tseytlin solution and its
singular nonextremal generalization. The horizon of the solutions we construct
is of the precise form of nonextremal D3 branes. In the asymptotic region far
away from the horizon we observe a logarithmic behavior similar to that of the
Klebanov-Tseytlin solution.Comment: 40 pages, 15 figure