2,988 research outputs found
General treatment of isocurvature perturbations and non-Gaussianities
We present a general formalism that provides a systematic computation of the
linear and non-linear perturbations for an arbitrary number of cosmological
fluids in the early Universe going through various transitions, in particular
the decay of some species (such as a curvaton or a modulus). Using this
formalism, we revisit the question of isocurvature non-Gaussianities in the
mixed inflaton-curvaton scenario and show that one can obtain significant
non-Gaussianities dominated by the isocurvature mode while satisfying the
present constraints on the isocurvature contribution in the observed power
spectrum. We also study two-curvaton scenarios, taking into account the
production of dark matter, and investigate in which cases significant
non-Gaussianities can be produced.Comment: Substantial improvements with respect to the first version. In
particular, we added a discussion on the confrontation of the models with
future observational data. This version is accepted for publication in JCA
Nonlinear perturbations of cosmological scalar fields
We present a covariant formalism to study nonlinear perturbations of scalar fields. In particular, we consider the case of two scalar fields and introduce the notion of adiabatic and isocurvature covectors. We obtain differential equations governing the evolution of these two covectors, as well as the evolution equation for the covector associated to the curvature perturbation. The form of these equations is very close to the analogous equations obtained in the linear theory but our equations are fully nonlinear and exact. As an application of our formalism, we expand these equations at second order in the perturbations. On large scales, we obtain a closed system of coupled scalar equations giving the evolution of the second-order adiabatic and entropy perturbations in terms of the first-order perturbations. These equations in general contain a nonlocal term which, however, rapidly decays in an expanding universe
Scalar Kaluza-Klein modes in a multiply warped braneworld
The Kaluza-Klein (KK) modes of a massive scalar field on a 3-brane embedded
in six dimensional multiply warped spacetime are determined. Due to the
presence of warping along both the extra dimensions the KK mass spectrum splits
into two closely spaced branches which is a distinct feature of this model
compared to the five dimensional Randall-Sundrum model. This new cluster of the
KK mode spectrum is expected to have interesting phenomenological implications
for the upcoming collider experiments. Such a scenario may also be extended for
even larger number of orbifolded extra dimensions.Comment: 10 pages, Revte
Non-linear isocurvature perturbations and non-Gaussianities
We study non-linear primordial adiabatic and isocurvature perturbations and
their non-Gaussianity. After giving a general formulation in the context of an
extended delta N-formalism, we analyse in detail two illustrative examples. The
first is a mixed curvaton-inflaton scenario in which fluctuations of both the
inflaton and a curvaton (a light isocurvature field during inflation)
contribute to the primordial density perturbation. The second example is that
of double inflation involving two decoupled massive scalar fields during
inflation. In the mixed curvaton-inflaton scenario we find that the bispectrum
of primordial isocurvature perturbations may be large and comparable to the
bispectrum of adiabatic curvature perturbations.Comment: 24 pages, typos corrected, references adde
Influencia de la formulación del enunciado y del control didáctico sobre la actividad intelectual de los alumnos en la resolución de problemas
Using as reference the scientist instead of the expert for analysing the pupil's behaviour in problem solving, we proposed to students (17 years old) closed and open problems. The great diversity of the students' productions and their analysis in the theoretical framework of didactical contract, oblige us to build two analysis grids: one of the students' activities and the other one for the finalities which we attribute to those activities. We show how ranging the strategy of resolution depends on the text of the problem
Can transvaginal ultrasound detect endometrial disease among asymptomatic postmenopausal patients?
Transvaginal ultrasound should not replace endometrial biopsy for detection of endometrial disease among asymptomatic postmenopausal patients. Endometrial biopsy has been considered a standard for the clinical diagnosis of endometrial disease among asymptomatic patients, but it is invasive, may be uncomfortable, and may not be able to be performed for some patients with cervical stenosis. Ultrasound evaluation is less invasive and more comfortable and can be performed for patients with cervical stenosis. The positive predictive value of ultrasound is not adequate to allow it to replace endometrial biopsy for screening of asymptomatic women (strength of recommendation: B, based on cohort studies)
Solutions of gauge invariant cosmological perturbations in long-wavelength limit
We investigate gauge invariant cosmological perturbations in a spatially flat
Friedman-Robertson-Walker universe with scalar fields. It is well known that
the evolution equation for the gauge invariant quantities has exact solutions
in the long-wavelength limit. We find that these gauge invariant solutions can
be obtained by differentiating the background solution with respect to
parameters contained in the background system. This method is very useful when
we analyze the long-wavelength behavior of cosmological perturbation with
multiple scalar fields.Comment: 17 pages, will appear in Classical and Quantum Gravit
From heaviness to lightness during inflation
We study the quantum fluctuations of scalar fields with a variable effective
mass during an inflationary phase. We consider the situation where the
effective mass depends on a background scalar field, which evolves during
inflation from being frozen into a damped oscillatory phase when the Hubble
parameter decreases below its mass. We find power spectra with suppressed
amplitude on large scales, similar to the standard massless spectrum on small
scales, and affected by modulations on intermediate scales. We stress the
analogies and differences with the parametric resonance in the preheating
scenario. We also discuss some potentially observable consequences when the
scalar field behaves like a curvaton.Comment: 23 pages; 8 figures; published versio
Entrainment coefficient and effective mass for conduction neutrons in neutron star crust: II Macroscopic treatment
Phenomena such as pulsar frequency glitches are believed to be attributable
to differential rotation of a current of ``free'' superfluid neutrons at
densities above the ``drip'' threshold in the ionic crust of a neutron star.
Such relative flow is shown to be locally describable by adaption of a
canonical two fluid treatment that emphasizes the role of the momentum
covectors constructed by differentiation of action with respect to the
currents, with allowance for stratification whereby the ionic number current
may be conserved even when the ionic charge number Z is altered by beta
processes. It is demonstrated that the gauge freedom to make different choices
of the chemical basis determining which neutrons are counted as ``free'' does
not affect their ``superfluid'' momentum covector, which must locally have the
form of a gradient (though it does affect the ``normal'' momentum covector
characterising the protons and those neutrons that are considered to be
``confined'' in the nuclei). It is shown how the effect of ``entrainment''
(whereby the momentum directions deviate from those of the currents) is
controlled by the (gauge independent) mobility coefficient K, estimated in
recent microscopical quantum mechanical investigations, which suggest that the
corresponding (gauge dependent) ``effective mass'' m* of the free neutrons can
become very large in some layers. The relation between this treatment of the
crust layers and related work (using different definitions of ``effective
mass'') intended for the deeper core layers is discussed.Comment: 21 pages Latex. Part II of article whose Part I (Simple microscopic
models) is given by nucl-th/0402057. New version extended to include figure
Dynamical Evolution of the Extra Dimension in Brane Cosmology
The evolution of the extra dimension is investigated in the context of brane
world cosmology. New cosmological solutions are found. In particular, solutions
in the form of waves travelling along the extra dimension are identified.Comment: Latex file, 10 page
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