920 research outputs found
A Study of Gaussianity in CMB band maps
The detection of non-Gaussianity in the CMB data would rule out a number of
inflationary models. A null detection of non-Gaussianity, instead, would
exclude alternative models for the early universe. Thus, a detection or
non-detection of primordial non-Gaussianity in the CMB data is crucial to
discriminate among inflationary models, and to test alternative scenarios.
However, there are various non-cosmological sources of non-Gaussianity. This
makes important to employ different indicators in order to detect distinct
forms of non-Gaussianity in CMB data. Recently, we proposed two new indicators
to measure deviation from Gaussianity on large angular scales, and used them to
study the Gaussianity of the raw band WMAP maps with and without the KQ75 mask.
Here we extend this work by using these indicators to perform similar analyses
of deviation from Gaussianity of the foreground-reduced Q, V, and W band maps.
We show that there is a significant deviation from Gaussianity in the
considered full-sky maps, which is reduced to a level consistent with
Gaussianity when the KQ75 mask is employed.Comment: 5 pages, 2 PS figures, uses ws-ijmpd.cls ; to be published in the
International Journal of Modern Physics
Covariant conservation of energy momentum in modified gravities
An explicit proof of the vanishing of the covariant divergence of the
energy-momentum tensor in modified theories of gravity is presented. The
gravitational action is written in arbitrary dimensions and allowed to depend
nonlinearly on the curvature scalar and its couplings with a scalar field. Also
the case of a function of the curvature scalar multiplying a matter Lagrangian
is considered. The proof is given both in the metric and in the first-order
formalism, i.e. under the Palatini variational principle. It is found that the
covariant conservation of energy-momentum is built-in to the field equations.
This crucial result, called the generalized Bianchi identity, can also be
deduced directly from the covariance of the extended gravitational action.
Furthermore, we demonstrate that in all of these cases, the freely falling
world lines are determined by the field equations alone and turn out to be the
geodesics associated with the metric compatible connection. The independent
connection in the Palatini formulation of these generalized theories does not
have a similar direct physical interpretation. However, in the conformal
Einstein frame a certain bi-metricity emerges into the structure of these
theories. In the light of our interpretation of the independent connection as
an auxiliary variable we can also reconsider some criticisms of the Palatini
formulation originally raised by Buchdahl.Comment: 8 pages. v2: more discussio
Bianchi type-I string cosmological model in the presence of a magnetic flux: exact and qualitative solutions
A Bianchi type-I cosmological model in the presence of a magnetic flux along
a cosmological string is investigated. The objective of this study is to
generate solutions to the Einstein equations using a few tractable assumptions
usually accepted in the literature. The analytical solutions are supplemented
with numerical and qualitative analysis. In the frame of the present model the
evolution of the Universe and other physical aspects are discussed.Comment: 13 pages, 6 figure
Differences and overlap in self-reported symptoms of bipolar disorder and borderline personality disorder
Background: Differential diagnosis between bipolar disorder (BD) and borderline personality disorder (BPD) is often challenging due to some overlap in symptoms and comorbidity of disorders. We investigated correlations in self-reported symptoms of BD and BPD in screening questionnaires at the levels of both total scores and individual items and explored overlapping dimensions. Methods: The McLean Screening Instrument (MSI) for BPD and the Mood Disorder Questionnaire (MDQ) for BD were filled in by patients with unipolar and bipolar mood disorders (n = 313) from specialized psychiatric care within a pilot study of the Helsinki University Psychiatric Consortium. Pearson's correlation coefficients between total scores and individual items of the MSI and the MDQ were estimated. Relationships between MDQ and MSI were evaluated by exploratory factor analysis (EFA). Results: The correlation between total scores of the MDQ and MSI was moderate (r = 0.431, P <0.001). Significant correlations were found between the MSI items of "impulsivity'' and "mood instability'' and all MDQ items (P <0.01). In the EFA, the MSI "impulsivity'' and "mood instability'' items had significant cross-loadings (0.348 and 0.298, respectively) with the MDQ factor. The MDQ items of "irritability'', "flight of thoughts'' and "distractibility'' (0.280, 0.210 and 0.386, respectively) cross-loaded on the MSI factor. Conclusions: The MDQ and MSI items of "affective instability'', "impulsivity'', "irritability'', "flight of thoughts'' and "distractibility'' appear to overlap in content. The other scale items are more disorder-specific, and thus, may help to distinguish BD and BPD. (C) 2015 Elsevier Masson SAS. All rights reserved.Peer reviewe
Bianchi type-I model with cosmic string in the presence of a magnetic field: spinor description
A Bianchi type-I cosmological model in the presence of a magnetic flux along
a cosmic string is investigated. A nonlinear spinor field is used to simulate
the cosmological cloud of strings. It is shown that the spinor field simulation
offer the possibility to solve the system of Einstein's equation without any
additional assumptions. It is shown that the present model is nonsingular at
the end of the evolution and does not allow the anisotropic Universe to turn
into an isotropic one.Comment: 14 pages, 4 figures, new figus are added, singularity and
isotropization process are discussed in detai
Cosmological perturbations in the Palatini formulation of modified gravity
Cosmology in extended theories of gravity is considered assuming the Palatini
variational principle, for which the metric and connection are independent
variables. The field equations are derived to linear order in perturbations
about the homogeneous and isotropic but possibly spatially curved background.
The results are presented in a unified form applicable to a broad class of
gravity theories allowing arbitrary scalar-tensor couplings and nonlinear
dependence on the Ricci scalar in the gravitational action. The gauge-ready
formalism exploited here makes it possible to obtain the equations immediately
in any of the commonly used gauges. Of the three type of perturbations, the
main attention is on the scalar modes responsible for the cosmic large-scale
structure. Evolution equations are derived for perturbations in a late universe
filled with cold dark matter and accelerated by curvature corrections. Such
corrections are found to induce effective pressure gradients which are
problematical in the formation of large-scale structure. This is demonstrated
by analytic solutions in a particular case. A physical equivalence between
scalar-tensor theories in metric and in Palatini formalisms is pointed out.Comment: 14 pages; the published version (+ an appendix). Corrected typos in
eqs. 30,33 and B
Bianchi type II models in the presence of perfect fluid and anisotropic dark energy
Spatially homogeneous but totally anisotropic and non-flat Bianchi type II
cosmological model has been studied in general relativity in the presence of
two minimally interacting fluids; a perfect fluid as the matter fluid and a
hypothetical anisotropic fluid as the dark energy fluid. The Einstein's field
equations have been solved by applying two kinematical ans\"{a}tze: we have
assumed the variation law for the mean Hubble parameter that yields a constant
value of deceleration parameter, and one of the components of the shear tensor
has been considered proportional to the mean Hubble parameter. We have
particularly dwelled on the accelerating models with non-divergent expansion
anisotropy as the Universe evolves. Yielding anisotropic pressure, the fluid we
consider in the context of dark energy, can produce results that can be
produced in the presence of isotropic fluid in accordance with the \Lambda CDM
cosmology. However, the derived model gives additional opportunities by being
able to allow kinematics that cannot be produced in the presence of fluids that
yield only isotropic pressure. We have obtained well behaving cases where the
anisotropy of the expansion and the anisotropy of the fluid converge to finite
values (include zero) in the late Universe. We have also showed that although
the metric we consider is totally anisotropic, the anisotropy of the dark
energy is constrained to be axially symmetric, as long as the overall energy
momentum tensor possesses zero shear stress.Comment: 15 pages; 5 figures; matches the version published in The European
Physical Journal Plu
Modified gravity and its reconstruction from the universe expansion history
We develop the reconstruction program for the number of modified gravities:
scalar-tensor theory, , and string-inspired, scalar-Gauss-Bonnet
gravity. The known (classical) universe expansion history is used for the
explicit and successful reconstruction of some versions (of special form or
with specific potentials) from all above modified gravities. It is demonstrated
that cosmological sequence of matter dominance, decceleration-acceleration
transition and acceleration era may always emerge as cosmological solutions of
such theory. Moreover, the late-time dark energy FRW universe may have the
approximate or exact CDM form consistent with three years WMAP data.
The principal possibility to extend this reconstruction scheme to include the
radiation dominated era and inflation is briefly mentioned. Finally, it is
indicated how even modified gravity which does not describe the
matter-dominated epoch may have such a solution before acceleration era at the
price of the introduction of compensating dark energy.Comment: LaTeX file, 24 pages, no figure, prepared for the proceedings of ERE
2006, minor correction
Cosmology of a Scalar Field Coupled to Matter and an Isotropy-Violating Maxwell Field
Motivated by the couplings of the dilaton in four-dimensional effective
actions, we investigate the cosmological consequences of a scalar field coupled
both to matter and a Maxwell-type vector field. The vector field has a
background isotropy-violating component. New anisotropic scaling solutions
which can be responsible for the matter and dark energy dominated epochs are
identified and explored. For a large parameter region the universe expands
almost isotropically. Using that the CMB quadrupole is extremely sensitive to
shear, we constrain the ratio of the matter coupling to the vector coupling to
be less than 10^(-5). Moreover, we identify a large parameter region,
corresponding to a strong vector coupling regime, yielding exciting and viable
cosmologies close to the LCDM limit.Comment: Refs. added, some clarifications. Published in JHEP10(2012)06
On compatibility of string effective action with an accelerating universe
In this paper, we fully investigate the cosmological effects of the moduli
dependent one-loop corrections to the gravitational couplings of the string
effective action to explain the cosmic acceleration problem in early (and/or
late) universe. These corrections comprise a Gauss-Bonnet (GB) invariant
multiplied by universal non-trivial functions of the common modulus
and the dilaton . The model exhibits several features of cosmological
interest, including the transition between deceleration and acceleration
phases. By considering some phenomenologically motivated ansatzs for one of the
scalars and/or the scale factor (of the universe), we also construct a number
of interesting inflationary potentials. In all examples under consideration, we
find that the model leads only to a standard inflation () when the
numerical coefficient associated with modulus-GB coupling is positive,
while the model can lead also to a non-standard inflation (), if
is negative. In the absence of (or trivial) coupling between the GB term and
the scalars, there is no crossing between the phases, while
this is possible with non-trivial GB couplings, even for constant dilaton phase
of the standard picture. Within our model, after a sufficient amount of e-folds
of expansion, the rolling of both fields and can be small. In
turn, any possible violation of equivalence principle or deviations from the
standard general relativity may be small enough to easily satisfy all
astrophysical and cosmological constraints.Comment: 30 pages, 8 figures; v2 significant changes in notations, appendix
and refs added; v3 significant revisions, refs added; v4 appendix extended,
new refs, published versio
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