73 research outputs found
Internal space structure generalization of the quintom cosmological scenario
We introduce the Lagrangian for a multi-scalar field configuration in a
-dimensional internal space endowed with a constant metric and
generalize the quintom cosmological scenario. We find the energy momentum
tensor of the model and show that the set of dual transformations, that
preserve the form of the Einstein equations in the Friedmann-Robertson-Walker
(FRW) cosmology, is enlarged. We show that the stability of the power law
solutions leads to an exponential potential which is invariant under linear
transformations in the internal space. Moreover, we obtain the general exact
solution of the Einstein-Klein-Gordon equations for that potential. There exist
solutions that cross the phantom divide and solutions that blow up at a finite
time, exhibiting a superaccelerated behavior and ending in a big rip. We show
that the quintom model with a separable potential can be identified with a
mixture of several fluids. This framework includes the CDM model, a
bouncing model, and a setting sourced by a cosmic string network plus a
cosmological constant. The we concentrate on the case where the dimension of
the internal quintessence sector exceeds the dimension of the internal
phantom sector . For the dark energy density
derived from the 3-scalar field crosses the phantom divide and its negative
component plays the role of the negative part of a classical Dirac Field.Comment: 10 pages, 2 figure
Thin-shell wormholes with a generalized Chaplygin gas in Einstein-Born-Infeld theory
We construct spherically symmetric thin-shell wormholes supported by a
generalized Chaplygin gas in Born-Infeld electrodynamics coupled to Einstein
gravity, and we analyze their stability under radial perturbations. For
different values of the Born-Infeld parameter and the charge, we compare the
results with those obtained in a previous work for Maxwell electrodynamics. The
stability region in the parameter space reduces and then disappears as the
value of the Born-Infeld parameter is modified in the sense of a larger
departure from Maxwell theory.Comment: 9 pages, 6 figures; v2: improved versio
Crossing the phantom divide with k-essence in brane-worlds
We study a flat 3-brane in presence of a linear field with nonzero
cosmological constant . In this model the crossing of the phantom
divide (PD) occurs when the -essence energy density becomes negative. We
show that in the high energy regime the effective equation of state has a
resemblance of a modified Chaplygin gas while in the low energy regime it
becomes linear. We find a scale factor that begins from a singularity and
evolves to a de Sitter stable stage while other solutions have a
super-accelerated regime and end with a big rip. We use the energy conditions
to show when the effective equation of state of the brane-universe crosses the
PD.Comment: 8 pages, 5 figures. The article was fully rewritten. References
added. Accepted for publication in MPLA (2010
Wormhole Geometries In Gravity
We study wormhole solutions in the framework of f (R,T) gravity where R is
the scalar curvature, and T is the trace of the stress-energy tensor of the
matter. We have obtained the shape function of the wormhole by specifying an
equation of state for the matter field and imposing the flaring out condition
at the throat. We show that in this modified gravity scenario, the matter
threading the wormhole may satisfy the energy conditions, so it is the
effective stress-energy that is responsible for violation of the null energy
condition.Comment: 9 pages, 4 figures, published version, references adde
Preliminary evidence for association of genetic variants in pri-miR-34b/c and abnormal miR-34c expression with attention deficit and hyperactivity disorder
Attention deficit and hyperactivity disorder (ADHD) is a prevalent neurodevelopmental disorder characterized by impairment to sustain attention and inability to control impulses and activity level. The etiology of ADHD is complex, with an estimated heritability of 70-80%. Under the hypothesis that alterations in the processing or target binding of microRNAs (miRNAs) may result in functional alterations predisposing to ADHD, we explored whether common polymorphisms potentially affecting miRNA-mediated regulation are involved in this psychiatric disorder. We performed a comprehensive association study focused on 134 miRNAs in 754 ADHD subjects and 766 controls and found association between the miR-34b/c locus and ADHD. Subsequently, we provided preliminary evidence for overexpression of the miR-34c-3p mature form in peripheral blood mononuclear cells of ADHD subjects. Next, we tested the effect on gene expression of single-nucleotide polymorphisms within the ADHD-associated region and found that rs4938923 in the promoter of the pri-miR-34b/c tags cis expression quantitative trait loci for both miR-34b and miR-34c and has an impact on the expression levels of 681 transcripts in trans, including genes previously associated with ADHD. This gene set was enriched for miR-34b/c binding sites, functional categories related to the central nervous system, such as axon guidance or neuron differentiation, and serotonin biosynthesis and signaling canonical pathways. Our results provide preliminary evidence for the contribution to ADHD of a functional variant in the pri-miR-34b/c promoter, possibly through dysregulation of the expression of mature forms of miR-34b and miR-34c and some target genes. These data highlight the importance of abnormal miRNA function as a potential epigenetic mechanism contributing to ADHD
Linearized stability analysis of gravastars in noncommutative geometry
In this work, we find exact gravastar solutions in the context of
noncommutative geometry, and explore their physical properties and
characteristics. The energy density of these geometries is a smeared and
particle-like gravitational source, where the mass is diffused throughout a
region of linear dimension due to the intrinsic uncertainty
encoded in the coordinate commutator. These solutions are then matched to an
exterior Schwarzschild spacetime. We further explore the dynamical stability of
the transition layer of these gravastars, for the specific case of
, where M is the black hole mass, to linearized
spherically symmetric radial perturbations about static equilibrium solutions.
It is found that large stability regions exist and, in particular, located
sufficiently close to where the event horizon is expected to form.Comment: 6 pages, 3 figure
Self-interacting holographic dark energy
We investigate a spatially flat Friedmann-Robertson-Walker (FRW) universe
where dark matter exchanges energy with a self-interacting holographic dark
energy (SIHDE). Using the --statistical method on the Hubble function,
we obtain a critical redshift that seems to be consistent with both BAO and CMB
data. We calculate the theoretical distance modulus for confronting with the
observational data of SNe Ia for small redshift and large redshift
. The model gets accelerate faster than the CDM
one and it can be a good candidate to alleviate the coincidence problem. We
also examine the age crisis at high redshift associated with the old quasar APM
08279+5255.Comment: 9 pages, 5 figures. Title and motivation changed. Statistical
analysis improved. Accepted for publication in Modern Physics Letters A
(2012). arXiv admin note: text overlap with arXiv:1012.0883 by other author
Rotating thin-shell wormhole from glued Kerr spacetimes
We construct a model of a rotating wormhole made by cutting and pasting two
Kerr spacetimes. As a result, we obtain a rotating thin-shell wormhole with
exotic matter at the throat. Two candidates for the exotic matter are
considered: (i) a perfect fluid; (ii) an anisotropic fluid. We show that a
perfect fluid is unable to support a rotating thin-shall wormhole. On the
contrary, the anisotropic fluid with the negative energy density can be a
source for such a geometry.Comment: 8 pages, 3 figures, accepted for publication in Gravitation and
Cosmolog
Exome chip analyses in adult attention deficit hyperactivity disorder
Attention-deficit/hyperactivity disorder (ADHD) is a highly heritable childhood-onset neuropsychiatric condition, often persisting into adulthood. The genetic architecture of ADHD, particularly in adults, is largely unknown. We performed an exome-wide scan of adult ADHD using the Illumina Human Exome Bead Chip, which interrogates over 250 000 common and rare variants. Participants were recruited by the International Multicenter persistent ADHD CollaboraTion (IMpACT). Statistical analyses were divided into 3 steps: (1) gene-level analysis of rare variants (minor allele frequency (MAF)<1%); (2) single marker association tests of common variants (MAFgreater than or equal to1%), with replication of the top signals; and (3) pathway analyses. In total, 9365 individuals (1846 cases and 7519 controls) were examined. Replication of the most associated common variants was attempted in 9847 individuals (2077 cases and 7770 controls) using fixed-effects inverse variance meta-analysis. With a Bonferroni-corrected significance level of 1.82E−06, our analyses of rare coding variants revealed four study-wide significant loci: 6q22.1 locus (P=4.46E−08), where NT5DC1 and COL10A1 reside; the SEC23IP locus (P=6.47E−07); the PSD locus (P=7.58E−08) and ZCCHC4 locus (P=1.79E−06). No genome-wide significant association was observed among the common variants. The strongest signal was noted at rs9325032 in PPP2R2B (odds ratio=0.81, P=1.61E−05). Taken together, our data add to the growing evidence of general signal transduction molecules (NT5DC1, PSD, SEC23IP and ZCCHC4) having an important role in the etiology of ADHD. Although the biological implications of these findings need to be further explored, they highlight the possible role of cellular communication as a potential core component in the development of both adult and childhood forms of ADHD
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