155 research outputs found
The (p,q) String Tension in a Warped Deformed Conifold
We find the tension spectrum of the bound states of p fundamental strings and
q D-strings at the bottom of a warped deformed conifold. We show that it can be
obtained from a D3-brane wrapping a 2-cycle that is stabilized by both electric
and magnetic fluxes. Because the F-strings are Z_M-charged with non-zero
binding energy, binding can take place even if (p,q) are not coprime.
Implications for cosmic strings are briefly discussed.Comment: 17 pages, 1 figur
Holography: 2-D or not 2-D?
As was recently pointed out by Cadoni, a certain class of two-dimensional
gravitational theories will exhibit (black hole) thermodynamic behavior that is
reminiscent of a free field theory. In the current letter, a direct
correspondence is established between these two-dimensional models and the
strongly curved regime of (arbitrary-dimensional) anti-de Sitter gravity. On
this basis, we go on to speculatively argue that two-dimensional gravity may
ultimatley be utilized for identifying and perhaps even understanding
holographic dualities.Comment: 8 pages, Revtex; (v2) references and footnote added; (v3) discussion
on page 5 revise
Holographic Central Charge for 2-Dimensional de Sitter Space
Recently, investigations have begun into a holographic duality for
two-dimensional de Sitter space. In this paper, we evaluate the associated
central charge, using a modified version of the canonical Hamiltonian method
that was first advocated by Catelani {\it et al}. Our computation agrees with
that of a prior work (Cadoni {\it et al}), but we argue that the method used
here is, perhaps, aesthetically preferable on holographic grounds. We also
confirm an agreement between the Cardy and thermodynamic entropy, thus
providing further support for the conjectured two-dimensional de
Sitter/conformal field theory correspondence.Comment: 19 pages, Latex; discussion (Section 4) and references adde
Null Deformed Domain Wall
We study null 1/4 BPS deformations of flat domain wall solutions (NDDW) in
N=2, d=5 gauged supergravity with hypermultiplets and vector multiplets
coupled. These are uncharged time-dependent configurations and contain as
special case, 1/2 supersymmetric flat domain walls (DW), as well as 1/2 BPS
null solutions of the ungauged supergravity. Combining our analysis with the
classification method initiated by Gauntlett et al., we prove that all the
possible deformations of the DW have origin in the hypermultiplet sector or/and
are null. Here, we classify all the null deformations: we show that they
naturally organize themselves into "gauging" (v-deformation) and "non gauging"
(u-deformation). They have different properties: only in presence of
v-deformation is the solution supported by a time-dependent scalar potential.
Furthermore we show that the number of possible deformations equals the number
of matter multiplets coupled. We discuss the general procedure for constructing
explicit solutions, stressing the crucial role taken by the integrability
conditions of the scalars as spacetime functions. Two analytical solutions are
presented. Finally, we comment on the holographic applications of the NDDW, in
relation to the recently proposed time-dependent AdS/CFT.Comment: 38 pages; minor changes, references added; text revised, minor
changes, final version published in JHE
Effects of eight neuropsychiatric copy number variants on human brain structure
peer reviewedMany copy number variants (CNVs) confer risk for the same range of neurodevelopmental symptoms and psychiatric conditions including autism and schizophrenia. Yet, to date neuroimaging studies have typically been carried out one mutation at a time, showing that CNVs have large effects on brain anatomy. Here, we aimed to characterize and quantify the distinct brain morphometry effects and latent dimensions across 8 neuropsychiatric CNVs. We analyzed T1-weighted MRI data from clinically and non-clinically ascertained CNV carriers (deletion/duplication) at the 1q21.1 (n = 39/28), 16p11.2 (n = 87/78), 22q11.2 (n = 75/30), and 15q11.2 (n = 72/76) loci as well as 1296 non-carriers (controls). Case-control contrasts of all examined genomic loci demonstrated effects on brain anatomy, with deletions and duplications showing mirror effects at the global and regional levels. Although CNVs mainly showed distinct brain patterns, principal component analysis (PCA) loaded subsets of CNVs on two latent brain dimensions, which explained 32 and 29% of the variance of the 8 Cohen’s d maps. The cingulate gyrus, insula, supplementary motor cortex, and cerebellum were identified by PCA and multi-view pattern learning as top regions contributing to latent dimension shared across subsets of CNVs. The large proportion of distinct CNV effects on brain morphology may explain the small neuroimaging effect sizes reported in polygenic psychiatric conditions. Nevertheless, latent gene brain morphology dimensions will help subgroup the rapidly expanding landscape of neuropsychiatric variants and dissect the heterogeneity of idiopathic conditions. © 2021, The Author(s)
Space as a Tool for Astrobiology: Review and Recommendations for Experimentations in Earth Orbit and Beyond
Investigation of X-ray lasing in a capillary discharge
Using a new technique of an induced MHD instability in a capillary made of polyacetal we observed an intense spike (signal) of the Balmer-[MATH] line of C VI at 18.22 nm during the second half cycle of the discharge. The spike is identified as Amplified Spontaneous Emission (ASE), and enhancements are derived for capillaries of lengths between 15 and 50 mm. This ASE is explained as a result of charge exchange between plasma ions produced in the neck of the MHD instability, where m=0, and low temperature ions which are present in the same plasma column. Different wavelengths of carbon and oxygen were scanned and no spike was seen with the exception of the one mentioned above. The amplitude of the spike was increased when a plane multilayer mirror of Mo/Si was introduced and a gain of 12 cm-1 was obtained
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