Wilsonian dark matter in string derived Z' model

The dark matter issue is among the most perplexing in contemporary physics. The problem is more enigmatic due to the wide range of possible solutions, ranging from the ultra-light to the super-massive. String theory gives rise to plausible dark matter candidates due to the breaking of the non--Abelian Grand Unified Theory (GUT) symmetries by Wilson lines. The physical spectrum then contains states that do not satisfy the quantisation conditions of the unbroken GUT symmetry. Given that the Standard Model states are identified with broken GUT representations, and provided that any ensuing symmetry breaking is induced by components of GUT states, leaves a remnant discrete symmetry that forbid the decay of the Wilsonian states. A class of such states are obtained in a heterotic-string derived $Z^\prime$ model. The model exploits the spinor-vector duality symmetry, observed in the fermionic $Z_2\times Z_2$ heterotic-string orbifolds, to generate a $Z^\prime\in E_6$ symmetry that may remain unbroken down to low energies. The $E_6$ symmetry is broken at the string level with discrete Wilson lines. The Wilsonian dark matter candidates in the string derived model are $SO(10)$, and hence Standard Model, singlets and possess non-$E_6$ $U(1)_{Z^\prime}$ charges. Depending on the $U(1)_{Z^\prime}$ breaking scale and the reheating temperature they give rise to different scenarios for the relic abundance, and in accordance with the cosmological constraints.Comment: 24 pages. 5 figures. Standard LaTex. Additional comments and clarifications. Published versio

Expected spectral characteristics of (101955) Bennu and (162173) Ryugu, targets of the OSIRIS-REx and Hayabusa2 missions

NASA's OSIRIS-REx and JAXA's Hayabusa2 sample-return missions are currently on their way to encounter primitive near-Earth asteroids (101955) Bennu and (162173) Ryugu, respectively. Spectral and dynamical evidence indicates that these near-Earth asteroids originated in the inner part of the main belt. There are several primitive collisional families in this region, and both these asteroids are most likely to have originated in the Polana-Eulalia family complex. We present the expected spectral characteristics of both targets based on our studies of our primitive collisional families in the inner belt: Polana-Eulalia, Erigone, Sulamitis, and Clarissa. Observations were obtained in the framework of our PRIMitive Asteroids Spectroscopic Survey (PRIMASS). Our results are especially relevant to the planning and interpretation of in-situ images and spectra to be obtained by the two spacecraft during the encounters with their targets.Comment: 22 pages, 11 figures. Accepted for publication in Icarus on May 11, 201

Damage detections in nonlinear vibrating thermally loaded plates

In this work, geometrically nonlinear vibrations of fully clamped rectangular plates subjected to thermal changesare used to study the sensitivity of some vibration response parameters to the presence of damage and elevated temperature. The geometrically nonlinear version of the Mindlin plate theory is used to model the plate behaviour.Damage is represented as a stiffness reduction in a small area of the plate. The plates are subjected to harmonicloading leading to large amplitude vibrations and temperature changes. The plate vibration response is obtained by a pseudo-load mode superposition method. The main results are focussed on establishing the influence of damage on the vibration response of the heated and the unheated plates and the change in the time-history diagrams and the Poincaré maps caused by damage and elevated temperature. The damage criterion formulated earlier for nonheated plates, based on analyzing the points in the Poincaré sections of the damaged and healthy plate, is modified and tested for the case of plates additionally subjected to elevated temperatures. The importance of taking into account the actual temperature in the process of damage detection is shown

Suppressing dimension-5 operators in general SU(5) models

We discuss dimension-5 operators in supersymmetric models containing extra hypercharge 1/3 color-triplets. We derive a general formula relating dimension-5 operator to the color-triplet mass matrix. We show that certain zeros in the triplet mass-matrix together with some triplet coupling selection rules can lead to elimination of dimension-5 operators. In particular we focus on SU(5) models and show that (a) Dimension-5 operators can be eliminated in the standard SU(5) model by the introduction of an extra pair of 5+5b Higgses with specific couplings (b) Flipped SU(5) models with extra 10+10b Higgses are free of dimension-5 operators (c) Flipped SU(5) models with extra 5+5b and/or extra 10+10b Higgses can be made free of dimension-5 operators for a textured form of the triplet mass-matrix accompanied by constraints on the 5-plet couplings to matter. Our analysis is motivated by the recently put forward M-theory phenomenological framework that requires a strong string coupling and reintroduces the problem of eliminating dimension-5 operators.Comment: 10 pages, Latex2e, minor changes, references adde

Fully Anisotropic String Cosmologies, Maxwell Fields and Primordial Shear

We present a class of exact cosmological solutions of the low energy string effective action in the presence of a homogeneous magnetic fields. We discuss the physical properties of the obtained (fully anisotropic) cosmologies paying particular attention to their vacuum limit and to the possible isotropization mechanisms. We argue that quadratic curvature corrections are able to isotropize fully anisotropic solutions whose scale factors describe accelerated expansion. Moreover, the degree of isotropization grows with the duration of the string phase. We follow the fate of the shear parameter in a decelerated phase where, dilaton, magnetic fields and radiation fluid are simultaneously present. In the absence of any magnetic field a long string phase immediately followed by radiation is able to erase large anisotropies. Conversely, if a short string phase is followed by a long dilaton dominated phase the anisotropies can be present, in principle, also at later times. The presence of magnetic seeds after the end of the string phase can induce further anisotropies which can be studied within the formalism reported in this paper.Comment: 19 pages in Revtex style, 14 Encapsulated figure

Overcoming the Challenges Associated with Image-based Mapping of Small Bodies in Preparation for the OSIRIS-REx Mission to (101955) Bennu

The OSIRIS-REx Asteroid Sample Return Mission is the third mission in NASA's New Frontiers Program and is the first U.S. mission to return samples from an asteroid to Earth. The most important decision ahead of the OSIRIS-REx team is the selection of a prime sample-site on the surface of asteroid (101955) Bennu. Mission success hinges on identifying a site that is safe and has regolith that can readily be ingested by the spacecraft's sampling mechanism. To inform this mission-critical decision, the surface of Bennu is mapped using the OSIRIS-REx Camera Suite and the images are used to develop several foundational data products. Acquiring the necessary inputs to these data products requires observational strategies that are defined specifically to overcome the challenges associated with mapping a small irregular body. We present these strategies in the context of assessing candidate sample-sites at Bennu according to a framework of decisions regarding the relative safety, sampleability, and scientific value across the asteroid's surface. To create data products that aid these assessments, we describe the best practices developed by the OSIRIS-REx team for image-based mapping of irregular small bodies. We emphasize the importance of using 3D shape models and the ability to work in body-fixed rectangular coordinates when dealing with planetary surfaces that cannot be uniquely addressed by body-fixed latitude and longitude.Comment: 31 pages, 10 figures, 2 table

Selective Loss of Wild-Type p16INK4a Expression in Human Nevi

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The structure of Chariklo's rings from stellar occultations

Two narrow and dense rings (called C1R and C2R) were discovered around the Centaur object (10199) Chariklo during a stellar occultation observed on 2013 June 3. Following this discovery, we planned observations of several occultations by Chariklo's system in order to better characterize the physical properties of the ring and main body. Here, we use 12 successful occulations by Chariklo observed between 2014 and 2016. They provide ring profiles (physical width, opacity, edge structure) and constraints on the radii and pole position. Our new observations are currently consistent with the circular ring solution and pole position, to within the $\pm 3.3$ km formal uncertainty for the ring radii derived by Braga-Ribas et al. The six resolved C1R profiles reveal significant width variations from $\sim 5$ to 7.5 km. The width of the fainter ring C2R is less constrained, and may vary between 0.1 and 1 km. The inner and outer edges of C1R are consistent with infinitely sharp boundaries, with typical upper limits of one kilometer for the transition zone between the ring and empty space. No constraint on the sharpness of C2R's edges is available. A 1$\sigma$ upper limit of $\sim 20$ m is derived for the equivalent width of narrow (physical width <4 km) rings up to distances of 12,000 km, counted in the ring plane

String-Inspired Higher-Curvature Terms and the Randall-Sundrum Scenario

We consider the O(a') string effective action, with Gauss-Bonnet curvature-squared and fourth-order dilaton-derivative terms, which is derived by a matching procedure with string amplitudes in five space-time dimensions. We show that a non-factorizable metric of the Randall-Sundrum (RS) type, with four-dimensional conformal factor Exp(-2 k|z|), can be a solution of the pertinent equations of motion. The parameter k is found proportional to the string coupling g_s and thus the solution appears to be non-perturbative. It is crucial that the Gauss-Bonnet combination has the right (positive in our conventions) sign, relative to the Einstein term, which is the case necessitated by compatibility with string (tree) amplitude computations. We study the general solution for the dilaton and metric functions, and thus construct the appropriate phase-space diagram in the solution space. In the case of an anti-de-Sitter bulk, we demonstrate that there exists a continuous interpolation between (part of) the RS solution at z=infinity and an (integrable) naked singularity at z=0. This implies the dynamical formation of domain walls (separated by an infinite distance), thus restricting the physical bulk space time to the positive z axis. Some brief comments on the possibility of fine-tuning the four-dimensional cosmological constant to zero are also presented.Comment: 28 pages Latex, three eps figures incorporated, minor change

First evidence of overlaps between HIV-Associated Dementia (HAD) and non-viral neurodegenerative diseases: proteomic analysis of the frontal cortex from HIV+ patients with and without dementia

<p>Abstract</p> <p>Background</p> <p>The pathogenesis of HIV-associated dementia (HAD) is poorly understood. To date, detailed proteomic fingerprinting directly from autopsied brain tissues of HAD and HIV non-dementia patients has not been performed.</p> <p>Result</p> <p>Here, we have analyzed total proteins from the frontal cortex of 9 HAD and 5 HIV non-dementia patients. Using 2-Dimensional differential in-gel electrophoresis (2-DIGE) to analyze the brain tissue proteome, 76 differentially expressed proteins (p < 0.05; fold change>1.25) were identified between HAD and HIV non-dementia patients, of which 36 protein spots (based on 3D appearance of spots on the images) were chosen for the mass spectrometry analysis. The large majority of identified proteins were represented in the energy metabolic (mitochondria) and signal transduction pathways. Furthermore, over 90% of the protein candidates are common to both HAD and other non-viral neurodegenerative disease, such as Alzheimer's disease. The data was further validated using specific antibodies to 4 proteins (CA2, GS, CKMT and CRMP2) by western blot (WB) in the same samples used for 2D-DIGE, with additional confirmation by immunohistochemitsry (IHC) using frontal lobe tissue from different HAD and HIV+ non-dementia patients. The validation for all 4 antibodies by WB and IHC was in concordance with the DIGE results, lending further credence to the current findings.</p> <p>Conclusion</p> <p>These results suggest not only convergent pathogenetic pathways for the two diseases but also the possibility of increased Alzheimer's disease (AD) susceptibility in HAD patients whose life expectancy has been significantly increased by highly active antiretroviral therapy.</p