Trans-Planckian Dark Energy?

It has recently been proposed by Mersini et al. 01, Bastero-Gil and Mersini 02 that the dark energy could be attributed to the cosmological properties of a scalar field with a non-standard dispersion relation that decreases exponentially at wave-numbers larger than Planck scale (k_phys > M_Planck). In this scenario, the energy density stored in the modes of trans-Planckian wave-numbers but sub-Hubble frequencies produced by amplification of the vacuum quantum fluctuations would account naturally for the dark energy. The present article examines this model in detail and shows step by step that it does not work. In particular, we show that this model cannot make definite predictions since there is no well-defined vacuum state in the region of wave-numbers considered, hence the initial data cannot be specified unambiguously. We also show that for most choices of initial data this scenario implies the production of a large amount of energy density (of order M_Planck^4) for modes with momenta of order M_Planck, far in excess of the background energy density. We evaluate the amount of fine-tuning in the initial data necessary to avoid this back-reaction problem and find it is of order H/M_Planck. We also argue that the equation of state of the trans-Planckian modes is not vacuum-like. Therefore this model does not provide a suitable explanation for the dark energy.Comment: RevTeX - 15 pages, 7 figures: final version to appear in PRD, minor changes, 1 figure adde

Fine-Tuning Constraints on Supergravity Models

We discuss fine-tuning constraints on supergravity models. The tightest constraints come from the experimental mass limits on two key particles: the lightest CP even Higgs boson and the gluino. We also include the lightest chargino which is relevant when universal gaugino masses are assumed. For each of these particles we show how fine-tuning increases with the experimental mass limit, for four types of supergravity model: minimal supergravity, no-scale supergravity (relaxing the universal gaugino mass assumption), D-brane models and anomaly mediated supersymmetry breaking models. Among these models, the D-brane model is less fine tuned.The experimental propects for an early discovery of Higgs and supersymmetry at LEP and the Tevatron are discussed in this framework.Comment: 17 pages, Latex, including 5 eps figure

A note on inflation and transplanckian physics

In this paper we consider the influence of transplanckian physics on the CMBR anisotropies produced by inflation. We consider a simple toy model that allows for analytic calculations and argue on general grounds, based on ambiguities in the choice of vacuum, that effects are expected with a magnitude of the order of $H/\Lambda$, where $H$ is the Hubble constant during inflation and $\Lambda$ the scale for new physics, e.g. the Planck scale.Comment: 12 pages. v2: typos corrected and references added. v3: final version accepted for publication by PRD. Improved discussion of adiabatic vacuu

Miniaturization of Planar Microwave Devices by Means of Complementary Spiral Resonators (CSRs): Design of Quadrature Phase Shifters

In this work, two compact quadrature phase shifters based on metamaterial transmission lines implemented by means of complementary spiral resonators (CSRs) have been designed, fabricated and measured. The structures consist on Y-junctions with output lines exhibiting 90º phase balance. The reported metamaterial-based devices present a size reduction of 64% and 77% as compared to the conventional one

Bounds on Generic High-Energy Physics Modifications to the Primordial Power Spectrum from Back-Reaction on the Metric

Modifications to the primordial power spectrum of inflationary density perturbations have been studied recently using a boundary effective field theory approach. In the approximation of a fluctuating quantum field on a fixed background, the generic effect of new physics is encoded in parameters of order H/M. Here, we point out that the back-reaction on the metric can be neglected only when these parameters obey certain bounds that may put them beyond the reach of observation.Comment: 6 pages, Latex. References added, misprints corrected. To appear in Phys. Lett.

Appropriateness of oral anticoagulants for long-term treatment of atrial fibrillation in older people: results of an evidence-based review and international consensus validation process (OAC-FORTA 2016)

Background: Age appropriateness of anticoagulants for stroke prevention in atrial fibrillation is uncertain. Objective: To review oral anticoagulants for the treatment of atrial fibrillation in older (age >65 years) people and to classify appropriate and inappropriate drugs based on efficacy, safety and tolerability using the Fit-fOR-The-Aged (FORTA) classification. Methods: We performed a structured comprehensive review of controlled clinical trials and summaries of individual product characteristics to assess study and total patient numbers, quality of major outcome data and data of geriatric relevance. The resulting evidence was discussed in a round table with an interdisciplinary panel of ten European experts. Decisions on age appropriateness were made using a Delphi process. Results: For the eight drugs included, 380 citations were identified. The primary outcome results were reported in 32 clinical trials with explicit and relevant data on older people. Though over 24,000 patients aged >75/80 years were studied for warfarin, data on geriatric syndromes were rare (two studies reporting on frailty/falls/mental status) and missing for all other compounds. Apixaban was rated FORTA-A (highly beneficial). Other non-vitamin K antagonist oral anticoagulants (including low/high-intensity dabigatran and high-intensity edoxaban) and warfarin were assigned to FORTA-B (beneficial). Phenprocoumon, acenocoumarol and fluindione were rated FORTA-C (questionable), mainly reflecting the absence of data. Conclusions: All non-vitamin K antagonist oral anticoagulants and warfarin were classified as beneficial or very beneficial in older persons (FORTA-A or -B), underlining the overall positive assessment of the risk/benefit ratio for these drugs. For other vitamin-K antagonists regionally used in Europe, the lack of evidence should challenge current practice

The fate of spiral galaxies in clusters: The star formation history of the anemic Virgo cluster galaxy NGC 4569

We present a new method for studying the star formation history of late-type cluster galaxies undergoing gas starvation or a ram pressure stripping event by combining bidimensional multifrequency observations with multizone models of galactic chemical and spectrophotometric evolution. This method is applied to the Virgo Cluster anemic galaxy NGC 4569. We extract radial profiles from recently obtained UV GALEX images at 1530 and 2310 Å, from visible and near-IR narrow (Hα) and broadband images at different wavelengths (u, B, g, V, r, i, z, J, H, and K), from Spitzer IRAC and MIPS images, and from atomic and molecular gas maps. The model in the absence of interaction (characterized by its rotation velocity and spin parameter) is constrained by the unperturbed H-band light profile and by the Hα rotation curve. We can reconstruct the observed total gas radial density profile and the light surface brightness profiles at all wavelengths in a ram pressure stripping scenario by making simple assumptions about the gas removal process and the orbit of NGC 4569 inside the cluster. The observed profiles cannot be reproduced by simply stopping gas infall, thus mimicking starvation. Gas removal is required, which is more efficient in the outer disk, inducing radial quenching in the star formation activity, as observed and reproduced by the model. This observational result, consistent with theoretical predictions that a galaxy cluster-IGM interaction is able to modify structural disk parameters without gravitational perturbations, is discussed in the framework of the origin of lenticular galaxies in cluster

New Light in Star-Forming Dwarf Galaxies: The PMAS Integral Field View of the Blue Compact Dwarf Galaxy Mrk 409

We present an integral field spectroscopic study of the central 2x2 kpc^2 of the blue compact dwarf galaxy Mrk 409, observed with the Potsdam MultiAperture Spectrophotometer. This study focuses on the morphology, two-dimensional chemical abundance pattern, excitation properties and kinematics of the ionized interstellar medium in the starburst component. We also investigate the nature of the extended ring of ionized gas emission surrounding the bright nuclear starburst region of Mrk 409. PMAS spectra of selected regions along the ring, interpreted with evolutionary and population synthesis models, indicate that their ionized emission is mainly due to a young stellar population with a total mass of ~1.5x10^6 M_sun, which started forming almost coevally ~10 Myr ago. This stellar component is likely confined to the collisional interface of a spherically expanding, starburst-driven super-bubble with denser, swept-up ambient gas, ~600 pc away from the central starburst nucleus. The spectroscopic properties of the latter imply a large extinction (C_H-beta>0.9), and the presence of an additional non-thermal ionization source, most likely a low-luminosity Active Galactic Nucleus. Mrk 409 shows a relatively large oxygen abundance (12+log(O/H)~8.4) and no chemical abundance gradients out to R~600 pc. The ionized gas kinematics displays an overall regular rotation on a northwest-southwest axis, with a maximum velocity of 60 km/s; the total mass inside the star-forming ring is about 1.4x10^9 M_sun.Comment: Accepted for publication in Ap

Anderson localization in a periodic photonic lattice with a disordered boundary

We investigate experimentally the light evolution inside a two-dimensional finite periodic array of weakly- coupled optical waveguides with a disordered boundary. For a completely localized initial condition away from the surface, we find that the disordered boundary induces an asymptotic localization in the bulk, centered around the initial position of the input beam.Comment: 3 pages, 4 figure

Influence of Light and Heavy Thresholds on SUSY Unification

In this paper we study and compare susy unification using two different approaches in order to take into account the effect of light particle thresholds on the evolution of gauge couplings: the step--function approximation, on the one hand, and a mass dependent procedure, which gives a more accurate description of the dependence of the results on the masses, on the other. We also include the effect of heavy thresholds, when $SU(5)$ is chosen as the unifying group. We find that the mass--dependent procedure excludes scenarios where all susy masses are below $1\;TeV$, and favors a value of $\alpha_3(m_Z)$ near its upper experimental bound, contrary to the results obtained with the step--function approximation. We underline the dependence of the results on the procedure chosen to deal with light thresholds.Comment: 18 pages,LAEFF-93/014,REVTEX-2.1, 5 figures not included, available upon request (include FAX number)