Superstring Relics, Supersymmetric Fragmentation and UHECR

Superstring theory predicts the existence of relic metastable particles whose average lifetime is longer than the age of the universe and which could, in principle, be good dark matter candidates. At the same time, these states would be responsible for the Ultra High Energy Cosmic Rays (UHECR) events which will be searched for by various experimental collaborations in the near future. We describe a possible phenomenological path which could be followed in order to search for new physics in their detection.Comment: 7 pages 4 Figs. Plenary Talk presented by Claudio Coriano' at the 1st Intl. Conf. on String Phenomenology, Oxford, UK, July 6-11, 200

Double transverse-spin asymmetries in Drell--Yan and J/ψJ/\psi production from proton--antiproton collisions

We perform a NLO numerical study of the double transverse-spin asymmetries in the $J/\psi$ resonance region for proton--antiproton collisions. We analyze the large $x$ kinematic region, relevant for the proposed PAX experiment at GSI, and discuss the implication of the results for the extraction of the transversity densities.Comment: 8 pages, 6 figures, Talk given at "Transversity 2005" Como, Italy 7-10 Sep. 2005; eds. World Scientific in pres

Redefining Burnout: Exploring Common Conceptualizations and the Neurophysiology of Chronic Stress to Establish an Integrated Allostatic Model

Burnout is a widely researched stress-related phenomenon associated with numerous adverse outcomes for employees and organizations. Unfortunately, burnout is not well understood and research to this point has been flawed due to a lack of consensus on the definition, dimensionality, and context of the construct. Prevalent conceptualizations of burnout have been criticized for being arbitrarily developed without solid theoretical foundation and for failing to clearly distinguish burnout from depression or other work-related conditions such as compassion fatigue, secondary traumatization, and vicarious traumatization. The current project first examines relevant literature to identify commonalities among prevalent burnout conceptualizations. Then relevant stress research is explored to identify possible neurophysiological explanations for the general presentation and progression of burnout. Finally, burnout and stress literature are integrated to create a definition and model of burnout that is non-arbitrary, theoretically driven, and that distinguishes burnout from depression and other work-related conditions. Findings of the project indicated that prevalent burnout conceptualizations share three elements: a resources-and-demands framework; domains related to the individual, interpersonal relationships, and external factors; and an underlying implication of a chronic stress process involved in the development, presentation, and progression of burnout. Exploration of stress research indicated that the neurophysiological process that occurs during adaptation to chronic stress, namely allostasis, accounts for the development, presentation, and progression of burnout, with depression being a potential outcome of the process. Clinical implications, limitations, and recommendations are discussed. Keywords: burnout, chronic stress, allostasis, neurophysiology, appraisal, work, depression, compassion fatigue, secondary traumatization, vicarious traumatizatio

Thermal unfolding of holo and apo pseudoazurin

The role of the copper ion in the thermal unfolding of pseudoazurin has been investigated by differential scanning calorimetry, optical density and fluorescence. In the presence of copper the denaturation of pseudoazurin (holo form) is irreversible and scan rate dependent. The melting temperature ranges between 60.0 and 67.3◦C, depending on the scan rate and the technique used. The DSC data analysis indicates that the denaturation pathway of the holo pseudoazurin is described by the classical Lumry-Eyring model, N ⇔ U ⇒ F. The simulation of the experimental DSC profiles according to this model has allowed the calculation of the thermodynamic and kinetic parameters related to the two steps. The destabilization of the copper active site and of the hydrophobic core precedes the global denaturation of the protein. The removal of the copper ion (apo from) significantly reduces the stability of the protein: the denaturation occurs at 41.8◦C. Moreover, the thermal unfolding of apo pseudoazurin is compatible with a two-state reversible process, N ⇔ U

Spin and energy relaxation in germanium studied by spin-polarized direct-gap photoluminescence

Spin orientation of photoexcited carriers and their energy relaxation is investigated in bulk Ge by studying spin-polarized recombination across the direct band gap. The control over parameters such as doping and lattice temperature is shown to yield high polarization degree, namely larger than 40%, as well as a fine-tuning of the angular momentum of the emitted light with a complete reversal between right- and left-handed circular polarization. By combining the measurement of the optical polarization state of band-edge luminescence and Monte Carlo simulations of carrier dynamics, we show that these very rich and complex phenomena are the result of the electron thermalization and cooling in the multi-valley conduction band of Ge. The circular polarization of the direct-gap radiative recombination is indeed affected by energy relaxation of hot electrons via the X valleys and the Coulomb interaction with extrinsic carriers. Finally, thermal activation of unpolarized L valley electrons accounts for the luminescence depolarization in the high temperature regime

Searching for an axion-like particle at the Large Hadron Collider

Axion-like particles are an important part of the spectrum of anomalous gauge theories involving modified mechanisms of cancellation of the gauge anomalies. Among these are intersecting brane models, which are characterized by the presence of one physical axion. We overview a recent study of their supersymmetric construction and some LHC studies of the productions rates for a gauged axion

Cosmological Properties of a Gauged Axion

We analyze the most salient cosmological features of axions in extensions of the Standard Model with a gauged anomalous extra U(1) symmetry. The model is built by imposing the constraint of gauge invariance in the anomalous effective action, which is extended with Wess-Zumino counterterms. These generate axion-like interactions of the axions to the gauge fields and a gauged shift symmetry. The scalar sector is assumed to acquire a non-perturbative potential after inflation, at the electroweak phase transition, which induces a mixing of the Stuckelberg field of the model with the scalars of the electroweak sector, and at the QCD phase transition. We discuss the possible mechanisms of sequential misalignments which could affect the axions of these models, and generated, in this case, at both transitions. We compute the contribution of these particles to dark matter, quantifying their relic densities as a function of the Stuckelberg mass. We also show that models with a single anomalous U(1) in general do not account for the dark energy, due to the presence of mixed U(1)-SU(3) anomalies.Comment: 29 pages, 5 figures. Revised version, accepted by Phys. Rev.

Automatic Differentiation for Inverse Problems in X-ray Imaging and Microscopy

Computational techniques allow breaking the limits of traditional imaging methods, such as time restrictions, resolution, and optics flaws. While simple computational methods can be enough for highly controlled microscope setups or just for previews, an increased level of complexity is instead required for advanced setups, acquisition modalities or where uncertainty is high; the need for complex computational methods clashes with rapid design and execution. In all these cases, Automatic Differentiation, one of the subtopics of Artificial Intelligence, may offer a functional solution, but only if a GPU implementation is available. In this paper, we show how a framework built to solve just one optimisation problem can be employed for many different X-ray imaging inverse problems

High Performances Corrugated Feed Horns for Space Applications at Millimetre Wavelengths

We report on the design, fabrication and testing of a set of high performance corrugated feed horns at 30 GHz, 70 GHz and 100 GHz, built as advanced prototypes for the Low Frequency Instrument (LFI) of the ESA Planck mission. The electromagnetic designs include linear (100 GHz) and dual shaped (30 and 70 GHz) profiles. Fabrication has been achieved by direct machining at 30 GHz, and by electro-formation at higher frequencies. The measured performances on side lobes and return loss meet the stringent Planck requirements over the large (20%) instrument bandwidth. Moreover, the advantage in terms of main lobe shape and side lobes levels of the dual profiled designs has been demonstrated.Comment: 16 pages, 7 figures, accepted for publication in Experimental Astronom