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Search Results: 1 - 10 of 20 matches for " Ubaldi "
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Effects of theta on the deuteron binding energy and the triple-alpha process
Ubaldi, Lorenzo
High Energy Physics - Phenomenology , 2008, DOI: 10.1103/PhysRevD.81.025011
Abstract: We study the effects that a non zero strong-CP-violating parameter theta would have on the deuteron and diproton binding energies and on the triple-alpha process. Both these systems exhibit fine tuning, so it is plausible that a small change in the nuclear force would produce catastrophic consequences. Such a nuclear force is here understood in the framework of an effective Lagrangian for pions and nucleons, and the strength of the interaction varies with theta. We find that the effects are not too dramatic.
White dwarfs constraints on dark sector models with light particles
Lorenzo Ubaldi
Physics , 2013, DOI: 10.1063/1.4883421
Abstract: The white dwarf luminosity function is well understood in terms of standard model physics and leaves little room for exotic cooling mechanisms related to the possible existence of new weakly interacting light particles. This puts significant constraints on the parameter space of models that contain a massive dark photon and light dark sector particles.
Cosmic Ray-Dark Matter Scattering: a New Signature of (Asymmetric) Dark Matter in the Gamma Ray Sky
Stefano Profumo,Lorenzo Ubaldi
Physics , 2011, DOI: 10.1088/1475-7516/2011/08/020
Abstract: We consider the process of scattering of Galactic cosmic-ray electrons and protons off of dark matter with the radiation of a final-state photon. This process provides a novel way to search for Galactic dark matter with gamma rays. We argue that for a generic weakly interacting massive particle, barring effects such as co-annihilation or a velocity-dependent cross section, the gamma-ray emission from cosmic-ray scattering off of dark matter is typically smaller than that from dark matter pair-annihilation. However, if dark matter particles cannot pair-annihilate, as is the case for example in asymmetric dark matter scenarios, cosmic-ray scattering with final state photon emission provides a unique window to detect a signal from dark matter with gamma rays. We estimate the expected flux level and its spectral features for a generic supersymmetric setup, and we also discuss dipolar and luminous dark matter. We show that in some cases the gamma-ray emission might be large enough to be detectable with the Fermi Large Area Telescope.
Gamma Rays from Cosmic-Ray Proton Scattering in AGN Jets: the Intra-Cluster Gas vastly outshines Dark Matter
Profumo, Stefano;Ubaldi, Lorenzo;Gorchtein, Mikhail
High Energy Physics - Phenomenology , 2013, DOI: 10.1088/1475-7516/2013/04/012
Abstract: Active Galactic Nuclei (AGN) host powerful jets containing high-energy electrons and protons. The astrophysical environment where AGNs and their jets are found is characterized by large concentrations of both dark matter (DM) and intra-cluster medium (ICM) gas. As the high-energy jet particles transverse the DM and the ICM, elastic and inelastic scattering processes generically lead to the production of final-state photons. As first envisioned by Bloom and Wells (1998), and as more recently pointed out by us and others, the scattering of electrons off of DM could lead to a potentially detectable gamma-ray signal, with the parton-level contribution from protons offering dimmer perspectives. Recently, Chang et al. argued that taking into account photons from hadronization and showering, the actual photon flux is substantially increased. Here, we point out that the proton-jets have to be highly collimated, contrary to what predicted by simple blob-geometry jet-models sometimes employed in these studies, otherwise they would produce a very large flux of photons from inelastic collisions with ICM nucleons, which would outshine by many orders of magnitude the signal from DM, for almost any reasonable ICM and DM density profiles.
A Synchronization Control Scheme for Videoconferencing Services
Ivano Bartoli,Giovanni Iacovoni,Fabio Ubaldi
Journal of Multimedia , 2007, DOI: 10.4304/jmm.2.4.1-9
Abstract: We propose a synchronization control scheme which achieves both speech/video Intra-Stream synchronizations and Inter-Stream synchronization for videoconferencing services over IP networks. The driving principle of our scheme is to guarantee the Intra-Sync speech timing relationships (hence the speech quality) and to adjust the video Intra-Sync and the Inter-Sync accordingly. Towards this aim we use a preventive control for the speech stream and a reactive control for the video stream. More precisely, we use an adaptive playout algorithm that keeps the Intra- Sync constraints within the talkspurts, while the network jitters are compensated by modifying only the silence period lengths on the basis of both speech and video packet delays. We implemented our scheme in a prototype, which allowed us to test the effectiveness of our solution. Actually, we could appreciate both perfect speech intelligibility and very satisfactory user perceived lip-sync. The latter is because the Inter-Sync error is concentrated only at the beginning of the talkspurts, where known experimental tests have shown that it is not detectable.
Can we discover dual-component thermal WIMP dark matter?
Stefano Profumo,Kris Sigurdson,Lorenzo Ubaldi
Physics , 2009, DOI: 10.1088/1475-7516/2009/12/016
Abstract: We address the question of whether the upcoming generation of dark matter search experiments and colliders will be able to discover if the dark matter in the Universe has two components of weakly interacting massive particles (WIMPs). We outline a model-independent approach, and we study the specific cases of (1) direct detection with low-background 1 ton noble-gas detectors and (2) a 0.5 TeV center of mass energy electron-positron linear collider. We also analyze the case of indirect detection via two gamma-ray lines, which would provide a verification of such a discovery, although multiple gamma-ray lines can in principle originate from the annihilation of a single dark matter particle. For each search "channel", we outline a few assumptions to relate the very small set of parameters we consider (defining the masses of the two WIMPs and their relative abundance in the overall dark matter density) with the relevant detection rates. We then draw general conclusions on which corners of a generic dual-component dark matter scenario can be explored with current and next generation experiments. We find that in all channels the ideal setup is one where the relative mass splitting between the two WIMP species is of order 1, and where the two dark matter components contribute in a ratio close to 1:1 to the overall dark matter content of the Universe. Interestingly, in the case of direct detection, future experiments might detect multiple states even if only ~ 10% of the energy-density of dark matter in the Universe is in the subdominant species.
Probing Dark Matter with AGN Jets
Mikhail Gorchtein,Stefano Profumo,Lorenzo Ubaldi
Physics , 2010, DOI: 10.1103/PhysRevD.82.083514
Abstract: We study the possibility of detecting a signature of particle dark matter in the spectrum of gamma-ray photons from active galactic nuclei (AGNs) resulting from the scattering of high-energy particles in the AGN jet off of dark matter particles. We consider particle dark matter models in the context of both supersymmetry and universal extra-dimensions (UED), and we present the complete lowest-order calculation for processes where a photon is emitted in dark matter-electron and/or dark matter-proton scattering, where electrons and protons belong to the AGN jet. We find that the process is dominated by a resonance whose energy is dictated by the particle spectrum in the dark matter sector (neutralino and selectron for the case of supersymmetry, Kaluza-Klein photon and electron for UED). The resulting gamma-ray spectrum exhibits a very characteristic spectral feature, consisting of a sharp break to a hard power-law behavior. Although the normalization of the gamma-ray flux depends strongly on assumptions on both the AGN jet geometry, composition and particle spectrum as well as on the particle dark matter model and density distribution, we show that for realistic parameters choices, and for two prominent nearby AGNs (Centaurus A and M87), the detection of this effect is in principle possible. Finally, we compare our predictions and results with recent gamma-ray observations from the Fermi, H.E.S.S. and VERITAS telescopes.
Superdiffusion and Transport in 2d-systems with Lévy Like Quenched Disorder
Raffaella Burioni,Enrico Ubaldi,Alessandro Vezzani
Physics , 2014, DOI: 10.1103/PhysRevE.89.022135
Abstract: We present an extensive analysis of transport properties in superdiffusive two dimensional quenched random media, obtained by packing disks with radii distributed according to a L\'evy law. We consider transport and scaling properties in samples packed with two different procedures, at fixed filling fraction and at self-similar packing, and we clarify the role of the two procedures in the superdiffusive effects. Using the behavior of the filling fraction in finite size systems as the main geometrical parameter, we define an effective L\'evy exponents that correctly estimate the finite size effects. The effective L\'evy exponent rules the dynamical scaling of the main transport properties and identify the region where superdiffusive effects can be detected.
Singlet Scalar Dark Matter: monochromatic gamma rays and metastable vacua
Stefano Profumo,Lorenzo Ubaldi,Carroll Wainwright
Physics , 2010, DOI: 10.1103/PhysRevD.82.123514
Abstract: We calculate the pair-annihilation cross section of real scalar singlet dark matter into two mono-energetic photons. We derive constraints on the theory parameter space from the Fermi limits on gamma-ray lines, and we compare with current limits from direct dark matter detection. We show that the new limits, albeit typically relevant only when the dark matter mass is close to half the Standard Model Higgs mass, rule out regions of the theory parameter space that are otherwise not constrained by other observations or experiments. In particular, the new excluded regions partly overlap with the parameter space where real scalar singlet dark matter might explain the anomalous signals observed by CDMS. We also calculate the lifetime of unstable vacuum configurations in the scalar potential, and show that the gamma-ray limits are quite relevant in regions where the electro-weak vacuum is meta-stable with a lifetime longer than the age of the universe.
CTLA-4 Engagement Inhibits Th2 but not Th1 Cell Polarisation
Vanessa Ubaldi,Lucia Gatta,Luigia Pace,Gino Doria,Claudio Pioli
Clinical and Developmental Immunology , 2003, DOI: 10.1080/10446670310001598519
Abstract: CTLA-4 deficient mice show severe lymphoproliferative disorders with T helper sub-population skewed toward the Th2 phenotype. In the present work, we investigated the role of CTLA-4 in T helper cell subset differentiation. Naïve CD4
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