4,839 research outputs found

    Chiral symmetry breaking in QCD-like gauge theories with a confining propagator and dynamical gauge boson mass generation

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    We study chiral symmetry breaking in QCD-like gauge theories introducing a confining effective propagator, as proposed recently by Cornwall, and considering the effect of dynamical gauge boson mass generation. The effective confining propagator has the form 1/(k2+m2)21/(k^2+m^2)^2 and we study the bifurcation equation finding limits on mm below which a satisfactory fermion mass solution is generated. Since the coupling constant and gauge boson propagator are damped in the infrared, due to the presence of dynamically massive gauge bosons, the major part of the chiral breaking is only due to the confining propagator. We study the asymptotic behavior of the gap equation containing confinement and massive gauge boson exchange, and find that the symmetry breaking can be approximated at some extent by an effective four-fermion interaction generated by the confining propagator. We compute some QCD chiral parameters as a function of mm, finding values compatible with the experimental data. Within this approach we expect that lattice simulations should not see large differences between the confinement and chiral symmetry breaking scales independent of the fermionic representation and we find a simple approximate relation between the fermion condensate and dynamical mass for a given representation as a function of the parameters appearing in the effective confining propagator.Comment: 32 pages, 9 figures, new references added, matchs published versio

    Medium effects in the pion pole mechanism (photon photon --> pion-zero --> neutrino-R antineutrino-L (neutrino-L antineutrino-R)) of neutron star cooling

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    Nuclear medium effects in the neutrino cooling of neutron stars through the exotic reaction channel \gamma \gamma --> \pi^0--> \nu_R \bar{\nu_L} (\nu_L \bar{\nu_R}) are incorporated. Throughout the paper we discuss different possibilities of right-handed neutrinos, massive left-handed neutrinos and standard massless left-handed neutrinos (reaction is then allowed only with medium modified vertices). It is demonstrated that multi-particle effects suppress the rate of this reaction channel by 6-7 orders of magnitude that does not allow to decrease existing experimental upper limit on the corresponding \pi^0\nu\bar{\nu} coupling. Other possibilities of the manifestation of the given reaction channel in differente physical situations, e.g. in the quark color superconducting cores of some neutron stars, are also discussed. We demonstrate that in the color-flavor-locked superconducting phase for temperatures T < (0.1-10) MeV (depending on the effective pion mass and the decay width) the process is feasibly the most efficient neutrino cooling process, although the absolute value of the reaction is rather small.Comment: Replaced with revised version. New appendix, many clarifying comments, corrected figs 3 and

    Chiral symmetry breaking with a confining propagator and dynamically massive gluons

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    Chiral symmetry breaking in QCD is studied introducing a confining effective propagator, as proposed recently by Cornwall, and considering the effect of dynamically massive gluons. The effective confining propagator has the form 1/(k2+m2)21/(k^2+m^2)^2 and we study the bifurcation equation finding limits on the parameter mm below which a satisfactory fermion mass solution is generated. Since the coupling constant and gluon propagator are damped in the infrared, due to the presence of a dynamical gluon mass, the major part of the chiral breaking is only due to the confining propagator and related to the low momentum region of the gap equation. We study the asymptotic behavior of the gap equation containing this confinement effect and massive gluon exchange, and find that the symmetry breaking can be approximated by an effective four-fermion interaction generated by the confining propagator. We compute some QCD chiral parameters as a function of mm, finding values compatible with the experimental data. We find a simple approximate relation between the fermion condensate and dynamical mass for a given representation as a function of the parameters appearing in the effective confining propagator.Comment: 12 pages, 2 figures. Talk presented at the International Workshop on QCD Green's Functions, Confinement, and Phenomenology - QCD-TNT II, September 05-09 2011, ECT* Trento, Italy; ANN.PHYS.(NY, 2011

    Diffraction and the Gluon Mass

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    We recently proposed a QCD-Pomeron described by the exchange of two non-perturbative gluons characterized by a dynamically generated gluon mass. It is here shown that data on elastic scattering, exclusive ρ\rho production in deep inelastic scattering and the J/ΨJ/\Psi-nucleon total cross-section can be successfully described in terms of a single gluon mass mg≃0.37m_g\simeq0.37~GeV. We observe that the total cross sections of hadrons with small radii, such as J/ΨJ/\Psi, have a marked dependence on the effective gluon mass.Comment: 10 pages, Latex, 3 figures available by fax or conventional mail. MAD/PH/75

    Continuous Estimation of Emotions in Speech by Dynamic Cooperative Speaker Models

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    Automatic emotion recognition from speech has been recently focused on the prediction of time-continuous dimensions (e.g., arousal and valence) of spontaneous and realistic expressions of emotion, as found in real-life interactions. However, the automatic prediction of such emotions poses several challenges, such as the subjectivity found in the definition of a gold standard from a pool of raters and the issue of data scarcity in training models. In this work, we introduce a novel emotion recognition system, based on ensemble of single-speaker-regression-models (SSRMs). The estimation of emotion is provided by combining a subset of the initial pool of SSRMs selecting those that are most concordance among them. The proposed approach allows the addition or removal of speakers from the ensemble without the necessity to re-build the entire machine learning system. The simplicity of this aggregation strategy, coupled with the flexibility assured by the modular architecture, and the promising results obtained on the RECOLA database highlight the potential implications of the proposed method in a real-life scenario and in particular in WEB-based applications

    A genetic algorithm-assisted semi-adaptive MMSE multi-user detection for MC-CDMA mobile communication systems

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    In this work, a novel Minimum-Mean Squared-Error (MMSE) multi-user detector is proposed for MC-CDMA transmission systems working over mobile radio channels characterized by time-varying multipath fading. The proposed MUD algorithm is based on a Genetic Algorithm (GA)-assisted per-carrier MMSE criterion. The GA block works in two successive steps: a training-aided step aimed at computing the optimal receiver weights using a very short training sequence, and a decision-directed step aimed at dynamically updating the weights vector during a channel coherence period. Numerical results evidenced BER performances almost coincident with ones yielded by ideal MMSE-MUD based on the perfect knowledge of channel impulse response. The proposed GA-assisted MMSE-MUD clearly outperforms state-of-the-art adaptive MMSE receivers based on deterministic gradient algorithms, especially for high number of transmitting users

    Recupero delle ex Officine Ducrot, oggi Cantieri culturali alla Zisa a Palermo

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    Il costante aumento della popolazione delle grandi città, ha indotto i comuni a reperire, spesso in maniera più o meno disordinata, nuove aree edificabili destinate, soprattutto, ad edilizia residenziale. Tale attività ha soventemente portato ad inglobare, all’interno delle città, particolari strutture come ad esempio, carceri, mercati ortofrutticoli, mercati ittici, agglomerati industriali, ecc. Nello specifico, le attività industriali, in seguito ad oculate pianificazioni, hanno spesso abbandonato gli antichi siti, per trasferirsi in aree industriali moderne e idoneamente attrezzate. La memoria, prendendo in esame le “Officine Ducrot”, realizzate alla fine dei XIX secolo a Palermo, vuole evidenziare come una corretta azione “politica” sul patrimonio di archeologia industriale, può rifunzionalizzare i siti rendendoli fruibili, consentendone una riappropriazione da parte della società e, al contempo, fare in modo che possano divenire fonte di sviluppo culturale ed economico del territorio stesso. Per raggiungere questo scopo occorre porsi l’obiettivo di offrire strutture, percorsi e attrezzature che ne consentano la piena godibilità a tutti, nel rispetto del contest

    Il Patrimonio Culturale tra esigenze e funzionalità quotidiane

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    La memoria vuole evidenziare come la politica che una nazione adotta sul patrimonio storico, ed in particolare sulle aree urbane, se adeguatamente correlata agli aspetti della Conservazione, della Valorizzazione, della Fruizione etc., puà migliorare, anche in modo significativo, lo sviluppo economico di un territorio che spesso, essendo depositario di specifiche caratteristiche, è Patrimonio non soltanto del singolo paese ma dell’intera Umanità. Una città accessibile a tutti i fruitori, dal turista, allo studioso, al portatore di handicap, etc., puà divenire fattore trainante di uno sviluppo culturale ed economico del territorio stesso. Per raggiungere questo scopo occorre proporsi l’obiettivo di offrire strutture, percorsi e attrezzature che ne consentano la piena godibilità a tutti, nel rispetto del contesto

    Non-perturbative fixed points and renormalization group improved effective potential

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    The stability conditions of a renormalization group improved effective potential have been discussed in the case of scalar QED and QCD with a colorless scalar. We calculate the same potential in these models assuming the existence of non-perturbative fixed points associated to a conformal phase. In the case of scalar QED the barrier of instability found previously is barely displaced as we approach the fixed point, and in the case of QCD with a colorless scalar not only the barrier is changed but the local minimum of the potential is also changed.Comment: 6 pages, 8 figures, References added. Matching the journal versio
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