Sound propagation in elongated superfluid fermion clouds

We use hydrodynamic equations to study sound propagation in a superfluid Fermi gas inside a strongly elongated cigar-shaped trap, with main attention to the transition from the BCS to the unitary regime. We treat first the role of the radial density profile in the quasi-onedimensional limit and then evaluate numerically the effect of the axial confinement in a configuration in which a hole is present in the gas density at the center of the trap. We find that in a strongly elongated trap the speed of sound in both the BCS and the unitary regime differs by a factor sqrt{3/5} from that in a homogeneous three-dimensional superfluid. The predictions of the theory could be tested by measurements of sound-wave propagation in a set-up such as that exploited by M.R. Andrews et al. [Phys. Rev. Lett. 79, 553 (1997)] for an atomic Bose-Einstein condensate

Antisymmetrized Green's function approach to (e,e′)(e,e') reactions with a realistic nuclear density

A completely antisymmetrized Green's function approach to the inclusive quasielastic $(e,e')$ scattering, including a realistic one-body density, is presented. The single particle Green's function is expanded in terms of the eigenfunctions of the nonhermitian optical potential. This allows one to treat final state interactions consistently in the inclusive and in the exclusive reactions. Nuclear correlations are included in the one-body density. Numerical results for the response functions of $^{16}$O and $^{40}$Ca are presented and discussed.Comment: 45 pages, 3 figure

Inclusive electron scattering in a relativistic Green function approach

A relativistic Green function approach to the inclusive quasielastic (e,e') scattering is presented. The single particle Green function is expanded in terms of the eigenfunctions of the nonhermitian optical potential. This allows one to treat final state interactions consistently in the inclusive and in the exclusive reactions. Numerical results for the response functions and the cross sections for different target nuclei and in a wide range of kinematics are presented and discussed in comparison with experimental data.Comment: 12 pages, 7 figures, REVTeX

Transition to hydrodynamics in colliding fermion clouds

We study the transition from the collisionless to the hydrodynamic regime in a two-component spin-polarized mixture of 40K atoms by exciting its dipolar oscillation modes inside harmonic traps. The time evolution of the mixture is described by the Vlasov-Landau equations and numerically solved with a fully three-dimensional concurrent code. We observe a master/slave behaviour of the oscillation frequencies depending on the dipolar mode that is excited. Regardless of the initial conditions, the transition to hydrodynamics is found to shift to lower values of the collision rate as temperature decreases.Comment: 11 pages, iop style. submitted to the proceedings of the Levico 2003 worksho

Effects of collisions against thermal impurities in the dynamics of a trapped fermion gas

We present a theoretical study of the dynamical behavior of a gas made of ultracold fermionic atoms, which during their motions can collide with a much smaller number of thermal bosonic impurities. The atoms are confined inside harmonic traps and the interactions between the two species are treated as due to s-wave scattering with a negative scattering length modeling the 40K-87Rb fermion-boson system. We set the fermions into motion by giving a small shift to their trap center and examine two alternative types of initial conditions, referring to (i) a close-to-equilibrium situation in which the two species are at the same temperature (well below the Fermi temperature and well above the Bose-Einstein condensation temperature); and (ii) a far-from-equilibrium case in which the impurities are given a Boltzmann distribution of momenta while the fermions are at very low temperatures. The dynamics of the gas is evaluated by the numerical solution of the Vlasov-Landau equations for the one-body distribution functions, supported by some analytical results on the collisional properties of a fermion gas. We find that the trapped gaseous mixture is close to the collisionless regime for values of the parameters corresponding to current experiments, but can be driven towards a collisional regime even without increasing the strength of the interactions, either by going over to heavier impurity masses or by matching the width of the momentum distribution of the impurities to the Fermi momentum of the fermion gas.Comment: 7 pages, 4 figures, RevTeX 4, accepted in PR

Comment on ``Sound velocity and multibranch Bogoliubov spectrum of an elongated Fermi superfluid in the BEC-BCS crossover"

The work by T. K. Ghosh and K. Machida [cond-mat/0510160 and Phys. Rev. A 73, 013613 (2006)] on the sound velocity in a cylindrically confined Fermi superfluid obeying a power-law equation of state is shown to make use of an improper projection of the sound wave equation. This inaccuracy fully accounts for the difference between their results and those previously reported by Capuzzi et al. [cond-mat/0509323 and Phys. Rev. A 73, 021603(R) (2006)]. In this Comment we show that both approaches lead exactly to the same result when the correct weight function is used in the projection. Plots of the correct behavior of the phonon and monopole-mode spectra in the BCS, unitary, and BEC limits are also shown.Comment: Comment on cond-mat/051016

EXPLAINING CITIZEN SUPPORT FOR EU POLICY GOVERNANCE: THE ROLE OF MICRO, MESO, AND MACRO DETERMINANTS

Questa tesi contribuisce al dibattito sulla Europeizzazione delle preferenze di policy dei cittadini. Questa forma di Europeizzazione si sostanzia nel sostegno dei cittadini per una governance Europea in strategici settori di policy. Utilizzando dati di sondaggio provenienti dalla ricerca Intune 2009 e da Eurobarometro, questo lavoro studia la struttura del sostegno per una governance Europea, distinguendo tra una generica preferenza per una maggiore governance e una specifica preferenza che varia tra i diversi settori di policy. Inoltre, questa tesi analizza quali sono i fattori che influenzano lo sviluppo di questi due tipi di sostegno. Nel Capitolo 1 attraverso uno studio della letteratura sulle macro teorie dell\u2019integrazione Europea vengono presentati tre modelli alternativi che definiscono la struttura del sostegno per una governance politica Europea. Questi tre modelli sono in seguito testati e dibattuti nel prosieguo della tesi. Il Capitolo 2 fornisce una definizione del concetto di \u2018EU support\u2019 basata su precedenti studi teorici e empirici. Questa definizione identifica quattro dimensioni che sottostanno al concetto di \u2018EU support\u2019: \u2022 \u2018Output legitimacy\u2019: sostegno per gli output prodotti dall\u2019Unione Europea; \u2022 \u2018EU governance legitimacy\u2019: sostegno come generica propensione ad affidare le decisioni di policy all\u2019Unione Europea; \u2022 \u2018European identification\u2019: sostegno inteso come identificazione nella comunit\ue0 politica europea; \u2022 \u2018EU democracy\u2019: sostegno inteso come percezione di rappresentanza politica a livello europeo. Il Capitolo 3 misura queste quattro dimensioni attraverso un modello a dimensioni latenti sui dati della ricerca Intune 2009, confermando che queste dimensioni sono sufficientemente stabili e invarianti attraverso i diversi paesi dell\u2019Unione Europea. Il Capitolo 4 affronta l\u2019analisi delle determinanti di queste quattro dimensioni del sostegno. I risultati dimostrano che quattro fattori influenzano in modo significativo il sostegno all\u2019UE: 1) \u2018identificazione nazionale esclusiva\u2019 2) \u2018attaccamento alla nazione\u2019 3) \u2018fiducia nelle istituzioni nazionali\u2019 4) \u2018valori politici\u2019. Questi fattori influenzano il sostegno all\u2019UE in tutti i paesi (quindici) oggetto dell\u2019indagine, ma il loro effetto varia in base a quale dimensione del sostegno si considera: la propensione ad affidare le decisioni di policy all\u2019UE (\u2018EU governance legitimacy\u2019) viene influenzata solamente dal fattore \u2018identificazione nazionale esclusiva\u2019. Inoltre, questo capitolo indaga anche la presenza di una gerarchia tra le quattro dimensioni del sostegno, derivando questa ipotesi dalle teorie neo e post-funzionaliste e da alcuni studi empirici. Tuttavia, i risultati provano che le dimensioni di \u2018Output legitimacy\u2019, \u2018European identification\u2019 e \u2018EU democracy\u2019 non influenzano in modo considerevole e diffuso quella di \u2018EU governance legitimacy\u2019. Partendo da questo risultato, il Capitolo 5 esplora un percorso diverso, facendo un\u2019analisi policy per policy. Infatti si concentra sull\u2019influenza di questi ed altri fattori sulla propensione ad affidare le decisioni di policy all\u2019Unione Europea in specifici settori politici. Da questa analisi emerge che fattori legati all\u2019utilit\ue0 soggettiva, all\u2019identit\ue0 europea e alla rappresentanza politica giocano un ruolo differente nei diversi settori: \u2018Output legitimacy\u2019 e \u2018European identification\u2019 sono le pi\uf9 importanti determinanti della propensione a sostenere una governance europea, ma i loro effetti sono rafforzati (o depotenziati) dalle specifiche caratteristiche delle diverse aree di policy. \u2018Output legitimacy\u2019 ha l\u2019influenza maggiore nelle aree dove la governance europea \ue8 pi\uf9 efficiente rispetto ad una nazionale o locale (spiegazione funzionale), mentre \u2018European identification\u2019 ha l\u2019effetto pi\uf9 consistente nelle aree politiche dove l\u2019azione europea pu\uf2 correggere gli effetti della globalizzazione (spiegazione modello sociale). Ulteriori analisi evidenziano come gli intervistati tendano a preferire il livello nazionale a quello europeo per le aree di policy che richiedono ingenti investimenti economici e per quelle in cui l\u2019Unione Europea gi\ue0 possiede estese competenze. Questo ultimo meccanismo evidenzia come un maggiore livello di integrazione europea non porti di per s\ue9 ad una ulteriore richiesta di governance europea (come sostenuto dai neo-funzionalisti), ma, anzi, conduca alla richiesta di ridiscutere l\u2019attuale allocazione delle competenze. Utilizzando dati raccolti nel 2009, queste analisi non confermano l\u2019influenza della dimensione di rappresentanza politica (\u2018EU democracy\u2019). Tuttavia, aggregando dati derivanti da Eurobarometro 86.2 e raccolti nel novembre del 2016 emerge come la percezione di rappresentanza politica diventi una importante e significativa determinante del sostegno per una governance europea delle politiche di immigrazione e della politica estera. Inoltre, il sostegno per una governance europea di queste due aree di policy viene anche influenzato direttamente dal numero di richiedenti asilo ospitati da ciascun paese. Infatti, maggiore \ue8 il numero di richiedenti asilo, maggiore \ue8 la richiesta di un\u2019iniziativa politica europea che affronti questo tema. Considerando insieme questi due risultati (aumento dell\u2019influenza della rappresentanza politica e del numero dei richiedenti asilo) viene confermata l\u2019idea che le recenti crisi Europee (economica e dei migranti) abbiano profondamente modificato il modo attraverso cui i cittadini guardano all\u2019Unione europea, e i motivi per cui sostengano o rifiutino una (maggiore) governance europea. In conclusione, il Capitolo 6 indaga i significati di identit\ue0 nazionale ed europea per scoprire come questi influenzino il supporto per una governance europea di specifiche aree di policy. Utilizzando dati della ricerca Intune 2009, l\u2019identit\ue0 nazionale ed europea viene scomposta in quattro componenti costitutive: \u2018European Civility\u2019, \u2018National Civility\u2019, \u2018Ancestry\u2019, e \u2018Citizenship\u2019. I risultati dimostrano come gli intervistati che ricostruiscono la propria identit\ue0 nazionale sulla base delle specifiche tradizioni culturali nazionali (componente di \u2018National Civility\u2019) siano portati a rifiutare una governance europea. All'opposto, il sostegno per una governance europea \ue8 pi\uf9 probabile per quelli che qualificano l\u2019identit\ue0 europea come una forma di europeismo \u2018banale\u2019, dove il significato di europeismo discende dalla condivisione delle esperienze quotidiane ed ordinarie come cittadini dell\u2019Europa (componente di \u2018European Civility\u2019). Le analisi mostrano l\u2019assenza di influenza sul sostegno da parte sia della componente pre-politica (\u2018Ancestry\u2019) dell\u2019identit\ue0 nazionale ed europea, sia di quella politica (\u2018Citizenship\u2019 intesa come esercitare i diritti di cittadinanza). Complessivamente, questi risultati corroborano l\u2019idea che pi\uf9 l\u2019Unione Europea \ue8 percepita come presente all\u2019interno dell\u2019ordinaria esperienza di vita dei cittadini, pi\uf9 probabile \ue8 il supporto per una maggiore integrazione politica. Tuttavia, a parit\ue0 di condizioni, i significati di identit\ue0 nazionale esercitano una decisa influenza sul sostegno. Infatti, maggiore \ue8 l\u2019enfasi sulle tradizioni culturali nazionali e sul loro ruolo nella definizione di identit\ue0 nazionale, minore \ue8 il sostegno per una governance europea. Questo \ue8 determinato dal fatto che le tradizioni culturali sono incorporate anche nelle leggi e nelle istituzioni politiche nazionali, ed un trasferimento di competenze all\u2019Unione Europea ridurrebbe il ruolo e l\u2019importanza di tali istituzioni, influenzando indirettamente l\u2019identit\ue0 nazionale.This dissertation contributes to the debate on Europeanization of citizen policy preferences. This form of Europeanization is defined as the support for a EU level governance instead of a national or sub-national governance of strategic policy domains. Using survey data from the Intune 2009 project and Eurobarometer surveys, this work studies how citizen support for EU policy governance is structured. It distinguishes a generic preference for more EU policy governance from a specific support for EU governance of distinct policy sectors. Moreover, this thesis analyses what influences the development of these two types of support for EU policy governance. Chapter 1 surveys the literature on macro theories of European integration and provides three alternative models of support for EU policy governance. These models are tested and debated in the proceeding of the dissertation to study the structure of support for EU policy governance. Chapters 2 provides a conceptual definition of EU support grounded in earlier theoretical and empirical works. Four dimensions of EU support are identified: \u2022 \u2018Output legitimacy\u2019: support as subjective utility of European integration; \u2022 \u2018EU governance legitimacy\u2019: support as a generic preference for EU policy governance; \u2022 \u2018European identification\u2019: support as identification (we-feeling) with the European political community; \u2022 \u2018EU democracy\u2019: support as political representation at the EU level. Chapter 3 measures these four dimensions of EU support, modelling them as latent dimensions using individual-level survey data. This chapter confirms that these dimensions are rather stable and invariant across EU member countries. Chapter 4 analyses the determinants of these four dimensions. Results demonstrate that \u2018exclusive national identification\u2019, \u2018national attachment\u2019, \u2018confidence in national institutions\u2019, and \u2018political values\u2019 exert a significant influence on the levels of EU support across Europe, but their effects vary across the four dimensions of EU support. Notably, only \u2018exclusive national identification\u2019 influences the generic support for EU policy governance (\u2018EU governance legitimacy\u2019). This chapter also investigates the presence of a hierarchy among the four dimensions of EU support testing whether generic support for EU policy governance depends upon holding one of the other three forms of EU support, following some suggestions included in theories of European integration (mainly neo and post-functionalism) and in empirical studies on EU support. However, results demonstrate that \u2018Output legitimacy\u2019, \u2018European identification\u2019, and \u2018EU democracy\u2019 do not have consistent effects on \u2018EU governance legitimacy\u2019 across European countries. Chapter 5 explores this result performing a policy by policy analysis. It emerges that \u2018Output legitimacy\u2019, \u2018European identification\u2019, and \u2018EU democracy\u2019 play a role in driving support for EU governance of distinct policy domains. \u2018Output legitimacy\u2019 and \u2018European identification\u2019 are the most important determinants, but their effects are strengthened (or weakened) by specific policy domain characteristics. \u2018Output legitimacy\u2019 has the greatest influence on support for EU governance of policies where the EU governance is more effective (functional interdependence explanation); whereas \u2018European identification\u2019 has the highest effect on policies that work as market-correcting policies (social-model explanation) that guarantee a EU level protection from market and globalisation failures. Further analyses show that respondents tend to prefer high-expenditure policy to be governed at the national level, and, ceteris paribus, they are likely to oppose further EU integration in policy domains where EU governance is already high. This last mechanism is telling because it shows that EU governance does not lead to further integration (as argued by neo-functionalists), but on the contrary respondents favour a retrenchment from prior agreements on EU policy competencies. The analyses with 2009 data do not confirm the influence of political representation (\u2018EU democracy\u2019), but pooling data from November 2016 (Eurobarometer 86.2), respondents\u2019 perception of political representation within the EU becomes a highly significant determinant of support for EU governance of Immigration and Foreign policies. Moreover, the number of asylum seekers within each country contributes to explain individual-level support. These two findings confirm the idea that the recent European refugees and economic crises have profoundly modified how European citizens look to the EU, and why they support or reject EU policy governance. Finally, Chapter 6 investigates the meanings of national and European identities and their influence on support for EU governance of specific policy domains. Using Intune 2009 data, national and European identities are unpacked in four constitutive components: \u2018European Civility\u2019, \u2018National Civility\u2019, \u2018Ancestry\u2019, and \u2018Citizenship\u2019. The results show that respondents who conceive their national identity as something rooted in national cultural traditions (\u2018National Civility\u2019 component) are likely to reject EU policy governance. On the contrary, those who qualify European identity as a form of banal Europeanism where Europeanness is a matter of common and ordinary experiences as Europeans that forms a European way of life (\u2018European Civility\u2019 component) are, ceteris paribus, more likely to support EU governance. Both pre-political (\u2018Ancestry\u2019) and political (exercising \u2018Citizenship\u2019 rights) components do not have a consistent impact on this form of EU support. Overall, this corroborates the idea that the more the EU is present in ordinary experiences, the greater is support for EU policy governance. Conversely, a respondents\u2019 strong emphasis on national cultural traditions - also embedded in national laws and political institutions - hampers support for EU governance, since a transfer of competencies to the EU affects national laws and institutions, and, indirectly, national identities

Collective excitations in trapped boson-fermion mixtures: from demixing to collapse

We calculate the spectrum of low-lying collective excitations in a gaseous cloud formed by a Bose-Einstein condensate and a spin-polarized Fermi gas over a range of the boson-fermion coupling strength extending from strongly repulsive to strongly attractive. Increasing boson-fermion repulsions drive the system towards spatial separation of its components (``demixing''), whereas boson-fermion attractions drive it towards implosion (``collapse''). The dynamics of the system is treated in the experimentally relevant collisionless regime by means of a Random-Phase approximation and the behavior of a mesoscopic cloud under isotropic harmonic confinement is contrasted with that of a macroscopic mixture at given average particle densities. In the latter case the locations of both the demixing and the collapse phase transitions are sharply defined by the same stability condition, which is determined by the softening of an eigenmode of either fermionic or bosonic origin. In contrast, the transitions to either demixing or collapse in a mesoscopic cloud at fixed confinement and particle numbers are spread out over a range of boson-fermion coupling strength, and some initial decrease of the frequencies of a set of collective modes is followed by hardening as evidenced by blue shifts of most eigenmodes. The spectral hardening can serve as a signal of the impending transition and is most evident when the number of bosons in the cloud is relatively large. We propose physical interpretations for these dynamical behaviors with the help of suitably defined partial compressibilities for the gaseous cloud under confinement.Comment: 16 pages, 7 figures, revtex

Collective excitations of a trapped boson-fermion mixture across demixing

We calculate the spectrum of low-lying collective excitations in a mesoscopic cloud formed by a Bose-Einstein condensate and a spin-polarized Fermi gas as a function of the boson-fermion repulsions. The cloud is under isotropic harmonic confinement and its dynamics is treated in the collisional regime by using the equations of generalized hydrodynamics with inclusion of surface effects. For large numbers of bosons we find that, as the cloud moves towards spatial separation (demixing) with increasing boson-fermion coupling, the frequencies of a set of collective modes show a softening followed by a sharp upturn. This behavior permits a clear identification of the quantum phase transition. We propose a physical interpretation for the dynamical transition point in a confined mixture, leading to a simple analytical expression for its location.Comment: revtex4, 9 pages, 8 postscript file