Bubble-nucleation rates for cosmological phase transitions

We estimate bubble-nucleation rates for cosmological phase transitions. We concentrate on the evaluation of the pre-exponential factor, for which we give approximate analytical expressions. Our approach relies on the use of a real coarse-grained potential. We show how the coarse-graining scale can be determined in the studies of high-temperature phase transitions. We discuss the metastability bound on the Higgs-boson mass and the electroweak phase transition. We find that the saddle-point approximation is reliable in the first case and breaks down in the second case.Comment: 8 pages, 2 fig.s. Final versio

L'impero machiavellico. L'immagine della Turchia nei trattatisti italiani del Cinquecento e del primo Seicento

Scopo del saggio è descrivere come trattatisti storici e politici italiani del Cinquecento hanno valutato la struttura politica dell'impero ottomano. In quanto Stato non cristiano, la Turchia poteva essere vista come una perfetta realizzazione delle idee di Machiavelli concernenti la logica interna dell'assolutismo, compresa la manipolazione pragmatica delle credenze religiose. Traiano Boccalini usa il modello politico ottomano per criticare l'apologia della tolleranza religiosa di Jean Bodin. Gli scrittori occidentali sono particolarmente interessati all'organizzazione dell'esercito turco, che sembra offrire un esempio vivente dell'applicabilità dei punti di vista machiavelliani.The aim of the essay is to describe how Italian historians and political analysts of the sixteenth century appreased the political structure of the Osman empire. As a no Christian State, Turkey could be viewed as the perfect realization of Machiavellian ideas about the inner logic of absolutism, including pragmatic manipulation of religious beliefs. Traiano Boccalini employs the Osman political pattern in order to criticize Jean Bodin's apology of religious tolerance. Western writers are especially interested on the organization of Turkish army, which seems to offer a lively example of the practical viability of Machiavellian points of view

First observation of the Bs->K+K- decay mode, and measurement of the B0 and Bs mesons decay-rates into two-body charmless final states at CDF

The authors searched for decays of the type B{sub (s)}{sup 0} {yields} h{sup +}h{prime}{sup -} (where h, h{prime} = K or {pi}) in a sample corresponding to 180 pb{sup -1} of p{bar p} collisions at {radical}s = 1.96 TeV, collected by the upgraded Collider Detector at the Fermilab Tevatron. A total signal of approximately 900 events was reconstructed, and the relative branching fractions ({Beta}) of each decay mode were determined with a likelihood fit

Oscillations of solar and atmospheric neutrinos

Motivated by recent results from SuperKamiokande, we study both solar and atmospheric neutrino fluxes in the context of oscillations of the three known neutrinos. We aim at a global view which identifies the various possibilities, rather than attempting the most accurate determination of the parameters of each scenario. For solar neutrinos we emphasise the importance of performing a general analysis, independent of any particular solar model and we consider the possibility that any one of the techniques --- chlorine, gallium or water Cerenkov --- has a large unknown systematic error, so that its results should be discarded. The atmospheric neutrino anomaly is studied by paying special attention to the ratios of upward and downward going nu_e and nu_mu fluxes. Both anomalies can be described in a minimal scheme where the respective oscillation frequencies are widely separated or in non-minimal schemes with two comparable oscillation frequencies. We discuss explicit forms of neutrino mass matrices in which both atmospheric and solar neutrino fluxes are explained. In the minimal scheme we identify only two `zeroth order' textures that can result from unbroken symmetries. Finally we discuss experimental strategies for the determination of the various oscillation parameters.Comment: 20 pages, 7 figures. Final version: one reference added; fit of atmospheric neutrinos improve

DNS of compressible multiphase flows through the Eulerian approach

In this paper we present three multiphase flow models suitable for the study of the dynamics of compressible dispersed multiphase flows. We adopt the Eulerian approach because we focus our attention to dispersed (concentration smaller than 0.001) and small particles (the Stokes number has to be smaller than 0.2). We apply these models to the compressible ($\text{Ma} = 0.2,\,0.5$) homogeneous and isotropic decaying turbulence inside a periodic three-dimensional box ($256^3$ cells) using a numerical solver based on the OpenFOAM$^{R}$ C++ libraries. In order to validate our simulations in the single-phase case we compare the energy spectrum obtained with our code with the one computed by an eighth order scheme getting a very good result (the relative error is very small $4*10^{-4}$). Moving to the bi-phase case, initially we insert inside the box an homogeneous distribution of particles leaving unchanged the initial velocity field. Because of the centrifugal force, turbulence induce particle preferential concentration and we study the evolution of the solid-phase density. Moreover, we do an {\em a-priori} test on the new sub-grid term of the multiphase equations comparing them with the standard sub-grid scale term of the Navier-Stokes equations.Comment: 10 pages, 5 figures, preprint. Direct and Large Eddy Simulations 9, 201

Measurements of CP asymmetries and branching fractions of two-body charmless decays of B^0 and B^0_s mesons

The thesis is organized as follows: Chapter 1 describes the theoretical framework of non-leptonic B{sub (s)}{sup 0} {yields} H{sup +}h{prime}{sup -} decays, with a simple overview of the CP violation mechanism within the Standard Model and of the most used phenomenological approaches in the evaluation of strong interaction contributions. The chapter contains also a review of the theoretical expectations and the current experimental measurements along with a discussion about the importance of studying such decays. Chapter 2 contains a general description of the Tevatron collider and of the CDF II detector. Chapter 3 is devoted to the description of the data sample used for the measurement and the method used in extracting the signal from the background. Particular attention is dedicated to the on-line trigger selection, which is crucial to collect a sample enriched in B{sub (s)}{sup 0} {yields} h{sup +}h{prime}{sup -} decays. Chapter 4 shows how the information from kinematics and particle identification was used to achieve a statistical discrimination amongst modes to extract individual measurements. The available resolutions in mass or in particle identification are separately insufficient for an event-by-event separation of B{sub (s)}{sup 0} {yields} h{sup +}h{prime}{sup -} modes. The choice of observables and the technique used to combine them is an important and innovative aspect of the analysis described in this thesis. Chapter 5 is devoted to the accurate determination of the invariant mass lineshape. This is a crucial ingredient for resolving overlapping mass peaks. This chapter details all resolution effects with particular attention at the tails due to the emission of low-energy photons from charged kaons and pions in the final state (FSR). For the first time the effect of FSR has been accurately accounted for in a CDF analysis. Chapter 6 describes how kinematic and PID information, discussed in chap. 4 and chap. 5 were combined in a maximum Likelihood fit to statistically determine the composition of the B{sub (s)}{sup 0} {yields} h{sup +}h{prime}{sup -} sample. This kinematics-PID combined fit has been developed and performed for the first time at CDF in the analysis presented in this thesis and this methodology was later inherited by several other analyses. Chapter 7 is devoted to the study of the isolation variable, which is a crucial handle to enhance the signal-to-background ratio in the off-line selection. It exploits the property that the b-hadrons tend to carry a larger fraction of the transverse momentum of the particles produced in the fragmentation, with respect to lighter hadrons. Since the simulators do not accurately reproduce the fragmentation processes, this chapter is devoted to the study of the control data sample of B{sub (s)}{sup 0} {yields} J/{psi}X decays to probe the characteristics of this variable. Chapter 8 describes an innovative procedure used to optimize the selection to minimize the statistical uncertainty on the quantities one wishes to measure. The procedure is based on the fit of composition described in chap. 6. Chapter 9 reports the results of the fit of composition described in chap. 6 and the cross-checks performed to verify the goodness of the fit of composition. In order to translate the parameters returned from the fit into physics measurements the relative efficiency corrections between the various decay modes need to be applied. Chapter 10 is devoted to the description of these corrections. Chapter 11 describes the measurement of the detector-induced charge asymmetry between positively and negatively charged kaons and pions, due to their different probability of strong interaction in the tracker material using the real data. This allows to extract the acceptance correction factor for the CP asymmetries measurement without any external inputs from the simulation, and to perform a powerful check of whole analysis. Chapter 12 describes the main sources of systematic uncertainties and the method used to evaluate the significance of the results on rare modes. The final results of the measurements and their interpretation are discussed in chap. 13

Dynamical Feedback of Self-generated Magnetic Fields in Cosmic Rays Modified Shocks

We present a semi-analytical kinetic calculation of the process of non-linear diffusive shock acceleration (NLDSA) which includes magnetic field amplification due to cosmic ray induced streaming instability, the dynamical reaction of the amplified magnetic field and the possible effects of turbulent heating. This kinetic calculation allows us to show that the net effect of the amplified magnetic field is to enhance the maximum momentum of accelerated particles while reducing the concavity of the spectra, with respect to the standard predictions of NLDSA. This is mainly due to the dynamical reaction of the amplified field on the shock, which smoothens the shock precursor. The total compression factors which are obtained for parameters typical of supernova remnants are R{sub tot} {approx} 7-10, in good agreement with the values inferred from observations. The strength of the magnetic field produced through excitation of streaming instability is found in good agreement with the values inferred for several remnants if the thickness of the X-ray rims are interpreted as due to severe synchrotron losses of high energy electrons. We also discuss the relative role of turbulent heating and magnetic dynamical reaction in smoothening the shock precursor