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Quantum droplets and bright solitons in mixtures of Bose-Einstein condensates
Get PDFThe ultracold and ultradilute bosonic heteronuclear mixture (41K - 87Rb) of Bose-Einstein condensates with tunable interspecies interaction at zero temperature is studied in the self-bound regime, using numerical simulations based on Density Functional Theory within the Local Density Approximation. In particular, the beyond mean-field effects embodied in the Lee-Huang-Yang energy contribution are explicitly included in the total energy functional. The thermodynamic properties of the homogeneous system are investigated to set the stability conditions of the self-bound droplet. The surface properties are discussed with (i) a variational approach, (ii) a numerical method and (iii) by solving the two coupled Gross-Pitaevskii equations associated to the two components of the mixture. The validity of the liquid-drop model is verified by computing the total ground state energy for systems with a different number of particles and, after the confinement in a quasi-1D configuration by means of an optical waveguide, we also discuss the transition between quantum droplets and bright solitons, two localized states of different nature
Search for transient sources of high-energy neutrinos with IceCube: tests of the real-time analysis
Get PDFThe astrophysical sources of neutrinos with energy above GeV are to date unknown. A discovery of these objects would provide a smoking gun signature of the unknown cosmic rays sources, since their production is correlated. In addition, neutrinos are a unique tool to probe the most extreme environments in our Universe: their interaction cross section is low and they are electrically neutral, allowing them to travel undeflected and almost unabsorbed. The IceCube detector, located at the South Pole, observes neutrinos in the energy range from TeV to PeV. Real-time analyses process the IceCube data in order to rapidly identify signal neutrinos, sending alerts to the astrophysical community for follow-up observations in case of interesting results. Two of them are relevant for this work, both searching for signal neutrino clusters from individual sources: one monitors known transient gamma-ray sources, the other performs an unbiased all-sky search. This work focuses on testing the core algorithm of these real-time analyses. Neutrino clusters from point-like sources, characterised by number of signal neutrinos, flux spectral index and flare duration, are simulated for sources in different positions in the sky. The reconstruction quality of the cluster parameters is studied, highlighting the behaviour of the algorithm for different simulation conditions. The discovery potential, i.e. the flux that yields a 5σ discovery in 50% of the cases, is also evaluated for every simulated source. Finally, the possibility to identify sources emitting neutrinos during time scales shorter than few hours is discussed
Study of the 12C(p,g)13N at astrophysical energies at LUNA
Get PDFabstract:
The 12C/13C ratio is a sensitive indicator of the degree of stellar
nucleosynthesis and thus it can be used as a tracer of galactic chemical
evolution. Nevertheless, the C isotopic ratio variation after the dredge-up
phenomenons occuring in Asymptotic Giant Branch (AGB) and Red Giant Branch
(RGB) stars is highly dependant on the adopted rate for the proton capture
reaction on 12 C.
In a RGB star, the Gamow peak of the reaction lies between 20 and 70 keV. Given
the exponential drop of the cross section, the reactions at such low energies
are very difficult to measure because of the very low signal counting rate.
Nevertheless, a precise measurement of the 12C(p, γ)13N reaction magnitude is
necessary to make reliable predictions about the evolution of RGB stars. On the
contrary, the Gamow peak for an AGB stars lies between 50 and 150 keV. This
energy range can be measured through the detection of prompt γ-rays.
Measurements of the 12C(p,γ)13N reaction cross section were performed at the
Laboratory for Underground Nuclear Astrophysics (LUNA), located at the
Labaratori Nazionali del Gran Sasso (LNGS) in Italy. Being located underground,
the γ-ray background is suppressed by more than three orders of magnitude, thus
providing a unique environment for low-energy measurements of reaction cross
sections.
Prompt γ-rays associated with the formation of 13 N nuclei were analysed to
determine the non-resonant contribution to the reaction cross section. The total
non-resonant S-factor was determined at energies between E cm ≈ 75 − 350 keV,
obtained with great precision. Nevertheless, the preliminary results are
discordant with the literature data. The reason of such a discrepancy is still
unkown and has to be understood in future analysis
Caratteristiche delle aziende connesse alle organizzazioni criminali di stampo mafioso mediante indicatori contabili
Get PDFSchrödinger equation approach to the distribution of baryons in the Universe
Get PDFThe aim of this thesis is to study the evolution of the distribution of baryons in the Universe. It is used a Schrödinger equation approach which had already proven successful in the study of Cold Dark Matter. Both a semi-analytical (via quantum perturbation theory and limited to scales bigger than the Jeans wavelength) and a numerical study ( Strang time-splitting approximation) are presented. In addition we extended a previous study on a new candidate for DM, fuzzy DM, considering the possibility of a velocity dispersion modelled as a gas pressure
