Testing the very-short-baseline neutrino anomalies at the solar sector

Motivated by the accumulating hints of new sterile neutrino species at the eV scale, we explore the consequences of such an hypothesis on the solar sector phenomenology. After introducing the theoretical formalism needed to describe the MSW conversion of solar neutrinos in the presence of one (or more) sterile neutrino state(s) located "far" from the (nu_1,nu_2) "doublet", we perform a quantitative analysis of the available experimental results, focusing on the electron neutrino mixing. We find that the present data posses a sensitivity to the amplitude of the lepton mixing matrix element U_e4 --- encoding the admixture of the electron neutrino with a new mass eigenstate --- which is comparable to that achieved on the standard matrix element U_e3. In addition, and more importantly, our analysis evidences that, in a 4-flavor framework, the current preference for |U_e3|>0 is indistinguishable from that for |U_e4|>0, having both a similar statistical significance (which is ~ 1.3 sigma adopting the old reactor fluxes determinations, and ~ 1.8 sigma using their new estimates). We also point out that, differently from the standard 3-flavor case, in a 3+1 scheme the Dirac CP-violating phases cannot be eliminated from the description of solar neutrino conversions.Comment: 16 pages, 3 figures; minor changes; matches version published in PR

Phenomenology of light sterile neutrinos: a brief review

An increasing number of anomalous experimental results are emerging, which cannot be described within the standard 3-neutrino framework. We present a concise discussion of the most popular phenomenological interpretation of such findings, based on a hypothetical flavor conversion phenomenon of the ordinary "active" neutrinos into new light "sterile" species having mass m ~ O(1) eV.Comment: 12 pages, 5 figures, invited review for MPLA, added references, matches published versio

Consistent analysis of the νμ→νe\nu_\mu \to \nu_e sterile neutrinos searches of ICARUS and OPERA

The two long-baseline experiments ICARUS and OPERA have recently provided bounds on light ($\sim$ eV) sterile neutrinos exploiting the negative results of the $\nu_\mu \to \nu_e$ appearance searches. Both collaborations have performed the data analysis using an effective 2-flavor description. We show that such a simplified treatment neglects sizable genuine 4-flavor effects, which are induced by the interference of the new large squared-mass splitting $\Delta m^2 _{14}$ with the atmospheric one. The inclusion in the data analysis of such effects weakens the upper bounds on the effective appearance amplitude $\sin^2 2\theta_{\mu e}$ approximately by a factor of two. In addition, we evidence that, in a 4-flavor scheme, the flavor oscillations involve also the $\nu_e$ component of the CNGS beam and can suppress the theoretical expectation of the background in a substantial way. The inclusion in the data analysis of the $\nu_e$ disappearance effects leads to a further weakening of the upper bounds on $\sin^2 2\theta_{\mu e}$, which overall are relaxed by a factor of three with respect to those obtained in the effective 2-flavor description.Comment: 5 pages, 5 figures; references updated; to appear in PRD as a Rapid Communicatio

Application of Advanced Thermal-Hydraulic Simulation Codes for the Analysis of Heavy Liquid Metal Flows in the ADS Reactor Concept MYRRHA

Il codice termoidraulico di sistema ATHLET è stato sviluppato negli ultimi decenni dall’istituto di ricerca GRS (Gesellschaft für Anlagen- und Reaktorsicherheit) con l’obiettivo di facilitare e migliorare l’analisi della progettazione di base e della gestione dei reattori nucleari PWR e BWR. Recentemente è stata rilasciata una nuova versione del codice ATHLET, nella quale sono state implementate le proprietà fisiche, nonché le correlazioni di scambio termico convettivo di refrigeranti innovativi come elio, sodio, piombo e lega eutettica piombo-bismuto (LBE). Tale sviluppo consente di estendere le capacità del codice ATHLET all’analisi del comportamento termoidraulico dei futuri reattori nucleari appartenenti alla IV generazione. Inoltre, ATHLET è stato accoppiato con il codice di fluidodinamica computazionale (CFD) ANSYS CFX al fine di migliorarne le capacità di simulazione in regioni particolari del circuito di refrigerazione nel caso di flussi affetti da evidenti fenomeni tridimensionali, come ad esempio miscelazione o stratificazione termica. Nel presente lavoro di tesi, la nuova metodologia di accoppiamento tra il codice di sistema ATHLET ed il codice di CFD ANSYS CFX è stata applicata all’analisi del circuito di spallazione del reattore sperimentale MYRRHA, appartenente alla categoria dei reattori sottocritici di tipo ADS. Tale reattore ha tra i suoi obiettivi quello di permettere uno studio approfondito sulla trasmutazione efficiente delle scorie nucleari a più alto livello di radiotossicità. Nello specifico, le potenzialità del codice ANSYS CFX sono state sfruttate per simulare la zona più complessa dal punto di vista fluidodinamico dell’intero circuito di spallazione, vale a dire il target ”windowless”. La restante parte del circuito è stata invece simulata mediante il codice ATHLET. In questo studio è stata eseguita una prima simulazione utilizzando la tecnica di accoppiamento tra i codici ATHLET e ANSYS CFX allo scopo di verificare il corretto scambio di dati tra i due codici. A tal scopo è stato simulato in condizioni transitorie un semplice tubo con all’interno LBE come fluido refrigerante. In seguito, si è passati ad analizzare una configurazione semplificata del circuito di spallazione, in cui è stata simulata la sola zona del target. L’obiettivo è stato quello di verificare la stabilità della superficie conica di LBE, che rappresenta il bersaglio di spallazione, al variare della portata in ingresso alla regione del target. Le difficoltà legate al raggiungimento di un corretto bilancio della massa di LBE all’interno del dominio CFD durante i transitori incidentali simulati hanno reso necessaria una leggera modifica nella nodalizzazione ATHLET prima di iniziare la simulazione della configurazione ad anello chiuso. Le simulazioni di transitori con variazione rapida di portata in quest’ultima configurazione sono state eseguite agendo sulla velocità di rotazione della pompa. Nonostante la presenza delle due superfici libere di LBE abbia influenzato la conservazione della massa all’interno del dominio CFD durante le simulazioni transitorie, i risultati ottenuti con i codici accoppiati ATHLET – ANSYS CFX confermano la stabilità della superficie conica del target al variare della portata di LBE nel sistema, nonché la funzionalità dello schema numerico di accoppiamento

Cylindric Reverse Plane Partitions and 2D TQFT

The ring of symmetric functions carries the structure of a Hopf algebra. When computing the coproduct of complete symmetric functions $h_\lambda$ one arrives at weighted sums over reverse plane partitions (RPP) involving binomial coefficients. Employing the action of the extended affine symmetric group at fixed level $n$ we generalise these weighted sums to cylindric RPP and define cylindric complete symmetric functions. The latter are shown to be $h$-positive, that is, their expansions coefficients in the basis of complete symmetric functions are non-negative integers. We state an explicit formula in terms of tensor multiplicities for irreducible representations of the generalised symmetric group. Moreover, we relate the cylindric complete symmetric functions to a 2D topological quantum field theory (TQFT) that is a generalisation of the celebrated $\mathfrak{\widehat{sl}}_n$-Verlinde algebra or Wess-Zumino-Witten fusion ring, which plays a prominent role in the context of vertex operator algebras and algebraic geometry.Comment: 13 pages, 1 figure, accepted conference proceedings article for FPSAC2018 (Hanover

A Preliminary Exergy Analysis of the EU DEMO Fusion Reactor

Purpose of the present study is the exergy analysis of EU DEMO pulsed fusion power plant considering the Primary Heat Transfer Systems, the Intermediate Heat Transfer System (IHTS) including the Energy Storage System (ESS) as a first option to ensure the continuity of electric power released to the grid. A second option here considered is a methane fired auxiliary boiler replacing the ESS. The Power Conversion System (PCS) performance is evaluated as well in the overall balance. The performance analysis is based on the exergy method to specifically assess the amount of exergy destruction determined by irreversible phenomena along the whole cyclic process. The pulse and dwell phases of the reactor operation are evaluated considering the state of the art of the ESS adopting molten salts alternate heating and storage in a hot tank followed by a cooling and recovery of molten salt in a cold tank to ensure the continuity of power release to the electrical grid. The second option of the plant configuration is evaluated on the basis of an auxiliary boiler replacing the ESS with a 10% of the power produced by the reactor during both pulse and dwell modes

A beta based framework for (lower) bond risk premia.

We use a no-arbitrage essentially affine three-factor model to estimate term premia in US and German ten-year government bond yields. In line with the existing literature, we find that estimated premia have followed a downward trend since the 1980s: from 4.9 per cent in 1981 to 0.7 per cent in 2006 for the US bond and from 3.3 to 0.5 per cent for the German one. Subsequently, using an Error Correction Model (ECM) we prove that the decline is explained by a decrease in global output variability and an increase in the power of ten-year government bonds to diversify the investors’ portfolios. In addition, the ECM also forecasts both the US and the German term premia converging to around one percentage point over a five year horizon. Long-term return expectations for ten-year government bonds will have to incorporate bond risk premia that - while in line with average excess returns during the twentieth century - are significantly lower than average excess returns over the last two decades.Term structure model, bond risk premium, modern portfolio theory

Entry, Exit, Firm Dynamics, and Aggregate Fluctuations

How important are firm entry and exit in shaping aggregate dynamics? We address this question by characterizing the equilibrium allocation in Hopenhayn (1992)’s model of equilibrium industry dynamics, amended to allow for investment in physical capital and aggregate fluctuations. We find that entry and exit propagate the effects of aggregate shocks. In turn, this results in greater persistence and unconditional variation of aggregate time-series. In the aftermath of a positive productivity shock, the number of entrants increases. The new firms are smaller and less productive than the incumbents, as in the data. As the common productivity component reverts to its unconditional mean, the new entrants that survive become progressively more productive, keeping aggregate efficiency higher than in a scenario without entry or exit. We also find that both the mean and variance of the cross-sectional distribution of firm–level productivity are counter–cyclical, in spite of the assumption that innovations to firm–level productivity are i.i.d. and orthogonal to aggregate shocks. This happens because of selection: the idiosyncratic productivity of the marginal entrant is lower in expansion than during recessions. Since idiosyncratic productivity is mean–reverting, mean and variance of the distribution of productivity growth are pro–cyclical.Selection, Propagation, Persistence, Survival, Reallocation