B -> X_s gamma in supersymmetry: large contributions beyond the leading order

We discuss possible large contributions to B -> X_s gamma, which can occur at the next-to-leading order in supersymmetric models. They can originate from terms enhanced by tan(beta) factors, when the ratio between the two Higgs vacuum expectation values is large, or by logarithm of M_{susy}/M_W, when the supersymmetric particles are considerably heavier than the W boson. We give compact formulae which include all potentially large higher-order contributions. We find that tan(beta) terms at the next-to-leading order do not only appear from the Hall-Rattazzi-Sarid effect (the modified relation between the bottom mass and Yukawa coupling), but also from an analogous effect in the top-quark Yukawa coupling. Finally, we show how next-to-leading order corrections, in the large tan(beta) region, can significantly reduce the limit on the charged-Higgs mass, even if supersymmetric particles are very heavy.Comment: 18 pages, 5 figs, extended discussion of light stop case, notational improvement

Rischio e parit\ue0 di posizioni nei rimedi correttivi degli scambi di mercato

Nel contributo, la tematica dei rimedi giudiziali nella gestione del rischio economico, al centro di un denso dibattito della dottrina, \ue8 riguardata da un triplice punto di osservazione: a) sotto il profilo delle analisi empiriche ed economiche sul tipo di scambio realizzato dai contraenti; b) nel quadro della elaborazione moderna della figura generale e astratta dell\u2019obbligazione; c) nella prospettiva delle nuove discipline di settore, pi\uf9 sensibili alla formazione dell\u2019atto di autonomia e al corretto esercizio del potere negoziale. Il proposito del contributo, nel ripercorrere talune delle teorie impegnate a contendersi la riflessione giuridica sul tema, \ue8 di mostrare gli elementi empirici, sociologici ed economici, che in ultima analisi ne costituiscono il fondamento. La ricerca, che in una prospettiva interdisciplinare si schiude all\u2019indirizzo sociologico che ha indagato il rapporto, ambiguo e sfuggente, tra scambio e dono, ai relational contracts e agli studi di analisi economica del diritto \ue8 volta ad indicare il carattere specifico con cui talune categorie ed elaborazioni concettuali, provenienti da altri campi del sapere, si presentano nell\u2019ambito del diritto; mostrandosi talora incompatibili con il nostro ordinamento talora utili a fornire una chiave di lettura della sua evoluzione. Il contributo \ue8 stato pubblicato altres\uec in Scritti in onore di Giorgio Cian, I, Cedam, 2010, 1149-1173

Indication for Light Sneutrinos and Gauginos from Precision Electroweak Data

The present Standard Model fit of precision data has a low confidence level, and is characterized by a few inconsistencies. We look for supersymmetric effects that could improve the agreement among the electroweak precision measurements and with the direct lower bound on the Higgs mass. We find that this is the case particularly if the 3.6 sigma discrepancy between sin^2 theta_eff from leptonic and hadronic asymmetries is finally settled more on the side of the leptonic ones. After the inclusion of all experimental constraints, our analysis selects light sneutrinos, with masses in the range 55-80 GeV, and charged sleptons with masses just above their experimental limit, possibly with additional effects from light gauginos. The phenomenological implications of this scenario are discussed.Comment: 17 pages LaTex, 9 figures, uses epsfi

Two-loop electroweak top corrections: are they under control?

The assumption that two-loop top corrections are well approximated by the $O(G_mu^2 mt^4)$ contribution is investigated. It is shown that in the case of the ratio neutral-to-charged current amplitudes at zero momentum transfer the $O(G_mu^2 mt^2 M_Z^2)$ terms are numerically comparable to the $m_t^4$ contribution for realistic values of the top mass. An estimate of the theoretical error due to unknown two-loop top effect is presented for a few observables of LEP interest.Comment: 13 pages, LaTeX using equations, doublespace, cite macros. Hard copies of the paper including one figure are available from [email protected]

Using the transit of Venus to probe the upper planetary atmosphere

The atmosphere of a transiting planet shields the stellar radiation providing us with a powerful method to estimate its size and density. In particular, because of their high ionization energy, atoms with high atomic number (Z) absorb short-wavelength radiation in the upper atmosphere, undetectable with observations in visible light. One implication is that the planet should appear larger during a primary transit observed in high energy bands than in the optical band. The last Venus transit in 2012 offered a unique opportunity to study this effect. The transit has been monitored by solar space observations from Hinode and Solar Dynamics Observatory (SDO). We measure the radius of Venus during the transit in three different bands with subpixel accuracy: optical (4500A), UV (1600A, 1700A), Extreme UltraViolet (EUV, 171-335A) and soft X-rays (about 10A). We find that, while the Venus optical radius is about 80 km larger than the solid body radius (the expected opacity mainly due to clouds and haze), the radius increases further by more than 70 km in the EUV and soft X-rays. These measurements mark the densest ion layers of Venus' ionosphere, providing information about the column density of CO2 and CO. They are useful for planning missions in situ to estimate the dynamical pressure from the environment, and can be employed as a benchmark case for observations with future missions, such as the ESA Athena, which will be sensitive enough to detect transits of exoplanets in high-energy bands.Comment: 13 pages, 2 figures; published in Nature Communications; the full and copy-edited version is open access at http://www.nature.com/ncomms/2015/150623/ncomms8563/full/ncomms8563.htm

Lepton energy moments in semileptonic charm decays

We search for signals of Weak Annihilation in inclusive semileptonic D decays. We consider both the widths and the lepton energy moments, which are quite sensitive probes. Our analysis of Cleo data shows no clear evidence of Weak Annihilation, and allows us to put bounds on their relevance in charmless B semileptonic decays.Comment: 10 pages, 3 figures. Added discussion, version as publishe

La pietra naturale nei beni culturali

Le pietre ornamentali ricoprono un ruolo fondamentale per quei beni culturali costituiti parzialmente o interamente in materiale lapideo. In un contesto come quello italiano, la conoscenza dei litotipi utilizzati in ciascun ambito regionale, sia per le produzioni artistiche di pregio che per l’edilizia corrente, riveste certamente una particolare importanza. Infatti, l’impiego della pietra ha da sempre connotato in maniera determinante il paesaggio urbano e rurale. Lo studio dei litotipi ornamentali, la loro caratterizzazione e la loro conservazione rivolge l’attenzione sui materiali posti in opera e rappresenta una branca delle Scienze Geologiche e delle Scienze applicate ai Beni Culturali. Tale ricerca, regolata e normata secondo standard nazionali e internazionali, permette di ampliare l’esperienza scientifica e culturale. I materiali lapidei, la cui scelta d’impiego fu ed è tutt’oggi tutt’altro che casuale, rappresentano parte della storia e ne rappresentano il patrimonio tangibil

Updating the orbital ephemeris of the dipping source XB 1254-690 and the distance to the source

XB 1254-690 is a dipping low mass X-ray binary system hosting a neutron star and showing type I X-ray bursts. We aim at obtaining more accurate orbital ephemeris and at constraining the orbital period derivative of the system for the first time. In addition, we want to better constrain the distance to the source in order to locate the system in a well defined evolutive scenario. We apply for the first time an orbital timing technique to XB 1254-690, using the arrival times of the dips present in the light curves that have been collected during 26 years of X-ray pointed observations performed from different space missions. We estimate the dip arrival times using a statistical method that weights the count-rate inside the dip with respect to the level of the persistent emission outside the dip. We fit the obtained delays as a function of the orbital cycles both with a linear and a quadratic function. We infer the orbital ephemeris of XB 1254-690 improving the accuracy of the orbital period with respect to previous estimates. We infer a mass of M$_{2}=0.42\pm 0.04$ M$_{\odot}$ for the donor star, in agreement with the estimations already present in literature, assuming that the star is in thermal equilibrium while it transfers part of its mass via the inner Lagrangian point, and assuming a neutron star mass of 1.4 M$_{\odot}$. Using these assumptions, we also constrain the distance to the source, finding a value of 7.6$\pm 0.8$ kpc. Finally, we discuss the evolution of the system suggesting that it is compatible with a conservative mass transfer driven by magnetic braking.Comment: 13 pages, 5 figures, accepted for publication in Research in Astronomy and Astrophysics (RAA

Physics at the Linear Collider

The physics at the planned $e^+e^-$ colliders is discussed around three main topics corresponding to different manifestations of symmetry breaking: $W$ physics in the no Higgs scenario, studies of the properties of the Higgs and precision tests of SUSY. A comparison with the LHC is made for all these cases. The $\gamma \gamma$ mode of the linear collider will also be reviewed.Comment: 31 pages, 12 figures. Invited talk given at the Fifth Workshop on High Energy Physics Phenomenology, Inter-University Centre for Astronomy and Astrophysics, Pune, India, January 12 - 26, 199