We explore some fundamental differences in the phenomenology, cosmology and model building of Split Supersymmetry compared with traditional low-scale supersymmetry. We show how the mass spectrum of Split Supersymmetry naturally emerges from theories where the dominant source of supersymmetry breaking preserves an R symmetry, characterize the class of theories where the unavoidable R-breaking by gravity can be neglected, and point out a new possibility, where supersymmetry breaking is directly communicated at tree level to the visible sector via renormalizable interactions. Next, we discuss possible low-energy signals for Split Supersymmetry. The absence of new light scalars removes all the phenomenological difficulties of low-energy supersymmetry, associated with one-loop flavor and CP violating effects. However, the electric dipole moments of leptons and quarks do arise at two loops, and are automatically at the level of present limits with no need for small phases, making them accessible to several ongoing new-generation experiments. We also study proton decay in the context of Split Supersymmetry, and point out scenarios where the dimension-six induced decays may be observable. Finally, we show that the novel spectrum of Split Supersymmetry opens up new possibilities for the generation of dark matter, as the decays of ultraheavy gravitinos in the early universe typically increase the abundance of the lightest neutralino above its usual freeze-out value. This allows for lighter gauginos and Higgsinos, more accessible both to the LHC and to dark-matter detection experiments.

No abstract

The naturalness criterion applied to the cosmological constant implies a new-physics threshold at 10 −3 eV. Either the naturalness criterion fails, or this threshold does not influence particle dynamics at higher energies. It has been suggested that the Higgs naturalness problem may follow the same fate. We investigate this possibility and, abandoning the hierarchy problem, we use unification and dark matter as the only guiding principles. The model recently proposed by Arkani-Hamed and Dimopoulos emerges as a very interesting option. We study it in detail, analysing its structure, and the conditions for obtaining unification and dark matter. the anthropic principle [1], which could be operating in presence of a large number of metastable vacua, as in string theory [2].It is conceivable to ponder whether such an explanation could also apply to the hierarchy problem, imagining a mechanism (not necessarily based on the anthropic principle) which allows to extrapolate SM calculations to energies much larger than the TeV, without the need of introducing new dynamics, besides the Higgs.At first sight, this sounds like a devastating proposal. But, if we are willing to abandon the hierarchy problem, we can try to use other clues to drive the search for the theory beyond the SM. Gauge coupling unification could be one such clue: it is motivated by a theory that addresses questions related to the fundamental structure of the SM particle content.The failure of exact unification of gauge couplings in the SM suggests the existence of new particles, belonging to incomplete GUT irreps, which mend the mismatch. It is well known that low-energy supersymmetry provides precisely the necessary particles with the appropriate quantum numbers. Recently, Arkani-Hamed and Dimopoulos [3], setting aside the hierarchy problem, have noticed that gauge-coupling unification can be achieved in a supersymmetric model where all scalars, but one Higgs doublet, are much heavier than the electroweak scale. Most of the unpleasent aspects of supersymmetry (excessive flavour

We analyze the rare kaon decays K L → π 0 νν, K + → π + νν, K L → π 0 e + e − and K L → µ + µ − in conjunction with the CP violating ratio ε ′ /ε in a general class of supersymmetric models in which Z-and magnetic-penguin contributions can be substantially larger than in the Standard Model. We point out that radiative effects relate the double left-right mass insertion to the single left-left one, and that the phenomenological constraints on the latter reflect into a stringent bound on the supersymmetric contribution to the Z penguin. Using this bound, and those coming from recent data on ε ′ /ε, we find BR(, assuming the usual determination of the CKM parameters and neglecting the possibility of cancellations among different supersymmetric effects in ε ′ /ε. Larger values are possible, in principle, but rather unlikely. We stress the importance of a measurement of these three branching ratios, together with improved data and improved theory of ε ′ /ε, in order to shed light on the realization of various supersymmetric scenarios. We reemphasize that the most natural enhancement of ε ′ /ε, within supersymmetric models, comes from chromomagnetic penguins and show that in this case sizable enhancements of BR(K L → π 0 e + e − ) dir can also be expected.

A general operator expansion is presented for quark and lepton mass matrices in unified theories based on a U(2) flavor symmetry, with breaking parameter of order V cb ≈ m s /m b ≈ m c /m t . While solving the supersymmetric flavor-changing problem, a general form for the Yukawa couplings follows, leading to 9 relations among the fermion masses and mixings, 5 of which are precise. The combination of grand unified and U(2) symmetries provides a symmetry understanding for the anomalously small values of m u /m c and m c /m t . A fit to the fermion mass data leads to a prediction for the angles of the CKM unitarity triangle, which will allow a significant test of these unified U(2) theories. A particular SO(10) model provides a simple realization of the general operator expansion. The lighter generation masses and the non-trivial structure of the CKM matrix are generated from the exchange of a single U(2) doublet of heavy vector generations. This model suggests that CP is spontaneously broken at the unification scale -in which case there is a further reduction in the number of free parameters. * This work was supported in part by the

Texture zeros in the quark Yukawa matrices generally lead to precise and simple expressions for CKM matrix elements in terms of ratios of quark masses. Using the new data on b−decays we test a particularly promising texture zero solution and show that it is at best approximate. We analyse the approximate texture zero structure and show it is consistent with experiment. We investigate the implications for the CKM unitarity triangle, measurements at BaBar and BELLE as well as for the theories which invoke family symmetries.

The conclusions of the Physics Working Group of the International Scoping Study of a future Neutrino Factory and super-beam facility (the ISS) are presented. The ISS was carried out by the international community between NuFact05, (the 7th International Workshop on Neutrino Factories and Super-beams, Laboratori Nazionali di Frascati, Rome, 21-26 June 2005) and NuFact06 (Ivine, CA, 24-30 August 2006). The physics case for an extensive experimental programme to understand the properties of the neutrino is presented and the role of high-precision measurements of neutrino oscillations within this programme is discussed in detail. The performance of second-generation super-beam experiments, beta-beam facilities and the Neutrino Factory are evaluated and a quantitative comparison of the discovery potential of the three classes of facility is presented. High-precision studies of the properties of the muon are complementary to the study of neutrino oscillations. The Neutrino Factory has the potential to provide extremely intense muon beams and the physics potential of such beams is discussed in the final section of the report.

Assuming three-neutrino mixing, we study the capabilities of very long baseline neutrino oscillation experiments to verify and test the MSW effect and to measure the lepton mixing angle θ 13 . We suppose that intense neutrino and antineutrino beams will become available in so-called neutrino factories. We find that the most promising and statistically significant results can be obtained by studying ν e → ν µ andν e →ν µ oscillations which lead to matter enhancements and suppressions of wrong sign muon rates. We show the θ 13 ranges where matter effects could be observed as a function of the baseline. We discuss the scaling of rates, significances and sensitivities with the relevant mixing angles and experimental parameters. Our analysis includes fluxes, event rates and statistical aspects so that the conclusions should be useful for the planning of experimental setups. We discuss the subleading ∆m 2 21 effects in the case of the LMA MSW solution of the solar problem, showing that they are small for L 7000 km. For shorter baselines, ∆m 2 21 effects can be relevant and their dependence on L offers a further handle for the determination of the CP-violation phase δ. Finally we comment on the possibility to measure the specific distortion of the energy spectrum due to the MSW effect.