Fermion masses and symmetry breaking of a U(2) flavour symmetry

We show how a specific sequential breaking pattern of a U(2) flavour symmetry occurs automatically in a broad framework. The relative orientation in U(2) space of the spurion fields that breaks the U(2) symmetry is uniquely fixed, thus determining the form of the fermion mass matrices in a predictive way.Comment: 9 pages, uses amsmath.st

B-decay anomalies in Pati-Salam SU(4)

Attempts to incorporate in a coherent picture the $B$-decay anomalies presumably observed in $b\rightarrow c$ and $b\rightarrow s$ semi-leptonic decays have to face the absence of signals in other related experiments, both at low and at high energies. By extending and making more precise the content of Ref. [1], we describe one such attempt based on the Pati-Salam SU(4) group, that unifies colour and the $B$-$L$ charge, in the context of a new strongly interacting sector, equally responsible for producing a pseudo-Goldstone Higgs boson.Comment: 24 pages, 3 figure

Self-consistent Green's functions formalism with three-body interactions

We extend the self-consistent Green's functions formalism to take into account three-body interactions. We analyze the perturbative expansion in terms of Feynman diagrams and define effective one- and two-body interactions, which allows for a substantial reduction of the number of diagrams. The procedure can be taken as a generalization of the normal ordering of the Hamiltonian to fully correlated density matrices. We give examples up to third order in perturbation theory. To define nonperturbative approximations, we extend the equation of motion method in the presence of three-body interactions. We propose schemes that can provide nonperturbative resummation of three-body interactions. We also discuss two different extensions of the Koltun sum rule to compute the ground state of a many-body system.Comment: 26 pages, 19 figure

One or more Higgs bosons?

Now that one has been found, the search for signs of more scalars is a primary task of current and future experiments. In the motivated hypothesis that the extra Higgs bosons of the next-to-minimal supersymmetric Standard Model (NMSSM) be the lightest new particles around, we outline a possible overall strategy to search for signs of the CP-even states. This work complements Ref. arXiv:1304.3670.Comment: 14 pages, 7 figures. v2: references added, published in PR

Neutrino mixings from a U(2) flavour symmetry

We extend a previously developed description of the flavour parameters in the charged fermion sector, based on a U(2) flavour symmetry, to include two main features of the neutrino sector seemingly implied by recent data: a large mixing angle $\theta_{\mu \tau}$ and a large hierarchy in the neutrino squared mass differences. A unified description of quark and lepton masses and mixings emerges. The neatest quantitative predictions are for elements of the unitary mixing matrix in the lepton sector: |V_{\mu 1}| = |V_{e 3} / V_{\mu 3}| = |V_{e 2} / V_{\tau 3}| = \sqrt{m_e / m_\mu}, which go together with the analogous relations in the quark sector: |V_{ub} / V_{cb}| = \sqrt{m_u / m_c}, |V_{td} / V_{ts}| = \sqrt{m_d / m_s}Comment: 11 pages, uses amsmat

Membership in Citizen Groups

We address the coordination problem of individuals deciding to join an association that provides a public good and selective benefits to its members, when ability of the association to fulfill its purposes depends on membership size. In a global game formulation, we show that a unique equilibrium with non-trivial membership exists, and we perform meaningful comparative statics. A unique equilibrium also obtains when agents are heterogeneous, and we show that heterogeneity decreases membership size. In a two-period setting, where seniority of membership entails additional benefits, we provide conditions for uniqueness of equilibrium, and show that the presence of seniority benefits increases membership in both periods

Two-loop QCD corrections to charged-Higgs-mediated b→sγb\to s\gamma decay

The charged-Higgs-mediated contribution to the Wilson coefficient of the $b\to s\gamma$ magnetic penguin is expected to be one of the more promising candidates for a supersymmetric effect in B physics, probably the only one in gauge-mediated models. We compute the two-loop QCD correction to it. With naive dimensional regularization and MSbar subtraction, for reasonable values of the charged Higgs mass and for mu-bar = m_top, we find a (10--20)% reduction of the corresponding one-loop effect.Comment: 10 pages, 2 figures. Misprints corrected. Comparison with hep-ph/9710335 adde