arXiv subjects

A. Masiero

Publications and source records attributed to A. Masiero.

67 records · Page 4Linked to original sources

arXiv1997

SUSY in Rare and CP-Violating B Decays

In this talk we discuss rare B decays (b -> s gamma, b -> s g, b -> s l^+ l^-), B-\bar{B} oscillations and CP violation in B physics in the context of low-energy SUSY. We outline the variety of predictions that arise according to the choice of the SUSY extension ranging from what we call the "minimal" version of the MSSM to models without flavour universality or with broken R-parity. In particular, we provide a model-independent parameterization of the SUSY FCNC and CP-violating effects which is useful in tackling the problem in generic low-energy SUSY. We show how rare B decays and CP violation in B-decay amplitudes may be complementary to direct SUSY searches at colliders, in particular for what concerns extensions of the most restrictive version of the MSSM.

hep-ph↗

arXiv1997

CP Violating B Decays in the Standard Model and Supersymmetry

We study the uncertainties of the Standard Model (SM) predictions for CP violating B decays and investigate where and how supersymmetric (SUSY) contributions may be disentangled. The first task is accomplished by letting the relevant matrix elements of the effective Hamiltonian vary within certain ranges. The SUSY analysis makes use of a formalism which allows to obtain model-independent results. We show that in some cases it is possible a) to measure the CP B-\bar{B} mixing phase and b) to discriminate the SM and SUSY contributions to the CP decay phases. The golden-plated decays to this purpose are the B \to ϕK_S and B \to K_S π^0 channels.

hep-ph↗

arXiv1996

The Beauty of SUSY

B physics represents a privileged place to look for supersymmetry (SUSY) through its virtual effects. Here we discuss rare B decays ($b \to s γ$, $b \to s g$, $b \to s l^{+} l^{-}$) and $B-\bar{B}$ oscillations in the context of low-energy SUSY. We outline the variety of predictions that arise according to the choice of the SUSY extension ranging from what we call the ``minimal" version of the MSSM to models without flavour universality or with broken R-parity. In particular, we provide a model-independent parameterization of the SUSY FCNC effects which is useful in tackling the problem in generic low-energy SUSY. We show how rare B physics may be complementary to direct SUSY searches at colliders, in particular for what concerns extensions of the most restrictive version of the MSSM.

hep-ph↗

arXiv1996

Fermion Virtual Effects in $e^+ e^- -> W^+ W^-$ Cross Section

We analyse the contribution of new heavy virtual fermions to the $e^+e^- \rightarrow W^+W^-$ cross section. We find that there exists a relevant interplay between trilinear and bilinear oblique corrections. The result strongly depends on the chiral or vector--like nature of the new fermions. As for the chiral case we consider sequential fermions: one obtains substantial deviation from the Standard model prediction, making the effect possibly detectable at $\sqrt{s}=500$ or $1000$ GeV linear colliders. As an example for the vector--like case we take a SUSY extension with heavy charginos and neutralinos: due to cancellation, the final effect turns out to be negligible.

hep-ph↗

arXiv1996

A complete analysis of FCNC and CP constraints in general SUSY extensions of the standard model

We analyze the full set of constraints on gluino- and photino-mediated SUSY contributions to FCNC and CP violating phenomena. We use the mass insertion method, hence providing a model-independent parameterization which can be readily applied in testing extensions of the MSSM. In addition to clarifying controversial points in the literature, we provide a more exhaustive analysis of the CP constraints, in particular concerning $\varepsilon^\prime/\varepsilon$. As physically meaningful applications of our analysis, we study the implications in SUSY-GUT's and effective supergravities with flavour non-universality. This allows us to detail the domain of applicability and the correct procedure of implementation of the FC mass insertion approach.

hep-ph↗

arXiv1996

Searches For New Physics

Review of prospects for discovery of new physics signals at LEP2. The areas covered include SUSY, exotic fermions, BESS models, leptoquarks, virtual effects and CP violating observables.

hep-ph↗

arXiv1995

Constraints on supersymmetry from FCNC and CP violation

We consider FCNC and CP violating processes mediated by gluino exchange in generalized supersymmetric theories. We present the constraints on flavour (F) changing squark mass terms at the electroweak energy scale, focusing our analysis on $ΔF = 2$ transitions. Results are also given for $ΔF = 1$ CP conserving processes both in the hadronic and leptonic sectors, while we limit ourselves to some remarks on the relevance of box diagrams in the evaluation of $ε^{\prime}/ε$.

hep-ph↗

arXiv1995

Flavour changing neutral currents and CP violating processes in generalized supersymmetric theories

We consider supersymmetric extensions of the standard model with general non-universal soft breaking terms. We analyse in a model-independent way the constraints on these terms at the electroweak energy scale coming from gluino mediated flavour (F) changing neutral current and CP-violating processes. We have computed the complete $ΔF=1$ and $ΔF=2$ effective hamiltonian for gluino mediated processes, including for the first time the effect of box diagrams in the evaluation of $ε^{\prime}/ε$. We present numerical results for the constraints on these non-universal soft breaking terms for different values of the parameters, extending the analysis also to the leptonic sector. A comparison with previous results in the literature is given.

hep-ph↗

arXiv1995

Bounds on Heavy Chiral Fermions

We derive the low-energy electroweak effective lagrangian for the case of additional heavy, unmixed, sequential fermions. Present data still allow for the presence of a new quark and/or lepton doublet with masses greater than $M_Z/2$, provided that these multiplets are sufficiently degenerate. Deviations of the effective lagrangian predictions from a full one-loop computation are sizeable only for fermion masses close to the threshold $M_Z/2$. Some of the constraints on new sequential fermions coming from accelerator results and cosmological considerations are presented. We point out that the new fermions can significantly affect the production and decay rate into $γγ$ of the intermediate Higgs at LHC.

hep-ph↗

arXiv1995

Mixed Dark Matter and the Fate of Baryon and Lepton Symmetries

The available data on large scale structures seem to favour models with mixed dark matter (MDM), i.e. with a hot and cold component in a rather well--defined amount, or with some form of ``warm" dark matter. I discuss some prospects for these new scenarios for DM in the context of supersymmetric extensions of the electroweak standard model. In particular, I emphasize the intriguing link which exists between the present prospects of solution of the DM puzzle and the explicit or spontaneous breaking of baryon and/or lepton number symmetries. Some consequences on the issue of baryogenesis are worked out.

hep-ph↗

arXiv1993

Bardeen-Anomaly and Wess-Zumino Term in the Supersymmetric Standard Model

We construct the Bardeen anomaly and its related Wess-Zumino term in the supersymmetric standard model. In particular we show that it can be written in terms of a composite linear superfield related to supersymmetrized Chern-Simons forms, in very much the same way as the Green-Schwarz term in four-dimensional string theory. Some physical applications, such as the contribution to the g-2 of gauginos when a heavy top is integrated out, are briefly discussed.

hep-th↗

arXiv1993

Spontaneous Breaking of R parity in the Minimal Supersymmetric Standard Model Revisited

We reconsider the possibility of spontaneous breaking of $R$ parity in the Minimal Supersymmetric Standard Model. By a renormalization group analysis we find the parameter space in which a sneutrino gets a vacuum expectation value, leading to the spontaneous breaking of the lepton number and to the appearance of a phenomenologically unacceptable massless Goldstone boson. We then analyze the effect of operators giving rise to a tiny amount of explicit violation of lepton number, which could emerge as remnants of physics at some superheavy (Planck or GUT) scale in the low energy effective theory. We show that the conspiracy between the spontaneous and the explicit breaking scales can provide a mass to the Goldstone boson larger than the ${\rm Z}^0$ boson mass, hence allowing for a non vanishing sneutrino vacuum expectation value without increasing the invisible width of the ${\rm Z}^0$.

hep-ph↗

arXiv1992

The Supersymmetric Singlet Majoron

We study the supersymmetrized version of the singlet majoron model and, performing an analysis of the renormalization group equation improved potential, we find that a spontaneous breaking of $R$-parity can be achieved for a wide range of the parameters. Studying the finite temperature effective potential, we show that the phase transition leading to $R$-parity breaking can be of the first order and can occur at temperatures below the weak scale, thus avoiding any constraint coming from the requirement of the preservation of the baryon asymmetry in the early Universe.

hep-ph↗