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Ferruccio Feruglio

Publications and source records attributed to Ferruccio Feruglio.

88 records · Page 5Linked to original sources
arXiv2000

From Minimal to Realistic Supersymmetric SU(5) Grand Unification

We construct and discuss a "realistic" example of SUSY SU(5) GUT model, with an additional U(1) flavour symmetry, that is not plagued by the need of large fine tunings, like those associated with doublet-triplet splitting in the minimal model, and that leads to an acceptable phenomenology. This includes coupling unification with a value of alpha_s(m_Z) in much better agreement with the data than in the minimal version, an acceptable hierarchical pattern for fermion masses and mixing angles, also including neutrino masses and mixings, and a proton decay rate compatible with present limits (but the discovery of proton decay should be within reach of the next generation of experiments). In the neutrino sector the preferred solution is one with nearly maximal mixing both for atmospheric and solar neutrinos.

hep-ph↗
arXiv1999

Large Neutrino Mixing from Small Quark and Lepton Mixings

We discuss the special class of models where nearly maximal neutrino mixing is produced through the see-saw mechanism, starting from only nearly diagonal matrices for charged leptons, Dirac neutrinos and Majorana right-handed neutrinos.

hep-ph↗
arXiv1999

A Simple Grand Unification View of Neutrino Mixing and Fermion Mass Matrices

Assuming three light neutrinos and the see-saw mechanism we present a semiquantitative model of fermion masses based on (SUSY) SU(5) and abelian horizontal charges. A good description of the observed pattern of quark and lepton masses is obtained. For neutrinos we naturally obtain widely split masses and large atmospheric neutrino mixing as a consequence of SU(5)-related asymmetric mass matrices for d quarks and charged leptons.

hep-ph↗
arXiv1999

Signals of a superlight gravitino at e^+ e^- colliders when the other superparticles are heavy

If the gravitino G is very light and all the other supersymmetric particles are above threshold, supersymmetry may still be found at colliders, by looking at processes with only gravitinos and ordinary particles in the final state. We compute here the cross-section for the process e^+ e^- ==> G G gamma, whose final state can give rise to a distinctive photon plus missing energy signal at present and future e^+ e^- colliders. We describe how the present LEP data can be used to establish a lower bound on the gravitino mass of order 10^{-5} eV. We conclude with a critical discussion of our results, comparing them with related ones and outlining possible generalizations.

hep-ph↗
arXiv1999

Aspects of spontaneously broken N = 1 global supersymmetry in the presence of gauge interactions

We discuss models where N=1 global supersymmetry is spontaneously broken, at the classical level, in the presence of non-anomalous gauge interactions. We take such models as effective theories, valid up to some suitable scale and arising from supergravity models with a light gravitino, and therefore we allow them to contain non-renormalizable interactions. First, we examine the case where the goldstino is a gauge singlet. We elucidate the model-independent relations between supersymmetry-breaking masses and some associated interactions, with special attention to the behaviour of some four-particle scattering amplitudes in the high- and low-energy limits. The former gives constraints from tree-level unitarity, the latter affects the phenomenological lower bounds on the gravitino mass. In particular, we give new results for the annihilation of photons into gravitinos, and discuss their implications. We then examine the case with no neutral chiral superfields, so that the goldstino is charged, and the gauge symmetry is also broken. In this context, we discuss the singularity structure and the associated unitarity constraints, relating the scales of supersymmetry and gauge symmetry breaking. We conclude by commenting on possible realistic examples, where the broken gauge symmetry is associated with grand or electroweak unification.

hep-ph↗
arXiv1998

Models of Neutrino Masses from Oscillations with Maximal Mixing

We discuss models of neutrino masses that lead to a large mixing angle for atmospheric neutrino oscillations. In particular we study a mechanism where a simple texture for the Dirac matrix leads to the observed pattern of mixings for a continuous range of Majorana matrices in a reasonably natural way. Both nearly maximal and small mixing solutions for solar neutrinos are compatible with this model. Possible dynamical realizations are discussed and a detailed example in terms of horizontal U(1) charges is presented.

hep-ph↗
arXiv1998

Four-fermion interactions and sgoldstino masses in models with a superlight gravitino

We discuss the role of the effective interactions among four matter fermions in supersymmetric models with a very light gravitino. We show that, from a field-theoretical viewpoint, no model-independent bound on the gravitino mass can be derived from such interactions. Making use of a naturalness criterion, however, we are able to derive some interesting but not very stringent bounds, complementary to those obtained from the direct production of supersymmetric particles. We also show that, generically, masses for the spin-0 partners of the goldstino (sgoldstinos) of the order of the gravitino mass and much smaller than squark and slepton masses do not obey a naturalness criterion.

hep-ph↗
arXiv1998

Neutrino Mass Textures from Oscillations with Maximal Mixing

We study the implications of neutrino oscillations with maximal mixing for the neutrino Dirac and Majorana matrices in the see-saw mechanism for three non degenerate neutrino masses. We find the form of the Dirac matrix for a structure-less Majorana matrix and, conversely, the structure of the Majorana matrix if the Dirac matrix is according to our naive intuition. We give some examples of Majorana matrices that, in a 3 X 3 context, lead to maximal mixing without too much fine tuning and cross talk with the Dirac input.

hep-ph↗
arXiv1998

A smooth massless limit for supersymmetric QCD

We analyse in detail the behaviour of supersymmetric QCD with a number of flavours M smaller than the number of colours N, for quark masses smaller than the dynamically generated scale. In this regime, we find it useful to move from meson superfields to Nambu-Goldstone-like variables. In particular we work out the mass spectrum and the set of decay constants that specify the interactions of the low-energy theory. We explicitly check that masses and decay constants have a consistent behaviour under decoupling and that they satisfy current algebra requirements. Finally we speculate about the massless limit. For vanishing quark masses, and only in this case, the relation between mesons and Nambu-Goldstone variables becomes singular. When analysed in terms of the Nambu-Goldstone superfields, the massless limit exhibits a spontaneous breaking of the flavour symmetry, with massless Goldstone modes embedded in an M^2-dimensional complex moduli space. The symmetry-breaking order parameter is formally infinite, but this has the only effect of turning off the interactions between the chiral superfields.

hep-th↗
arXiv1997

Low-energy Gravitino Interactions

I discuss the low-energy limit of several processes involving only ordinary particles and gravitinos. Astrophysical and laboratory applications are briefly addressed.

hep-ph↗
arXiv1997

On the effective interactions of a light gravitino with matter fermions

If the gravitino is light and all the other supersymmetric particles are heavy, we can consider the effective theory describing the interactions of its goldstino components with ordinary matter. To discuss the model-dependence of these interactions, we take the simple case of spontaneously broken supersymmetry and only two chiral superfields, associated with the goldstino and a massless matter fermion. We derive the four-point effective coupling involving two matter fermions and two goldstinos, by explicit integration of the heavy spin-0 degrees of freedom in the low-energy limit. Surprisingly, our result is not equivalent to the usual non-linear realization of supersymmetry, where a pair of goldstinos couples to the energy-momentum tensor of the matter fields. We solve the puzzle by enlarging the non-linear realization to include a second independent invariant coupling, and we show that there are no other independent couplings of this type up to this order in the low-energy expansion. We conclude by commenting on the interpretation of our results and on their possible phenomenological implications.

hep-th↗
arXiv1996

Phenomenological implications of light stop and higgsinos

We examine the phenomenological implications of light $\tilde{t}_R$ and higgsinos in the Minimal Supersymmetric Standard Model, assuming $\tan^2 β< m_t / m_b$ and heavy $\tilde{t}_L$ and gauginos. In this simplified setting, we study the contributions to $Δm_{B_d}$, $ε_K$, $BR(b \rightarrow s γ)$, $R_b \equiv Γ(Z \rightarrow b \overline{b}) / Γ( Z \to {\rm hadrons})$, $BR(t \to b W)$, and their interplay.

hep-ph↗
arXiv1995

Higgs and super-Higgs effects with naturally vanishing vacuum energy

We construct $N=1$ supergravity models where the gauge symmetry and supersymmetry are both spontaneously broken, with naturally vanishing classical vacuum energy and unsuppressed Goldstino components along gauge non-singlet directions. We discuss some physically interesting situations where such a mechanism could play a role, and identify the breaking of a grand-unified gauge group as the most likely possibility. We show that, even when the gravitino mass is much smaller than the scale $m_X$ of gauge symmetry breaking, important features can be missed if we first naively integrate out the degrees of freedom of mass ${\cal O} (m_X)$, in the limit of unbroken supersymmetry, and then describe the super-Higgs effect in the resulting effective theory. We also comment on possible connections with extended supergravities and realistic four-dimensional string constructions.

hep-th↗
arXiv1994

The Physics of the Chiral Fermions

We review the aspects of chiral gauge theories related to the violation of the decoupling property. The case of the top quark is worked out in detail. The mechanism of anomaly cancellation in the low-energy effective theory is illustrated in a simple model.

hep-ph↗