One-loop Kahler potential in non-renormalizable theories

We consider a general d=4 N=1 globally supersymmetric lagrangian involving chiral and vector superfields, with arbitrary superpotential, Kahler potential and gauge kinetic function. We compute perturbative quantum corrections by employing a component field approach that respects supersymmetry and background gauge invariance. In particular, we obtain the full one-loop correction to the Kahler potential in supersymmetric Landau gauge. Two derivations of this result are described. The non-renormalization of the superpotential and the quadratic correction to the Fayet-Iliopoulos terms are further checks of our computations.Comment: 17 pages, LaTe

The supersymmetric Higgs boson with flavoured A-terms

We consider a supersymmetric scenario with large flavour violating A-terms in the stop/scharm sector and study their impact on the Higgs mass, the electroweak rho parameter and the effective Higgs couplings to gluons, photons and charm quarks. For each observable we present explicit analytical expressions which exhibit the relevant parametric dependences, both in the general case and in specific limits. We find significant effects and comment on phenomenological implications for the LHC and future colliders.Comment: 21 pages, 6 figures; v2: minor changes, references added (journal version

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.Comment: 9 A4 pages, 1 figure, LATEX, uses axodraw.sty. Version to be published in Phys. Lett. B: an important spin-off on sgoldstino masses adde

Lepton Flavour Violating Decays of Supersymmetric Higgs Bosons

We compute the lepton flavour violating couplings of Higgs bosons in the Minimal Supersymmetric Standard Model, and show that they can induce the decays (h,H,A) --> mu tau at non-negligible rates, for large tan(beta) and sizeable smuon-stau mixing. We also discuss the prospects for detecting such decays at LHC and other colliders, as well as the correlation with other flavour violating processes, such as tau --> mu gamma and tau --> 3 mu.Comment: 13 LaTeX pages, 2 postscript figures, uses epsfig and axodra

On the muon anomalous magnetic moment in models with a superlight gravitino

We perform a general analysis of the contributions to the muon anomalous magnetic moment in models with a superlight gravitino. We discuss the interpretation and the phenomenological implications of the results. We find that present constraints on the model parameters are comparable and complementary to the ones coming from collider searches and from perturbative unitarity. However, the Brookhaven E821 experiment will probe large unexplored regions of parameter space.Comment: Now 19 A4 pages, 2 figures. Expanded version to be published in JHEP. A section of final comments and other minor comments adde

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.Comment: 12 pages, 1 figure, plain LaTeX. An important proof added in section 5. Final version to be published in JHE

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.Comment: 17 pages, 5 figures, plain Latex. Sign of an interference term corrected, physics unchange

Signals of a superlight gravitino at hadron 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-sections for some distinctive signals at hadron colliders: photon plus missing energy, induced by (q antiquark -> G G photon), and jet plus missing energy, induced by (q antiquark -> G G g), (q g -> G G q), and (g g -> G G g). From the present Tevatron data, we estimate the bound m_{3/2} > 2.3 10^-5 eV on the gravitino mass, corresponding to the bound sqrt{F} > 310 GeV on the supersymmetry-breaking scale. We foresee that the upgraded Tevatron and the LHC will be sensitive to values of m_{3/2} up to 4.0 10^-5 eV and 6.2 10^-4 eV, corresponding to sqrt{F} up to 410 GeV and 1.6 TeV, respectively.Comment: 19 pages, Latex, epsfig, 13 figures This revised version supersedes that published in Nucl. Phys. B526 (1998) 136, and contains important changes. The correction of a sign error modifies the relevant partonic cross-sections. The sensitivity to the supersymmetry-breaking scale (gravitino mass) is only slightly weakene