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E. Gabrielli

Publications and source records attributed to E. Gabrielli.

At least 55 records · Page 3Linked to original sources
arXiv2000

Extended Gauge Theories in Euclidean Space with Higher Spin Fields

The extended Yang-Mills gauge theory in Euclidean space is a renormalizable (by power counting) gauge theory describing a local interacting theory of scalar, vector, and tensor gauge fields (with maximum spin 2). In this article we study the quantum aspects and various generalizations of this model in Euclidean space. In particular the quantization of the pure gauge model in a common class of covariant gauges is performed. We generalize the pure gauge sector by including matter fermions in the adjoint representation of the gauge group and analyze its N=1 and N=2 supersymmetric extensions. We show that the maximum half-integer spin contained in these fermion fields in dimension 4 is 3/2. Moreover we develop an extension of this theory so as to include internal gauge symmetries and the coupling to bosonic matter fields. The spontaneous symmetry breaking of the extended gauge symmetry is also analyzed.

hep-th↗
arXiv2000

Initial Scales, Supersymmetric Dark Matter and Variations of Neutralino-Nucleon Cross Sections

The neutralino-nucleon cross section in the context of the MSSM with universal soft supersymmetry-breaking terms is compared with the limits from dark matter detectors. Our analysis is focussed on the stability of the corresponding cross sections with respect to variations of the initial scale for the running of the soft terms, finding that the smaller the scale is, the larger the cross sections become. For example, by taking $10^{10-12}$ GeV rather than $M_{GUT}$, which is a more sensible choice, in particular in the context of some superstring models, we find extensive regions in the parameter space with cross sections in the range of $10^{-6}$--$10^{-5}$ pb, i.e. where current dark matter experiments are sensitive. For instance, this can be obtained for $\tanβ\gsim 3$.

hep-ph↗
arXiv2000

The $b\to sγ$ decay in SUSY models with non-universal A-terms

We analyse the predictions for the inclusive branching ratio for $b\to sγ$ decay in a class of string-inspired SUSY models with non-universal soft-breaking A-terms. These models are particularly interesting since the non-universality of the A-terms plays an important role in providing new significant contributions to CP violation effects in kaon physics while respecting the severe bounds on electric dipole moments. We show that $b\to sγ$ do not severely constrain the non-universality of these models. In particular, at low $\tanβ$ $(\tanβ\simeq 2)$, our predictions are close to the universal case. For large $\tanβ$ ($\tanβ\gsim 15$),the effect of non-universality is enhanced and stronger constraints hold. We find that the parameter regions which are important for generating sizeable contribution to $ε'/ε$, of order $2 \times 10^{-3}$, are not excluded.

hep-ph↗
arXiv2000

Model independent constraints on leptoquarks from MU and TAU lepton rare processes

We perform a model independent analysis so as to constrain the leptoquark (LQ) models from negative searches for $μ\to e γ$, $μ\to 3e$ decays (and analogous processes in the $τ$ sector), and coherent $μ-e$ conversion in nuclei. We considerably improve some constraints obtained by analyses known in the literature, analyses which we show have by far underestimated the LQ contributions to the $μ\to 3e$. In particular we find that the coherent $μ-e$ conversion in nuclei mediated by the photon--conversion mechanism and the $μ\to 3e$ decay are golden plates where the flavor changing leptoquark couplings, involving the second and third quark generations, can be strongly constrained. This is due to the fact that these processes get the enhancements by large $\log(m_q^2/m^2_{LQ})$ terms which are induced by the so-called ``photon-penguin'' diagrams. These enhancements, which produce a mild GIM suppression in the amplitudes, have not been taken into account in the previous analyses. We show that the $μ\to e γ$ decay can set weaker constraints on the LQ models and this is because its amplitude is strongly GIM suppressed by the terms of order $O(m_q^2/m^2_{LQ})$. We also present the results for the corresponding constraints in the $τ$ sector. Finally the prospects of the future muon experiments for the improvement of the present bounds are analyzed and discussed.

hep-ph↗
arXiv1999

Anomalous gamma-gamma-H and Z-gamma-H couplings in the process e,gamma->e,H

The bounds on the anomalous contributions to the ggh and zgh vertices that can be obtained via the process eg->eh are discussed through a model independent analysis based on SU(2) X U(1) invariant operators of dim=6. A light Higgs boson with m_H ~ 120 GeV and center-of-mass energies of \sqrt{S}=500 GeV and \sqrt{S}=1500 GeV are assumed. The process eg->eh is shown to provide an excellent way to strongly constraint both the CP-even and CP-odd anomalous contributions in the ggH and ZgH couplings.

hep-ph↗
arXiv1999

Looking for anomalous gamma-gamma-H and Z-gamma-H couplings at future linear collider

We consider the possibility of studying anomalous contributions to the gamma-gamma-H and Z-gamma-H vertices through the process e-gamma--> e-H at future e-gamma linear colliders, with Sqrt(S)=500-1500 GeV. We make a model independent analysis based on SU(2)xU(1) invariant effective operators of dim=6 added to the standard model lagrangian. We consider a light Higgs boson (mostly decaying in bar(b)-b pairs), and include all the relevant backgrounds. Initial e-beam polarization effects are also analyzed. We find that the process e-gamma--> e-H provides an excellent opportunity to strongly constrain both the CP-even and the CP-odd anomalous contributions to the gamma-gamma-H and Z-gamma-H vertices.

hep-ph↗
arXiv1999

Z-gamma-Higgs vertex effects in Higgs production at future e-gamma linear colliders

One-loop production of a Higgs boson in electro-photon collisions at future accelerators is studied via the process (e gamma -> e H), for intermediate Higgs masses. Exact cross sections, including the possibility of longitudinally polarized initial beams, are presented. Confirming previous estimates made in the Weizsäcker-Williams approximation, they are found to be more than two orders of magnitude larger than the cross sections for the crossed process (e e-> gamma H), in the energy range $\sqrt{s}=(0.5-2)$ TeV. We show that, not only (e gamma -> e H) has a similar potential as the (gamma gamma -> H) process for testing the one-loop gamma-gamma-H vertex, but, by requiring a final electron tagged at large angle in (e gamma -> e H), the (H e) production provides an excellent way of testing the Z-gamma-H vertex, too. Kinematical distributions for the (e gamma -> e H -> e bb) process with a tagged final electron are analyzed, and strategies for controlling the main irreducible background are found. Initial-state-radiation effects are checked to be within a few percent.

hep-ph↗
arXiv1999

N=1 Supersymmetric Yang-Mills on the lattice at strong coupling

We study N=1 supersymmetric SU(N) Yang-Mills theory on the lattice at strong coupling. Our method is based on the hopping parameter expansion in terms of random walks, resummed for any value of the Wilson parameter r in the small hopping parameter region. Results are given for the mesonic (2-gluino) and fermionic (3-gluino) propagators and spectrum.

hep-th↗
arXiv1999

Bounds on anomalous gamma-gamma-H and Z-gamma-H couplings at future e-gamma linear colliders

We study the bounds on the anomalous contributions to the gamma-gamma-H and Z-gamma-H vertices that can be obtained via the process e-gamma-->e H. We consider the representative case of an intermediate Higgs mass production of MH=120 GeV and for a center of mass energy of Sqrt{S}=500 GeV and Sqrt{S}=1500 GeV. We use a model independent analysis based on SU(2)xU(1) invariant operators of dimension 6 added to the Standard Model lagrangian. We find that this process provides an excelent way to put strong constraints both in the sector of CP-even and CP-odd anomalous couplings contribution to the gamma-gamma-H and Z-gamma-H vertices.

hep-ph↗
arXiv1999

N=1 Super-Yang-Mills on the Lattice: Weak and Strong Coupling Limits

We present a general review about the N=1 supersymmetric SU(Nc) Yang-Mills on the lattice focusing our attention on the quenched approximation in supersymmetry. Finally we analyse and discuss the recent results obtained at strong coupling and large Nc for the mesonic and fermionic propagators and spectrum.

hep-th↗
arXiv1998

Quenched Supersymmetry

We study the effects of quenching in Super-Yang-Mills theory. While supersymmetry is broken, the lagrangian acquires a new flavour U(1 | 1) symmetry. The anomaly structure thus differs from the unquenched case. We derive the corresponding low-energy effective lagrangian. As a consequence, we predict the mass splitting expected in numerical simulations for particles belonging to the lowest-lying supermultiplet. An estimate of the systematic error due to quenching follows.

hep-th↗
arXiv1998

Quenched Supersymmetry

We study the effects of quenching in Super-Yang-Mills theory. While supersymmetry is broken, the lagrangian acquires a new flavour $U(1 \mid 1)$ symmetry. The anomaly structure thus differs from the unquenched case. We derive the corresponding low-energy effective lagrangian. As a consequence, we predict the mass splitting expected in numerical simulations for particles belonging to the lowest-lying supermultiplet.

hep-lat↗
arXiv1997

$ZγH$ Vertex Effects at Future Colliders

We show that the Higgs production in $eγ$ collisions, through the one-loop reaction $eγ\to eH$ at large transverse momentum, can provide a precise determination of the $ZγH$ vertex. We concentrate on the analysis of signal rates vs background looking for strategies to improve the ratio $S/B$. Possible bounds on anomalous contributions to the $ZγH$ vertex are derived.

hep-ph↗
arXiv1997

Measuring Z-gamma-Higgs vertex effects at e-gamma linear colliders

The one-loop process e,gamma->e,h for intermediate Higgs masses is considered. Exact cross sections for unpolarized and longitudinally polarized beams are computed and found to be more than two orders of magnitude larger than the rates for the crossed process e,e->gamma,h, in the energy range \sqrt{s}=(0.5-2) TeV. We show that, apart from being competitive with the gamma,gamma->H process for testing the one-loop gamma-gamma-H vertex, by requiring a final electron tagged at large angle the channel e,gamma->e,h provides an excellent way of testing the Z-gamma-H vertex.

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

The Chromomagnetic Dipole Operator and the B Semileptonic Branching Ratio

We consider the possibility of having a large branching ratio for the decay $b\to s g$ coming from an enhanced Wilson coefficient of the chromomagnetic dipole operator. We show that values of $BR(b\to s g)$ up to $\sim 10\%$ or more are compatible with the constraints coming from the CLEO experimental results on $BR(B\to X_sγ)$ and $BR(B\to X_sϕ)$. Such large values can reconcile the predictions of both the semileptonic branching ratio and the charm counting with the present experimental results. We also discuss a supersymmetric model with gluino-mediated flavour violations, which can account for such large values of $BR(b\to s g)$.

hep-ph↗