arXiv subjects

Fabio Zwirner

Publications and source records attributed to Fabio Zwirner.

At least 37 records · Page 2Linked to original sources

arXiv2007

Higgs Boson Properties in the Standard Model and its Supersymmetric Extensions

We review the realization of the Brout-Englert-Higgs mechanism in the electroweak theory and describe the experimental and theoretical constraints on the mass of the single Higgs boson expected in the minimal Standard Model. We also discuss the couplings of this Higgs boson and its possible decay modes as functions of its unknown mass. We then review the structure of the Higgs sector in the minimal supersymmetric extension of the Standard Model (MSSM), noting the importance of loop corrections to the masses of its five physical Higgs bosons. Finally, we discuss some non-minimal models.

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arXiv2006

D terms from D-branes, gauge invariance and moduli stabilization in flux compactifications

We elucidate the structure of D terms in N=1 orientifold compactifications with fluxes. As a case study, we consider a simple orbifold of the type-IIA theory with D6-branes at angles, O6-planes and general NSNS, RR and Scherk-Schwarz geometrical fluxes. We examine in detail the emergence of D terms, in their standard supergravity form, from an appropriate limit of the D-brane action. We derive the consistency conditions on gauged symmetries and general fluxes coming from brane-localized Bianchi identities, and their relation with the Freed-Witten anomaly. We extend our results to other N=1 compactifications and to non-geometrical fluxes. Finally, we discuss the possible role of U(1) D terms in the stabilization of the untwisted moduli from the closed string sector.

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arXiv2005

de-Sitter vacua via consistent D-terms

We introduce a new mechanism for producing locally stable de-Sitter or Minkowski vacua, with spontaneously broken N=1 supersymmetry and no massless scalars, applicable to superstring and M-theory compactifications with fluxes. We illustrate the mechanism with a simple N=1 supergravity model that provides parametric control on the sign and the size of the vacuum energy. The crucial ingredient is a gauged U(1) that involves both an axionic shift and an R-symmetry, and severely constrains the F- and D-term contributions to the potential.

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arXiv2005

N=1 effective potential from dual type-IIA D6/O6 orientifolds with general fluxes

We consider N=1 compactifications of the type-IIA theory on the T6/(Z2xZ2) orbifold and O6 orientifold, in the presence of D6-branes and general NSNS, RR and Scherk-Schwarz geometrical fluxes. Introducing a suitable dual formulation of the theory, we derive and solve the Bianchi identities, and show how certain combinations of fluxes can relax the constraints on D6-brane configurations coming from the cancellation of RR tadpoles. We then compute, via generalized dimensional reduction, the N=1, D=4 effective potential for the seven main moduli, and comment on the relation with truncated N=4 gaugings. As a byproduct, we obtain a general geometrical expression for the superpotential. We finally identify a family of fluxes, compatible with all Bianchi identities, that perturbatively stabilize all seven moduli in supersymmetric AdS4.

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arXiv2005

Superpotentials in IIA compactifications with general fluxes

We derive the effective N=1, D=4 supergravity for the seven main moduli of type IIA orientifolds with D6 branes, compactified on T^6/(Z_2xZ_2) in the presence of general fluxes. We illustrate and apply a general method that relates the N=1 effective Kahler potential and superpotential to a consistent truncation of gauged N=4 supergravity. We identify the correspondence between various admissible fluxes, N=4 gaugings and N=1 superpotential terms. We construct explicit examples with different features: in particular, new IIA no-scale models and a model which admits a supersymmetric AdS_4 vacuum with all seven main moduli stabilized.

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arXiv2005

Phenomenology of a leptonic goldstino and invisible Higgs boson decays

Non-linearly realized supersymmetry, combined with the Standard Model field content and SU(3)XSU(2)XU(1) gauge invariance, permits local dimension-six operators involving a goldstino, a lepton doublet and a Higgs doublet. These interactions preserve total lepton number if the left-handed goldstino transforms as an antilepton. We discuss the resulting phenomenology, in the simple limit where the new couplings involve only one lepton family, thus conserving also lepton flavour. Both the Z boson and the Higgs boson can decay into a neutrino and a goldstino: the present limits from the invisible Z width and from other observables leave room for the striking possibility of a Higgs boson decaying dominantly, or at least with a sizable branching ratio, via such an invisible mode. We finally comment on the perspectives at hadron and lepton colliders, and on possible extensions of our analysis.

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arXiv2004

The minimal N=4 no-scale model from generalized dimensional reduction

We consider the generalized dimensional reduction of pure ungauged N=4, D=5 supergravity, where supersymmetry is spontaneously broken to N=2 or N=0 with identically vanishing scalar potential. We explicitly construct the resulting gauged D=4 theory coupled to a single vector multiplet, which provides the minimal N=4 realization of a no-scale model. We discuss its relation with the standard classification of N=4 gaugings, extensions to non-compact twists and to higher dimensions, the N=2 theories obtained via consistent Z_2 orbifold projections and prospects for further generalizations.

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arXiv2004

Potentials and superpotentials in the effective N=1 supergravities from higher dimensions

We consider N=1 superpotentials corresponding to gaugings of an underlying extended supergravity for a chiral multiplet in the SU(1,1)/U(1) manifold of curvature 2/3. We analyze the resulting D=4 scalar potentials, and show that they can describe different N=1 phases of higher-dimensional supergravities, with broken or unbroken supersymmetry, flat or curved backgrounds, sliding or stabilized radius. As an application, we discuss the D=4 effective theory of the detuned supersymmetric Randall-Sundrum model in two different approximation schemes.

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arXiv2002

Equivalent effective Lagrangians for Scherk-Schwarz compactifications

We discuss the general form of the mass terms that can appear in the effective field theories of coordinate-dependent compactifications a la Scherk-Schwarz. As an illustrative example, we consider an interacting five-dimensional theory compactified on the orbifold S^1/Z_2, with a fermion subject to twisted periodicity conditions. We show how the same physics can be described by equivalent effective Lagrangians for periodic fields, related by field redefinitions and differing only in the form of the five-dimensional mass terms. In a suitable limit, these mass terms can be localized at the orbifold fixed points. We also show how to reconstruct the twist parameter from any given mass terms of the allowed form. Finally, after mentioning some possible generalizations of our results, we re-discuss the example of brane-induced supersymmetry breaking in five-dimensional Poincare' supergravity, and comment on its relation with gaugino condensation in M-theory.

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arXiv2002

On the O(alpha_t^2) two-loop corrections to the neutral Higgs boson masses in the MSSM

We compute the O(alpha_t^2) two-loop corrections to the neutral CP-even Higgs boson mass matrix in the Minimal Supersymmetric Standard Model, for arbitrary values of mA and of the parameters in the stop sector, in the effective potential approach. In a large region of parameter space these corrections are sizeable, increasing the prediction for mh by several GeV. We present explicit analytical formulae for a simplified case. We discuss the inclusion of momentum-dependent corrections and some possible ways of assigning the input parameters.

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arXiv2002

Brane-induced supersymmetry breaking

We study spontaneous supersymmetry breaking induced by brane-localized dynamics in five-dimensional supergravity compactified on S^1/Z_2. We consider a model with gravity in the bulk and matter localized on tensionless branes at the orbifold fixed points. We assume that the brane dynamics give rise to effective brane superpotentials that trigger the supersymmetry breaking. We analyze in detail the super-Higgs effect. We compute the full spectrum and show that the symmetry breaking is spontaneous but nonlocal in the fifth dimension. We demonstrate that the model can be interpreted as a new, non-trivial implementation of a coordinate-dependent Scherk-Schwarz compactification.

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arXiv2002

Generalized symmetry breaking on orbifolds

We reconsider the phenomenon of mass generation via coordinate-dependent compatifications of higher-dimensional theories on orbifolds. For definiteness, we study a generic five-dimensional (5D) theory compactified on S^1/Z_2. We show that the presence of fixed points, where the fields or their derivatives may be discontinuous, permits new realizations of the Scherk-Schwarz mechanism where, for example, the mass terms are localized at the orbifold fixed points. Our technique can be used to describe the explicit breaking of global flavor symmetries and supersymmetries by brane-localized mass terms. It can also be applied to the spontaneous breaking of local symmetries, such as gauge symmetries or supergravities.

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arXiv2001

The Higgs puzzle: experiment and theory

The present experimental and theoretical knowledge of the physics of electroweak symmetry breaking is reviewed. Data still favor a light Higgs boson, of a kind that can be comfortably accommodated in the Standard Model or in its Minimal Supersymmetric extension, but exhibit a non-trivial structure that leaves some open questions. The available experimental information may still be reconciled with the absence of a light Higgs boson, but the price to pay looks excessive. Recent theoretical ideas, linking the weak scale with the size of possible extra spatial dimensions, are briefly mentioned. It is stressed once more that experiments at high-energy colliders, such as the Tevatron and the LHC, are the crucial tool for eventually solving the Higgs puzzle.

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arXiv2001

On the neutral Higgs boson masses in the MSSM for arbitrary stop mixing

We compute the O(alpha_t alpha_s) two-loop corrections to the neutral Higgs boson masses in the Minimal Supersymmetric extension of the Standard Model. An appropriate use of the effective potential allows us to obtain simple analytical formulae, valid for arbitrary values of mA and of the mass parameters in the stop sector. We elucidate some subtleties of the effective potential calculation, and find full agreement with the numerical output of the existing diagrammatic calculation. We discuss in detail the limit of heavy gluino.

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arXiv2000

Signatures of massive sgoldstinos at e+e- colliders

In supersymmetric extensions of the Standard Model with a very light gravitino, the effective theory at the weak scale should contain not only the goldstino G, but also its supersymmetric partners, the sgoldstinos. In the simplest case, the goldstino is a gauge-singlet and its superpartners are two neutral spin-0 particles, S and P. We study possible signals of massive sgoldstinos at e+e- colliders, focusing on those that are most relevant at LEP energies. We show that the LEP constraints on e+e- => photon+S (photon+P), Z+S (Z+P) or e+e-S (e+e-P), followed by S (P) decaying into two gluon jets, can lead to stringent combined bounds on the gravitino and sgoldstino masses.

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arXiv2000

Signatures of massive sgoldstinos at hadron colliders

In supersymmetric extensions of the Standard Model with a very light gravitino, the effective theory at the weak scale should contain not only the goldstino, but also its supersymmetric partners, the sgoldstinos. In the simplest case, the goldstino is a gauge-singlet and its superpartners are two neutral spin-0 particles, S and P. We study possible signals of massive sgoldstinos at hadron colliders, focusing on those that are most relevant for the Tevatron. We show that inclusive production of sgoldstinos, followed by their decay into two photons, can lead to observable signals or to stringent combined bounds on the gravitino and sgoldstino masses. Sgoldstino decays into two gluon jets may provide a useful complementary signature.

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arXiv1999

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.

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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.

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