Alex Pomarol

Bulk fields and supersymmetry in a slice of AdS

Five-dimensional models where the bulk is a slice of AdS have the virtue of solving the hierarchy problem. The electroweak scale is generated by a “warp” factor of the induced metric on the brane where the standard model fields live. However, it is not necessary to confine the standard model fields on the brane and we analyze the possibility of having the fields actually living in the slice of AdS. Specifically, we study the behaviour of fermions, gauge bosons and scalars in this geometry and their implications on electroweak physics. These scenarios can provide an explanation of the fermion mass hierarchy by warp factors. We also consider the case of supersymmetry in the bulk, and analyze the conditions on the mass spectrum. Finally, a model is proposed where the warp factor generates a small (TeV) supersymmetry-breaking scale, with the gauge interactions mediating the breaking to the scalar sector.

A custodial symmetry for Zbb

We show that a subgroup of the custodial symmetry O(3) that protects �ρ from radiative corrections can also protect the Zbcoupling. This allows one to build models of electroweak symmetry breaking, such as Higgsless, Little Higgs or 5D composite Higgs models, that are safe from corrections to Z → bb. We show that when this symmetry protects Zbit cannot simultaneously protect Ztand W t ¯. Therefore one can expect to measure sizable deviations from the SM predictions of these couplings at future collider experiments. We also show under what circumstances ZbRR can receive corrections in the right direction to explain the anomaly in the LEP/SLD forward-backward asymmetry A b B.

Gauge bosons in a five-dimensional theory with localized gravity

Abstract We consider the possibility of gauge bosons living in the recently proposed five-dimensional theory with localized gravity. We study the mass spectrum of the Kaluza-Klein (KK) excitations of the gauge fields and calculate their couplings to the boundaries of the fifth dimension. We find a different behaviour from the case of the graviton. In particular, we find that the massless mode is not localized in the extra dimension and that the KK excitations have sizeable couplings to the two boundaries. We also discuss possible phenomenological implications for the case of the standard model gauge bosons.

What is the γγ resonance at 750 GeV

A bstractRun 2 LHC data show hints of a new resonance in the diphoton distribution at an invariant mass of 750 GeV. We analyse the data in terms of a new boson, extracting information on its properties and exploring theoretical interpretations. Scenarios covered include a narrow resonance and, as preliminary indications suggest, a wider resonance. If the width indications persist, the new particle is likely to belong to a strongly-interacting sector. We also show how compatibility between Run 1 and Run 2 data is improved by postulating the existence of an additional heavy particle, whose decays are possibly related to dark matter.

Horizontal symmetries for the supersymmetric flavor problem

The heaviness of the third family fermions and the experimental absence of large flavor-violating processes suggest, in supersymmetric theories, that the three families belong to a 2 + 1 representation of a horizontal symmetry GH. In this framework, we discuss a class of models, based on the group U(2), that describe the flavor structure of the fermion masses and are compatible with an underlying GUT. We study the phenomenology of these models and focus on two interesting scenarios: In the first one, the first and second family scalars are assumed to be heavier than the weak scale, allowing for complex soft supersymmetry-breaking terms. In the second one, all the CP-violating phases are assumed to be small. Both scenarios present a rich phenomenology in agreement with constraints from flavor-violating processes and electric dipole moments.

Supersymmetry and Electroweak breaking from extra dimensions at the TeV-scale ∗

We analyze some features of the role that extra dimensions, of radius R in the TeV 1 range, can play in the soft breaking of supersymmetry and the spontaneous breaking of electroweak symmetry. We use a minimal model where the gauge and Higgs sector of the MSSM are living in the bulk of five dimensions and the chiral multiplets in a four-dimensional boundary. Supersymmetry is broken in the bulk by the Scherk-Schwarz mechanism and transmitted to the boundary by radiative corrections. The particle spectrum is completely predicted as a function of a unique R-charge. The massless sector corresponds to the pure Standard Model and elec- troweak symmetry is radiatively broken with a light Higgs weighing < 110 GeV. The µ-problem is solved and Higgsinos, gauginos and heavy Higgses acquire masses ∼ 1/R. Chiral sfermions acquire radiative squared-masses ∼ �i/R 2 . The effective potential is explicitly computed in the bulk of extra dimensions and some cosmolog- ical consequences can be immediately drawn from it. Gauge coupling running and unification is studied in the presence of Scherk-Schwarz supersymmetry breaking. The unification is similar to that in the supersymmetric theory.

Soft masses in theories with supersymmetry breaking by TeV compactification

Abstract We study the sparticle spectroscopy and electroweak breaking of theories where supersymmetry is broken by compactification (Scherk-Schwarz mechanism) at a TeV The evolution of the soft terms above the compactification scale and the resulting sparticle spectrum are very different from those of the usual MSSM and gauge-mediated theories. This is traced to the softness of the Scherk-Schwarz mechanism which leads to scalar sparticle masses that are only logarithmically sensitive to the cutoff starting at two loops. As a result, the mass-squareds of the squarks and sleptons are a loop factor smaller than those of the gauginos. In addition, the mechanism is very predictive and the sparticle spectrum depends on just two new parameters. A significant advantage of this mechanism relative to gauge mediation is that a Higgsino mass μ ≈ Msusy is automatically generated when supersymmetry is broken. Our analysis applies equally well to theories where the cutoff is near a TeV or M Pl or some intermediate scale. We also use these observations to show how we may obtain compactification radii which are hierarchically larger than the fundamental cutoff scale.

THE MU -PROBLEM IN THEORIES WITH GAUGE-MEDIATED SUPERSYMMETRY BREAKING

We point out that the µ-problem in theories in which supersymmetry breaking is communicated to the observable sector by gauge interactions is more severe than the one encountered in the conventional gravity-mediated scenarios. The difficulty is that once µ is generated by a one-loop diagram, then usually Bµ is also generated at the same loop order. This leads to the problematic relation Bµ ∼ µ�, where � ∼ 10–100 TeV is the effective supersymmetry-breaking scale. We present a class of theories for which this problem is naturally solved. Here, without any fine tuning among parameters, µ is generated at one loop, while Bµ arises only at the two-loop level. This mechanism can naturally lead to an interpretation of the Higgs doublets as pseudo-Goldstone bosons of an approximate global symmetry.

Sparticle masses from the superconformal anomaly

We discuss a recently proposed scenario where the sparticle masses are purely mediated by gravity through the superconformal anomaly. This scenario elegantly evades the supersymmetric flavor problem since soft masses, like the anomaly, are not directly sensitive to ultraviolet physics. However, its minimal incarnation fails by predicting tachyonic sleptons. We study the conditions for decoupling of heavy threshold effects and how these conditions are evaded. We use these results to build a realistic class of models where the non-decoupling effects of ultra-heavy vectorlike matter fields eliminate the tachyons. These models have a flavor invariant superspectrum similar to that of gauge mediated models. They, however, differ in several aspects: the gaugino masses are not unified, the colored sparticles are not much heavier than the others, the mu problem is less severe and the gravitino mass is well above the weak scale, m(3/2) greater than or similar to 10 TeV. We also show that in models where an R-symmetry can be gauged, the associated D-term gives rise to soft terms that are similarly insensitive to the ultraviolet.

Anomalous U(1) as a mediator of Supersymmetry Breaking

We point out that an anomalous gauge U(1) symmetry is a natural candidate for being the mediator and messenger of supersymmetry breaking. It facilitates dynamical supersymmetry breaking even in the flat limit. Soft masses are induced by both gravity and the U(1) gauge interactions giving an unusual mass hierarchy in the sparticle spectrum which suppresses flavor violations. This scenario does not suffer from the Polonyi problem. {copyright} {ital 1996 The American Physical Society.}