arXiv subjects
Publications and source records attributed to Nir Polonsky.
A fairly non-technical introduction to and survey of supersymmetry phenomenology with pedagogical emphasis, including exercises. Suitable for both theorists and experimentalists. The manuscript appeared as a Springer-Verlag monograph in physics. The body of the manuscript is provided here with the publisher`s permission.
While supersymmetric extensions of the Standard Model can be fully described in terms of explicitly broken global supersymmetry, this description is only effective. Once related to spontaneous breaking in a more fundamental theory, the effective parameters translate to functions of two distinct scales, the scale of spontaneous supersymmetry breaking and the scale of its mediation to the standard-model fields. The scale dependence will be written explicitly and the full spectrum of supersymmetry breaking operators which emerges will be explored. It will be shown that, contrary to common lore, scale-dependent operators can play an important role in determining the phenomenology. For example, theories with low-energy supersymmetry breaking, such as gauge mediation, may correspond to a scalar potential which is quite different than in theories with high-energy supersymmetry breaking, such as gravity mediation. As a concrete example, the Higgs mass prediction will be discussed in some detail and its upper bound will be shown to be sensitive to the supersymmetry breaking scale.
In supersymmetry, the Higgs quartic couplings is given by the sum in quadrature of the weak gauge couplings. This leads to the prediction of a light Higgs boson, which still holds when considering loop corrections from soft supersymmetry breaking. However, another source of corrections, which explicitly depends on the scale of the mediation of supersymmetrey breaking, is from generic hard breaking terms. We show that these corrections can significantly modify the Higgs mass prediction in models of low-energy supersymmetry breaking, for example, gauge mediation. Conversely, the Higgs mass measurement can be used to constrain the scale of mediation of supersymmetry breaking.
Given its non-renormalization properties, low-energy supersymmetry provides an attractive framework for extending the Standard Model and for resolving the hierarchy problem. Models with softly broken N =1 supersymmetry were extensively studied and are phenomenologically successful. However, it could be that an extended N = 2 supersymmetry survives to low energies, as suggested by various constructions. We examine the phenomenological viability and implications of such a scenario. We show that consistent chiral fermion mass generation emerges in N=2 theories, which are vectorial, as a result of supersymmetry breaking at low energies. A rich mirror quark and lepton spectrum near the weak scale with model-dependent decay modes is predicted. A Z_{2} mirror parity is shown to play an important role in determining the phenomenology of the models. It leads, if conserved, to a new stable particle, the LMP. Consistency of the N=2 framework and its unique spectrum with electroweak precision data is considered, and the discovery potential in the next generation of hadron collider experiments is stressed. Mirror quark pair production provides the most promising discovery channel. Higgs searches are also discussed and it is shown that there is no upper bound on the prediction for the Higgs boson mass in the framework of low-energy supersymmetry breaking, in general, and in the N=2 framework, in particular. Possible N = 2 realizations of flavor symmetries and of neutrino masses are also discussed.
It is shown that the radiation of a charged Higgs boson off a third-generation quark (charged-Higgs-strahlung) provides an important channel for the discovery of the charged Higgs at hadron colliders. Equivalently, in supersymmetric models with explicit lepton-number (R-parity) violation, sleptons may also be produced in association with quarks (slepton-strahlung). Higgs- and slepton-strahlung production cross sections are given for both the Tevatron and the LHC. The LHC cross sections imply that heavy ${\cal{O}}$(TeV) charged Higgs bosons can be produced via charged-Higgs-strahlung and that strahlung production of charged sleptons is possible even for small R-parity violating couplings. The possible discovery of sleptons through this channel offers a surprising handle on models of neutrino masses.
The possibility of radiatively generated fermion masses arising from chiral flavor violation in soft supersymmetry-breaking terms is explored. Vacuum stability constraints are considered in various classes of models, and allow in principle all of the first- and second-generation quarks and leptons and the $b$-quark to obtain masses radiatively. Radiatively induced Higgs-fermion couplings have non-trivial momentum-dependent form factors, which at low momentum are enhanced with respect to the case of tree-level Yukawa couplings. These form factors may be probed by various sum rules and relations among Higgs boson decay widths and branching ratios to fermion final states. An apparent, large, hard violation of supersymmetry also results for Higgsino couplings. Mixing between left- and right-handed scalar superpartners is enhanced. A radiative muon mass is shown to lead to a relatively large and potentially measurable contribution to the muon anomalous magnetic moment. If the light-quark masses arise radiatively, the neutron electric dipole moment is suppressed by a natural phase alignment between the masses and dipole moment, and is below the current experimental bound. The possibility of neutrino masses arising from softly broken lepton number, and concomitant enhanced sneutrino-antisneutrino oscillations, is briefly discussed.
The Higgsino mass, or equivalently the $μ$-parameter, plays an essential role in determining the phenomenology of any supersymmetric model. Particularly, the size of the supersymmetry conserving mu-parameter must be correlated with the size of the soft supersymmetry breaking parameters. The source of this correlation in the underlying ultra-violet theory is one of the mysteries of supersymmetry model building. The puzzle and the various possibilities for its resolution are reviewed, stressing both phenomenological and theoretical aspects. New proposals in the context of supergravity and gauge-mediation frameworks for the soft supersymmetry breaking parameters are examined in some detail.
In supersymmetric models, the well-known tension between naturalness and experimental constraints is relieved if the squarks and sleptons of the first two generations are superheavy, with masses of order 10 TeV, and all other superpartners are light, with masses of order 1 TeV. We show that even if all scalar masses and trilinear A parameters are of order 10 TeV at some high scale, a mass-squared hierarchy of order 400 may be generated dynamically through renormalization group evolution. The required high energy relations are consistent with grand unification, or, alternatively, may be realized in moduli-dominated supersymmetry-breaking scenarios.
In the gauge-mediation framework the soft supersymmetry breaking mass parameters of the supersymmetric standard model are induced by the gauge interactions of some messenger fields. The parameters exhibit flavor universality which is dictated by the gauge interactions and which efficiently eliminates new dangerous contributions to flavor changing neutral currents. However, the Higgs potential in this framework typically contains an unacceptable hierarchy between its dimensionful parameters (the $μ$-problem of gauge mediation). We show that the problem can be resolved if the Higgs potential arises dynamically once an intermediate U(1)' sector is integrated out rather than arising radiatively from some Yukawa interactions at the messenger scale. As an added benefit, such models may naturally avoid new contribution to CP violating amplitudes. The proposed framework is described, explicit examples are given and its phenomenology is explored. The $μ$ problem is resolved in this case by the low-energy U(1)' dynamics which could be tested in future collider experiments.
The supersymmetric flavor, CP and Polonyi problems are hints that the fundamental scale of the soft supersymmetry breaking parameters may be above a TeV, in apparent conflict with naturalness. We consider the possibility that multi-TeV scalar masses are generated by Planck- or unification-scale physics, and find the conditions under which the masses of scalars with large Yukawa couplings are driven, radiatively and asymptotically, to the weak scale through renormalization group evolution. Light third generation scalars then satisfy naturalness, while first and second generation scalars remain heavy to satisfy experimental constraints. We find that this mechanism is beautifully realized in the context of grand unified theories. In particular, the existence of right-handed neutrinos plays an important role in allowing remarkably simple scenarios. For example, for SO(10) boundary conditions with the squared masses of Higgs scalars double those of sleptons and squarks, we find that the entire scalar mass scale may be increased to 4 TeV at the unification scale without sacrificing naturalness.
The supersymmetric flavor problem may be solved if the first and second generation scalars are heavy (with multi-TeV masses) and scalars with large Higgs couplings are light (with sub-TeV masses). We show that such an inverted spectrum may be generated radiatively; that is, from initial conditions where all scalar masses are multi-TeV at some high scale, those with large Higgs couplings may be driven asymptotically to the weak scale in the infra-red. The lightness of third generation scalars is therefore a direct consequence of the heaviness of third generation fermions, and fine-tuning is avoided even though the fundamental scale of the soft supersymmetry breaking parameters is multi-TeV. We investigate this possibility in the framework of the usual Yukawa quasi-fixed point solutions. The required high scale boundary conditions are found to be simple and highly predictive. This scenario also alleviates the supersymmetric CP and Polonyi problems.
The properties of singlet fields in supergravity background are discussed. Particularly, it is shown that the ${\cal{O}}(Λ^{2})$ contributions to their one-point function lead to novel derivations of effective scales such as the $μ$ parameter, a messenger scale, an intermediate symmetry-breaking scale, and the unification scale, in terms of the scale of spontaneous supersymmetry-breaking in a hidden sector.The singlet one-point function effectively serves as a messenger of supersymmetry breaking.
Radiatively generated fermion masses without tree level Yukawa couplings are re-analyzed within supersymmetric models. Special emphasis is given to the possible appearance of color and charge breaking vacua. Several scenarios in which the radiative mechanism can be accomodated for the first, second, and third generation fermion masses are presented. Some of these require a low scale of supersymmetry breaking.
It is demonstrated how the hierarchy between the gauge coupling unification scale of minimal supersymmetry and the Planck (or string) scale, which resembles in order of magnitude a loop factor, can actually be explained as such in supergravity-coupled supersymmetry. A gauge and global singlet field acquires a linear potential term due to its one-loop supergravity interactions and slides to the desired scale. The singlet field can then provide the seed for the breaking of the unified theory at the appropriate scale via its couplings to fields in the adjoint representation.
Within the context of supergravity-coupled supersymmetry, fields which are gauge and global singlets are usually considered anathema. Their vacuum expectation values are shifted by quadratically divergent tadpole diagrams which are cutoff at the Planck scale, destabilizing the classical potential and driving the singlet field to large values. We demonstrate a new and generic mechanism which stabilizes the singlet in the presence of an extended gauge symmetry. Such a symmetry will be broken down to the Standard Model by the supergravity interactions near the scale of spontaneous supersymmetry-breaking in the hidden-sector (about 10^{10-11} GeV). The resulting singlet expectation value is stabilized and naturally of order the gravitino mass, providing therefore a weak-scale mass for the Higgs fields of the supersymmetric Standard Model (a "mu-parameter"). The resulting low-energy theory is the minimal supersymmetric Standard Model, with all new fields decoupling at the intermediate scale.
The importance of Yukawa contributions to the renormalization of the spectrum in non-minimal supersymmetric models is illustrated in the cases of explicit lepton number violation (leading to the possibility of singly produced sneutrinos at LEP energies), an intermediate scale singlet neutrino and negative mass squared parameters (possibly modifying fine-tuning considerations), and a grand-unified sector. The relevance of model-dependent renormalization to the supersymmetric flavor problem is emphasized. Sources of the flavor problem, some of which are newly identified, as well as possible solutions, are discussed and classified. It is then shown that gravitational interactions could lead (via a quadratically divergent singlet) to simple realizations of some of the low-energy frameworks that attempt to resolve the flavor problem.
Gravitational divergences associated with singlet fields in supersymmetric theories are reexamined, and their possible contributions to the low-energy effective theory are pointed out. We demonstrate that such divergences are not necessarily harmful and that Planck-scale physics could play an important role in models of low-energy supersymmetry breaking via a radiatively induced tadpole term in the scalar potential. In this case, gravitational divergences play the role of the supersymmetry breaking mediator, leading to a simple realization of the so-called messenger model. We also point out a new mechanism for the generation of mass terms for the Higgs fields in models of low-energy supersymmetry breaking, as well as a horizontal messenger mechanism in which the horizontally charged scalars are rendered heavy. Implications to the flavor problem in supersymmetric models are also discussed.
Supersymmetric particles at the multi-TeV scale will escape direct detection at planned future colliders. However, such particles induce non-decoupling corrections in processes involving the accessible superparticles through violations of the supersymmetric equivalence between gauge boson and gaugino couplings. In a previous study, we parametrized these violations in terms of super-oblique parameters and found significant deviations in well-motivated models. Here, we systematically classify the possible experimental probes of such deviations, and present detailed investigations of representative observables available at a future linear collider. In some scenarios, the $e^-e^-$ option and adjustable beam energy are exploited to achieve high precision. It is shown that precision measurements are possible for each of the three coupling relations, leading to significant bounds on the masses and properties of heavy superparticles and possible exotic sectors.