No-scale Models Research Articles

New Class ofN=1No-Scale Supergravity Models

We introduce a new N=1 no-scale supergravity model with F- and D-term breaking. It contains a single chiral supermultiplet T and a single U(1) vector multiplet U, gauging a nonanomalous axionic shift symmetry. Both supersymmetry and the gauge symmetry are spontaneously broken, with the spin-3/2, spin-1, and spin-1/2 masses sliding along a classical flat direction, with a single real massless scalar in the spectrum. The other degrees of freedom are absorbed by the massive gravitino and vector. We extend our model, under very mild conditions, to general gauge groups and matter content.

Constricted SUSY from No-Scale ℱ-SU(5): A “blind spot” for LHC top quark reconstruction?

We describe a region of the No-Scale supersymmetric model with TeV-scale vector-like matter multiplets that is potentially opaque to LHC observations based upon top quark reconstruction. Possessing a 100% on-shell branching fraction for gluino-to-light stop decays, the gluino-light stop mass splitting in lies very close to the top quark rest mass in the region . For unboosted gluino pair production, this could render two soft top quarks in the dominant 4-top signature, greatly reducing the likelihood for discrimination from the combinatoric background. We therefore suggest that caution is warranted when gluino exclusion bounds on models possessing a similar spectral character (gluino heavier than the light stop but lighter than all other squarks) using multijet SUSY search tactics. Alternate search methods are highlighted, including those based upon same-sign dileptons and multiple heavy flavor tags, which are more sensitive to this delicate kinematic “blind spot” crease.

On the Starobinsky model of inflation from supergravity

We discuss how the higher-derivative Starobinsky model of inflation originates from N=1 supergravity. It is known that, in the old-minimal supergravity description written by employing a chiral compensator in the superconformal framework, the Starobinsky model is equivalent to a no-scale model with F-term potential. We show that the Starobinsky model can also be originated within the so-called new-minimal supergravity, where a linear compensator superfield is employed. In this formulation, the Starobinsky model is equivalent to standard supergravity coupled to a massive vector multiplet whose lowest scalar component plays the role of the inflaton and the vacuum energy is provided by a D-term potential. We also point out that higher-order corrections to the supergravity Lagrangian represent a threat to the Starobinsky model as they can destroy the flatness of the inflaton potential in its scalar field equivalent description.

SUPER-screening

We present a framework for embedding scalar–tensor models of screened modified gravity such as chameleons, symmetrons and environmental dilatons into global supersymmetry. This achieved by secluding the dark sector from both the observable and supersymmetry breaking sectors. We examine the resulting supersymmetric features in a model-independent manner and find that, when the theory follows from an underlying supergravity, the mediation of supersymmetry breaking to the dark sector induces a soft mass for the scalar of order the gravitino mass. This is enough to forbid the construction of supersymmetric symmetrons and ensures that when other screening mechanisms operate, no object in the Universe is unscreened thereby precluding any observable signatures. In view of a possible origin of modified gravity within fundamental physics, we find that only no-scale models can circumvent these features. We also present a novel mechanism where the coupling of the scalar to two other scalars charged under U(1) can dynamically generate a small cosmological constant at late times in the form of a Fayet–Iliopoulos term.

Gaugino anomaly mediated SUSY breaking: phenomenology and prospects for the LHC

We examine the supersymmetry phenomenology of a novel scenario of supersymmetry (SUSY) breaking which we call Gaugino Anomaly Mediation, or inoAMSB. This is suggested by recent work on the phenomenology of flux compactified type IIB string theory. The essential features of this scenario are that the gaugino masses are of the anomaly-mediated SUSY breaking (AMSB) form, while scalar and trilinear soft SUSY breaking terms are highly suppressed. Renormalization group effects yield an allowable sparticle mass spectrum, while at the same time avoiding charged LSPs; the latter are common in models with negligible soft scalar masses, such as no-scale or gaugino mediation models. Since scalar and trilinear soft terms are highly suppressed, the SUSY induced flavor and CP-violating processes are also suppressed. The lightest SUSY particle is the neutral wino, while the heaviest is the gluino. In this model, there should be a strong multi-jet +etmiss signal from squark pair production at the LHC. We find a 100 fb^{-1} reach of LHC out to m_{3/2}\sim 118 TeV, corresponding to a gluino mass of \sim 2.6 TeV. A double mass edge from the opposite-sign/same flavor dilepton invariant mass distribution should be visible at LHC; this, along with the presence of short-- but visible-- highly ionizing tracks from quasi-stable charginos, should provide a smoking gun signature for inoAMSB.

Light moduli in almost no-scale models

We discuss the stabilization of the compact dimension for a class of five-dimensional orbifold supergravity models. Supersymmetry is broken by the superpotential on a boundary. Classically, the size L of the fifth dimension is undetermined, with or without supersymmetry breaking, and the effective potential is of no-scale type. The size L is fixed by quantum corrections to the Kähler potential, the Casimir energy and Fayet–Iliopoulos (FI) terms localized at the boundaries. For an FI scale of order M GUT , as in heterotic string compactifications with anomalous U ( 1 ) symmetries, one obtains L ∼ 1 / M GUT . A small mass is predicted for the scalar fluctuation associated with the fifth dimension, m ρ ≲ m 3 / 2 / ( L M ) .

Constructing de Sitter vacua in no-scale string models without uplifting

We develop a method for constructing metastable de Sitter vacua in N = 1 supergravity models describing the no-scale volume moduli sector of Calabi-Yau string compactifications. We consider both heterotic and orientifold models. Our main guideline is the necessary condition for the existence of metastable vacua coming from the Goldstino multiplet, which constrains the allowed scalar geometries and supersymmetry-breaking directions. In the simplest non-trivial case where the volume is controlled by two moduli, this condition simplifies and turns out to be fully characterised by the intersection numbers of the Calabi-Yau manifold. We analyse this case in detail and show that once the metastability condition is satisfied it is possible to reconstruct in a systematic way the local form of the superpotential that is needed to stabilise all the fields. We apply then this procedure to construct some examples of models where the superpotential takes a realistic form allowed by flux backgrounds and gaugino condensation effects, for which a viable vacuum arises without the need of invoking corrections to the Kahler potential breaking the no-scale property or uplifting terms. We finally discuss the prospects of constructing potentially realistic models along these lines.

Higgs boson exempt no-scale supersymmetry with a neutrino seesaw mechanism: Implications for lepton flavor violation and leptogenesis

Motivated by the observation of neutrino oscillations, we extend the Higgs boson exempt no-scale supersymmetry model by adding three heavy right-handed neutrino chiral supermultiplets to generate the light neutrino masses and mixings. The neutrino Yukawa couplings can induce new lepton-flavor violating couplings among the soft terms in the course of renormalization group running down from the boundary scale. We study the effects this has on the predictions for low-energy probes of lepton-flavor violation (LFV). Heavy right-handed neutrinos also provide a way to generate the baryon asymmetry through leptogenesis. We find that consistency with LFV and leptogenesis puts strong requirements on either the form of the Yukawa mass matrix or the smallness of the Higgs up soft mass. In all cases, we generically expect that new physics LFV is nonzero and can be found in a future experiment.

Higgs boson exempt no-scale supersymmetry and its collider and cosmology implications

One of the most straightforward ways to address the flavor problem of low-energy supersymmetry is to arrange for the scalar soft terms to vanish simultaneously at a scale M{sub c} much larger than the electroweak scale. This occurs naturally in a number of scenarios, such as no-scale models, gaugino mediation, and several models with strong conformal dynamics. Unfortunately, the most basic version of this approach that incorporates gaugino mass unification and zero scalar masses at the grand unification scale is not compatible with collider and dark matter constraints. However, experimental constraints can be satisfied if we exempt the Higgs bosons from flowing to zero mass value at the high scale. We survey the theoretical constructions that allow this and investigate the collider and dark matter consequences. A generic feature is that the sleptons are relatively light. Because of this, these models frequently give a significant contribution to the anomalous magnetic moment of the muon, and neutralino-slepton coannihilation can play an important role in obtaining an acceptable dark matter relic density. Furthermore, the light sleptons give rise to a large multiplicity of lepton events at colliders, including a potentially suggestive clean trilepton signal at the Tevatron, and a substantial four leptonmore » signature at the LHC.« less

Kähler corrections for the volume modulus of flux compactifications

No-scale models arise in many compactifications of string theory and supergravity, the most prominent recent example being type IIB flux compactifications. Focussing on the case where the no-scale field is a single unstabilized volume modulus (radion), we analyse the general form of supergravity loop corrections that affect the no-scale structure of the Kähler potential. These corrections contribute to the 4d scalar potential of the radion in a way that is similar to the Casimir effect. We discuss the interplay of this loop effect with string-theoretic α′ corrections and its possible role in the stabilization of the radion.

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 2 × Z 2 ) in the presence of general fluxes. We illustrate and apply a general method that relates the N = 1 effective Kähler 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.

Formula omitted] gauged supergravities from generalized dimensional reduction

We construct new N = 6 gauged supergravities in four and five dimensions using generalized dimensional reduction. Supersymmetry is spontaneously broken to N = 4 , 2 , 0 with vanishing cosmological constant. We discuss the gaugings of the broken phases, the scalar geometries and the spectrum. Generalized orbifold reduction is also considered and an N = 3 no-scale model is obtained with three independent mass parameters.

The minimalN= 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.

Quasi-degenerate neutrinos and lepton flavor violationin supersymmetric models

In supersymmetric models the misalignment between fermion and sfermion families introduces unsuppressed flavor-changing processes. Even if the mass parameters are chosen to give no flavor violation, family dependent radiative corrections make this adjustment not stable. We analyze the rate of $\ell\rightarrow\ell'\gamma$ in SUSY-GUT models with three quasi-degenerate neutrinos and universal scalar masses at the Planck scale. We pay special attention to a recently proposed scenario where the low-energy neutrino mixings are generated from identical quark and lepton mixings at large scales. We show the following. (i) To take universal slepton masses at the GUT scale is a very poor approximation, even in no-scale models. (ii) For large neutrino Yukawa couplings the decay $\mu\rightarrow e\gamma$ would be observed in the planned experiment at PSI. (iii) For large values of $\tan\beta$ the tau coupling gives important corrections, pushing $\mu\rightarrow e\gamma$ and $\tau\rightarrow \mu\gamma$ to accessible rates. In particular, the non-observation of these processes in the near future would exclude the scenario with unification of quark and lepton mixing angles. (iv) The absence of lepton flavor violating decays in upcoming experiments would imply a low value of $\tan\beta$ , small neutrino couplings, and large ( $\gtrsim 250$ GeV) SUSY-breaking masses.

Phenomenological constraints on patterns of supersymmetry breaking

Specific models of supersymmetry breaking predict relations between the trilinear and bilinear soft supersymmetry breaking parameters A0 and B0 at the input scale. In such models, the value of tanβ can be calculated as a function of the scalar masses m0 and the gaugino masses m1/2, which we assume to be universal. The experimental constraints on sparticle and Higgs masses, b→sγ decay and the cold dark matter density ΩCDMh2 can then be used to constrain tanβ in such specific models of supersymmetry breaking. In the simplest Polonyi model with A0=(3−3)m0=B0+m0, we find 11≲tanβ≲20 (tanβ≃4.15) for μ>0 (μ<0). We also discuss other models with A0=B0+m0, finding that only the range −1.9≲A0/m0≲2.5 is allowed for μ>0, and the range 1.25≲A0/m0≲4.8 for μ<0. In these models, we find no solutions in the rapid-annihilation ‘funnels’ or in the ‘focus-point’ region. We also discuss the allowed range of tanβ in the no-scale model with A0=B0=0. In all these models, most of the allowed regions are in the χ−τ̃1 coannihilation ‘tail’.

N=1 no-scale supergravity from IIB orientifolds

We describe the low-energy effective theory of N=1 spontaneously broken supergravity obtained by flux-induced breaking in the presence of n D3-branes. This theory can be obtained by integrating out three massive gravitino multiplets in the hierarchical breaking N=4→3→2→1 of a N=4 orientifold. This integration also eliminates the IIB complex dilaton. The resulting theory is a no-scale supergravity model, whose moduli are the three chiral multiplets that correspond to the three radii of T2×T2×T2 in T6, together with the 6n brane coordinates. The U(n) gauge interactions on the branes respect the no-scale structure, and the N=1 goldstino is the fermionic partner of the T6 volume.

Investigation of no-scale supersymmetry breaking models with a gaugedU(1)B−Lsymmetry

Noscale supersymmetry (SUSY) breaking model is investigated in the minimal extension of the minimal supersymmetric standard model (MSSM) with a gauged U(1)_{B-L} symmetry. We specifically consider a unification-inspired model with the gauge groups SU(3)_{C} \times SU(2)_{L} \times U(1)_Y \times U(1)_{B-L} \subset SU(5) \times U(1)_{5} for illustration. While the noscale boundary condition at the grand unification scale (M_{G}\simeq 2\times 10^{16} GeV) in the MSSM is not consistent with phenomenological constraints, we show that it is if the gaugino of the U(1)_{5} multiplet is several times heavier than the gauginos of the MSSM. However, if SU(5) \times U(1)_{5} is further embedded in a larger simple group, e.g. SO(10), the noscale boundary condition at M_{G} is inconsistent with phenomenological constraints. If we relax the noscale boundary condition and allow non-zero soft scalar masses for the Higgs fields which spontaneously break the U(1)_{5} symmetry, the resultant spectrum of SUSY particles becomes consistent with all the phenomenological constraints, even if we impose the GUT relation on the gauge coupling and the gaugino mass of the U(1)_{5}. In this case, the SUSY CP problem is also solved, since the condition B\mu =0 at the boundary can be imposed consistently with the electroweak symmetry breaking.

Probing the messenger of supersymmetry breaking by the muon anomalous magnetic moment

Motivated by the recently measured muon's anomalous magnetic moment $a_{\mu}$, we examine the supersymmetry contribution to $a_{\mu}$ in various mediation models of supersymmetry breaking which lead to predictive flavor conserving soft parameters at high energy scale. The studied models include dilaton/modulus-mediated models in heterotic string/$M$ theory, gauge-mediated model, no-scale or gaugino-mediated model, and also the minimal and deflected anomaly-mediated models. For each model, the range of $a^{SUSY}_{\mu}$ allowed by other experimental constraints, e.g. b --> s\gamma and the collider bounds on superparticle masses, is obtained together with the corresponding parameter region of the model. Gauge-mediated models with low messenger scale can give any $a^{SUSY}_{\mu}$ within the $2\sigma$ bound. In many other models, b --> s\gamma favors $a^{SUSY}_{\mu}$ smaller than either the $-1\sigma$ value ($26\times 10^{-10}$) or the central value ($42\times 10^{-10}$).

F-term hybrid inflation in effective supergravity theories

We show that a particular class of effective low energy supergravity theories motivated by string theory can provide a promising framework for models of hybrid inflation in which the potential energy which drives inflation originates from the F-term of the effective supergravity theory. In the class of models considered the inflaton is protected from receiving mass during inflation by a generalisation of the Heisenberg symmetry present in no-scale supergravity models. The potential during inflation takes the positive definite form V ∼ | F S | 2 + | F T | 2 − 3, which allows the possibili that V ⪡ m 3 2 2M P 2 through the cancelation of the positive dilaton and moduli contribution against the negative term. We discuss a toy example where this is realised, then describe the application of this result to realistic models focusing on a particular example in which the μ problem and the strong CP problem are addressed.

New Precision Electroweak Tests in Supergravity Models

We update the analysis of the precision electroweak tests in terms of four epsilon parameters, ε1,2,3,b, to obtain more accurate experimental values of them by taking into account the new LEP data released at the 28th ICHEP (Poland, 1996). We also compute ε1 and εb in the context of the no-scale SU (5)× U (1) supergravity model to obtain the updated constraints by imposing the correlated constraints in terms of the experimental ellipses in the ε1–εb plane and also by imposing the new conservative bound on the lightest chargino mass, [Formula: see text]. Upon imposing these new experimental results, we find that the situations in the no-scale model are much more favorable than those in the standard model, and if mt≳ 170 GeV, then the allowed regions at the 95% C.L. in the no-scale model are tan β≳ 4 and [Formula: see text] for μ&gt;0 (μ&lt; 0), which are in fact much more stringent than in our previous analysis. Therefore, assuming that mt≳ 170 GeV, if the lightest chargino mass bound were to be pushed up to 82 GeV, the sign on the Higgs mixing term μ in the no-scale model could well be determined from the ε1–εb constraint to be positive at the 95% C.L. At any rate, better accuracy in the measured mt from the Tevatron in the near future combined with the LEP data is most likely to provide a decisive test of the no-scale SU (5)× U (1) supergravity model.