Supersymmetric Mass Spectrum Research Articles

Electroweak symmetry breaking and large extradimensions

In supersymmetric theories with large extradimensions a finite radiative electroweaksymmetry breaking can be triggered if the top/stopmultiplet propagates in the bulk of the extra dimensions. We haveconstructed a consistent supersymmetric five-dimensional model wherethe extra coordinate is compactified on the orbifold S1/ℤ2,with radius R, and exhibiting as generic features:large tan β≃mt/mb, a well defined pattern of Higgs and supersymmetricmass spectra, sneutrinos as the LSP and perturbative couplings for scalesas large as ~ 40/R. In order to understand thefiniteness of the Higgs mass, which requires thecontribution of KK-modes heavier than the cut-off of thefive-dimensional theory (Λ~Ms, the stringscale), we have introduced a string-motivatedregularization where those heavy KK-modes decoupleexponentially as exp {-M2KK/2Λ2}. The regularization does not spoil the five-dimensionalstructure and the finite result is recovered in the limit Λ→∞. We stress that a top in the bulk should lead toobservable phenomenological and experimental consequences.

Supersymmetry and finite radiative electroweak breaking from an extra dimension

A five dimensional N=1 supersymmetric theory compactified on the orbifold $S^1/\mathbb{Z}_2$ is constructed. Gauge fields and $SU(2)_L$ singlets propagate in the bulk ($U$-states) while $SU(2)_L$ doublets are localized at an orbifold fixed point brane ($T$-states). Zero bulk modes and localized states constitute the MSSM and massive modes are arranged into N=2 supermultiplets. Superpotential interactions on the brane are of the type $UTT$. Supersymmetry is broken in the bulk by a Scherk-Schwarz mechanism using the $U(1)_R$ global $R$-symmetry. A radiative finite electroweak breaking is triggered by the top-quark/squark multiplet $\mathbb{T}$ propagating in the bulk. The compactification radius $R$ is fixed by the minimization conditions and constrained to be $1/R \simlt 10-15$ TeV. It is also constrained by precision electroweak measurements to be $1/R \simgt 4$ TeV. The pattern of supersymmetric mass spectrum is well defined. In particular, the lightest supersymmetric particle is the sneutrino and the next to lightest supersymmetric particle the charged slepton, with a squared-mass difference $\sim M_Z^2$. The theory couplings, gauge and Yukawa, remain perturbative up to scales $E$ given, at one-loop, by $ER \simlt 30-40$. Finally, LEP searches on the MSSM Higgs sector imply an absolute lower bound on the SM-like Higgs mass, around 145 GeV in the one-loop approximation.

The $b \to X_s \gamma$ rate and Higgs boson limits in the constrained minimal supersymmetric model

New NLO b->sgamma calculations have become available using resummed radiative corrections. Using these calculations we perform a global fit of the supergravity inspired constrained minimal supersymmetric model (CMSSM). We find that the resummed calculations show similar constraints as the LO calculations, namely that only with a relatively heavy supersymmetric mass spectrum of the order of 1 TeV the b-\tau Yukawa unification and the b->sgamma rate can coexist in the large tanb scenario. The resummed b->sgamma calculations are found to reduce the renormalization scale uncertainty considerably. The low tanb scenario is excluded by the present Higgs limits from LEP II. The constraint from the Higgs limit in the $m_0,m_{1/2}$ plane is severe, if the trilinear coupling A_0 at the GUT scale is fixed to zero, but is considerably reduced for $A_0\le -2m_0$. The relatively heavy SUSY spectrum required by \besg corresponds to a Higgs mass of $m_h=119\pm 1~ (stop masses)}\pm 2~(theory)~\pm~3 (top mass) GeV $ in the CMSSM.

Resonant sneutrino production at Tevatron run II

We consider the single chargino production at Tevatron p p ̄ → ν ̃ i→ χ ̃ ± 1l i ∓ as induced by the resonant sneutrino production via a dominant R-parity violating coupling of type λ′ ijk L i Q j D k c . Within a supergravity model, we study the three leptons final state. The comparison with the expected background demonstrate that this signature allows to extend the sensitivity on the supersymmetric mass spectrum beyond the present LEP limits and to probe the relevant R-parity violating coupling down to values one order of magnitude smaller than the most stringent low energy indirect bounds. The trilepton signal offers also the opportunity to reconstruct the neutralino mass in a model independent way with good accuracy.

U(1)textures and lepton flavor violation

U(1) family symmetries have led to successful predictions of the fermion mass spectrum and the mixing angles of the hadronic sector. In the context of the supersymmetric unified theories, they further imply a non-trivial mass structure for the scalar partners, giving rise to new sources of flavor violation. In the present work, lepton flavor non-conserving processes are examined in the context of the minimal supersymmetric standard model augmented by a U(1)-family symmetry. We calculate the mixing effects on the \mu-> e\gamma and \tau -> \mu\gamma rare decays. All supersymmetric scalar masses involved in the processes are determined at low energies using two loop renormalization group analysis and threshold corrections. Further, various novel effects are considered and found to have important impact on the branching ratios. Thus, a rather interesting result is that when the see-saw mechanism is applied in the (12 X 12)-sneutrino mass matrix, the mixing effects of the Dirac matrix in the effective light sneutrino sector are canceled at first order. In this class of models and for the case that soft term mixing is already present at the GUT scale, tau -> \mu \gamma decays are mostly expected to arise at rates significantly smaller than the current experimental limits. On the other hand, the $\mu \ra e \gamma$ rare decays impose important bounds on the model parameters, particularly on the supersymmetric scalar mass spectrum. In the absence of soft term mixing at high energies, the predicted branching ratios for rare decays are, as expected, well below the experimental bounds.

Supersymmetric dark matter with a cosmological constant

Recent measurements of cosmological parameters from the microwave background radiation, type Ia supernovae, and the age of globular clusters help determine the relic matter density in the universe. It is first shown with mild cosmological assumptions that the relic matter density satisfies Ω Mh 2<0.6 independent of the cosmological constant and independent of the SNIa data. Including the SNIa data, the constraint becomes Ω Mh 2<0.35 . This result is then applied to supersymmetric models motivated by generic features in supergravity mediated supersymmetry breaking. The result is an upper bound on gaugino masses within reach of the LHC and a 1.5 TeV lepton collider. Thus, cosmological considerations are beginning to limit the supersymmetric mass spectra in the experimentally verifiable range without recourse to finetuning arguments, and without assuming a zero cosmological constant.

SUSYGEN 2.2 — A Monte Carlo event generator for MSSM sparticle production at e +e − colliders

SUSYGEN is a Monte Carlo program designed for computing distributions and generating events for MSSM sparticle production in e +e − collisions. The Supersymmetric (SUSY) mass spectrum may either be supplied by the user, or can alternatively be calculated in two different models of SUSY breaking: gravity mediated supersymmetry breaking (SUGRA), and gauge mediated supersymmetry breaking (GMSB). The program incorporates the most important production processes and decay modes, including the full set of R-parity violating decays, and the decays to the gravitino in GMSB models. Initial state radiation corrections take into account PT/PL effects in the Structure Function formalism, and an optimised hadronisation interface to JETSET 7.4 including final state radiation is also provided.

Calculating fermion masses in superstring derived standard-like models

One of the intriguing achievements of the superstring derived standard-like models in the free fermionic formulation is the possible explanation of the top quark mass hierarchy and the successful prediction of the top quark mass. An important property of the superstring derived standard-like models, which enhances their predictive power, is the existence of three and only three generations in the massless spectrum. Up to some motivated assumptions with regard to the light Higgs spectrum, it is then possible to calculate the fermion masses in terms of string tree-level amplitudes and some VEVs that parameterize the string vacuum. I discuss the calculation of the heavy generation masses in the superstring derived standard-like models. The top quark Yukawa coupling is obtained from a cubic-level mass term while the bottom quark and tau lepton mass terms are obtained from non-renormalizable terms. The calculation of the heavy fermion Yukawa couplings is outlined in detail in a specific toy model. The dependence of the effective bottom quark and tau lepton Yukawa couplings on the flat directions at the string scale is examined. The gauge and Yukawa couplings are extrapolated from the string unification scale to low energies. Agreement with α strong, sin 2 θ w and α em at M z is imposed, which necessitates the existence of intermediate matter thresholds. The needed intermediate matter thresholds exist in the specific toy model. The effect of the intermediate matter thresholds on the extrapolated Yukawa couplings in studied. It is observed that the intermediate matter thresholds also help to maintain the correct b τ mass relation. It is found that for a large portion of the parameter space, the LEP precision data for α strong, sin 2 θ w and α em, as well the top quark mass and the b τ mass relation can all simultaneously be consistent with the superstring derived standard-like models. Possible corrections due to the supersymmetric mass spectrum are studied as well as the minimization of the supersymmetric Higgs potential. It is demonstrated that the calculated values of the Higgs VEV ratio, tan β = η 1 η 2 , can be compatible with the minimization of the one-loop effective Higgs potential.

Supersymmetric unification with radiative breaking ofRparity

We show how $R$ parity can break spontaneously as a result of radiative corrections in unified $N=1$ supergravity models. We illustrate this with a concrete rank-four unified model, where the spontaneous breaking of $R$ parity is accompanied by the existence of a physical Majoron. We determine the resulting supersymmetric particle mass spectrum and show that $R$-parity-breaking signals may be detectable at CERN LEP 200.

Low energy implications of minimal superstring unification

We study the phenomenological implications of effective supergravities based on string vacua with spontaneously broken N = 1 supersymmetry by dilaton and moduli F-terms. We further require minimal string unification, namely that large string threshold corrections ensure the correct unification of the gauge couplings at the grand unification scale. The whole supersymmetric mass spectrum turns out to be determined in terms of only two independent parameters, the dilaton-moduli mixing angle and the gravitino mass. In particular we discuss the region of the parameter space where at least one superpartner is “visible” at LEPII. We find that the most likely candidates are the scalar partner of the right-handed electron and the lightest chargino, with interesting correlations between their masses and with the mass of the lightest higgs. We show how discovering SUSY particles at LEPII might rather sharply discriminate between scenarios with pure dilation SUSY breaking and mixed dilaton-moduli breaking.

Supersymmetric particle spectrum.

We examine the spectrum of supersymmetric particles predicted by grand unified theoretical (GUT) models where the electroweak symmetry breaking is accomplished radiatively. We evolve the soft-supersymmetry-breaking parameters according to the renormalization group equations (RGE). The minimization of the Higgs potential is conveniently described by means of tadpole diagrams. We present complete one-loop expressions for these minimization conditions, including contributions from the matter and the gauge sectors. We concentrate on the low tan $\ensuremath{\beta}$ fixed point region (that provides a natural explanation of a large top quark mass) for which we find solutions to the RGE satisfying both experimental bounds and fine-tuning criteria. We also find that the constraint from the consideration of the lightest supersymmetric particle as the dark matter of the Universe is accommodated in much of parameter space where the lightest neutralino is predominantly gaugino. The supersymmetric mass spectrum displays correlations that are model independent over much of the GUT parameter space.

Phenomenological implications of supersymmetry breaking by the dilaton

We investigate the low energy properties of string vacua with spontaneously broken N = 1 supersymmetry by a dilaton F-term. As a consequence of the universal couplings of the dilaton, the supersymmetric mass spectrum is determined in terms of only three independent parameters and more constrained than in the minimal supersymmetric Standard Model. For a μ-term induced by the Kähler potential the parameter space becomes two-dimensional; in the allowed regions of this parameter space we find that most supersymmetric particles are determined solely by the gluino mass. The Higgs is rather light and the top-quark mass always lower than 180 GeV.

Supersymmetric mass spectrum in SU(5) supergravity grand unification.

A detailed analysis of predictions of SU(5) supergravity grand unification within the framework of radiative breaking of SU(2){times}U(1) is given. The masses of the 31 new supersymmetric particles depend on only four parameters. The full parameter space is explored and found to be strongly restricted by proton decay bounds if one requires no extreme fine tuning and the Higgs triplet mass to be {le}3{ital M}{sub {ital G}}. The 31 sparticle masses are then strongly correlated, e.g., {ital m}{sub {ital {tilde W}}1}{approx lt}1/3{ital m}{sub {ital {tilde g}}}, {ital m}{sub {ital {tilde W}}1}{congruent}{ital M}{sub {ital {tilde Z}}2}{congruent}2{ital m}{sub {ital {tilde Z}}1}, {ital m}{sub {ital h}}{approx lt}110 GeV.