The price of deriving the standard model from the string

Antoniadis, I.; Ellis, John; Kelley, Stephen; Nanopoulos, Dimitri V.

doi:10.1016/0370-2693(91)91007-i

Cited by 97 publications

(103 citation statements)

References 11 publications

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“…[23] it was shown, in a wide range of realistic free fermionic models, that heavy string threshold corrections, non-standard hypercharge normalizations [24], light SUSY thresholds or intermediate gauge structure, do not resolve the disagreement with α strong (M Z ) and sin 2 θ W (M Z ). Instead, as was previously suggested [37,22,40], the problem may be resolved in the free fermionic models due to the existence of additional color triplets and electroweak doublets beyond the MSSM. Indeed, additional color triplets and electroweak doublets in vector-like representations, beyond the MSSM, in general appear in the massless spectrum of the realistic string models.…”

Section: The Effect Of Intermediate Matter Thresholdsmentioning

confidence: 96%

“…Graviton exchange is forbidden because of gauge symmetry, as two of the fields must annihilate into a singlet to allow graviton propagation, which is not the case for the terms in Eq. (37). Thus A 4 is directly related to the coefficient of the nonrenormalizable term in the superpotential.…”

Section: Calculation Of the Bottom Quark And Tau Lepton Mass Termsmentioning

confidence: 99%

“…(49a,49b) must be positive definite, since |χ k | 2 ≥ 0. However, as the total charge of these singlets must have Q A < 0 to cancel the "anomalous" U(1) D-term equation, in many models a phenomenologically realistic solution was not found [17,37]. Among the free fermionic standard-like model, that use the NAHE set to obtain three generations, the only models that were found to admit a solution are models with ∆ 1,2,3 = 1.…”

Section: Calculation Of the Effective Yukawa Couplingsmentioning

confidence: 99%

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Calculating fermion masses in superstring derived standard-like models

Faraggi

1997

Nuclear Physics B

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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 nonrenormalizable 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 as 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 = v 1 /v 2 , can be compatible with the minimization of the one-loop effective Higgs

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Section: The Effect Of Intermediate Matter Thresholdsmentioning

confidence: 96%

Section: Calculation Of the Bottom Quark And Tau Lepton Mass Termsmentioning

confidence: 99%

Section: Calculation Of the Effective Yukawa Couplingsmentioning

confidence: 99%

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Calculating fermion masses in superstring derived standard-like models

Faraggi

1997

Nuclear Physics B

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“…Finally, we examine possible string models that contain additional (3, 2) 1/6 representations. These representations are obtained, for example, in the flipped SU(5) × U(1) model [57] and in the SO(6) × SO(4) models [58], and arise from the additional 16 and 16 representations. These may also arise in the standard-like string models.…”

Section: Intermediate Matter Thresholdsmentioning

confidence: 99%

Gauge coupling unification in realistic free-fermionic string models

1995

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We discuss the unification of gauge couplings within the framework of a wide class of realistic free-fermionic string models which have appeared in the literature, including the flipped SU (5), SO(6) × SO(4), and various SU (3) × SU (2) × U (1) models. If the matter spectrum below the string scale is that of the Minimal Supersymmetric Standard Model (MSSM), then string unification is in disagreement with experiment. We therefore examine several effects that may modify the minimal string predictions. First, we develop a systematic procedure for evaluating the one-loop heavy string threshold corrections in free-fermionic string models, and we explicitly evaluate these corrections for each of the realistic models. We find that these string threshold corrections are small, and we provide general arguments explaining why such threshold corrections are suppressed in string theory. Thus heavy thresholds cannot resolve the disagreement with experiment. We also study the effect of non-standard hypercharge normalizations, light SUSY thresholds, and intermediate-scale gauge structure, and similarly conclude that these effects cannot resolve the disagreement with low-energy data. Finally, we examine the effects of additional color triplets and electroweak doublets beyond the MSSM. Although not required in ordinary grand unification scenarios, such states generically appear within the context of certain realistic free-fermionic string models. We show that if these states exist at the appropriate thresholds, then the gauge couplings will indeed unify at the string scale. Thus, within these string models, string unification can be in agreement with low-energy

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“…For the following analysis we only need ∇ Our numerical calculation also takes into account the effects of the supersymmetry threshold. † Another possibility would be to assume extra light states in the spectrum, which decouple at some intermediate scale [14], but we do not entertain this option here.…”

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confidence: 99%

Phenomenological implications of supersymmetry breaking by the dilaton

1993

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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. CERN-TH.6856/93 April 1993The leading candidate for consistently incorporating quantum gravity into the standard interactions of particle physics is a heterotic superstring theory. However, despite its numerous attractions it has not been possible to identify quantitatively the Standard Model (SM) as the low energy limit of string theory. In part this is due to our lack of conceptual understanding of the theory; so far we only enjoy control over (some of) its perturbative regime. Unfortunately, low energy string phenomenology does seem to depend crucially on non-perturbative properties of string theory. The mechanism for supersymmetry breaking, the choice of the string vacuum, or the determination of the gauge couplings are believed to be governed by (possibly 'stringy') non-perturbative effects; our current techniques are inappropriate to incorporate such effects into the low energy effective Lagrangian.Ultimately, we have to come to terms with this deficiency; in the mean time various strategies have been employed in order to investigate and/or constrain the low energy limit of the string. We refrain here from systematically reviewing the subject, instead we briefly outline the method that we are going to follow in this letter. Based on work in the context of gaugino condensation [1, 2] and duality-invariant effective Lagrangians [2-4] it was recently suggested [5] to simply parametrize the unknown non-perturbative physics. All relevant low energy interactions are expressed in terms of couplings calculable in string perturbation theory and couplings encoding the nonperturbative dynamics; the latter then appear as arbitrary parameters in the low energy effective theory. Surprisingly, even in such a general framework this effective theory can display rather distinct properties. In ref.[5] the non-perturbative couplings are constrained by some assumptions about the nature of the non-perturbative dynamics and the nature of supersymmetry breaking. In particular, it was assumed that supersymmetry is spontaneously broken in the moduli/dilaton sector of string theory. Such scalar multiplets are always present in the massless string spectrum and the couplings of the low energy effective Lagrangian are determined by their vacuum expectation values (VEVs). In string perturbation theory, both the moduli and the dilaton are exact flat directions of the effective potential, leavin...

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The price of deriving the standard model from the string

Cited by 97 publications

References 11 publications

Calculating fermion masses in superstring derived standard-like models

Calculating fermion masses in superstring derived standard-like models

Gauge coupling unification in realistic free-fermionic string models

Phenomenological implications of supersymmetry breaking by the dilaton

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