The search for a realistic flipped SU(5) string model

López, Jorge L.; Nanopoulos, Dimitri V.; Yuan, Ke

doi:10.1016/0550-3213(93)90513-o

Cited by 162 publications

(168 citation statements)

References 75 publications

Supporting

Mentioning

166

Contrasting

Unclassified

Order By: Relevance

“…We now turn to the effects induced by additional matter below the string scale [17,27,54]. As we shall see, such matter appears naturally in the string models we have examined.…”

Section: Intermediate Matter Thresholdsmentioning

confidence: 90%

See 1 more Smart Citation

Gauge coupling unification in realistic free-fermionic string models

1995

View full text Add to dashboard Cite

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

show abstract

“…We now turn to the effects induced by additional matter below the string scale [17,27,54]. As we shall see, such matter appears naturally in the string models we have examined.…”

Section: Intermediate Matter Thresholdsmentioning

confidence: 90%

“…The realistic models in the free-fermionic formulation are then generated by specifying a special basis of boundary-condition vectors [20,26,24,21,13,22,27] for these worldsheet fermions. This basis is constructed in two stages.…”

Section: Realistic Free-fermionic Modelsmentioning

confidence: 99%

Gauge coupling unification in realistic free-fermionic string models

1995

View full text Add to dashboard Cite

show abstract

“…Moreover, the gauge symmetry constraints entail superpotential interactions which suppress naturally dangerous dimension-five proton decay operators, provide an elegant solution to the doublet-triplet splitting problem, and a novel see-saw mechanism for neutrino masses [8]. The model also predicts the existence of intermediate-scale vector-like particles (Q,Q and D c ,D c ) contained in one set of 10,10 representations, with masses consistent [6] with those that allow unification of the gauge couplings at the string scale (i.e., m Q ∼ 10 12 GeV, m D c ∼ 10 6 GeV [9]) .In Ref.[1] a study was performed of the constraints imposed by no-scale supergravity on free-fermionic string model-building. No-scale supergravity requires particular forms of the Kähler function such that the vacuum energy vanishes and the potential possesses flat directions which leave the gravitino mass undetermined [3].…”

mentioning

confidence: 99%

String no-scale supergravity model and its experimental consequences

1995

Self Cite

View full text Add to dashboard Cite

We propose a string-derived model based on the gauge group SU (5) × U (1) which satisfies the stringent constraints from no-scale supergravity, allows gauge coupling unification at the string scale, and entails previously unexplored correlations among various sectors of the model. All supersymmetric observables are given in terms of a single mass parameter with self-consistency of the model determining the rest, including tan β = 2.2 − 2.3 and m t ≈ 175 GeV. A small non-universality of the scalar masses at the string scale produces a downward shift in the right-handed slepton masses at the electroweak scale, such that for m 1/2 > ∼ 180 GeV these particles become lighter than the lightest neutralino. This cutoff in the parameter space entails the imminent discovery of charginos at the Tevatron via trilepton events (m χ ± 1 < 90 GeV). Also, the lightest Higgs boson (m h < 90 GeV), the lightest chargino, and the right-handed sleptons (ml R < 50 GeV) should be readily observable at LEPII. We also discuss the model predictions for B(b → sγ), (g − 2) µ , R b , and the prospects for direct neutralino dark matter detection. CTP-TAMU-06/95 ACT-02/95 February 1995Despite all the experimental evidence in support of the Standard Model of the strong and electroweak interactions, many physicists believe that it must be extended so that its many ad-hoc parameters may find explanation in a more fundamental theory. Among the various avenues that lead away from the Standard Model, the ideas of supersymmetry, supergravity, and superstrings are particularly compelling in tackling the shortcomings of the Standard Model. Low-energy supersymmetry predicts the existence of a superpartner for each of the Standard Model particles with well determined interactions but undetermined supersymmetry-breaking masses, although these should not exceed the TeV scale if the gauge hierarchy problem is to remain at a tolerable level. Supergravity provides an effective theory of supersymmetry breaking in terms of two input functions, the Kähler function and the gauge kinetic function. With these inputs all supersymmetry-breaking masses can be calculated in terms of a single parameter: the gravitino mass (m 3/2 ). Superstrings provide the final link by allowing a first-principles calculation of these two input functions in any given string model, therefore having a single parameter effectively describing the physics of supersymmetry breaking. At low-energies a new parameter arises, namely the ratio of vacuum expectation values (tan β) of the two Higgs-boson doublets minimally required in supersymmetric models. However, minimization of the electroweak scalar potential with respect to the two neutral Higgs fields provides two additional constraints which effectively reduce the number of parameters to zero, and a no-parameter model is obtained.In this Letter we describe one such no-parameter model obtained in the context of string no-scale supergravity [1,2]. In contrast with traditional unified models with ad-hoc "string-inspired" choices for the...

show abstract

“…The known model with Q 0 closest to zero is that derived in Ref. [11], which gives Q 0 = 4 (and V 0 = 0) [10]. Other known calculations of |Q 0 | yield much larger values, perhaps not unrelated to the fact that V 0 = 0 in those models.…”

mentioning

confidence: 82%

“…At this point we can say that we have carried out this exercise in the model of Ref. [11], which has Q 0 = 4, and have found sets of values for the vevs that indeed shift Q 0 down to zero. Details of this particular application are given elsewhere [13].…”

mentioning

confidence: 96%

Vanishing Str 2 in the presence of anomalous UA(1)

López

Nanopoulos

1996

Physics Letters B

Self Cite

View full text Add to dashboard Cite

We show that the presence of an anomalous U A (1) factor in the gauge group of string-derived models may have the new and important phenomenological consequence of allowing the vanishing of Str M 2 in the "shifted" vacuum, that results in the process of cancelling the anomalous U A (1). The feasibility of this effect seems to be enhanced by a vanishing vacuum energy, and by a "small" value of Str M 2 in the original vacuum. In the class of free-fermionic models with vanishing vacuum energy that we focus on, a necessary condition for this mechanism to be effective is that Str M 2 > 0 in the original vacuum. A vanishing Str M 2 ameliorates the cosmological constant problem and is a necessary element in the stability of the no-scale mechanism.

show abstract

The search for a realistic flipped SU(5) string model

Cited by 162 publications

References 75 publications

Gauge coupling unification in realistic free-fermionic string models

Gauge coupling unification in realistic free-fermionic string models

String no-scale supergravity model and its experimental consequences

Vanishing Str 2 in the presence of anomalous UA(1)

Contact Info

Product

Resources

About