Phenomenological implications of supersymmetry breaking by the dilaton

Abstract

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...

Probing μ-term generation mechanism in string models

“…This result is consistent with those in Ref. [14]. Further we find no region satisfying µ ±Z = 0 with d = 0 from in Fig.2 and µ Z /m 3/2 = 1.…”

“…† Study on the Higgs sector has been done, e.g. within the framework of string models without D-term contribution [14] and SUSY grand unified theory (SUSY-GUT) with Dterm contributions [15].…”

“…[9,10,11]. Then the soft scalar masses, the µ-term and B-term are written at the tree level as [11,14] …”

Relating incomplete data and incomplete theory

“…In that limit the soft terms are given by M 1/2 = −A 0 = √ 3m 0 = √ 3m 3/2 , where m 3/2 is the gravitino mass. This model has been studied at length in the literature [33,34,35] and it represents a special case of the mSUGRA paradigm. By couching it in the language of D 5 -branes, however, one is at liberty to set the boundary condition (string) scale as a free parameter.…”

Renormalization group invariants in the MSSM and its extensions

“…Clearly, RG invariance is not a requisite property for an observable to probe supersymmetry breaking sector; however, if it is RG-invariant it is not necessary to integrate the RGEs and it is possible to use results of different experiments without RG scaling (irrespective of if they are obtained from a reanalysis of LEP data or from Tevatron or from LHC). The patterns of the RG invariants (I 4 -I 9 ) within no-scale [26], dilaton domination [27] and fluxed MSSM [28] supersymmetry breaking schemes.…”