arXiv subjects

H. P. Nilles

Publications and source records attributed to H. P. Nilles.

26 records · Page 2Linked to original sources

arXiv1995

Gaugino Condensation and the Vacuum Expectation Value of the Dilaton

The mechanism of gaugino condensation has emerged as a prime candidate for supersymmetry breakdown in low energy effective supergravity (string) models. One of the open questions in this approach concerns the size of the gauge coupling constant which is dynamically fixed through the vev of the dilaton. We argue that a nontrivial gauge kinetic function $f(S)$ could solve the potential problem of a runaway dilaton. The actual form of $f(S)$ might be constrained by symmetry arguments.

hep-th↗

arXiv1995

Gaugino Condensation, S-Duality and Supersymmetry Breaking in Supergravity Models

The status of the gaugino condensation as the source of supersymmetry breaking is reexamined. It is argued that one cannot have stable minima with broken supersymmetry in models where the dilaton is coupled only linearly to the gaugino condensate. We show that the problems of the gaugino condensate mechanism can be solved by considering nonstandard gauge kinetic functions, created by nonperturbative effects. As an example we use the principle of S-duality to modify the coupling of the gaugino condensate to effective supergravity (superstring) Lagrangians. We show that such an approach can solve the problem of the runaway dilaton and lead to satisfactory supersymmetry breaking in models with a {\em single} gaugino condensate. We exhibit a general property of theories containing a symmetry acting on the dilaton and also shed some light on the question whether it is generically the auxiliary field of the modulus $T$, which dominates supersymmetry breaking.

hep-th↗

arXiv1994

S-Dual Gaugino Condensation and Supersymmetry Breaking

The principle of S-duality is used to incorporate gaugino condensates into effective supergravity (superstring) Lagrangians. We discuss two implementations of S-duality which differ in the way the coupling constant is transformed. Both solve the problem of the runaway dilaton and lead to satisfactory supersymmetry breaking in models with a {\em single} gaugino condensate. The breakdown of supersymmetry is intimately related to a nontrivial transformation of the condensate under T-duality.

hep-th↗

arXiv1994

Aspects of Supersymmetry at LEP II

We give a short introduction to the concept of low energy supersymmetric models and their phenomenological predictions. In view of the future LEP II results we have to parametrize these predictions in a model independent way without too many simplifying assumptions. The study must therefore include models with {\it non--universal} soft supersymmetry breaking terms. We show that such non--universalities might have significant influence on the properties of these models.

hep-ph↗

arXiv1994

Implications of non-universality of soft terms in supersymmetric grand unified theories

Most discussions of supersymmetric grand unified theories assume universality of the soft supersymmetry breaking terms at the grand scale. We point out that the behaviour of these theories might change significantly in the presence of non--universal soft terms. Particularly in SO(10)--like models with a large value of tan$β$ we observe a decisive change of predictions, allowing the presence of relatively light gauginos as well as small supersymmetric corrections to the b--quark mass. Some results remain rather stable, including the $μ$--$M_{1/2}$ correlation. Models with small tan$β$ seem to be less affected by non--universality which mainly leads to the new possibility of small $m_{0}$ (i.e. the squark and slepton soft mass parameter), excluded in the universal case.

hep-ph↗

arXiv1993

String Unification and Threshold Corrections

The interpretation of the apparent unification of gauge couplings within supersymmetric theories depends on uncertainties induced through heavy particle thresholds. While in standard grand unified theories these effects can be estimated easily, the corresponding calculations are quite complicated in string unified theories and do exist only in models with unbroken $E_6$. We present results for heavy particle thresholds in more realistic models with gauge group $SU(3)\times SU(2)\times U(1)$. Effects of Wilson line background fields as well as the universal part of the (rather mild) threshold corrections indicate a strong model dependence. We discuss the consequences of our results for the idea of string unification without a grand unified gauge group.

hep-th↗

arXiv1993

Light Gluinos and Unification of Couplings

We analyze the implications of the light gluino scenario for the unification of gauge and Yukawa couplings within the minimal supersymmetric standard model. Within this scheme all fermionic supersymmetric particles are naturally light, while the scalar partners of quarks and leptons, together with the heavy Higgs doublet may be heavy. This implies both a bound on $\tanβ< 2.3$, in order to fulfill the experimental constraints on the chargino masses, and a strong correlation between $\sin^2θ_W(M_Z)$ and $α_3(M_Z)$, due to the suppression of the supersymmetric threshold corrections to the low energy values of the gauge couplings. Assuming the scalar sparticles to be lighter than 10 TeV, the physical top quark mass is constrained to be 145 GeV $< M_T <$ 210 GeV for $\tanβ>1$, while the strong gauge coupling values, $0.122\leqα_3(M_Z) \leq 0.133$, are in good agreement with the measured LEP ones. We also show that a relaxation of some of the conventional assumptions is necessary in order to achieve radiative breaking of the electroweak symmetry within the grand unification scheme.

hep-ph↗

arXiv1992

Axino Mass

The mass of the axino is computed in realistic supersymmetric extensions of the standard model. It is found to be strongly model dependent and can be as small as a few keV but also as large as the gravitino mass. Estimates of this mass can only be believed once a careful analysis of the scalar potential has been performed.

hep-ph↗