arXiv subjects

Hans Peter Nilles

Publications and source records attributed to Hans Peter Nilles.

96 records · Page 6Linked to original sources

arXiv1999

String Dualities in the Presence of Anomalous U(1) Symmetries

Anomalous U(1) gauge symmetries in type II orientifold theories show some unexpected properties. In contrast to the heterotic case, the masses of the gauge bosons are in general of order of the string scale even in the absence of large Fayet-Iliopoulos terms. Despite this fact, the notion of heterotic-type II orientifold duality remains a useful concept, although this symmetry does not seem to hold in all cases considered. We analyse the status of this duality symmetry, clarify the properties of anomalous U(1) gauge symmetry in the orientifold picture and comment on the consequences for phenomenological applications of such anomalous gauge symmetries.

hep-th↗

arXiv1997

Gravitational divergences as a mediator of supersymmetry breaking

Gravitational divergences associated with singlet fields in supersymmetric theories are reexamined, and their possible contributions to the low-energy effective theory are pointed out. We demonstrate that such divergences are not necessarily harmful and that Planck-scale physics could play an important role in models of low-energy supersymmetry breaking via a radiatively induced tadpole term in the scalar potential. In this case, gravitational divergences play the role of the supersymmetry breaking mediator, leading to a simple realization of the so-called messenger model. We also point out a new mechanism for the generation of mass terms for the Higgs fields in models of low-energy supersymmetry breaking, as well as a horizontal messenger mechanism in which the horizontally charged scalars are rendered heavy. Implications to the flavor problem in supersymmetric models are also discussed.

hep-ph↗

arXiv1996

Dynamical Gauge Coupling Constants

In string theory the coupling parameters are functions of moduli fields. The actual values of the coupling constants are then dynamically determined through the vacuum expextation values of these fields. We review the attempts to connect such theories to low energy effective field theories with realistic gauge coupling constants. This includes a discussion of supersymmetry breakdown, the question of a running dilaton, string threshold calculations and the possibility of string unification.

hep-ph↗

arXiv1995

Phenomenological aspects of supersymmetry

We discuss the possible applications supersymmetric theories might find in the field of elementary particle physics. The supersymmetric generalization of the $SU(3)\times SU(2)\times U(1)$ standard model is discussed in detail. Special attention has been devoted to the question of gauge coupling constant unification in the framework of supersymmetric grand unified models.

hep-ph↗

arXiv1994

Symmetry Principles toward Solutions of $μ$ Problem

We stress that a natural solution of the $μ$ problem requires two ingredients: a symmetry that would enforce $μ= 0$ as well as the occurence of a small breaking parameter that generates a nonzero $μ$. It is suggested that both the Peccei-Quinn symmetry and the spontaneously broken $R$ symmetry may be the sources of the needed $μ$ term in the minimal supersymmetric standard model provided that they are spontaneously broken at a scale $10^{10}-10^{12}$ GeV. To solve the strong CP problem with a hidden sector confining group, both of these symmetries are needed in superstring models with an anomalous $U(1)_A$.

hep-ph↗

arXiv1994

Cosmological Constant and Soft Terms in Supergravity

Some of the soft SUSY breaking parameters in hidden sector supergravity model depend on the expectation value of the hidden sector scalar potential, $ $, whose tree level value is equal to the tree level cosmological constant. The current practice of calculating soft parameters assumes that $ =0$. Quantum correction to the cosmological constant can differ from the correction to $ $ by an amount of order $m^2_{3/2}M_{Pl}^2/8π$. This implies that, for the vanishing cosmological constant, the $ $--dependent parts of soft terms can be sizable, and hence the supergravity phenomenology should be accordingly modified.

hep-ph↗