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Theses

String theory : Supersymmetry breaking, moduli stabilitzation and cosmological considerations

Abstract : The purpose of this thesis is to explore various aspects of string theory, a unified theory of matter and all fundamental interactions including gravity. In a first chapter, we start by describing some useful key ingredients of the theory and its construction to motivate the works presented in this manuscript. We then explore three different aspects of the theory. First, a new supersymmetry-breaking mechanism in unoriented open-string models is developed. The features of this breaking are described, commented and put into perspective with other existing mechanisms. Second, one-loop masses acquired by tree-level moduli are studied in a type I string context with N=2 N=0 spontaneous breaking of supersymmetry implemented by a Scherk--Schwarz mechanism. Different strategies are followed to conclude on the stability or not at one loop of the wide variety of moduli present in the model. These strategies range from the Taylor expansion of the effective potential up to quadratic order, to the evaluation of genus-1 two-point correlation functions, through arguments arising from the duality between the heterotic and type I string. Once all the masses are computed, we give explicit models (brane configurations) where there is no instability induced at one loop and where the potential is exponentially suppressed thanks to a Bose/Fermi degeneracy at the massless level. Eventually, in heterotic string models, the backreaction of the one-loop potential generated by a spontaneous Scherk--Schwarz supersymmetry breaking on the cosmology is studied. Flat and ever-expanding solutions are looked for to establish if the classical cosmological dynamics of such solutions is perturbed or not by the one-loop quantum corrections. We then describe a new process for generating a non-relativistic dark-matter relic density in models with spontaneously broken supersymmetry and implementation of the finite temperature through compactification of the Euclidean time.
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Submitted on : Thursday, October 14, 2021 - 3:02:18 PM
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Thibaut Coudarchet. String theory : Supersymmetry breaking, moduli stabilitzation and cosmological considerations. High Energy Physics - Theory [hep-th]. Institut Polytechnique de Paris, 2021. English. ⟨NNT : 2021IPPAX071⟩. ⟨tel-03378186⟩

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