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We adapt the spinorial geometry method to investigate supergravity backgrounds with near maximal number of supersymmetries. We then apply the formalism to show that the IIB supergravity backgrounds with 31 supersymmetries preserve an additional supersymmetry and so they are maximally supersymmetric. This rules out the existence of IIB supergravity preons., 7 pages

We show that eleven-dimensional supergravity backgrounds with thirty one supersymmetries, N=31, admit an additional Killing spinor and so they are locally isometric to maximally supersymmetric ones. This rules out the existence of simply connected eleven-dimensional supergravity preons. We also show that N=15 solutions of type I supergravities are locally isometric to Minkowski spacetime., 17 pages

We present a pedagogical discussion of the emergence of gauged supergravities from M-theory. First, a review of maximal supergravity and its global symmetries and supersymmetric solutions is given. Next, different procedures of dimensional reduction are explained: reductions over a torus, a group manifold and a coset manifold and reductions with a twist. Emphasis is placed on the consistency of the truncations, the resulting gaugings and the possibility to generate field equations without an action. Using these techniques, we construct a number of gauged maximal supergravities in diverse dimensions with a string or M-theory origin. One class consists of the CSO gaugings, which comprise the analytic continuations and group contractions of SO(n) gaugings. We construct the corresponding half-supersymmetric domain walls and discuss their uplift to D- and M-brane distributions. Furthermore, a number of gauged maximal supergravities are constructed that do not have an action.

We investigate half-supersymmetric domain wall solutions of three maximally supersymmetric D = 9 massive supergravity theories obtained by Scherk-Schwarz reduction of D = 10 IIB supergravity. The three theories have superpotentials leading to half-supersymmetric domain wall solutions, one of which has zero potential but non-zero superpotential. The uplifting of these domain wall solutions to ten dimensions leads to three classes of half-supersymmetric type IIB 7-brane solutions. All solutions within each class are related by SL (2, R) transformations. The three classes together contain solutions carrying all possible (quantized) 7-brane charges. One class contains the well-known D7-brane solution and its dual partners and we provide the explicit solutions for the other two classes. The domain wall solution with zero potential lifts up to a half-supersymmetric conical space-time. The results in this talk are taken from [1].

We investigate half-supersymmetric domain wall solutions of four maximally supersymmetric D=9 massive supergravity theories obtained by Scherk-Schwarz reduction of D=10 IIA and IIB supergravity. One of the theories does not have a superpotential and does not allow domain wall solutions preserving any supersymmetry. The other three theories have superpotentials leading to half-supersymmetric domain wall solutions, one of which has zero potential but non-zero superpotential. The uplifting of these domain wall solutions to ten dimensions leads to three classes of half-supersymmetric Type IIB 7-brane solutions. All solutions within each class are related by SL(2,R) transformations. The three classes together contain solutions carrying all possible (quantised) 7-brane charges. One class contains the well-known D7-brane solution and its dual partners and we provide the explicit solutions for the other two classes. The domain wall solution with zero potential lifts up to a half-supersymmetric conical space-time., 24 pages, Latex. v3: statements about G7-brane solution refined

In the early universe, the dynamics of the Higgs field can give rise to many interesting phenomena. In the first part of this thesis, we study the behavior of the Higgs field during the reheating phase after cosmological inflation. We investigate the stability of the electroweak vacuum when the Higgs field is nonminimally coupled to gravity. We also study reheating in the scenario where the Higgs field itself drives inflation. In the second part, we study the possibility of generating the asymmetry between matter and antimatter during the electroweak phase transition -- the moment when the Higgs field starts to give mass to the other particles of the Standard Model. We show that it is not possible to constrain this process in a model-independent way. We also demonstrate that the predicted value of the baryon asymmetry is enhanced when leptons are included in the computation.

Cosmological inflation is the most successful theory that explains the homogeneity and flatness of the early universe. It also provides a quantum origin for the primordial perturbations that we observe in the Cosmic Microwave Background Radiation (CMB). The simplest models make use of a single scalar field, which produces the exponential expansion of the early universe. In this thesis the effects of additional heavy fields is studied from several points of view. On the one hand, possible signatures due to the presence of such fields are searched for in the current CMB data, and a new formalism is developed, allowing the analytical study of features arising from the presence of these fields. On the other hand, in the context of supergravity theories, the presence of additional heavy fields is ubiquitous, and their stability is needed in order to not spoil the basic predictions of single-field inflation. The viability of inflation in the presence of an additional heavy supersymmetric sector is studied, and several stability constraints are derived. The conclusion is that CMB data might be already sensitive enough to the presence of additional heavy fields, and that the landscape of supergravity scenarios which stabilize these fields is very constrained