Particle dynamics of branes

The aim of this thesis is to develop a technique with which we can formulate brane solutions easier. Brane solutions play an important role in string theory since they represent the degrees of freedom of the non-perturbative string theory of which little is known. We choose to let the dynamics of the branes depend on one coordinate r perpendicular to the worldvolume of the brane. As a first step to find brane solutions we reduce over the worldvolume of the brane or over all the directions perpendicular to the worldvolume, with the exception of r. When we reduce over the worldvolume, the lower-dimensional solutions are S(-1)-branes or instantons. This depends on whether time is part of the worldvolume or is the transversal direction r. As it turns out, both solutions describe geodesic motion on the scalar manifold G/H of the lower-dimensional theory. We present the generating geodesic. With this we mean that if we act with the symmetry group G on this solution, we automatically find the most general solution possible. If we then proceed by undoing the steps of the reduction, we end up with a brane solution with the most general worldvolume. On the other hand, we can also reduce the brane over the directions perpendicular to the worldvolume. These solutions are domain-walls or cosmologies (again this depends on whether time is part of the worldvolume or is the transversal direction r). We have analyzed under which circumstances both solutions satisfy first order equations. In case the solutions also satisfy scaling behaviour, they turn out to be geodesics on the scalar manifold again. We finish by considering how the domain-wall / cosmology correspondence can sometimes be embedded in a supergravity setting.

Dynamics of Generalized Assisted Inflation

We study the dynamics of multiple scalar fields and a barotropic fluid in an FLRW-universe. The scalar potential is a sum of exponentials. All critical points are constructed and these include scaling and de Sitter solutions. A stability analysis of the critical points is performed for generalized assisted inflation, which is an extension of assisted inflation where the fields mutually interact. Effects in generalized assisted inflation which differ from assisted inflation are emphasized. One such a difference is that an (inflationary) attractor can exist if some of the exponential terms in the potential are negative.Comment: 27 page

Pseudo-supersymmetry and a Tale of Alternate Realities

We discuss how all variant 10d and 11d maximal supergravities, including star supergravities and supergravities in different signatures, can be obtained as different real slices of three complex actions. As an application we study the recently introduced domain-wall/cosmology correspondence in this approach. We give an example in 9d and 10d where the domain-wall and corresponding cosmology can be viewed as different real slices of the same complex solution. We argue how in this case the pseudo-supersymmetry of the cosmological solutions can be understood as the invariance under supersymmetry of a variant supergravity.Comment: 32 page

Non-Extremal D-instantons and the AdS/CFT Correspondence

We investigate non-extremal D-instantons in an asymptotically $AdS_5 \times S^5$ background and the role they play in the $AdS_5 / CFT_4$ correspondence. We find that the holographic dual operators of non-extremal D-instanton configurations do not correspond to self-dual Yang-Mills instantons, and we compute explicitly the deviation from self-duality. Furthermore, a class of non-extremal D-instantons yield Euclidean axionic wormhole solutions with two asymptotic boundaries. After Wick rotating, this provides a playground for investigating holography in the presence of cosmological singularities in a closed universe.Comment: 30 pages, 3 figure

Screen for ISG15-crossreactive deubiquitinases

Background. The family of ubiquitin-like molecules (UbLs) comprises several members, each of which has sequence, structural, or functional similarity to ubiquitin. ISG15 is a homolog of ubiquitin in vertebrates and is strongly upregulated following induction by type I interferon. ISG15 can be covalently attached to proteins, analogous to ubiquitination and with actual support of ubiquitin conjugating factors. Specific proteases are able to reverse modification with ubiquitin or UbLs by hydrolyzing the covalent bond between their C-termini and substrate proteins. The tail regions of ubiquitin and ISG15 are identical and we therefore hypothesized that promiscuous deubiquitinating proteases (DUBs) might exist, capable of recognizing both ubiquitin and ISG15. Results. We have cloned and expressed 22 human DUBs, representing the major clades of the USP protease family. Utilizing suicide inhibitors based on ubiquitin and ISG15, we have identified USP2, USP5 (IsoT1), USP13 (IsoT3), and USP14 as ISG15-reactive proteases, in addition to the bona fide ISG15-specific protease USP18 (UBP43). USP14 is a proteasome-associated DUB, and its ISG15 isopeptidase activity increases when complexed with the proteasome. Conclusions. By evolutionary standards, ISG15 is a newcomer among the UbLs and it apparently not only utilizes the conjugating but also the deconjugating machinery of its more established relative ubiquitin. Functional overlap between these two posttranslational modifiers might therefore be more extensive than previously appreciated and explain the rather innocuous phenotype of ISG15 null mice. Citation: Catic A, Fiebiger E, Korbel GA, Blom D, Galardy PJ, et al (2007) Screen for ISG15-crossreactive Deubiquitinases. PLoS ONE 2(7): e679

ElaD, a Deubiquitinating protease expressed by E. coli.

BACKGROUND: Ubiquitin and ubiquitin-like proteins (Ubl) are designed to modify polypeptides in eukaryotes. Covalent binding of ubiquitin or Ubls to substrate proteins can be reversed by specific hydrolases. One particular set of cysteine proteases, the CE clan, which targets ubiquitin and Ubls, has homologs in eukaryotes, prokaryotes, and viruses. FINDINGS: We have cloned and analyzed the E. coli protein elaD, which is distantly related to eukaryotic CE clan members of the ULP/SENP protease family that are specific for SUMO and Nedd8. Previously misannotated as a putative sulfatase/phosphatase, elaD is an efficient and specific deubiquitinating enzyme in vitro. Interestingly, elaD is present in all intestinal pathogenic E. coli strains, but conspicuously absent from extraintestinal pathogenic strains (ExPECs). Further homologs of this protease can be found in Acanthamoeba Polyphaga Mimivirus, and in Alpha-, Beta-and Gammaproteobacteria. CONCLUSION: The expression of ULP/SENP-related hydrolases in bacteria therefore extends to plant pathogens and medically relevant strains of Escherichia coli, Legionella pneumophila, Rickettsiae, Chlamydiae, and Salmonellae, in which the elaD ortholog sseL has recently been identified as a virulence factor with deubiquitinating activity. As a counterpoint, our phylogenetic and functional examination reveals that ancient eukaryotic ULP/SENP proteases also have the potential of ubiquitin-specific hydrolysis, suggesting an early common origin of this peptidase clan