Gauge theories are one of the corner stones of modern theoretical physics. They describe the nature of all fundamental interactions and have been applied in multiple branches of physics. The most challenging problem of gauge theories, which has not been solved yet, is their strong coupling dynamics. A class of gauge theories that admits simplifications allowing to deal with the strong coupling regime are supersymmetric ones. For example, recently proposed method of supersymmetric localization allows to reduce expectation values of supersymmetric observables, expressed through the path integral, to finite-dimensional matrix integral. The last one is usually easier to deal with compared to the original infinite-dimensional integral. This thesis deals with the matrix models obtained from the localization of different 5D gauge theories. The focus of our study is N=1 super Yang-Mills theory with different matter content as well as N=1 Chern-Simons-Matter theory with adjoint hypermultiplets. Both theories are considered on the five-spheres. We make use of the saddle-point approximation of the matrix integrals, obtained from localization, to evaluate expectation values of different observables in these theories. This approximation corresponds to the large-N limit of the localized gauge theory. We derive <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?N%5E%7B3%7D" /> behavior for the free energy of 5D N=1* super Yang-Mills theory at strong coupling. This result is important in light of the relation between 5D theory and the world-volume theories of M5-branes, playing a significant role in string theory. We have also explored rich phase structure of 5D SU(N) N=1 super Yang-Mills theory coupled to massive matter in different representations of the gauge group. We have shown that in the case of the massive adjoint hypermultiplet theory undergoes infinite chain of the third order phase transitions while interpolating between weak and strong coupling in the decompactification limit. Finally, we obtain several interesting results for 5D Chern-Simons theory, suggesting existence of the holographic duals to this theory. In particular, we derive <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?N%5E%7B5/2%7D" /> behavior of the free energy of this theory, which reproduces the behavior of the free energy for 5D theories with known  holographic duals.

The gauge/string duality, a.k.a. the holographic principle is a profound assertion that emerged from string theory. It relates strongly-coupled gauge theories to weakly coupled string theories living in a higher-dimensional curved geometry. Nevertheless, it is a conjecture, and only a few instances of its more concrete form, the AdS/CFT correspondence, are well-understood. The most well-studied example is the duality between N=4 SYM, which is a CFT, and type IIB string theory in AdS5xS5 background. Generalization to less symmetric cases is a must, and the next logical step is to add a mass scale to N=4 SYM, therefore breaking its conformal symmetry and leading to N=2* SYM, the theory we study in this thesis. It is supersymmetric enough to employ the powerful localization method that reduces its partition function to a matrix model. We will see that the mass scale causes non-trivial phase structures in its vacuum configuration, visible in the holographic regime. We will probe them using Wilson loops in different representations of the gauge group. On the other hand, the dual supergravity background was derived by Pilch-Warner, making N=2* theory an explicitly testable non-conformal holographic case, which is a rare example. We will prove that the duality works for the dual observables (string action, D-branes) we managed to compute, even at a quantum-level.

We present the supersymmetry and localization of an N=2 theory on S3b along with that of an N=(2,2) theory on S2. Performing the dimensional reduction of the theory on S3b produces a theory on S2 with no flux-sectors. A re-evaluated version of twisted reduction is applied on the level of the S3b partition function, arguing for a splitting of the partition function into pieces. The splitting produces flux-like sectors correspondent to the S2 theory but holds the potential for superfluous sectors. An argument interpreting these sectors as true flux is given and utilized to remove superfluous sectors due to topological restrictions on S2. The final result is a method which gives a bijective mapping ZS3b to ZS2 . / Vi utför konstruktionen av två supersymmetriska teorier på en deformerad 3-sfär samt en 2-sfär. Den utökade symmetrin tillåter oss att använda en lokaliseringsmetod för att reducera partitionsfunktionerna till ändligt-dimensionella integraler. På 2-sfären finner vi diskreta konfigurationer vars tolkning vi vill finna i konstruktionen på 3-sfären. Vi utför en dimensionell reduktion ifrån 3-sfären till 2-sfären och finner en ekvivalens som saknar dessa konfigurationer. Som substitut presenteras en metod där integralen delas upp i delar som kan tolkas att vara ekvivalenta med de avsaknade diskreta konfigurationerna. Slutligen framförs ett argument för vilka delar av integralen som kan existera på 2-sfären och resterande delar avfärdas. Resultatet är en exakt avbilding mellan partitionsfunktionerna.