Curriculum Vitae et Studiorum of Silvia Penati - Dipartimento di ...

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XI. SCIENTIFIC ACTIVITY My research activity develops in the area of theoretical high energy particle physics. It is mainly focused on string theory, supersymmetric quantum field theory applied to the study of the fundamental interactions and continuum statistical models. String theory is one of the most promising candidates for a fundamental, microscopic theory of Nature. In fact, it provides a consistent description of quantum gravity and black holes, it contains the standard model of particle physics as an effective low energy theory and allows for possible (supersymmetric and higher dimensional) extensions of the standard model beyond the electroweak scale, so giving a possible explanation to the hierarchy problem and to the unification of the fundamental interactions. In the last decade, one of the main products of string theory has been the AdS/CFT correspondence. The correspondence states that a quantum field theory describing interacting particles in strong coupling regime in d dimensions is equivalent to a weakly coupled gravity (or string) theory in (d+1) dimensions. This opens the possibility to use string theory for modeling strongly coupled systems via an holographic perturbative description, in many areas of physics. Applications in particle physics point towards the direction of understanding QCD confinement and quarkgluon plasma phase transition, while applications have been recently attempted in condensed matter systems where a quantum critical point is present (high-T superconductors, superfluids etc..). The main topics of my recent research activity are: • AdS/CFT correspondence: In order to prove the correspondence, there are a number of tests which can be performed on the predictions coming from the dual gravity theory on some quantities of physical interest of the corresponding 4d field theory (correlation functions and anomalous dimensions of composite operators). Main results have been obtained by performing some of these tests from the field theory side. It is important to extend the correspondence beyond its original formulation which predicts a dual gravity description only for supersymmetric conformal field theories. My main contributions in this direction concern the study of deformations of the correspondence which partially or totally breaking of supersymmetry. • AdS/Chern–Simons correspondence: AdS/CFT correspondence can be formulated in different dimensions. When studying AdS solutions of gravity in four dimensions we obtain a dual description of a supersymmetric three dimensional Chern–Simons theory. The study of these models are motivated by the attempt to increase our knowledge on the correspondence and its range of applications, but also by the direct attempt to apply it to condensed matter systems. Within this context, my main results are the determination of the complete spectrum of conformal fixed points which should have a dual gravity description and the study of their properties under renormalization group flows. • Non(anti)commutative Quantum Field Theories: In one of its phases, string theory gives rise at low energies to non(anti)commutative fields theories, that is theories defined on (super)spaces with non(anti)commuting bosonic or spinorial coordinates. A crucial contribution has been given in this context with the formulation of the nonanticommutative superspace. Our paper has been the inspiring paper which has opened the interest in this subject. I have developed a systematic investigation of nonanticommutative theories at quantum level. Since nonanticommutativity partially breaks supersymmetry it is not an easy task to formulate theories which are renormalizable. I have found various classes of renormalizable theories which are nontrivial generalizations of ordinary theories of some physical interest (WZ model, Yang–Mills theories). • Scattering amplitudes: One of the main tasks of quantum field theory is the description of scattering processes, since any prediction in this context has a direct connection with experimental data. Recently, the interest in the structure of scattering amplitudes, in particular for supersymmetric theories, has been also triggered by string theory. In fact, the AdS/CFT correspondence predicts a direct correspondence between scattering amplitudes in supersymmetric Yang–Mills theories and Wilson loops in AdS. The most powerful technique for computing scattering amplitudes is perturbative field theory. However, it is well known that as soon as the perturbative order and/or the number of particles involved increase, an ordinary Feynman diagram approach becomes unfeasible. An alternative approach has been developed, the so-called unitarity cuts method. This method, although very powerful, predicts a number of interesting properties for supersymmetric amplitudes, but it is not suitable for understanding the actual origin of these properties. We have been developing an alternative approach for computing scattering amplitudes in supersymmetric theories which makes use of supergraph techniques and background field method. The final goal is to give a set of rules which can be easily implemented by computer programs. 8
• ABJM theories: Besides the well known realization of the AdS/CFT correspondence that involves the maximally supersymmetric Yang–Mills theory in four dimensions, a second explicit realization involves a three dimensional Chern–Simons–matter theory with non–maximal N=6 supersymmetry. The investigation of dualities and symmetries in the on–shell sector of the theory is an important task aimed at disclosing model–independent features of the AdS/CFT correspondence. The explicit evaluation of scattering amplitudes and Wilson loops and the study of their properties are currently under investigation. In the past, important results have been obtained in the area of (supersymmetric and non-supersymmetric) two dimensional Conformal Field Theories, Integrable models, Theories with boundaries which describe statistical models with defects, Topological theories, Nonlinear sigma models. 9
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