Sharif Digital Repository

Jets originating from bottom (b) quarks, play an important role in the study of Standard Model processes together with the search for new physics. In the CMS experiment a considerable e?ort is dedicated to the development and the performance study of so-called b-tagging algorithms. On the other hand, the top quark which is produced in pair (tt¯) with a high rate at the LHC, decays near 99% of the time to a b-quark. Hence it provides a rich source of b-quark jets, suitable for b-jet identi?cation studies. In this thesis, a fully data-driven method to measure the b-tagging e?ciency, using top quark events in its semi-electron ?nal state, is developed. The results of the application of the... 

In this Thesis we study the string theory discription of non-relativistic quantum ?eld theories.In other statement we study the duality between gravity and gauge theory with non-relativistic symmetry.We discuss that this duality works in non rel- ativistic sense.We study two kind of non-relativistic theories that one of them camefrom string theory and other model obtained by special transformation of original relativistic theory and we see that how duality can be work for these models.Also dual picture of semi-classical string in the background that found from string theorystudied.We also study the motion of particle in a hot plasma and we ?nd a sign of non-relativisic duality really works  

In this thesis at ?rst, we review the magnetic monopole with andwithout electric charge in the ?at and also in the curved space and wereview the multimonopoles with axial and crystalline symmetry. In thisthesis also we review the holography principle and AdS/CFT duality andthe holographic renormalization. as the main part of the thesis the Julia-Zee dyon is studied in the context of AdS/CFT correspodence. We showthat for a solution of the dyon, the scalar ?eld in the model plays the roleof an order parameter. At high temperatures the vacuum expectationvalue of the dual scalar operator is zero and by lowering the temperature,it becomes nonzero and dual ?eld theory experiences a phase... 

Exact Renormalization Equations (ERGE) are powerful non-perturbative tools to study the dynamics of Quantum Field theories, with respect to the change of energy. Putting cut-off on momentums of the system, is the specific regularization that is used to obtain ERGEs. This regularization breaks the gauge symmetry in the case of gauge theories. So the symmetry will be lost through the energy flow as well.Finding a gauge symmetry for a regularized system is the aim of this research. Also we have investigated the related ERGEs and the behavior of symmetry through the flow  

Up to now, many seismic design methods and construction technologies have been investigated to reduce the seismic responses of bridges, buildings and potentially vulnerable structures. [1] Introducing a new effective systems aim to control of vibration caused by earthquake on the structures will be useful. This system is based on repelling of imposed force to the structures with tuned mass dampers (TMDs), to gain minimum damage. The detuning of the structures by equipped with TMDs resulted from nonlinear behavior due to dynamic loads such as strong ground motions are real concern in the practical applications. The application of TMDs, as expected, can reduce the deformation of the... 

We extend the non-relativistic AdS/CFT correspondence to the fermionic fields. In particular we study the two point function of a fermionic perator in non-relativistic CFTs by making use of a massive fermion propagating in geometries with Schrodinger group isometry. Although the boundary of the geometries with Schrodinger group isometry differ from that in AdS geometries where the dictionary of AdS/CFT is established، using the general procedure of AdS/CFT correspondence، we see that the resultant two point function has the expected form for fermionic operators in non-relativistic CFTs، though a non-trivial regularization may be needed. Also we study Weyl symmetry for non-relativistic... 

We search for supersymmetry in the same-sign dilepton final state in the first 35 pb1 of data collected by the CMS detector and find no evidence of new physics at this point. Since true same-sign physics backgrounds, such asWWjj, are negligible for this amount of integrated luminosity, we focus our attention on data-driven estimations of the backgrounds where one (W+jets and tt backgrounds) or both of the leptons (QCD background) are fake. We use the generalized fake ratio method documented to estimate the rates for these fake backgrounds. Another source of backgrounds in the case of electrons is the charge-flip, where the charge of one of the electrons in an opposite-sign di-electron pair... 

In this thesis, we review the properties of the two dimensional quantum electrodynamics, called Schwinger model and then we study the noncommutative version of the Schwinger model. The most important properties of the Schwinger model in commutative space are the production of dynamical mass for photon like the Higss mechanism and also the bosonization of the model by integrating out the fermionic degrees of freedom and describing it through the free bosonic action. The first section of this thesis includes two parts. At the first, we investigate the corrections to the dynamical photon mass in the noncommutative Schwinger model by using the photon’s vacuum polarization diagrams at one loop...