Sharif Digital Repository

Studying near-horizon space-time for Reissner-Nordstrom black hole when taking extremal limit, we see how the region between the inner and outer event horizons appears as a part of , while it seems to shrink when looking into the geometry of a bit far from each of two horizons. By a careful investigation of radial geodesics in this limit, it is shown that specific families of observers starting their motion form anywhere so close to outer horizon, always pass this region in a constant proper time; however, observers coming from somewhere, further, pass it in as extremely short time as it sounds this region is hardly tangible  

Double Field Theory tries to incorporate T-duality, one of fundamental features of string theory, as a symmetry of a field Theory on a doubled space. It sets fields depend on winding mode conjugate coordinates as well as conventional space-time coordinates. In this review after presenting a brief introduction to string theory we investigate O(d,d,ℤ) duality group. Subsequently, we focus on Double Field Theory construction putting our attention on massless sector of string theory. We investigate on 2D nonlinear sigma model action in DFT and its gauge algebra. We follow this review by discussing constraints of DFT and Double Geometry. At the end we present some unsolved questions in this... 

The study of quantum effects for black holes indicates that they can thermally radiate different particles.In this thesis, we investigte the radiation of charged spin zero particles and show that these particles can interact with each other and as a result produce photons.These produced photons make a correction to the emitted photons from the black hole. By caculating this correction, we conclude that interactions have a small effect on the radiation spectrum of the photon  

Supersymmetry breaking mechanism is an unanswered question. Which is not allowed to break at tree-level in MSSM due to supertrace restrictions. Most theories suppose it’s broken in a dark section, much higher energies than electro-weak and its impacts as soft SUSY breaking terms emerged in Lagrangian. Here, in a different approach, an extension of MSSM with a U(1) and Stueckelberg superfield along with nonlinear gauge transformation, provides an additional condition to present a tree-level SUSY breaking mechanism. Mass mixing term in Stueckelberg’s Lagrangian or kinetic mixing are two methods of such an extension. The particles mass terms, solving the Higgsino mass parameter problem µ,... 

Nowadays, condition monitoring and fault diagnosis are considered as one of the most important maintenance and diagnosis strategies in state-of-the-art industries. Serious damage such as machine and coupled equipment failure, machine failure in a neighborhood in case of severe damage, and production loss will be resulted in late fault detection. One of the critical information in condition monitoring is the machine's rotating speed. In many cases of condition monitoring, the rotating speed, and the machine's technical information (such as bearing characteristic frequency )is not available. In this study, a ruled-base model and an intelligent model are developed for machine running speed... 

Among the various types of black holes, dilatonic black holes can be mentioned which are in the center point of view at their extremality. In this study, we pay attention to these answers and their fields and the way they behave variously, especially when the coupling constant α is between 0and1. For doing so, in chapter one we attempt to study one of the simplest answers in General Relativity (Schwarzschild) and some beginning contexts. Then in chapter two, we try another answer (Reissner Nordstrom) which contains non-Extremal and Extremal states. In chapter three we introduce the concept of the higher theories. Chapter four is a hint about hawking radiation. And finally in chapter five, we... 

When we consider Klein-Gordon and Maxwell perturbation fields on the constant gravitational background, the Einstein-Maxwell equations solution will lead to Reissner-Nordstrom black hole which has decreasing mass because of Hawking radiation of bosons from its outer horizon; by reaching this balck hole to extremal case the evaporation will be stoped. The evaporation time is infinite. But String theory equations solution in General Relativity approximation shows that [11] if a Dilaton field ϕ has a exp⁡(-αϕ) coupling with electromagnetic field, the rate of reaching to extremal case will depend on α. We show that by increasing α from 0 to 1, the evaporation time will be initially infinite... 

In 2004 Ooguri, Strominger, and Vafa could write the partition function of 4D N=2 extremal black holes in type IIA superstring theory as the square of the absolute value of the partition function of type A closed topological string theory, which had already been introduced by Edward Witten in 1990. In this study, T and S dualities were applied to the original conjecture of Ooguri, Strominger, and Vafa. By using T duality, we have verified that the conjecture holds for 4D N=2 extremal black holes of type IIB superstring theory to the one loop order in string coupling. In other words, one can write the partition function of these kinds of black holes as the square of the absolute value of... 

Inthisthesiswe willuse curved space-time quantum mechanicsto solveDirac equationin the background of dilaton black hole. Graybodyfactors and Hawking radiation and evaporation rates of charged massive spin particles in the background of dilaton black holes is obtained. The results are analyzed and the lifetime of dilaton black hole in terms of different dilaton coupling constants is studied  

Langlands Program or Langlands Correspondence is a unified theme for many important results of number theory, which proposed by Robert Langlands in the late 1960's. The aim of this program is to relate intricate problems of arithmetic to analysis and use powerful methods of analysis to investigate these problems. One of the main aspects of this duality is the appearance of two dual groups in two sides of it that can be obtained from one another. In the 1980's, by the work of many mathematicians, it turns out that a geometrical version of this duality can be formulated. In the last ten years, a categorical version of duality is worked out. On the other hand, by the work of physicist like... 

Since 1980’s, String Theory is considered as one of the main candidates for the unified theory of nature. One of the important features of this theory, is describing the Gravity as a renormalizable quantum theory. An interesting and important problem is the interaction of the string with classical fields in spacetime such as gravity. The conclusions which can be deduced may be very different from the standard results in case of absence of these classical fields.On the other side, for giving a solution to one of the unsolved problems in standard model of particle physics, the hierarchy problem, Lisa Randall and Raman Sundrum in1999, suggested a model which assumes that spacetime may has... 

In this thesis we first discuss the final fate of a spherical symmetric distribution of matter which has undergone a gravitational collapse, by reviewing some classical collapse models. Our emphasis will be on the visibility of singularity after it forms. Then we will mention some general aspects of quantum field theories in curved space-time and after that we investigate the quantum background effects on the evolution of a spherical symmetric and homogeneous distribution of dust. In fact by calculating the quantum corrections—due to massless scalar fields which are arbitrarily coupled to the background geometry— on the geometry of collapsing sphere, one can obtain the quantum corrected... 

To investigate many interesting and rare physics processes at the Large Hadron Collider, we need much more data. The High Luminosity LHC (HL-LHC) is a foreseen upgrade for LHC to increase its luminosity and get ten times more data until the end of HL-LHC.Without any intervention, The CMS ECAL will face many challenges in HL-LHC. The end-caps must be fully replaced, and the electronic structure of the barrels will be modified. This thesis addresses the R&D studies of both sections.For the barrels, a test beam experiment has been performed on a prototype 5x5 matrix of legacy PbWO4 crystals with the new Very Front End (VFE) boards and the data has been analyzed.For endcaps, a 3x5 martix of... 

In this thesis we have used the low energy effective action of the string theory to find an asymptotic Anti-de sitter metric with a non-vanishing H field. Then we have used the AdS/CFT correspondence to study the effects of the added Kalb_Ramond field on two calculations in the boundary theory. The first one was the calculation of the drag force exerted on a moving quark in the quark-gluon plasma. In the second calculation we observed the effect of the added field on the confinement-de confinement phase transition