Sharif Digital Repository

Bonding gravity with Quantum mechanics has always been a challenging issue. So that, accomplishing a theory of quantum gravity is one of the most important research topics in High-Energy Physics.Information paradox in black holes is among such issues which connect quantum mechanics with gravity. Black holes as a natural solution of Einstein equations have a distinction, with other solutions, since there exists an event horizon that imparts space-time into two causally disconnected regions.According to Hawking’s calculations, black holes would evaporate over time by the thermal radiation. This resulting thermal radiation has less information than the initial collapsed matter in a pure state.... 

The information paradox is one of the most important questions around black hole physics. The problem is raised since the operators which are responsible for the evolutions in quantum mechanics are unitary while the black hole evaporation seems to be a nonunitary evolution (Since a black hole which has been formed from the collapse of matter in a pure state evaporates to a mixed thermal state eventually). This loss of information during the evaporation process is known as the information paradox.Recently many attempts have been made to investigate this problem holographically, actually to see if the information is really lost and if not how one can recover the information.Our main goal is to... 

Not all effective theories in the low energy limit are compatible with quantum gravity. The goal of the swampland program is bringing the necessary criteria to test these effective theories and examine their compatibility with quantum gravity. This set of conjectures determines which theory is effective in the perspective of the self-consistent theory of quantum gravity which is actually string theory. A very important connection (through the swamp program) between high energy physics (UV) And the physics of the low energy limit (IR) can provide very important explanations for our questions. Among them are the cosmological constant problem in general relativity and the hierarchy problem in... 

Not all low-energy effective theories are compatible with quantum gravity. The purpose of swampland program is to provide the necessary characteristics to test these theories and measure their compatibility with quantum gravity. Accordingly, this group of conjectures determine which effective theory is in the landscape of self-consistent quantum gravity which is String Theory. An important connection is provided through the swampland program between the high-energy limit physics (UV) and the low-energy limit physics (IR) that can provide immensely important fundamental explanations for our profound and consistent questions such as the hierarchy problem in elementary particle physics and... 

Gravity models in lower dimensions, particularly in two and three dimensions, are powerful tools for gaining a deeper understanding of the fundamental structure of gravitational and quantum theories. Three-dimensional gravity, due to its simpler and more controllable properties, provides a unique laboratory for studying the geometric and topological features of black holes, as well as the holographic nature of spacetime. On the other hand, two-dimensional gravity models, such as dilaton gravity, play a crucial role in exploring the dynamic mechanisms of horizons and phenomena like black hole evaporation. These models not only allow us to grasp the complexities of quantum gravity in a more... 

As a contribution to the subject of the information loss paradox in (1+1)-dimensional gravitational systems, we studied the evaporation of (1+1)-dimensional black holes in AdS gravity from a (3+1)-dimensional point of view. A partial dimensional reduction of Einstein-Hilbert action with a negative cosmological constant in four dimensions led to a black hole in AdS2 gravity. This method allowed us to effectively split the (3+1)-dimensional spacetime into a (1+1)-dimensional black hole and a remainder, which could be interpreted as a ‘bath’. We computed the fine-grained entropy of the radiation using geodesic lengths in the (3+1)-dimensional spacetime. We then focus on the finite temperature... 

The problem of quantum gravity has always posed significant challenges, particularly evident in black hole evaporation and the information paradox. Numerous proposals have been offered. Solutions such as semi-classical gravitational approximations aim to reconcile gravitational collapse and black hole evaporation with unitary quantum evolution. Symmetries, such as conformal symmetry and Anti-de Sitter geometry, Simplify the explanation of information recovery during black hole evaporation. Near the horizon of a spherically symmetric 4D black hole, gravity can be effectively described by a 2D dilaton theory. Studying the problem in 2D magnifies the strength of conformal symmetry. Holography,... 

In recent years, a series of deep connections have been found between the ideas that used to be in the Algebraic Theory of Quantum Fields and the important problems of High Energy and Fundamental Physics. In the 1960s and later, some people who were mostly closer to mathematicians were trying to formulate the basics and principles of Quantum Field Theory in mathematically precise way. Many and various efforts have been made in this direction. One of these important efforts has been the Algebraic Theory of Quantum Fields. The main motivation in the Algebraic Theory of Quantum Fields is to focus on the operators and observables of the theory and study the algebraic structure between them instead... 

According to general theory of relativity, collapse of matter under gravitational force leads to the formation of black holes. Considering the quantum effect shows that black holes have thermal radiation which cause them to evaporate. After a complete evaporation, the state of radiation can not contain all information of initial matter. In other word, this process does not obey unitary evolution of quantum mechanics. This is called the black hole information paradox, which has been one of the most challenging problem of theoretical physics for several recent decades. Recently, a deep connections between asymptotic symmetries, soft graviton theorem and gravitational memory effect has been... 

Investigating the 2−dimensional critical percolation still faces some challenges. According to the general belief the LCFT with central charge c = 0 should work, but in practice it isn’t clear where the logarithmic divergence appears in critical percolation. In the recent years numerical and Conformal bootstrap methods have led to a significant progress in the general theory of LCFTs. Yet finding explicit examples where the correlation functions exhibit logarithmic divergences and the explanation of such divergences in terms of the observables of the lattice has remained a challenge. Another difficulty in the percolation theory is that first the Q−state Potts model is solved on a lattice and... 

Entanglement is an immediate consequence of quantum mechanical pos- tulates and is thus an indispensable part of studying quantum systems. A very useful quantity which can appropriately quantify entanglement between the degrees of freedom of a composite quantum system is En- tanglement Entropy (EE).
Over the last few years, this subject has attracted a lot of interest both in QFT and in the context of holography. On the one hand, an intu- itive geometrical Holographic model for entanglement entropy has been proposed in the context of gauge/gravity duality, and on the other, var- ious issues concerning entanglement have been explored, e.g. in quan- tum computation, quantum information...