Search for: quantum-gravity
0.006 seconds

    Holographic two-point functions for 4d log-gravity

    , Article Journal of High Energy Physics ; Volume 2012, Issue 9 , 2012 ; 11266708 (ISSN) Johansson, N ; Naseh, A ; Zojer, T ; Sharif University of Technology
    Springer  2012
    We compute holographic one- and two-point functions of critical highercurvature gravity in four dimensions. The two most important operators are the stress tensor and its logarithmic partner, sourced by ordinary massless and by logarithmic nonnormalisable gravitons, respectively. In addition, the logarithmic gravitons source two ordinary operators, one with spin-one and one with spin-zero. The one-point function of the stress tensor vanishes for all Einstein solutions, but has a non-zero contribution from logarithmic gravitons. The two-point functions of all operators match the expectations from a three-dimensional logarithmic conformal field theory  

    Quantum jump from singularity to outside of black hole

    , Article Journal of High Energy Physics ; Volume 2016, Issue 2 , 2016 , Pages 1-20 ; 11266708 (ISSN) Dündar, F. S ; Hajian, K ; Sharif University of Technology
    Springer Verlag 
    Considering the role of black hole singularity in quantum evolution, a resolution to the firewall paradox is presented. It is emphasized that if an observer has the singularity as a part of his spacetime, then the semi-classical evolution would be non-unitary as viewed by him. Specifically, a free-falling observer inside the black hole would have a Hilbert space with non-unitary evolution; a quantum jump for particles encountering the singularity to outside of the horizon as late Hawking radiations. The non-unitarity in the jump resembles the one in collapse of wave function, but preserves entanglements. Accordingly, we elaborate the first postulate of black hole complementarity: freely... 

    Challenges Against The Front Grand Unified Theories

    , M.Sc. Thesis Sharif University of Technology Zavarbashi, Amin (Author) ; Golshani, Mehdi (Supervisor)
    Many physicists believed that all four forces were once unified at high energy levels but as the universe reduced into a lower-energy states the inherent symmetry between the forces began to break down.this broken symmetry caused the creation of four distinct forces of nature. The goal of the unified theory is an attempt to look back in time to when these forces where unified as one. In this thesis I tried to give an overview of the challenges which is againsted theorists in the way of unification. In the first chapter explores the theory that try to unify the electromagnetic and weak forces are investigated.it is done by considering guage principle and spontaneous symmetry breaking.in the... 

    An Expository Survey on Different Approaches to Quantum Gravity

    , M.Sc. Thesis Sharif University of Technology Molaei, Mohammad Reza (Author) ; Golshani, Mehdi (Supervisor) ; Azadegan, Ebrahim (Supervisor)
    The search for an empirically proven quantum theory of gravity is one of the greatest open problems of fundamental physics. Obstacles are formal and conceptual in nature. Our goal is to find a theory that somehow unites general relativity (Einstein's classical field gravity theory) and quantum field theory. In this research work, the problem of quantum gravity and the reason for its importance are investigated, as well as the proposed solutions; and what philosophical issues do these approaches and the issue itself create. Research has been carefully selected to remain managed in terms of size and content, however, some basic formalism is introduced to enter physics and the philosophy of... 

    On Swampland Conjectures and Relations to Entropy of States

    , M.Sc. Thesis Sharif University of Technology Rajabi Dahaki, Mahdi (Author) ; Torabian, Mahdi (Supervisor) ; Ashoorioon, Amjad (Co-Supervisor)
    In the framework of quantum field theory, countless consistent theories can be constructed. However, it is understood that only a small subset of these theories can be consistently embedded in a theory of quantum gravity (QG). In string theory, as the best candidate for quantum gravity, there is a landscape of effective field theories (EFTs) which are descended from some compactification of extra dimensions. EFTs which are not derived from a compactification is said to belong to swampland. From a bottom-up point of view, the aim of the swampland program is to find a list of criteria which an EFT must respect so that it survives the swampland. The trans-Planckian censorship conjecture (TCC)... 

    Investigation of Information Paradox in Charged Black Holes Using the Holography

    , M.Sc. Thesis Sharif University of Technology Shokouhi, Farhad (Author) ; Faraji Astaneh, Amin (Supervisor)
    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.... 

    Critique and Survey of Various Formulation of Multiverse Theory

    , Ph.D. Dissertation Sharif University of Technology Masoumi, Saeed (Author) ; Golshani, Mehdi (Supervisor) ; Sheikh Jabbari, Mohammad Mehdi (Supervisor)
    Multiverse scenario has been recently addressed by physicists and they have found it useful in many areas of physics. In this dissertation, I have treated some issues about multiverse such as the kinds of multiverses, the arguments for or against multiverse, areas in which multiverse is introduced, etc. This dissertation has six chapters and an appendix. In the chapter one, some classifications of multiverse is introduced, and also some definitions of the concept of a world is presented. Then, my classification and definition of a multiverse and a world is introduced. In the chapter two, the concept of possible worlds in philosophy and its relationship with multiverse hypothesis is examined.... 

    On String Swampland Conjectures from Black Holes Physics

    , M.Sc. Thesis Sharif University of Technology Barzegar Mirzaei, Shahrzad (Author) ; Torabian, Mahdi (Supervisor)
    Swampland conjectures are set of conditions that must be satisfied in a quantum field theory in order to be compatible with a theory of quantum gravity. These conditions have been deduced from the features of field theories, which are derived from the compactification of the additional dimensions of the string theory. However, it is thought that the mpatibility of these conditions with the theory of quantum gravity is independent of string theory. One of the important reasons is that the swampland conjectures can be obtained by examining the physics of black holes. Black hole is one of the quantum states of any quantum gravity theory. In this thesis, first we will have an overview of the... 

    An Investigation into Orch OR Theory of Consciousness

    , M.Sc. Thesis Sharif University of Technology Meshkati, Ahmad (Author) ; Golshani, Mehdi (Supervisor)
    According to Penrose-Hameroff's theory, Consciousness as an undeniable reality can, in some cases, be explained by a kind of orchestrated objective reduction of the wave function in the cytoskeleton of the brain neurons. Here, I have presented the subject, problem, and claim of this theory, as well as its argument, which consists of three main premises. In the first premise, first by rejecting the opposing theories and then by presenting reasons, it is shown that human thinking is, in some manner, sound but non-computable, and at the same time, accepting the Non-computability of human thinking requires believing in the objects in the universe that are non-computable, but They can be...