1,889 research outputs found
Dirac operator on complex manifolds and supersymmetric quantum mechanics
No full textSmilga, Andrei. (2012). Dirac operator on complex manifolds and supersymmetric quantum mechanics. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/120323
Digestible quantum field theory
No full textThis book gives an intermediate level treatment of quantum field theory, appropriate to a reader with a first degree in physics and a working knowledge of special relativity and quantum mechanics. It aims to give the reader some understanding of what QFT is all about, without delving deep into actual calculations of Feynman diagrams or similar. The author serves up a seven‐course menu, which begins with a brief introductory Aperitif. This is followed by the Hors d'oeuvres, which set the scene with a broad survey of the Universe, its theoretical description, and how the ideas of QFT developed during the last century. In the next course, the Art of Cooking, the author recaps on some basic facts of analytical mechanics, relativity, quantum mechanics and also presents some nutritious “extras” in mathematics (group theory at the elementary level) and in physics (theory of scattering). After these preparations, the reader should have a good appetite for the Entrées ‐ the central par t of the book where the Standard Model is described and explained. After Trou Normand, the restive pause including human stories about physicists and no formulas, the author serves the Dessert, devoted to supersymmetry (a very beautiful theory that is still awaiting a direct experimental confirmation), to general relativity and to the mystery of quantum gravity.
Multi-Agent Reinforcement Learning using Centralized Critics in Collaborative Environments
No full textAgents trained through single-agent reinforcement learning methods such as self-play can provide a good level of performance in multi-agent settings and even in fully cooperative environments. However, most of the time, training multiple agents together using single-agent self-play yields poor results as each agent tries to learn how to perform their task while their teammates are also learning. Thus, training models to reach an optimal behaviour in such situations becomes a challenging, if not impossible issue to overcome. One possible solution to deal with this problem is to facilitate a centralized training process in which the policies of all agents are evaluated by a centralized critic that has access to the observations and actions of all the agents in the environment. By using this approach, the environment becomes stationary and the agents learn in a similar way to using a single-agent algorithm in settings where only one agent needs to be trained. In this paper, we test whether by using a multi-agent reinforcement learning algorithm with centralized critics, as opposed to single-agent ones, we would obtain an agent that generalizes better to new partners in a collaborative environment such as Overcooked, where coordination is critical for good performance. The results display a similar performance between the two algorithms when evaluated through self-play and slightly better or worse results when paired with the human model, representing a mediocre agent, depending on the map. Thus, the multi-agent, centralized critics algorithm used in this study did not train agents that generalize better to new partners. However, the training metrics clearly indicate that the centralized critics method makes the agents learn and converge twice as fast as its single-agent version.https://github.com/andrei-07/rp-overcooked-centralized-critics Link to GitHub repositoryCSE3000 Research ProjectComputer Science and Engineerin
Andrei Tarkovsky:
No full textThe author studies the originality of the film language of Andrei Tarkovsky, one of the great filmmakers of the twentieth century. For this purpose he considers the symbolic, poetic, technical and mystical elements of Tarkovsky’s seven films. Beyond the standard critics, he builds an unitary language for the interpretation of a work reputedly tight.El autor estudia la originalidad del lenguaje cinematográfico de Andrei Tarkovsky, uno de los grandes directores de cine del siglo XX. Para este propósito considera los aspectos simbólicos, poéticos, técnicos y místicos de sus siete películas. Desecha el formato de ficha crítica y construye un lenguaje unitario para la interpretación de una obra reputada como hermética
História e Documentário no Cinema de Andrei Tarkóvski
No full textIn the article, the author discuses the Cinematic history and documentary of Andrei Tarkóvski
A comment on instantons and their fermion zero modes in adjoint QCD_2
No full textInternational audienceThe adjoint 2-dimensional with the gauge group admits topologically nontrivial gauge field configurations associated with nontrivial . The topological sectors are labelled by an integer . However, in contrast to and , this topology is not associated with an integral invariant like the magnetic flux or Pontryagin index. These instantons may admit fermion zero modes, but there is always an equal number of left-handed and right-handed modes, so that the Atiyah-Singer theorem, which determines in other cases the number of the modes, does not apply. The mod. 2 argument suggests that, for a generic gauge field configuration, there is either a single doublet of such zero modes or no modes whatsoever. However, the known solution of the Dirac problem for a wide class of gauge field configurations indicates the presence of zero mode doublets in the topological sector . In this note, we demonstrate in an explicit way that these modes are not robust under a generic enough deformation of the gauge background and confirm thereby the mod. 2 conjecture. The implications for the physics of this theory (screening vs. confinement issue) are briefly discussed
Comments on noncommutative quantum mechanical systems associated with Lie algebras
No full textInternational audienceWe consider quantum mechanics on the noncommutative spaces characterized by the commutation relations where are the structure constants of a Lie algebra. We note that this problem can be reformulated as an ordinary quantum problem in a commuting momentum space. The coordinates are then represented as linear differential operators . Generically, the matrix represents a certain infinite series over the deformation parameter : . The deformed Hamiltonian, describes the motion along the corresponding group manifolds with the characteristic size of order . Their metrics are also expressed into certain infinite series in , with having the meaning of vielbeins. For the algebras and , it has been possible to represent the operators in a simple finite form. A byproduct of our study are new nonstandard formulas for the metrics on all the spheres , on the corresponding projective spaces and on
Classical and quantum dynamics of higher-derivative systems
No full textInternational audienceA brief review of the physics of systems including higher derivatives in the Lagrangian is given. All such systems involve ghosts, i.e. the spectrum of the Hamiltonian is not bounded from below and the vacuum ground state is absent. Usually, this leads to collapse and loss of unitarity. In certain special cases, this does not happen, however, ghosts are benign. We speculate that the Theory of Everything is a higher-derivative field theory, characterized by the presence of such benign ghosts and defined in a higher-dimensional bulk. Our Universe then represents a classical solution in this theory, having the form of a 3-brane embedded in the bulk
Entanglement via nilpotent polynomials
No full textThis paper is an attempt to give a pedagogical presentation of the original work by Lorenza Viola, Andrei Smilga, and ourselvs published in Physical Review A 74, 022331 (2006). The readers are invited to consult that paper for more details as well as for the history of the entanglement concept and the relevant bibliography.SCOPUS: ch.binfo:eu-repo/semantics/publishe
Comments on the Dynamics of the Pais-Uhlenbeck Oscillator
No full textWe discuss the quantum dynamics of the Pais-Uhlenbeck oscillator. The Lagrangian of this higher-derivative model depends on two frequencies. When the frequencies are different, the free PU oscillator has a pure point spectrum that is dense everywhere. When the frequencies are equal, the spectrum is continuous. It is not bounded from below, running from minus to plus infinity, but this is not disastrous as the Hamiltonian is still Hermitian and the evolution operator is still unitary. Generically, the inclusion of interaction terms breaks unitarity, but in some special cases unitarity is preserved. We discuss also the nonstandard realization of the PU oscillator suggested by Bender and Mannheim, where the spectrum of the free Hamiltonian is positive definite, but wave functions grow exponentially for large real values of canonical coordinates. The free nonstandard PU oscillator is unitary when the frequencies are different, but unitarity is broken in the equal frequencies limit
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