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Symmetry
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Advances in Theoretical Physics, Quantum Gravity and Spacetime Symmetries
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Advances in Theoretical Physics, Quantum Gravity and Spacetime Symmetries

A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Physics".

Deadline for manuscript submissions: closed (28 February 2023) | Viewed by 1066

Special Issue Editors

Dr. Nils Albin Nilsson

E-Mail Website
Guest Editor
Center for Quantum Spacetime, Sogang University, Seoul, Korea
Interests: spacetime symmetries; quantum-gravity phenomenology; fundamental tests of gravity
Dr. Christophe Poncin-Lafitte

E-Mail Website
Guest Editor
SYRTE, Observatoire de Paris, LNE, CNRS, Université PSL, Sorbonne Université, 61 Avenue de l’Observatoire, 75014 Paris, France
Interests: general relativity; gravitational waves; astrometry
Dr. Quentin G. Bailey

E-Mail Website
Guest Editor
Physics Department, Embry-Riddle Aeronautical University, Prescott, AZ 86301, USA
Interests: fundamental theories of physics; the theory of gravity; general relativity

Special Issue Information

Dear Colleagues,

In the search for a theory of quantum gravity, a pressing question is, ‘what is the structure of spacetime at the Planck scale?’ Spacetime symmetries, and violations thereof, are promising probes for testing Planck-scale departures from known physics, and some of the most precise tests of Lorentz/CPT symmetry have Planck reach. Several approaches to Planck-scale physics can lead to the spontaneous breaking of spacetime symmetries in the gravitational sector, which could lead to observational signatures in current and future experiments. Therefore, it is of interest to study the theoretical mechanisms of spacetime-symmetry breaking in order to be able to identify any such observational hints of new physics.

Dr. Nils Albin Nilsson
Dr. Christophe Poncin-Lafitte
Dr. Quentin G. Bailey
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Symmetry is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • quantum gravity
  • Lorentz violation
  • CPT violation
  • Planck-scale physics

Published Papers (1 paper)

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Research

16 pages, 305 KiB  
Article
Quantization of Constrained Systems as Dirac First Class versus Second Class: A Toy Model and Its Implications
by Eyo Eyo Ita III, Chopin Soo and Abraham Tan
Symmetry 2023, 15(5), 1117; https://doi.org/10.3390/sym15051117 - 19 May 2023
Viewed by 942
Abstract
A toy model (suggested by Klauder) was analyzed from the perspective of first-class and second-class Dirac constrained systems. First-class constraints are often associated with the existence of important gauge symmetries in a system. A comparison was made by turning a first-class system into [...] Read more.
A toy model (suggested by Klauder) was analyzed from the perspective of first-class and second-class Dirac constrained systems. First-class constraints are often associated with the existence of important gauge symmetries in a system. A comparison was made by turning a first-class system into a second-class system with the introduction of suitable auxiliary conditions. The links between Dirac’s system of constraints, the Faddeev–Popov canonical functional integral method and the Maskawa–Nakajima procedure for reducing the phase space are explicitly illustrated. The model reveals stark contrasts and physically distinguishable results between first and second-class routes. Physically relevant systems such as the relativistic point particle and electrodynamics are briefly recapped. Besides its pedagogical value, the article also advocates the route of rendering first-class systems into second-class systems prior to quantization. Second-class systems lead to a well-defined reduced phase space and physical observables; an absence of inconsistencies in the closure of quantum constraint algebra; and the consistent promotion of fundamental Dirac brackets to quantum commutators. As first-class systems can be turned into well-defined second-class ones, this has implications for the soundness of the “Dirac quantization” of first-class constrained systems by the simple promotion of Poisson brackets, rather than Dirac brackets, to commutators without proceeding through second-class procedures. Full article
(This article belongs to the Special Issue Advances in Theoretical Physics, Quantum Gravity and Spacetime Symmetries)
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