The document discusses the canonical quantization of covariant fields on curved spacetimes, specifically the de Sitter spacetime. It introduces covariant fields that transform under representations of the spin group SL(2,C) and have covariant derivatives ensuring gauge invariance. Isometries of the spacetime generate Killing vectors and induce representations of the external symmetry group, which is the universal covering group of isometries and combines isometries with gauge transformations. Generators of these representations provide conserved observables that allow canonical quantization analogous to special relativity. The paper focuses on applying this framework to the Dirac field on de Sitter spacetime.
D. Mladenov - On Integrable Systems in CosmologySEENET-MTP
Lecture by Prof. Dr. Dimitar Mladenov (Theoretical Physics Department, Faculty of Physics, Sofia University, Bulgaria) on December 7, 2011 at the Faculty of Science and Mathematics, Nis, Serbia.
D. Mladenov - On Integrable Systems in CosmologySEENET-MTP
Lecture by Prof. Dr. Dimitar Mladenov (Theoretical Physics Department, Faculty of Physics, Sofia University, Bulgaria) on December 7, 2011 at the Faculty of Science and Mathematics, Nis, Serbia.
Lecture by prof. dr Neven Bilic from the Ruđer Bošković Institute (Zagreb, Croatia) at the Faculty of Science and Mathematics (Niš, Serbia) on October 29, 2014.
The visit took place in the frame of the ICTP – SEENET-MTP project PRJ-09 “Cosmology and Strings”.
Lecture by prof. dr Neven Bilic from the Ruđer Bošković Institute (Zagreb, Croatia) at the Faculty of Science and Mathematics (Niš, Serbia) on October 29, 2014.
The visit took place in the frame of the ICTP – SEENET-MTP project PRJ-09 “Cosmology and Strings”.
Game Industry in South East Asia is growing,..and its growing so fast, until you did not notice it,...why is that ?? because if you notice it then you all are already like me, quit from job and start working till late at night at your room doing some coding and 3D Modeling and Animating,...obsessed with it !
Marie-Eve Vallieres - Pinterest comme générateur de trafic pour votre blogueMade in
Avec plus de 70 millions d’usagers dont 80% de femmes, Pinterest est une plateforme sociale axée sur les images qui n’a rien à envier à Google en matière de clics. Mais aussi puissant soit-il, ce moteur de recherche d’un nouveau genre se doit d’être utilisé de façon judicieuse. Quand et comment épingler vos articles pour qu’ils ressortent du lot ? Quels plugins et techniques utiliser pour maximiser les épingles de vos lecteurs ? Comment interpréter les statistiques d’utilisation ?
Apprenez les 1001 manières d’utiliser Pinterest de façon efficace et pertinente avec les conseils éprouvés de la blogueuse et spécialiste média sociaux Marie-Eve Vallières, qui compte désormais plus de 100 000 abonnés.
Navigating through the South East Asia Mobile EcosystemRobin Ng
This is a slide deck that is presented at MGF Event in seoul. it provides an overview of the southeast asia mobile environment, smartphone distribution and the points to take note for publishing in the key countries in South East Asia.
This first lecture describes what EMT is. Its history of evolution. Main personalities how discovered theories relating to this theory. Applications of EMT . Scalars and vectors and there algebra. Coordinate systems. Field, Coulombs law and electric field intensity.volume charge distribution, electric flux density, gauss's law and divergence
We make use of the conformal compactification of Minkowski spacetime M# to explore a way of describing general, nonlinear Maxwell fields with conformal symmetry. We distinguish the inverse Minkowski spacetime [M#]−1 obtained via conformal inversion, so as to discuss a doubled compactified spacetime on which Maxwell fields may be defined. Identifying M# with the projective light cone in (4+2)-dimensional spacetime, we write two independent conformal-invariant functionals of the 6-dimensional Maxwellian field strength tensors - one bilinear, the other trilinear in the field strengths -- which are to enter general nonlinear constitutive equations. We also make some remarks regarding the dimensional reduction procedure as we consider its generalization from linear to general nonlinear theories.
Research Inventy : International Journal of Engineering and Science is published by the group of young academic and industrial researchers with 12 Issues per year. It is an online as well as print version open access journal that provides rapid publication (monthly) of articles in all areas of the subject such as: civil, mechanical, chemical, electronic and computer engineering as well as production and information technology. The Journal welcomes the submission of manuscripts that meet the general criteria of significance and scientific excellence. Papers will be published by rapid process within 20 days after acceptance and peer review process takes only 7 days. All articles published in Research Inventy will be peer-reviewed.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology.
Relative superior mandelbrot and julia sets for integer and non integer valueseSAT Journals
Abstract
The fractals generated from the self-squared function,
2 zz c where z and c are complex quantities have been studied
extensively in the literature. This paper studies the transformation of the function , 2 n zz c n and analyzed the z plane and
c plane fractal images generated from the iteration of these functions using Ishikawa iteration for integer and non-integer values.
Also, we explored the drastic changes that occurred in the visual characteristics of the images from n = integer value to n = non
integer value.
Keywords: Complex dynamics,
Relative Superior Julia set, Relative Superior Mandelbrot set.
A new kind of quantum gates, higher braiding gates, as matrix solutions of the polyadic braid equations (different from the generalized Yang–Baxter equations) is introduced. Such gates lead to another special multiqubit entanglement that can speed up key distribution and accelerate algorithms. Ternary braiding gates acting on three qubit states are studied in detail. We also consider exotic non-invertible gates, which can be related with qubit loss, and define partial identities (which can be orthogonal), partial unitarity, and partially bounded operators (which can be non-invertible). We define two classes of matrices, star and circle ones, such that the magic matrices (connected with the Cartan decomposition) belong to the star class. The general algebraic structure of the introduced classes is described in terms of semigroups, ternary and 5-ary groups and modules. The higher braid group and its representation by the higher braid operators are given. Finally, we show, that for each multiqubit state, there exist higher braiding gates that are not entangling, and the concrete conditions to be non-entangling are given for the obtained binary and ternary gates.
Classically, the point particle and the string exhibit the same kind of motion. For instance in flat space both of them move in straight lines albeit for string oscillations which occur because it has to obey the wave equation.
When we put it in AdS3 space both the point particle and the string move as if they are in a potential well. However, coordinate singularities arise in the numerical computation of the string so motion beyond ρ = 0 becomes computationally inac- cessible. Physically the string should still move beyond this point in empty AdS3 spacetime. This singularity is an artefact because coordinate systems in general are not physical. The behaviour of the string in the vicinity of a black hole background in AdS3 spacetime is well defined a fair bit away from the horizon. It moves in the same manner as in the AdS3 spacetime in the absence of the background. Un- fortunately, when the string approaches the horizon part of the string overshoots into the horizon. The solutions become divergent and the numerical solution fails before we can observe anything interesting.
El 7 de noviembre de 2016, la Fundación Ramón Areces organizó el Simposio Internacional 'Solitón: un concepto con extraordinaria diversidad de aplicaciones inter, trans, y multidisciplinares. Desde el mundo macroscópico al nanoscópico'.
Riemannian Laplacian Formulation in Oblate Spheroidal Coordinate System Using...iosrjce
IOSR Journal of Applied Physics (IOSR-JAP) is a double blind peer reviewed International Journal that provides rapid publication (within a month) of articles in all areas of physics and its applications. The journal welcomes publications of high quality papers on theoretical developments and practical applications in applied physics. Original research papers, state-of-the-art reviews, and high quality technical notes are invited for publications.
In this paper, we study semi symmetric and pseudo symmetric conditions in S -manifolds, those are RR = 0 , RC = 0 , C R = 0 , C C = 0 , = ( , ) R R L1Q g R , = ( , ) RC L2Q g C , = ( , ) CR L3Q g R , and = ( , ) C C L4Q g C , where C is the Concircular curvature tensor and 1 2 3 4 L ,L ,L ,L are the smooth functions on M , further we discuss about Ricci soliton
Slide 1: Title Slide
Extrachromosomal Inheritance
Slide 2: Introduction to Extrachromosomal Inheritance
Definition: Extrachromosomal inheritance refers to the transmission of genetic material that is not found within the nucleus.
Key Components: Involves genes located in mitochondria, chloroplasts, and plasmids.
Slide 3: Mitochondrial Inheritance
Mitochondria: Organelles responsible for energy production.
Mitochondrial DNA (mtDNA): Circular DNA molecule found in mitochondria.
Inheritance Pattern: Maternally inherited, meaning it is passed from mothers to all their offspring.
Diseases: Examples include Leber’s hereditary optic neuropathy (LHON) and mitochondrial myopathy.
Slide 4: Chloroplast Inheritance
Chloroplasts: Organelles responsible for photosynthesis in plants.
Chloroplast DNA (cpDNA): Circular DNA molecule found in chloroplasts.
Inheritance Pattern: Often maternally inherited in most plants, but can vary in some species.
Examples: Variegation in plants, where leaf color patterns are determined by chloroplast DNA.
Slide 5: Plasmid Inheritance
Plasmids: Small, circular DNA molecules found in bacteria and some eukaryotes.
Features: Can carry antibiotic resistance genes and can be transferred between cells through processes like conjugation.
Significance: Important in biotechnology for gene cloning and genetic engineering.
Slide 6: Mechanisms of Extrachromosomal Inheritance
Non-Mendelian Patterns: Do not follow Mendel’s laws of inheritance.
Cytoplasmic Segregation: During cell division, organelles like mitochondria and chloroplasts are randomly distributed to daughter cells.
Heteroplasmy: Presence of more than one type of organellar genome within a cell, leading to variation in expression.
Slide 7: Examples of Extrachromosomal Inheritance
Four O’clock Plant (Mirabilis jalapa): Shows variegated leaves due to different cpDNA in leaf cells.
Petite Mutants in Yeast: Result from mutations in mitochondrial DNA affecting respiration.
Slide 8: Importance of Extrachromosomal Inheritance
Evolution: Provides insight into the evolution of eukaryotic cells.
Medicine: Understanding mitochondrial inheritance helps in diagnosing and treating mitochondrial diseases.
Agriculture: Chloroplast inheritance can be used in plant breeding and genetic modification.
Slide 9: Recent Research and Advances
Gene Editing: Techniques like CRISPR-Cas9 are being used to edit mitochondrial and chloroplast DNA.
Therapies: Development of mitochondrial replacement therapy (MRT) for preventing mitochondrial diseases.
Slide 10: Conclusion
Summary: Extrachromosomal inheritance involves the transmission of genetic material outside the nucleus and plays a crucial role in genetics, medicine, and biotechnology.
Future Directions: Continued research and technological advancements hold promise for new treatments and applications.
Slide 11: Questions and Discussion
Invite Audience: Open the floor for any questions or further discussion on the topic.
The increased availability of biomedical data, particularly in the public domain, offers the opportunity to better understand human health and to develop effective therapeutics for a wide range of unmet medical needs. However, data scientists remain stymied by the fact that data remain hard to find and to productively reuse because data and their metadata i) are wholly inaccessible, ii) are in non-standard or incompatible representations, iii) do not conform to community standards, and iv) have unclear or highly restricted terms and conditions that preclude legitimate reuse. These limitations require a rethink on data can be made machine and AI-ready - the key motivation behind the FAIR Guiding Principles. Concurrently, while recent efforts have explored the use of deep learning to fuse disparate data into predictive models for a wide range of biomedical applications, these models often fail even when the correct answer is already known, and fail to explain individual predictions in terms that data scientists can appreciate. These limitations suggest that new methods to produce practical artificial intelligence are still needed.
In this talk, I will discuss our work in (1) building an integrative knowledge infrastructure to prepare FAIR and "AI-ready" data and services along with (2) neurosymbolic AI methods to improve the quality of predictions and to generate plausible explanations. Attention is given to standards, platforms, and methods to wrangle knowledge into simple, but effective semantic and latent representations, and to make these available into standards-compliant and discoverable interfaces that can be used in model building, validation, and explanation. Our work, and those of others in the field, creates a baseline for building trustworthy and easy to deploy AI models in biomedicine.
Bio
Dr. Michel Dumontier is the Distinguished Professor of Data Science at Maastricht University, founder and executive director of the Institute of Data Science, and co-founder of the FAIR (Findable, Accessible, Interoperable and Reusable) data principles. His research explores socio-technological approaches for responsible discovery science, which includes collaborative multi-modal knowledge graphs, privacy-preserving distributed data mining, and AI methods for drug discovery and personalized medicine. His work is supported through the Dutch National Research Agenda, the Netherlands Organisation for Scientific Research, Horizon Europe, the European Open Science Cloud, the US National Institutes of Health, and a Marie-Curie Innovative Training Network. He is the editor-in-chief for the journal Data Science and is internationally recognized for his contributions in bioinformatics, biomedical informatics, and semantic technologies including ontologies and linked data.
(May 29th, 2024) Advancements in Intravital Microscopy- Insights for Preclini...Scintica Instrumentation
Intravital microscopy (IVM) is a powerful tool utilized to study cellular behavior over time and space in vivo. Much of our understanding of cell biology has been accomplished using various in vitro and ex vivo methods; however, these studies do not necessarily reflect the natural dynamics of biological processes. Unlike traditional cell culture or fixed tissue imaging, IVM allows for the ultra-fast high-resolution imaging of cellular processes over time and space and were studied in its natural environment. Real-time visualization of biological processes in the context of an intact organism helps maintain physiological relevance and provide insights into the progression of disease, response to treatments or developmental processes.
In this webinar we give an overview of advanced applications of the IVM system in preclinical research. IVIM technology is a provider of all-in-one intravital microscopy systems and solutions optimized for in vivo imaging of live animal models at sub-micron resolution. The system’s unique features and user-friendly software enables researchers to probe fast dynamic biological processes such as immune cell tracking, cell-cell interaction as well as vascularization and tumor metastasis with exceptional detail. This webinar will also give an overview of IVM being utilized in drug development, offering a view into the intricate interaction between drugs/nanoparticles and tissues in vivo and allows for the evaluation of therapeutic intervention in a variety of tissues and organs. This interdisciplinary collaboration continues to drive the advancements of novel therapeutic strategies.
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
Cancer cell metabolism: special Reference to Lactate PathwayAADYARAJPANDEY1
Normal Cell Metabolism:
Cellular respiration describes the series of steps that cells use to break down sugar and other chemicals to get the energy we need to function.
Energy is stored in the bonds of glucose and when glucose is broken down, much of that energy is released.
Cell utilize energy in the form of ATP.
The first step of respiration is called glycolysis. In a series of steps, glycolysis breaks glucose into two smaller molecules - a chemical called pyruvate. A small amount of ATP is formed during this process.
Most healthy cells continue the breakdown in a second process, called the Kreb's cycle. The Kreb's cycle allows cells to “burn” the pyruvates made in glycolysis to get more ATP.
The last step in the breakdown of glucose is called oxidative phosphorylation (Ox-Phos).
It takes place in specialized cell structures called mitochondria. This process produces a large amount of ATP. Importantly, cells need oxygen to complete oxidative phosphorylation.
If a cell completes only glycolysis, only 2 molecules of ATP are made per glucose. However, if the cell completes the entire respiration process (glycolysis - Kreb's - oxidative phosphorylation), about 36 molecules of ATP are created, giving it much more energy to use.
IN CANCER CELL:
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
introduction to WARBERG PHENOMENA:
WARBURG EFFECT Usually, cancer cells are highly glycolytic (glucose addiction) and take up more glucose than do normal cells from outside.
Otto Heinrich Warburg (; 8 October 1883 – 1 August 1970) In 1931 was awarded the Nobel Prize in Physiology for his "discovery of the nature and mode of action of the respiratory enzyme.
WARNBURG EFFECT : cancer cells under aerobic (well-oxygenated) conditions to metabolize glucose to lactate (aerobic glycolysis) is known as the Warburg effect. Warburg made the observation that tumor slices consume glucose and secrete lactate at a higher rate than normal tissues.
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
I. Cotaescu - "Canonical quantization of the covariant fields: the Dirac field on the de Sitter spacetime"
1. Canonical quantization of the covariant fields:
the Dirac field on the de Sitter spacetime
Ion I. Cotaescu
Abstract
The properties of the covariant fields on the de Sitter spacetimes are
investigated focusing on the isometry generators and Casimir operators in
order to establish the equivalence among the covariant representations (CR)
and the unitary irreducuble ones (UIR) of the de Sitter isometry group. For
the Dirac field it is shown that the spinor CR transforming the Dirac field under
de Sitter isometries is equivalent to a direct sum of two UIRs of the Sp(2, 2)
group transforming alike the particle and antiparticle field operators in momentum
representation (rep.). Their basis generators and Casimir operators are written
down finding that these reps. are equivalent to a UIR from the principal series
whose canonical labels are determined by the fermion mass and spin.
Pacs: 04.20.Cv, 04.62.+v, 11.30.-j
arXiv:1602.06810
Keywords: Sitter isometries; Dirac fermions; covariant rep.; unitary rep.; basis generators;
Casimir operators; conserved observables; canonical quantization.
1
4. 1. Introduction
Our world is governed by four fundamental interactions that can be investigated at two
levels:
- the classical level of continuous matter neutral or electrically charged,
- the quantum level of interacting quantum fields whose quanta are the elementary
particles, fermions of spin 1/2 and gauge bosons of spin 1.
The actual physical evidences (up to the scale of the LHC energies ∼ 10−20
m) give
the following picture
CLASSICAL QUANTUM
Gravity NO DATA
Electromagnetism Electromagnetism
NO DATA Nuclear weak
NO DATA Nuclear strong
At this scale we can adopt the semi-classical picture of quantum fields in the
presence of the classical gravity of curved spacetimes without torsion.
The principal measured quantities are the conserved ones corresponding to symmetries
(via Noether theorem). These are the mass, the spin and different charges.
4
6. It is known that in special relativity the isometries play a crucial role in quantizing free
fields since the principal particle properties, the mass and spin, are eigenvalues of the
Casimir operators of the Poincar´e group. Then it is natural to ask what happens in
the case of the curved spacetimes - how the mass and spin can be defined by the
isometry invariants. The answer could be found taking into account that:
1. The theory of quantum fields with spin on curved (1 + 3)-dimensional local-
Minkowskian manifolds (M, g), having the Minkowski flat model (M0, η), can be
correctly constructed only in orthogonal (non-holonomic) local frames [1, 2].
2. The entire theory must be invariant under the orthogonal transformations of the local
frames, i. e. gauge transformations that form the gauge group G(η) = SO(1, 3)
which is the isometry group of the flat model M0.
3. Since the transformations of the isometry group I(M) can change this gauge
we proposed to enlarge the concept of isometry considering external symmetry
transformations that preserve not only the metric but the gauge too [3, 4]. The group
of external symmetry S(M) is isomorphic to the universal covering group of the
isometry group I(M).
6
7. 4. The quantum fields transform according to the covariant reps. (CRs) of the group
S(M) which are induced by the (non-unitary) finite-dimensional reps. of the group
Spin(1, 3) ∼ SL(2, C), i. e. the universal covering group of the gauge group
G(η) = L↑
+ ⊂ SO(1, 3) [3]-[5].
5. The conserved observables are the generators of the CRs, i. e. the differential
operators produced by the Killing vectors (associated to isometries) according to the
generalized Carter and McLenagan formula [25, 3, 4].
The main purpose of the present talk is to present the general theory of the CRs
pointing out the role of their generators in canonical quantization.
The examples we give are the well-known case of special relativity as well as the CRs
on the (1+3)-dimensional de Sitter spacetime where the specific SO(1, 4) isometries
generate conserved observables with a well-defined physical meaning [20] that allow us
to perform the canonical quantization just as in special relativity.
We must stress that in the case of the de Sitter spacetime our theory of induced CRs,
we use here, is equivalent to that proposed by Nachtmann [16] many years ago, and is
completely different from other approaches [13]-[15] that are using linear reps. of the
universal covering group of the de Sitter isometry group [9, 10].
7
8. Figure 2: The external symmetry combines the isometries with suitable gauge
transformations preserving thus the metric and the relative positions of the local frames
with respect to the natural ones.
8
9. 2. Covariant quantum fields
Natural and local frames
Let (M, g) be a (1+3)-dimensional local-Minkowskian spacetime equipped with local
frames {x; e} formed by a local chart (or natural frame) {x} and a non-holonomic
orthogonal frame {e}.
The coordinates xµ
of the local chart are labelled by natural indices µ, ν, ... =
0, 1, 2, 3. The orthogonal frames are defined by the vector fields,
eˆα = eµ
ˆα∂µ , (1)
while the corresponding coframes are defined by the 1-forms
ωˆα
= ˆeˆα
µdxµ
. (2)
These are called tetrad fields, are labelled by local indices, ˆα, ...ˆµ, ˆν, ... = 0, 1, 2, 3
and obey the usual duality relations
ˆeˆµ
α eα
ˆν = δˆµ
ˆν , ˆeˆµ
α eβ
ˆµ = δβ
α , (3)
9
10. and the orthonormalization conditions,
eˆµ · eˆν
def
= gαβeα
ˆµeβ
ˆν = ηˆµˆν , ωˆµ
· ωˆν def
= gαβ
ˆeˆµ
αˆeˆν
β = ηˆµˆν
, (4)
where η = diag(1, −1, −1, −1) is the metric of the Minkowski model (M0, η) of
(M, g). Then the line element can be written as
ds2
= ηˆα ˆβωˆα
ω
ˆβ
= gµνdxµ
dxν
. (5)
which means that gµν = ηˆα ˆβ ˆeˆα
µˆe
ˆβ
ν . This is the metric tensor which raises or lowers the
natural indices while for the local ones we have to use the flat metric η.
The vector fields eˆν satisfy the commutation rules
[eˆµ, eˆν] = eα
ˆµeβ
ˆν (ˆeˆσ
α,β − ˆeˆσ
β,α)ˆ∂ˆσ = C ··ˆσ
ˆµˆν·
ˆ∂ˆσ (6)
defining the Cartan coefficients which help us to write the conecttion coefficients in
local frames as
ˆΓˆσ
ˆµˆν = eα
ˆµeβ
ˆν (ˆeˆσ
γΓγ
αβ − ˆeˆσ
β,α) =
1
2
ηˆσˆλ
(Cˆµˆνˆλ + Cˆλˆµˆν + Cˆλˆν ˆµ) . (7)
We specify that this connection is often called spin connection (and denoted by Ωˆσ
ˆµˆν) but
it is the same as the natural one. The notation Γ stands for the usual Christoffel symbols
representing the connection coefficients in natural frames.
10
11. Covariant fields on curved spacetimes
The metric η remains invariant under the transformations of the group O(1, 3) which
includes as subgroup the gauge group G(η) = L↑
+, whose universal covering group
is Spin(1, 3) = SL(2, C). In the usual covariant parametrization, with the real
parameters, ˜ωˆα ˆβ
= −˜ω
ˆβ ˆα
, the transformations
A(˜ω) = exp −
i
2
˜ωˆα ˆβ
Sˆα ˆβ ∈ SL(2, C) (8)
depend on the covariant basis-generators Sˆα ˆβ of the sl(2, C) Lie algebra which satisfy
[Sˆµˆν, Sˆσˆτ] = i(ηˆµˆτ Sˆνˆσ − ηˆµˆσ Sˆνˆτ + ηˆνˆσ Sˆµˆτ − ηˆνˆτ Sˆµˆσ) . (9)
The matrix elements in local frames of the SO(1, 3) transformation associated to A(˜ω)
through the canonical homomorphism can be expanded as
Λˆµ ·
· ˆν(˜ω) = δˆµ
ˆν + ˜ωˆµ ·
· ˆν + · · · ∈ SO(1, 3) (10)
We denote by I = A(0) ∈ SL(2, C) and 1 = Λ(0) ∈ SO(1, 3) the identity
transformations of these groups.
11
12. The covariant fields, ψ(ρ) : M → V(ρ), are locally defined over M with values in the
vector spaces V(ρ) carrying the finite-dimensional non-unitary reps. ρ of the group
SL(2, C) (briefly presented in the Appendix A). In general, these representations are
reducible as arbitray sums of irreducible ones, (j1, j2). For example, the vector field
transforms according to the irreducible rep. ρv = (1/2, 1/2) while for the Dirac field we
use the reducible rep. ρs = (1/2, 0) ⊕ (0, 1/2).
The covariant derivatives of the field ψ(ρ) in local frames (or natural ones),
D
(ρ)
ˆα = eµ
ˆαD(ρ)
µ = eµ
ˆα∂µ +
i
2
ρ(S
ˆβ ·
· ˆγ ) ˆΓˆγ
ˆα ˆβ
, (11)
assure the covariance of the whole theory under the (point-dependent) gauge
transformations,
ω(x) → Λ[A(x)]ω(x) (12)
ψ(ρ)(x) → ρ[A(x)]ψ(ρ)(x), (13)
produced by the sections A : M → SL(2, C) of the spin fiber bundle.
Note that in the case of the vector and tensor fields the local derivatives coincide with the
covariant ones acting as DµT···ν···
= ∂µT···ν···
· · · + Γν
µαT···α···
+ · · · . This means
that the local frames are needful only in the case of the field with half integer spin.
12
13. (M, g) may have isometries, x → x = φg(x), given by the (non-linear) rep. g → φg
of the isometry group I(M) with the composition rule φg◦φg = φgg , ∀g, g ∈ I(M).
Then we denote by id = φe the identity function, corresponding to the unit e ∈ I(M),
and deduce φ−1
g = φg−1. In a given parametrization, g = g(ξ) (with e = g(0)), the
isometries
x → x = φg(ξ)(x) = x + ξa
ka(x) + ... (14)
lay out the Killing vectors ka = ∂ξa
φg(ξ)|ξ=0 associated to the parameters ξa
(a, b, ... = 1, 2...N).
The isometries may change the relative position of the local frames. For this reason we
proposed the theory of external symmetry [3] where the combined transformations
(Ag, φg) are able to correct the position of the local frames preserving thus not only
the metric but the gauge too, i. e.
⇒ ω(x) → ω (x ) def
= ω[φg(x)] = Λ[Ag(x)]ω(x) . (15)
Hereby, we deduce [3],
Λˆα ·
· ˆβ
[Ag(x)] = ˆeˆα
µ[φg(x)]
∂φµ
g(x)
∂xν
eν
ˆβ
(x) , (16)
13
14. assuming, in addition, that Ag=e(x) = 1. We obtain thus the desired transformation
laws under isometries,
(Ag, φg) :
e(x) → e (x ) = e[φg(x)] ,
ψ(ρ)(x) → ψ(ρ)(x ) = ρ[Ag(x)]ψ(ρ)(x) . (17)
that preserve the gauge.
The set of combined transformations (Ag, φg) form the group of external symmetry,
denoted by S(M). This is isomorphic with the universal covering group of I(M). The
multiplication rule is defined as
(Ag , φg ) ∗ (Ag, φg) def
= ((Ag ◦ φg) × Ag, φg ◦ φg) = (Ag g, φg g) , (18)
such that the unit element is (Ae, φe) = (I, id) while the inverse of the element
(Ag, φg) reads (Ag, φg)−1
= (Ag−1 ◦ φg−1, φg−1). For other mathematical details
see Ref. [3].
In a given parametrization, g = g(ξ), for small values of ξa
, the SL(2, C) parameters
of Ag(ξ)(x) ≡ A[˜ωξ(x)] can be expanded as ˜ωˆα ˆβ
ξ (x) = ξa
Ωˆα ˆβ
a (x) + · · · where
Ωˆα ˆβ
a ≡
∂˜ωˆα ˆβ
ξ
∂ξa
|ξ=0
= ˆeˆα
µ kµ
a,ν + ˆeˆα
ν,µkµ
a eν
ˆλ
η
ˆλ ˆβ
(19)
14
15. are skew-symmetric functions, Ωˆα ˆβ
a = −Ω
ˆβ ˆα
a , only when ka are Killing vectors [3].
The last of Eqs. (17) defines the CRs induced by the finite-dimensional rep., ρ, of the
group SL(2, C). These are operator-valued reps., T(ρ)
: (Ag, φg) → T
(ρ)
g , of the
group S(M) whose covariant transformations,
⇒ (T(ρ)
g ψ(ρ))[φg(x)] = ρ[Ag(x)]ψ(ρ)(x) , (20)
leave the field equation invariant since their basis-generators [3],
⇒ X(ρ)
a = i∂ξaT
(ρ)
g(ξ)|ξ=0
= −ikµ
a ∂µ +
1
2
Ωˆα ˆβ
a ρ(Sˆα ˆβ) , (21)
commute with the operator of the field equation. These satisfy the commutation rules
[X(ρ)
a , X
(ρ)
b ] = icabcX(ρ)
c (22)
where cabc are the structure constants of the algebras s(M) ∼ i(M) - they are
the basis-generators of a CR of the s(M) algebra induced by the rep. ρ of the
spin(1, 3) = sl(2, C) algebra.
15
16. These generators can be put in (general relativistic) covariant form either in non-
holonomic frames [3],
⇒ X(ρ)
a = −ikµ
a D(ρ)
µ +
1
2
ka µ;ν eµ
ˆα eν
ˆβ
ρ(Sˆα ˆβ
) , (23)
or even in holonomic ones [4], generalizing thus the formula given by Carter and
McLenaghan for the Dirac field [25].
The generators (21) have, in general, point-dependent spin terms which do not commute
with the orbital parts. However, there are tetrad-gauges in which at least the generators
of a subgroup H ⊂ I(M) may have point-independent spin terms commuting with
the orbital parts. Then we say that the restriction to H of the CR T(ρ)
is manifest
covariant [3].
Obviously, if H = I(M) then the whole rep. T(ρ)
is manifest covariant. In particular,
the linear CRs on the Minkowski spacetime have this property. This gives rise to the so
called Lorentz covariance which, according to our theory, is universal for any (1 + 3)-
dimensional local-Minkowskian manifold.
16
17. Lagrangian formalism
In the Lagrangian theory the Lagrangian densities must be invariant positively defined
quantities. Since the finite-dimensional reps. ρ of the SL(2, C) group are non-unitary,
we must use the (generalized) Dirac conjugation, ψ(ρ) = ψ+
ρ γ(ρ), where the matrix
γ(ρ) = γ+
(ρ) = γ−1
(ρ) satisfies ρ(A) = γ(ρ)ρ(A)+
γ(ρ) = ρ(A−1
). Then the form
ψ(ρ)ψ(ρ) is invariant under the gauge transformations. In general, the Dirac conjugation
can be defined for the reducible reps. of the form ρ = ...(j1, j2) ⊕ (j2, j1)....
The covariant equations of the free fields can be derived from actions of the form
S[ψ(ρ), ψ(ρ)] =
∆
d4
x
√
g L(ψ(ρ), ψ(ρ);µ, ψ(ρ), ψ(ρ);µ) , g = |det gµν| , (24)
depending on the field ψ(ρ), its Dirac adjoint ψ(ρ) and their corresponding covariant
derivatives ψ(ρ);µ = D
(ρ)
µ ψ(ρ) and ψ(ρ);µ = D
(ρ)
µ ψ(ρ) defined by the rep. ρ of the
group SL(2, C).
17
18. The action S is extremal if the covariant fields satisfy the Euler-Lagrange equations
∂L
∂ψ(ρ)
−
1
√
g
∂µ
∂(
√
g L)
∂ψ(ρ),µ
= 0 ,
∂L
∂ψ(ρ)
−
1
√
g
∂µ
∂(
√
g L)
∂ψ(ρ),µ
= 0 . (25)
Any transformation ψ(ρ) → ψ(ρ) = ψ(ρ) + δψ(ρ) leaving the action invariant,
S[ψ(ρ), ψ(ρ)] = S[ψ(ρ), ψ(ρ)], is a symmetry transformation. The Noether theorem
shows that each symmetry transformation gives rise to the current
Θµ
∝ δψ(ρ)
∂L
∂ψ(ρ),µ
+
∂L
∂ψ(ρ),µ
δψ(ρ) (26)
which is conserved in the sense that Θµ
;µ = 0.
In the case of isometries we have δψ(ρ) = −iξa
X
(ρ)
a ψ(ρ). Consequently, each
isometry of parameter ξa
give rise to the corresponding conserved current
Θµ
a = i X
(ρ)
a ψ(ρ)
∂L
∂ψ(ρ),µ
−
∂L
∂ψ(ρ),µ
X(ρ)
a ψ(ρ) , a = 1, 2...N . (27)
18
19. Then we may define the relativistic scalar product , as
⇒ ψ, ψ = i
∂∆
dσµ
√
g ψ
∂L
∂ψ ,µ
−
∂L
∂ψ,µ
ψ , (28)
such that the conserved quantities (charges) can be represented as expectation values
of isometry generators,
⇒ Ca =
∂∆
dσµ
√
g Θµ
a = ψ(ρ), X(ρ)
a ψ(ρ) , (29)
Notice that the operators X are self-adjoint with respect to this scalar product, i. e.
Xψ, ψ = ψ, Xψ .
From the algebra freely generated by the isometry generators we may select the sets
of commuting operators {A1, A2, ...An} determining the fundamental solutions of
particles, Uα ∈ F+
, and antiparticles, Vα ∈ F−
, that depend on the set of the
corresponding eigenvalues α = {a1, a2, ...an} spanning a discrete or continuous
spectra of the common eigenvalue problems
AiUα = aiUα , AiVα = −aiVα , i = 1, 2...n . (30)
19
20. After determining the fundamental solutions we may write the mode expansion
⇒ ψ(ρ)(x) =
α∈Σd
+
α∈Σc
d(α)
[Uα(x)a(α) + Vα(x)b∗
(α)] , (31)
where we sum over the discrete part (Σd) and integrate over the continuous part (Σc) of
the spectrum Σ = Σd ∪ Σc.
The fundamental solutions are orthogonal with respect to the relativistic scalar product
and can be normalized such that
Uα, Uα = ± Vα, Vα = δ(α, α ) =
δα,α if α, α ∈ Σd
δ(α − α ) if α, α ∈ Σc
(32)
Uα, Vα = Vα, Uα = 0 , (33)
where the sign + arises for fermions while the sign − is obtained for bosons.
20
21. Canonical quantization
The theory get a physical meaning only after performing the second quantization
postulating canonical non-vanishing rules (with the notation [x, y]± = xy ± yx) as
a(α), a†
(α )
±
= b(α), b†
(α )
±
= δ(α, α ) . (34)
Then the fields ψ(ρ) become quantum fields (with b†
instead of b∗
) while the conserved
quantities (29) become one-particle operators,
⇒ Ca → X(ρ)
a =: ψ(ρ), X(ρ)
a ψ(ρ) : (35)
calculated respecting the normal ordering of the operator products [26]. Now the one
particle operators X
(ρ)
a are the basis generators of a rep. of the algebra s(M) with
values in operator algebra. In a similar manner one can define the generators of the
internal symmetries as for example the charge one-particle operator Q =: ψ, ψ :.
Thus we obtain a reach operator algebra formed by field operators and the one-particle
ones which have the obvious properties
[X, ψ(x)] = −(Xψ)(x) , [X, Y] =: ψ, ([X, Y ]ψ) : . (36)
21
22. In general, if the one-particle operator X does not mix among themselves the subspaces
of fundamental solutions it can be expanded as
X = : ψ, Xψ := X(+)
+ X(−)
=
α∈Σ α ∈Σ
˜X(+)
(α, α )a†
(α)a(α ) + ˜X(−)
(α, α )b†
(α)b(α ) , (37)
where
˜X(+)
(α, α ) = Uα, XUα , ˜X(−)
(α, α ) = Vα, XVα . (38)
When there are differential operators ˜X(±)
acting on the continuous variables of the set
{α} such that ˜X(±)
(α, α ) = δ(α, α ) ˜X(±)
we say that ˜X(±)
are the operators of
the rep. {α} (in the sense of the relativistic QM).
We stress that all the isometry generators have this property such that the corresponding
operators ˜X
(±)
a are the basis generators of the isometry transformations of the field
operators a and b . However, the algebraic relations (34) remain invariant only if a and
b transform according to UIRs of the isometry group.
A crucial problem is now the equivalence between the CR transformimg the
covariant field ψ(ρ) and the set of UIRs transforming the particle and antiparticle
operators a and b. This will be referred here as the CR-UIR equivalence.
22
23. Figure 3: The CR-UIR equivalence of the reps. of the group S(M) and its algebra s(M)
23
24. 3. Covariant fields in special relativity
The problem of CR-UIR equivalence is successfully solved in special relativity thanks to
the Wigner theory of induced reps. of the Poincar´e group.
On the Minkowski spacetime, (M0, η), the fields ψ(ρ) transform under isometries
according to manifest CRs in inertial (local) frames defined by eµ
ν = ˆeµ
ν = δµ
ν .
Generators of manifest CRs
The isometries are just the transformations x → x = Λ[A(ω)]x − a of the Poincar´e
group I(M0) = P↑
+ = T(4) L↑
+ [24] whose universal covering group is S(M0) =
˜P↑
+ = T(4) SL(2, C). The manifest CRs, T(ρ)
: (A, a) → T
(ρ)
A,a, of the S(M0)
group have the transformation rules
⇒ (T
(ρ)
A,aψ(ρ))(x) = ρ(A)ψ(ρ) Λ(A)−1
(x + a) , (39)
24
25. and the well-known basis-generators of the s(M0) algebra,
ˆPµ ≡ ˆX
(ρ)
(µ) = i∂µ , (40)
ˆJ(ρ)
µν ≡ ˆX
(ρ)
(µν) = i(ηµαxα
∂ν − ηναxα
∂µ) + S(ρ)
µν , (41)
which have point-independent spin parts denoted by S
(ρ)
ˆµˆν instead of ρ(Sˆµˆν). Hereby, it is
convenient to denote the energy operator as ˆH = ˆP0 and write the sl(2, C) generators,
ˆJ
(ρ)
i =
1
2
εijk
ˆJ
(ρ)
jk = −iεijkxj
∂k + S
(ρ)
i , S
(ρ)
i =
1
2
εijkS
(ρ)
jk , (42)
ˆK
(ρ)
i = ˆJ
(ρ)
0i = i(xi
∂t + t∂i) + S
(ρ)
0i , i, j, k... = 1, 2, 3 , (43)
denoting S2
= SiSi and S2
0 = S0iS0i. Thus we lay out the standard basis of the
s(M0) algebra, { ˆH, ˆPi, ˆJ
(ρ)
i , ˆK
(ρ)
i }.
The invariants of the manifest covariant fields are the eigenvalues of the Casimir
operators of the reps. T(ρ)
that read
ˆC1 = ˆPµ
ˆPµ
, ˆC
(ρ)
2 = −ηµν
ˆW(ρ) µ ˆW(ρ) ν
, (44)
25
26. where the components of the Pauli-Lubanski operator [24],
ˆW(ρ) µ
= −
1
2
εµναβ ˆPν
ˆJ
(ρ)
αβ , (45)
are defined by the skew-symmetric tensor with ε0123
= −ε0123 = −1. Thus we obtain,
ˆW
(ρ)
0 = ˆJ
(ρ)
i
ˆPi = S
(ρ)
i
ˆPi , ˆW
(ρ)
i = ˆH ˆJ
(ρ)
i + εijk
ˆK
(ρ)
j
ˆPk . (46)
The first invariant (44a) gives the mass condition, ˆP2
ψ(ρ) = m2
ψ(ρ), fixing the orbit
in the momentum spaces on which the fundamental solutions are defined. The second
invariant is less relevant for the CRs since its form in configurations is quite complicated
ˆC
(ρ)
2 = −(S(ρ)
)2
∂2
t + 2(iS
(ρ)
0k − εijkS
(ρ)
i S
(ρ)
0j )∂k∂t
− (S0
(ρ)
)2
∆ − (S
(ρ)
i S
(ρ)
j + S
(ρ)
0i S
(ρ)
0j )∂i∂j . (47)
Consequently, we may study its action in the momentum reps. where it selects the
induced Wigner UIRs equivalent with the CR. Nevertheless, for fields with unique spin
with ρ = ρ(s) = (s, 0) ⊕ (0, s) we obtain in the rest frame where Pi ∼ 0 that
ˆC
ρ(s)
2 = m2
s(s + 1) (48)
26
27. since then S
ρ(s)
0i = ±iS
ρ(s)
i .
In the Poincar´e algebra we find the complete system of commuting operators
{ ˆH, ˆP1, ˆP2, ˆP3} defining the momentum rep.. The fundamental solutions are common
eigenfunctions of this system such that any covariant quantum field can be written as
ψ(ρ)(x) = d3
p
sσ
Up,sσ(x)asσ(p) + Vp,sσ(x)b†
sσ(p) (49)
where asσ and bsσ are the field operators of a particle and antiparticle of spin s and
polarization σ while the fundamental solutions have the form
Up,sσ(x) =
1
(2π)
3
2
usσ(p)e−iEt+ip·x
, Vp,sσ(x) =
1
(2π)
3
2
vsσ(p)eiEt−ip·x
. (50)
The vectors usσ(p) and vsσ(p) have to be determined by the concrete form of the field
equation and relativistic scalar product. However, when the field equations are linear we
can postulate the orthonormalization relations
usσ(p)us σ (p) = vsσ(p)vs σ (p) = δss δσσ , (51)
usσ(p)vs σ (p) = vsσ(p)us σ (p) = 0 . (52)
27
28. that guarantee the separation of the particle and antiparticle sectors.
For the massive fields of mass m the momentum spans the orbit Ωm = {p | p2
= m2
}
which means that p0 = ±E where E = m2 + p2. The solutions U are considered
of positive frequencies having p0 = E while for the negative frequency ones, V , we
must take p0 = −E. In this manner the general rule (30) of separating the particle and
antiparticle modes becomes
HUp,sσ = EUp,sσ , HVp,sσ = −EVp,sσ , (53)
PUp,sσ = p Up,sσ , PVp,sσ = −p Vp,sσ . (54)
Wigner’s induced UIRs
The Wigner theory of the induced UIRs is based on the fact that the orbits in
momentum space may be built by using Lorentz transformations [6, 7]. In the case
of massive particles we discuss here, any p ∈ Ωm can be obtained applying a boost
transformation Lp ∈ L↑
+ to the representative momentum ˚p = (m, 0, 0, 0) such that
p = Lp ˚p.
28
29. The rotations that leave ˚p invariant, R˚p = ˚p, form the stable group SO(3) ⊂ L↑
+
whose universal covering group SU(2) is called the little group associated to the
representative momentum ˚p.
We observe that the boosts Lp are defined up to a rotation since LpR ˚p = Lp ˚p.
Therefore, these span the homogeneous space L↑
+/SO(3). The corresponding
transformations of the SL(2, C) group are denoted by Ap ∈ SL(2, C)/SU(2)
assuming that these satisfy Λ(Ap) = Lp and A˚p = 1 ∈ SL(2, C).
In applications one prefers to chose genuine Lorentz transformatios Ap = e−iαni
S0i
with
α = atrctanhp
E and ni
= pi
p with p = |p|. In the spinor rep. ρs = (1
2, 0) ⊕ (0, 1
2) of
the Dirac theory one finds [27]
ρs(Ap) =
E + m + γ0
γi
pi
2m(E + m)
. (55)
where γµ
denote the Dirac matrices. The corresponding transformations of the L↑
+
group, Lp = Λ(Ap), have the matrix elements
(Lp)0 ·
· 0 =
E
m
, (Lp)0 ·
· i = (Lp)i ·
· 0 =
pi
m
, (Lp)i ·
· j = δij +
pi
pj
m(E + m)
. (56)
29
30. Furthermore, we look for the transformations in momentum rep. generated by the CR
under consideration. After a little calculation we obtain
s σ
us σ (p)(TA,aas σ )(p) =
sσ
ρ(A)usσ p asσ p e−ia·p
(57)
s σ
vs σ (p)(TA,ab†
s σ )(p) =
sσ
ρ(A)vsσ p b†
sσ p eia·p
(58)
where a · p = Ea0
− p · a and p = Λ(A)−1
p.
Focusing on the first equation, we introduce the Wigner mode functions
usσ(p) = ρ(Ap)˚usσ (59)
where the vectors ˚usσ ∈ V(ρ) are independent on p and satisfy ˚usσ˚us σ =
usσ(p)us σ (p) = δss δσσ according to Eq. (51). We obtain thus the transformation
rule of the Wigner reps. induced by the subgroup T(4) SU(2) that read [6, 8]
⇒ (TA,aasσ)(p) =
σ
Ds
σσ (A, p)asσ (p )eia·p
(60)
where
⇒ Ds
σσ (A, p) = ˚usσρ[W(A, p)]˚usσ , W(A, p) = A−1
p AAp (61)
30
31. The Wigner transformations W(A, p) = A−1
p AAp is of the little group SU(2) since
one can verify that Λ[W(A, p)] = L−1
p Λ(A)Lp ∈ SO(3) leaving invariant the
representative momentum ˚p.
Therefore the matrices Ds
realize the UIR of spin (s) of the little group SU(2) that
induces the Wigner UIR (60) denoted by (s, ±m) [8].
Note that the role of the vectors ˚usσ is to select the spin content of the CR determining
the Wigner UIRs whose direct sum is equivalent to the CR T(ρ)
.
A similar procedure can be applied for the antiparticle but selecting the normalized
vectors ˚vsσ ∈ V(ρ) such that ˚vsσ˚vs σ = δss δσσ and ˚vsσρ[W(A, p)]˚vsσ =
Ds
σσ (A, p)∗
since the operators a and b must transform alike under isometries [24].
Moreover, from Eq. (52) we deduce that the vectors ˚u and ˚v must be orthogonal,
˚usσ˚vs σ = ˚vsσ˚us σ = 0.
The conclusion is that the CRs are equivalent to direct sums of Wigner UIRs with an
arbitrary spin content defined by the vectors ˚usσ and ˚vsσ. For each spin s we meet the
31
32. UIR (±m, s) in the space Vs ⊂ V(ρ) of the linear UIR of the group SU(2) generated
by the matrices S
(s)
i .
The transformation (60) allows us to derive the generators of the UIRs in momentum
rep. (denoted by tilde) that are differential operator acting alike on the operators asσ(p)
and bsσ(p) seen as functions of p. Thus for each UIR (s, ±m) we can write down the
basis generators
˜J
(s)
i = −iεijkpj
∂pk + S
(s)
i , (62)
˜K
(s)
i = iE∂pi −
pi
2E
+
1
E + m
εijkpj
S
(s)
k . (63)
With their help we derive the components of the Pauli-Lubanski operator
˜W
(s)
0 = p · S(s)
, ˜W
(s)
i = mS
(s)
i +
pi
E + m
p · S(s)
, (64)
and we recover the well-known result [8]
⇒ ˜C1 = m2
, ˜C
(s)
2 = m2
(S(s)
)2
∼ m2
s(s + 1) (65)
32
33. Finally we stress that the Wigner theory determine completely the form of the covariant
fields without using field equations. Thus in special relativity we have two symmetric
equivalent procedures:
(i) to start with the covariant field equation that gives the form of the covariant field
determining its CR, or
(ii) to construct the Wigner covariant field and then to derive its field equation [24]. The
typical example is the Dirac field in Minkowski spacetime [8, 27].
33
34. 4. Covariant fields on de Sitter spacetime
The Wigner theory works only in local-Minkowskian manifold whose isometry group has
a similar structure as the Poincar´e one having an Abelian normal subgroup T(4).
Unfortunately the Abelian group T(3)P of the de Sitter isometry group is not a normal (or
invariant) subgroup such that the we must study of the de Sitter CRs in the configuration
space following to consider the UIRs in momentum representation after the field is
determined by a concrete field equation.
de Sitter isometries and Killing vectors
Let (M, g) be the de Sitter spacetime defined as the hyperboloid of radius 1/ω in
the five-dimensional flat spacetime (M5
, η5
) of coordinates zA
(labeled by the indices
A, B, ... = 0, 1, 2, 3, 4) and metric η5
= diag(1, −1, −1, −1, −1).
34
35. The local charts {x} can be introduced on (M, g) giving the set of functions zA
(x)
which solve the hyperboloid equation,
η5
ABzA
(x)zB
(x) = −
1
ω2
. (66)
Here we use the chart {t, x} with the conformal time t and Cartesian spaces
coordinates xi
defined by
z0
(x) = −
1
2ω2t
1 − ω2
(t2
− x2
)
zi
(x) = −
1
ωt
xi
, (67)
z4
(x) = −
1
2ω2t
1 + ω2
(t2
− x2
)
This chart covers the expanding part of M for t ∈ (−∞, 0) and x ∈ R3
while the
collapsing part is covered by a similar chart with t > 0. Both these charts have the
conformal flat line element,
ds2
= η5
ABdzA
(x)dzB
(x) =
1
ω2t2
dt2
− dx2
. (68)
35
37. In addition, we consider the local frames {t, x; e} of the diagonal gauge,
e0
0 = −ωt , ei
j = −δi
j ωt , ˆe0
0 = −
1
ωt
, ˆei
j = −δi
j
1
ωt
. (69)
The gauge group G(η5
) = SO(1, 4) is the isometry group of M, since its
transformations, z → gz, g ∈ SO(1, 4), leave the equation (66) invariant. Its universal
covering group Spin(η5
) = Sp(2, 2) is not involved directly in our construction since
the spinor CRs are induced by the spinor representations of its subgroup SL(2, C).
Therefore, we can restrict ourselves to the group SO(1, 4) for which we adopt the
parametrization
g(ξ) = exp −
i
2
ξAB
SAB ∈ SO(1, 4) (70)
with skew-symmetric parameters, ξAB
= −ξBA
, and the covariant generators SAB
of the fundamental representation of the so(1, 4) algebra carried by M5
. These
generators have the matrix elements,
(SAB)C ·
· D = i δC
A ηBD − δC
B ηAD . (71)
37
38. The principal so(1, 4) basis-generators with physical meaning [20] are the energy H =
ωS04, angular momentum Jk = 1
2εkijSij, Lorentz boosts Ki = S0i, and the Runge-
Lenz-type vector Ri = Si4. In addition, it is convenient to introduce the momentum
Pi = −ω(Ri + Ki) and its dual Qi = ω(Ri − Ki) which are nilpotent matrices
(i. e. (Pi)3
= (Qi)3
= 0) generating two Abelian three-dimensional subgroups,
T(3)P and respectively T(3)Q. All these generators may form different bases of the
algebra so(1, 4) as, for example, the basis {H, Pi, Qi, Ji} or the Poincar´e-type one,
{H, Pi, Ji, Ki}. We note that the four-dimensional restriction of the so(1, 3) subalegra
generate the vector representation of the group L↑
+.
Using these generators we can derive the SO(1, 4) isometries, φg, defined as
z[φg(x)] = g z(x). (72)
The transformations g ∈ SO(3) ⊂ SO(4, 1) generated by Ji, are simple rotations
of zi
and xi
which transform alike since this symmetry is global. The transformations
generated by H,
exp(−iξH) :
z0
→ z0
cosh α − z4
sinh α
zi
→ zi
z4
→ −z0
sinh α + z4
cosh α
(73)
38
39. whith α = ωξ, produce the dilatations t → t eα
and xi
→ xi
eα
, while the T(3)P
transformations
exp(−iξi
Pi) :
z0
→ z0
+ ω ξ · z + 1
2 ω2
ξ
2
(z0
+ z4
)
zi
→ zi
+ ω ξi
(z0
+ z4
)
z4
→ z4
− ω ξ · z − 1
2 ω2
ξ
2
(z0
+ z4
)
(74)
give rise to the space translations xi
→ xi
+ ξi
at fixed t. More interesting are the
T(3)Q transformations generated by Qi/ω,
exp(−iξi
Qi/ω) :
z0
→ z0
− ξ · z + 1
2 ξ
2
(z0
− z4
)
zi
→ zi
− ξi
(z0
− z4
)
z4
→ z4
− ξ · z + 1
2 ξ
2
(z0
− z4
)
(75)
which lead to the isometries
t →
t
1 − 2ω ξ · x − ω2ξ
2
(t2 − x2)
(76)
xi
→
xi
+ ωξi
(t2
− x2
)
1 − 2ω ξ · x − ω2ξ
2
(t2 − x2)
. (77)
39
40. We observe that z0
+ z4
= − 1
ω2t is invariant under translations (74), fixing the value of
t, while z0
− z4
= t2
−x2
t is left unchanged by the t(3)Q transformations (75).
The orbital basis-generators of the natural representation of the s(M) algebra (carried
by the space of the scalar functions over M5
) have the standard form
L5
AB = i η5
ACzC
∂B − η5
BCzC
∂A = −iKC
(AB)∂C (78)
which allows us to derive the corresponding Killing vectors of (M, g), k(AB), using the
identities k(AB)µdxµ
= K(AB)CdzC
. Thus we obtain the following components of the
Killing vectors:
k0
(04) = t , ki
(04) = xi
, k0
(0i) = k0
(4i) = ωtxi
(79)
kj
(0i) = ωxi
xj
+ δj
i
1
2ω
[ω2
(t2
− x2
) − 1] (80)
kj
(4i) = ωxi
xj
+ δj
i
1
2ω
[ω2
(t2
− x2
) + 1] (81)
kk
(ij) = δk
j xi
− δk
i xj
. (82)
40
41. Generators of induced CRs
In the covariant parametrization of the sp(2, 2) algebra adopted here, the generators
X
(ρ)
(AB) corresponding to the Killing vectors k(AB) result from equation (21) and the
functions (19) with the new labels a → (AB). Then we have
H = ωX
(ρ)
(04) = −iω(t∂t + xi
∂i) , (83)
J
(ρ)
i =
1
2
εijkX
(ρ)
(jk) = −iεijkxj
∂k + S
(ρ)
i , S
(ρ)
i =
1
2
εijkS
(ρ)
jk , (84)
K
(ρ)
i = X
(ρ)
(0i) = xi
H +
i
2ω
[1 + ω2
(x2
− t2
)]∂i − ωtS
(ρ)
0i + ωS
(ρ)
ij xj
, (85)
R
(ρ)
i = X
(ρ)
(i4) = −K
(ρ)
i +
1
ω
i∂i . (86)
where H is the energy (or Hamiltonian), J total angular momentum , K generators
of the Lorentz boosts , and R is a Runge-Lenz type vector. These generators form
the basis {H, J
(ρ)
i , K
(ρ)
i , R
(ρ)
i } of the covariant rep. of the sp(2, 2) algebra with the
following commutation rules:
41
42. J
(ρ)
i , J
(ρ)
j = iεijkJ
(ρ)
k , J
(ρ)
i , R
(ρ)
j = iεijkR
(ρ)
k , (87)
J
(ρ)
i , K
(ρ)
j = iεijkK
(ρ)
k , R
(ρ)
i , R
(ρ)
j = iεijkJ
(ρ)
k , (88)
K
(ρ)
i , K
(ρ)
j = −iεijkJ
(ρ)
k , R
(ρ)
i , K
(ρ)
j =
i
ω
δijH , (89)
and
H, J
(ρ)
i = 0 , H, K
(ρ)
i = iωR
(ρ)
i , H, R
(ρ)
i = iωK
(ρ)
i . (90)
In some applications it is useful to replace the operators K(ρ)
and R(ρ)
by the Abelian
ones, i. e. the momentum operator P and its dual Q(ρ)
, whose components are defined
as
Pi = −ω(R
(ρ)
i + K
(ρ)
i ) = −i∂i , Q
(ρ)
i = ω(R
(ρ)
i − K
(ρ)
i ) , (91)
obtaining the new basis {H, Pi, Q
(ρ)
i , J
(ρ)
i }.
The last two bases bring together the conserved energy (83) and momentum (91a) which
are the only genuine orbital operators, independent on ρ. What is specific for the de
Sitter symmetry is that these operators can not be put simultaneously in diagonal form
since they do not commute to each other.
42
43. Casimir operators
The first invariant of the CR T(ρ)
is the quadratic Casimir operator
C
(ρ)
1 = − ω21
2
X
(ρ)
(AB)X(ρ) (AB)
(92)
= H2
+ 3iωH − Q(ρ)
· P − ω2
J(ρ)
· J(ρ)
. (93)
After a few manipulation we obtain its definitive expression
C
(ρ)
1 = EKG + 2iωe−ωt
S
(ρ)
0i ∂i − ω2
(S(ρ)
)2
, (94)
depending on the Klein-Gordon operator EKG = −∂2
t − 3 ω∂t + e−2ωt
∆.
The second Casimir operator, C
(ρ)
2 = −η5
ABW(ρ) A
W(ρ) B
, is written with the help of
the five-dimensional vector-operator W(ρ)
whose components read [13]
W(ρ) A
=
1
8
ω εABCDE
X
(ρ)
(BC)X
(ρ)
(DE) , (95)
where ε01234
= 1 and the factor ω assures the correct flat limit. After a little calculation
we obtain the concrete form of these components,
43
44. W
(ρ)
0 = ω J(ρ)
· R(ρ)
, (96)
W
(ρ)
i = H J
(ρ)
i + ω εijkK
(ρ)
j R
(ρ)
k , (97)
W
(ρ)
4 = −ω J(ρ)
· K(ρ)
, (98)
which indicate that W(ρ)
plays an important role in theories with spin, similar to that of
the Pauli-Lubanski operator (45) of the Poincar´e symmetry. For example, the helicity
operator is now W
(ρ)
0 − W
(ρ)
4 = S
(ρ)
i Pi.
Then by using the components (96)-(98) we are faced with a complicated calculation but
which can be performed using algebraic codes on computer. Thus we obtain the closed
form of the second Casimir operator,
C
(ρ)
2 = −ω2
(S(ρ)
)2
(t2
∂2
t − 2t∂t + 2) + 2ω2
t2
(iS
(ρ)
0k − εijkS
(ρ)
i S
(ρ)
0j )∂k∂t
+ωt (S0
(ρ)
)2
∆ − (S
(ρ)
i S
(ρ)
j + S
(ρ)
0i S
(ρ)
0j )∂i∂j
−2iω2
t(S
(ρ)
i S
(ρ)
k S
(ρ)
0i + S
(ρ)
0k )∂k . (99)
44
45. In the case of fields with unique spin s we must select the reps. ρ(s) = (s, 0)⊕(0, s),
for which we have to replace S
ρ(s)
0i = ± iS
ρ(s)
i in equation (99) finding the remarkable
identity
C
ρ(s)
2 = C
ρ(s)
1 (Sρ(s)
)2
− 2ω2
(Sρ(s)
)2
+ ω2
[(Sρ(s)
)2
]2
. (100)
It is interesting to look for the invariants of the particles at rest in the chart {t, x}. These
have the vanishing momentum (Pi ∼ 0) so that H acts as i∂t and, therefore, it can
be put in diagonal form its eigenvalues being just the rest energies, E0. Then, for each
subspace Vs ⊂ V(ρ) of given spin, s, we obtain the eigenvalues of the first Casimir
operator,
C
ρ(s)
1 ∼ E2
0 + 3iωE0 − ω2
s(s + 1) , (101)
using Eq. (94) while those of the second Casimir operator,
C
ρ(s)
2 ∼ s(s + 1)(E2
0 + 3iωE0 − 2ω2
) , (102)
result from equation (99). These eigenvalues are real numbers so that the rest energies,
E0 = E0 − 3iω
2 , must be complex numbers whose imaginary parts are due to the
decay produced by the de Sitter expansion.
45
46. The above results indicate that the CRs are reducible to direct sums of UIRs of the
principal series [9]. These are labeled by two weights, (p, q), with p = s while q is a
solution of the equation q(1 − q) = 1
ω2 ( E0)2
+ 1
4.
In the flat limit we recover the Poincar´e generators. We observe that the generators (84)
are independent on ω having the same form as in the Minkowski case, J
(ρ)
k = ˆJ
(ρ)
k . The
other generators have the limits
lim
ω→0
H = ˆH = i∂t , lim
ω→0
(ωR
(ρ)
i ) = − ˆPi = i∂i , lim
ω→0
K
(ρ)
i = ˆK
(ρ)
i , (103)
which means that the basis {H, Pi, J
(ρ)
i , K
(ρ)
i } of the algebra s(M) = sp(2, 2) tends
to the basis { ˆH, ˆPi, ˆJ
(ρ)
i , ˆK
(ρ)
i } of the s(M0) algebra when ω → 0. Moreover, the
Pauli-Lubanski operator (45) is the flat limit of the five-dimensional vector-operator (95)
since
lim
ω→0
W
(ρ)
0 = ˆW
(ρ)
0 , lim
ω→0
W
(ρ)
i = ˆW
(ρ)
i , lim
ω→0
W
(ρ)
4 = 0 . (104)
Under such circumstances the limits of our invariants read
lim
ω→0
C
(ρ)
1 = ˆC1 = ˆP2
, lim
ω→0
C
(ρ)
2 = ˆC
(ρ)
2 , (105)
indicating that their physical meaning may be related to the mass and spin of the matter
fields in a similar manner as in special relativity.
46
47. Minkowski de Sitter
CRs manifest SL(2, C) CRs induced by SL(2, C)
H = i∂t H = −iω(t∂t + xi
∂i)
Pi
= −i∂i Pi
= −i∂i
J
(ρ)
i = −iεijkxj
∂k + S
(ρ)
i J
(ρ)
i = −iεijkxj
∂k + S
(ρ)
i
K
(ρ)
i = i(xi
∂t + t∂i) + S
(ρ)
0i K
(ρ)
i = xi
H + i
2ω[1 + ω2
(x2
− t2
)]∂i
−ωtS
(ρ)
0i + ωS
(ρ)
ij xj
UIR ˜P↑
+ = T(4) SL(2, C) UIR Spin(1, 4) = Sp(2, 2)
C1 = m2
C
ρ(s)
1 = M2
+ 9
4 ω2
− ω2
s(s + 1)
C
ρ(s)
2 = m2
s(s + 1) C
ρ(s)
2 = M2
+ 1
4 ω2
s(s + 1)
where m = E0 where M = E0
Scalar field s = 0 M = m2 − 9
4ω2 C1 = m2
C2 = 0
Dirac field s = 1
2 M = m C1 = m2
+ 3
2 ω2
C2 = 3
4 m2
+ 1
4 ω2
Proca field s = 1 M = m2 − 1
4ω2 C1 = m2
C2 = 2m2
47
48. 5. The Dirac field on de Sitter spacetimes
In the absence of a strong theory like the Wigner one in the flat case we must study
the CR-UIR equivalence resorting to the covariant field equations able to give us the
structure of the covariant field. Then, bearing in mind that the de Sitter UIRs are well-
studied [9, 10], we can establish the CR-UIR equivalence by studying the CR and UIR
Casimir operators in configurations and momentum rep..
In what follows we concentrate on the Dirac equation on the de Sitter spacetime since
this is the only equation on this background giving the natural rest energy E0 = m
[20].
Invariants of the spinor CR
In the frame {t, x; e} introduced above the free Dirac equation takes the form [18],
(ED − m)ψ(x) = −iωt γ0
∂t + γi
∂i +
3iω
2
γ0
− m ψ(x) = 0 , (106)
48
49. depending on the point-independent Dirac matrices γˆµ
that satisfy {γˆα
, γ
ˆβ
} = 2ηˆα ˆβ
giving rise to the basis-generators S(ρs) ˆα ˆβ
= i
4[γˆα
, γ
ˆβ
] of the spinor rep. ρs = ρ(1
2) =
(1
2, 0) ⊗ (0, 1
2) of the group ˆG = SL(2, C) that induces the spinor CR [3, 18, 19].
Eq. (106) can be analytically solved either in momentum or energy bases with correct
orthonormalization and completeness properties [18, 19] with respect to the relativistic
scalar product
ψ, ψ = d3
x (−ωt)−3
ψ(t, x)γ0
ψ (t, x) . (107)
The mode expansion in the spin-momentum rep. [19],
ψ(t, x) = d3
p
σ
Up,σ(x)a(p, σ) + Vp,σ(x)b†
(p, σ) , (108)
is written in terms of the field operators, a and b (satisfying canonical anti-commutation
rules), and the particle and antiparticle fundamental spinors of momentum p (with p =
|p|) and polarization σ = ±1
2,
Up,σ(t, x ) =
1
(2π)
3
2
up,σ(t)eip·x
, Vp,σ(t, x ) =
1
(2π)
3
2
vp,σ(t)e−ip·x
(109)
49
50. whose time-dependent terms have the form [19, 21]
up,σ(t) =
i
2
πp
ω
1
2
(ωt)2 e
1
2πµ
H
(1)
ν− (−pt) ξσ
e−1
2πµ
H
(1)
ν+ (−pt) σ·p
p ξσ
, (110)
vp,σ(t) =
i
2
πp
ω
1
2
(ωt)2 e−1
2πµ
H
(2)
ν− (−pt) σ·p
p ησ
e
1
2πµ
H
(2)
ν+ (−pt) ησ
, (111)
in the standard rep. of the Dirac matrices (with diagonal γ0
) and a fixed vacuum of
the Bounch-Davies type [21]. Obviously, the notation σi stands for the Pauli matrices
while the point-independent Pauli spinors ξσ and ησ = iσ2(ξσ)∗
are normalized as
ξ+
σ ξσ = η+
σ ησ = δσσ [19]. The terms giving the time modulation depend on the
Hankel functions H
(1,2)
ν± of indices
ν± =
1
2
± iµ , µ =
m
ω
. (112)
Based on their properties (presented in Appendix B) we deduce
u+
p,σ(t)up,σ(t) = v+
p,σ(t)vp,σ(t) = (−ωt)3
(113)
50
51. obtaining the ortonormalization relations [18]
Up,σ, Up ,σ = Vp,σ, Vp ,σ = δσσ δ3
(p − p ) , (114)
Up,σ, Vp ,σ = Vp,σ, Up ,σ = 0 , (115)
that yield the useful inversion formulas, a(p, σ) = Up,σ, ψ and b(p, σ) = ψ, Vp,σ .
Moreover, it is not hard to verify that these spinors are charge-conjugated to each other,
Vp,σ = (Up,σ)c
= C(Up,σ)T
, C = iγ2
γ0
, (116)
and represent a complete system of solutions in the sense that [18]
d3
p
σ
Up,σ(t, x)U+
p,σ(t, x ) + Vp,σ(t, x)V +
p,σ(t, x ) = e−3ωt
δ3
(x − x ) .
(117)
The Dirac field transforms under isometries x → x = φg(x) (with g ∈ I(M))
according to the CR Tg : ψ(x) → (Tgψ)(x ) = Ag(x)ψ(x) whose generators are
given by Eqs (83) - (86) where now ρ = ρs. Then, according to equations (94) and
(106) we obtain the identity
C
(ρs)
1 = E2
D +
3
2
ω2
14×4 ∼ m2
+
3
2
ω2
. (118)
51
52. This result and equation (101) yield the rest energy of the Dirac field,
E0 = −
3iω
2
± m , (119)
which has a natural simple form where the decay (first) term is added to the usual rest
energy of special relativity. A similar result can be obtained by solving the Dirac equation
with vanishing momentum.
The second invariant results from equations (100) and (118) if we take into account that
(S(ρs)
)2
= 3
4 14×4. Thus we find
C
(ρs)
2 =
3
4
E2
D +
3
16
ω2
14×4 ∼
3
4
m2
+
1
4
ω2
= ω2
s(s + 1)ν+ν− , (120)
where s = 1
2 is the spin and ν± = 1
2 ±im
ω are the indices of the Hankel functions giving
the time modulation of the Dirac spinors of the momentum basis [18].
These invariants define the UIRs that in the flat limit become Wigner’s UIRs (±m, 1
2)
since
lim
ω→0
C
(ρs)
1 ∼ m2
, lim
ω→0
C
(ρs)
2 ∼
3
4
m2
. (121)
52
53. Invariants of UIRs in momentum rep.
The above inversion formulas allow us to write the transformation rules in momentum
rep. as
(Tga)(p, σ) = Up,σ, [ρs(Ag)ψ] ◦ φ−1
g , (122)
(Tgb)(p, σ) = [ρs(Ag)ψ] ◦ φ−1
g , Vp,σ , (123)
but, unfortunately, these scalar product are complicated integrals that cannot be solved.
Therefore, we must restrict ourselves to study the corresponding Lie algebras focusing
on the basis generators in momentum rep..
Any self-adjoint generator X of the spinor rep. of the group S(M) gives rise to a
conserved one-particle operator of the QFT,
X =: ψ, Xψ := X(+)
+X(−)
= d3
p α†
(p) ˜X(+)
α(p) + β†
(p) ˜X(−)
β(p) ,
(124)
53
54. calculated respecting the normal ordering of the operator products [26]. The operators
˜X(±)
are the generators of CRs in momentum rep. acting on the operator valued Pauli
spinors,
α(p) =
a(p, 1
2)
a(p, −1
2)
, β(p) =
b(p, 1
2)
b(p, −1
2)
. (125)
As observed in Ref. [16], the straightforward method for finding the structure of these
operators is to evaluate the entire expression (124) by using the form (108) where the
field operators a and b satisfy the canonical anti-commutation rules [16, 18].
For this purpose we consider several identities written with the notation ∂pi
= ∂
∂pi
as
H Up,σ(t, x) = −iω pi
∂pi +
3
2
Up,σ(t, x) ,
H Vp,σ(t, x) = −iω pi
∂pi +
3
2
Vp,σ(t, x) ,
that help us to eliminate some multiplicative operators and the time derivative when
we inverse the Fourier transform. Furthermore, by applying the Green theorem and
54
55. calculating some terms on computer we find two identical reps. whose basis
generators read, ˜P
(±)
i = ˜Pi = pi and
˜H(±)
= ω ˜X
(±)
(04) = iω pi∂pi
+
3
2
(126)
˜J
(±)
i =
1
2
εijk
˜X
(±)
(jk) = −iεijkpj∂pk
+
1
2
σi (127)
˜K
(±)
i = ˜X
(±)
(0i) = i ˜H(±)
∂pi
+
ω
2
pi∆p − pi
p2
+ m2
2ωp2
+
1
2
εijk iω∂pj
− pj
m
2p2
σk (128)
˜R
(±)
i = ˜X
(±)
(i4) = − ˜K
(±)
i −
1
ω
˜Pi , (129)
where ∆p = ∂pi
∂pi
. These basis generators satisfy the specific sp(2, 2) commutation
rules of the form (87)-(90). Moreover, it is not difficult to verify that these are Hermitian
operators with respect to the scalar products of the momentum rep.
α, α = d3
p α†
(p)˜α(p) , β, β = d3
pβ†
(p) ˜β(p) . (130)
55
56. Therefore, we can conclude that these operators generate a pair of unitary reps. of the
group S(M).
Starting with the Pauli-Lubanski operator,
˜W
(±)
0 =
ω
4
(σ · p)∆p +
ων−
2
σ · ∂p +
im
2p2
(σ · p) p · ∂p
+
m2
− p2
+ 2iωm
4p2ω
σ · p , (131)
˜W
(±)
i =
i
2
(σ · p)∂pi
−
iν−
2p2
σi −
m
2ωp2
(σ · p)pi , (132)
˜W
(±)
4 = ˜W
(±)
0 +
1
2ω
σ · p , (133)
we calculate on computer the following Casimir operators,
˜C
(±)
1 = ω2
[−s(s + 1) − (q + 1)(q − 2)] = m2
+
3ω2
2
, (134)
˜C
(±)
2 = ω2
[−s(s + 1)q(q − 1)] = ω2
s(s + 1)ν+ν− =
3
4
m2
+
ω2
4
,(135)
recovering thus the results (118) and (120) obtained in configurations.
56
57. Dirac field on Minkowski Dirac field on de Sitter
UIR (1
2, ±m) of ˜P↑
+ (1
2, ν±) of Sp(2, 2)
Pi
= pi
Pi
= pi
˜H = E = m2 + p2 ˜H(±)
= iω pi∂pi
+ 3
2
˜J
(±)
i = −iεijkpj∂pk
+ 1
2σi
˜J
(±)
i = −iεijkpj∂pk
+ 1
2σi
˜K
(±)
i = iE∂pi − pi
2E
˜K
(±)
i = i ˜H(±)
∂pi
+ ω
2 pi∆p − pi
p2
+m2
2ωp2
+ 1
2(E+m) εijkpj
σk +1
2εijk iω∂pj
− pj
m
2p2 σk
˜W
(±)
0 = 1
2 p · σ ˜W
(±)
0 = ω
4 (σ · p)∆p + ων−
2 σ · ∂p
+im
2p2(σ · p) p · ∂p + m2
−p2
+2iωm
4p2ω σ · p
˜W
(±)
i = 1
2 mσi + pi
2(E+m)σ · p ˜W
(±)
i = i
2(σ · p)∂pi
− iν−
2p2 σi − m
2ωp2(σ · p)pi
˜W
(±)
4 = ˜W
(±)
0 + 1
2ω σ · p
˜C
(±)
1 = m2 ˜C
(±)
1 = m2
+ 3
2 ω2
˜C
(±)
2 = 3
4 m2 ˜C
(±)
2 = 3
4 m2
+ 1
4 ω2
57
58. CR-UIR equivalence
The above result shows that the identical spinor reps. we obtained here are UIRs of the
principal series corresponding to the canonical labels (s, q) with s = 1
2 and q = ν±. In
other words the spinor CR of the Dirac theory is equivalent with the orthogonal sum of
the equivalent UIRs of the particle and antiparticle sectors.
This suggests that the UIRs (s, ν±) of the group S(M) = Sp(2, 2) can be seen
as being analogous to the Wigner ones (s, ±m) of the Dirac theory in Minkowski
spacetime.
In general, the above equivalent spinor UIRs may not coincide since the expressions
of their basis generators are strongly dependent on the arbitrary phase factors of the
fundamental spinors whether these depend on p. Thus if we change
Up,σ → eiχ+
(p)
Up,σ , Vp,σ → e−iχ−
(p)
Vp,σ , (136)
with χ±
(p) ∈ R, performing simultaneously the associated transformations,
α(p) → e−iχ+
(p)
α(p) , β(p) → e−iχ−
(p)
β(p) , (137)
58
59. that preserves the form of ψ, we find that the operators ˜Pi keep their forms while the
other generators are changing, e. g. the Hamiltonian operators transform as, ˜H(±)
→
˜H(±)
+ pi
∂piχ±
(p). Obviously, these transformations are nothing other than unitary
transformations among equivalent UIRs. Note that thanks to this mechanism one can
fix suitable phases for determining desired forms of the basis generators keeping thus
under control the flat and rest limits of these operators in the Dirac [19] or scalar [16, 28]
field theory on M.
At the level of QFT, the operators {X(AB)}, given by Eq. (124) where we introduce the
differential operators (126) -(129), generate a reducible operator valued CR which can
be decomposed as the orthogonal sum of CRs - generated by {X
(+)
(AB)} and {X
(−)
(AB)}
- that are equivalent between themselves and equivalent to the UIRs (1
2, ν±) of the
sp(2, 2) algebra. These one-particle operators are the principal conserved quantities of
the Dirac theory corresponding to the de Sitter isometries via Noether theorem.
It is remarkable that in our formalism we have ˜X
(+)
AB = ˜X
(−)
AB which means that the
particle and antiparticle sectors bring similar contributions such that we can say that
these quantities are additive, e. g., the energy of a many particle system is the sum of
the individual energies of particles and antiparticles.
59
60. Other important conserved one-particle operators are the components of the Pauli -
Lubanski operator,
WA = W
(+)
A + W
(−)
A = d3
p α†
(p) ˜W
(+)
A α(p) + β†
(p) ˜W
(−)
A β(p) , (138)
as given by Eqs. (131)-(133).
The Casimir operators of QFT have to be calculated according to Eqs. (92) and (99) but
by using the one-particle operators X(AB) and WA instead of ˜X(AB) and ˜WA. We
obtain the following one-particle contributions
C1 = m2
+
3
2
ω2
N + · · · , C2 =
3
4
m2
+
1
4
ω2
N + · · · , (139)
where N = N(+)
+ N(−)
is the usual operator of the total number of particles and
antiparticles.
Thus the additivity holds for the entire theory of the spacetime symmetries in contrast
with the conserved charges of the internal symmetries that take different values for
particles and antiparticles as, for example, the charge operator corresponding to the
U(1)em gauge symmetry [21] that reads Q = q(N(+)
− N(−)
).
60
61. 6. Concluding remarks
The principal conclusion is that the QFT on the de Sitter background has similar features
as in the flat case. Thus the covariant quantum fields transforming according to CRs
induced by the reps. of the group ˆG = SL(2, C) that must be equivalent to orthogonal
sums of UIRs of the group S(M) = Sp(2, 2) whose specific invariants depend only
on particle masses and spins.
The example is the spinor CR of the Dirac theory that is induced by the linear rep.
(1
2, 0) ⊗ (0, 1
2) of the group ˆG but is equivalent to the orthogonal sum of two equivalent
UIRs of the group S(M) labelled by (1
2, ν±).
Thus at least in the case of the Dirac field we recover a similar conjuncture as in the
Wigner theory of the induced reps. of the Poincar´e group in special relativity.
However, the principal difference is that the transformations of the Wigner UIRs can be
written in closed forms while in our case this cannot be done because of the technical
difficulties in solving the integrals (122) and (123). For this reason we were forced to
restrict ourselves to study only the reps. of the corresponding algebras.
61
62. This is not an impediment since physically speaking we are interested to know the
properties of the basis generators (in configurations or momentum rep.) since these give
rise to the conserved observables (i. e. the one-particle operators) of QFT, associated
to the de Sitter isometries.
It is remarkable that the particle and antiparticle sectors of these operators bring
additive contributions since the particle and antiparticle operators transform alike under
isometries just as in special relativity.
Notice that this result was obtained by Nachtmann [16] for the scalar UIRs but this is less
relevant as long as the generators of the scalar rep. depend only on m2
. Now we see
that the generators of the spinor rep. which have spin terms depending on m preserve
this property such that we can conclude that all the one-particle operators corresponding
to the de Sitter isometries are additive, regardless the spin.
The principal problem that remains unsolved here is how to build on the de Sitter
manifolds a Wigner type theory able to define the structure of the covariant fields without
using field equations.
62
63. Appendix
A: Finite-dimensional reps. of the sl(2, C) algebra
The standard basis of the sl(2, C) algebra is formed by the generators J = (J1, J2, J3) and
K = (K1, K2, K3) that satisfy [30, 8]
[Ji, Jj] = iεijkJk , [Ji, Kj] = iεijkKk , [Ki, Kj] = −iεijkJk , (140)
having the Casimir operators c1 = iJ · K and c2 = J2
− K2
. The linear combinations Ai =
1
2 (Ji + iKi) and Bi = 1
2 (Ji − iKi) form two independent su(2) algebras satisfying
[Ai, Aj] = iεijkAk , [Bi, Bj] = iεijkBk , [Ai, Bj] = 0 . (141)
Consequently, any finite-dimensional irreducible rep. (IR) τ = (j1, j2) is carried by the space of
the direct product (j1)⊗(j2) of the UIRs (j1) and (j2) of the su(2) algebras (Ai) and respectively
(Bi). These IRs are labeled either by the su(2) labels (j1, j2) or giving the values of the Casimir
operators c1 = j1(j1 + 1) − j2(j2 + 1) and c2 = 2[j1(j1 + 1) + j2(j2 + 1)].
The fundamental reps. defining the sl(2, C) algebra are either the IR (1
2, 0) generated by
{1
2σi, −i
2σi} or the IR (0, 1
2) whose generators are {1
2σi, i
2σi}. Their direct sum form the spinor
63
64. IR ρs = (1
2, 0) ⊕ (0, 1
2) of the Dirac theory. In applications it is convenient to consider ρs as the
fundamental rep. since here invariant forms can be defined using the Dirac conjugation.
The spin basis of the IR τ can be constructed as the direct product,
|τ, sσ =
λ1+λ2=σ
Csσ
j1λ1,j2λ2
|j1, λ1 ⊗ |j2, λ2 , (142)
of su(2) canonical bases where the Clebsh-Gordan coefficients [8] give the spin content of the
IR τ, i. e. s = j1 + j2, j1 + j2 − 1, ..., |j1 − j2|. Note that for integer values of spin we can resort
to the tensor bases constructed as direct products of the vector bases {e1, e2, e3} of the vector
IR (j = 1) (which satisfy |1, ±1 = 1√
2
(e1 ± ie2) and |1, 0 = e3).
Given the IR τ = (j1, j2) we say that its adjoint IR is ˙τ = (j2, j1) and observe that these have
the same spin content while their generators are related as J( ˙τ)
= J(τ)
and K( ˙τ)
= −K(τ)
. On
the other hand, the operators A and B are Hermitian since we use UIRs of the su(2) algebra.
Consequently, we have J+
= J and K+
= −K for any finite-dimensional IR of the sl(2, C)
algebra, such that we can write
(J(τ)
)+
= J(τ)
, (K(τ)
)+
= K( ˙τ)
. (143)
64
65. Hereby we conclude that invariant forms can be constructed only when we use reducible reps.
ρ = · · · τ1 ⊕ τ2 · · · ˙τ1 ⊕ ˙τ2 · · · containing only pairs of adjoint reps.. Then the matrix γ(ρ) may
be constructed with the matrix elements
τ1, s1σ1|γ(ρ)|τ2, s2σ2 = δτ1 ˙τ2δs1s2δσ1σ2 . (144)
Note that the canonical basis {τ, jλ } defines the chiral rep. while a new basis in which γ(ρ)
becomes diagonal gives the so called standard rep.. This terminology comes from the Dirac
theory where γ(ρs) = γ0
is the Dirac matrix that may have these reps. [27].
B: Some properties of Hankel functions
According to the general properties of the Hankel functions [31], we deduce that those used here,
H
(1,2)
ν± (z), with ν± = 1
2 ± iµ and z ∈ R, are related among themselves through [H
(1,2)
ν± (z)]∗
=
H
(2,1)
ν (z) and satisfy the identities
e±πk
H(1)
ν (z)H(2)
ν±
(z) + e πk
H(1)
ν±
(z)H(2)
ν (z) =
4
πz
. (145)
65
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68