The spin representation

Author(s):  
Eckhard Meinrenken
Keyword(s):  
2014 ◽  
Vol 45 (4) ◽  
pp. 367-374
Author(s):  
Madline Al-Tahan ◽  
Mohammad N. Abdulrahim ◽  
Samer S. Habre

We consider the spin representation of Artin's braid group, which has a negative index of one and was originally given by D. D. Long and explicitly computed by J.P.Tian. In our work, we find sufficient conditions under which the complex specialization of that representation, namely $\alpha :B_{n}\to GL_{n^{2}}(\mathbb C)$, is unitary relative to a nonsingular hermitian matrix.


Author(s):  
Joseph Wilson ◽  
Matt Visser

We present a compact Baker–Campbell–Hausdorff–Dynkin formula for the composition of Lorentz transformations [Formula: see text] in the spin representation (a.k.a. Lorentz rotors) in terms of their generators [Formula: see text]: [Formula: see text] This formula is general to geometric algebras (a.k.a. real Clifford algebras) of dimension [Formula: see text], naturally generalizing Rodrigues’ formula for rotations in [Formula: see text]. In particular, it applies to Lorentz rotors within the framework of Hestenes’ spacetime algebra, and provides an efficient method for composing Lorentz generators. Computer implementations are possible with a complex [Formula: see text] matrix representation realized by the Pauli spin matrices. The formula is applied to the composition of relativistic 3-velocities yielding simple expressions for the resulting boost and the concomitant Wigner angle.


2004 ◽  
Vol 19 (05) ◽  
pp. 357-362 ◽  
Author(s):  
PAOLO MARANER

We emphasize that the group-theoretical considerations leading to SO (10) unification of electroweak and strong matter field components naturally extend to spacetime components, providing a truly unified description of all generation degrees of freedoms in terms of a single chiral spin representation of one of the groups SO (13,1), SO (9,5), SO (7,7) or SO (3,11). The realization of these groups as higher-dimensional spacetime symmetries produces unification of all fundamental fermions is a single spacetime spinor.


1965 ◽  
Vol 20 (5) ◽  
pp. 649-655 ◽  
Author(s):  
G. Braunss

It is supposed that there exists a system O′ (intrinsic system) in which the field equation for a spin ½ representation has the simple form γµ ∂Ψ′/∂ϰμ′=0. This system is related to the physical system (in which all measurements are performed) by an affine connection which is induced by a certain group of local transformations. The investigation given here deals with the group of local four-dimensional complex orthogonal transformations. Subjecting ψ' to such a transformation Ω one gets with ψ' (x′) = Ω (x) ψ (x) the following equation γλ ∂Ψ/∂xλ+γλ Ω-1 ∂Ω/∂xλ ψ=0. The interaction term splits up into a vector and a pseudovector part: γλ Ω-1 ∂Ω/∂xλ ≡ γλ Vλ+γλ γ5 Ρλ. The special cases of real local orthogonal (LORENTZ-) transformations (ξλμ= - ξμλ; ξkl real, ξ4l imaginary; ψ → χ) and special complex local orthogonal transformations (ηλμ=- ημλ; ηkl imaginary, η4l real; ψ → φ) are first separately considered. It is required that Vλ and Pλ are to be built up from the fundamental covariants of the field. In order that certain conservation laws hold at least approximately, the following assumptions are made:Im{Vk}=±k2 ɸ̅γkφ, Re {V4}=±k2γ4φ, Im {Pk} = ± l2 χ̅ γk γ5 χ, Re {P4}= ±l2χ̅γ4γ5χ together with the symmetry conditions for the transformation parameters, ξλ[μυ] ≡ 0, η〈λμ,υ〉 ≡ 0, which can be fulfilled by setting, for example, ξλμ,υ = π[λπμ,υ],ηλμ = ϑ[λ,μ]. The remaining parts of Vλ and Ρλ, which are determined by these relations, are of higher order and can be assumed to describe weaker interactions. Neglecting these terms one obtains the following set of equations:(a) γλ ∂χ/∂xλ±k2γλ(ɸ̅γλφ) χ±l2γλγ5(χ̅γλγ5χ) χ≈0(b) γλ ∂χ/∂xλ±k2γλ(ɸ̅γλφ) φ±l2γλγ5(χ̅γλγ5χ) φ≈0Since the pseudovector coupling possesses a greater symmetry, it is assumed that χ represents the baryon and φ the lepton states. Within the approximation, which holds with (a) and (b), it follows the conservation of χ̅γλχand ɸ̅γλφ resp. (conservation of electric charge) and χ̅γλγ5χ and ɸ̅ γ·λγ5φ resp. (conservation of baryonic and leptonic charge resp.). These conservation laws are exact only if the mentioned terms of higher order are neglected; this is equivalent to a strict “local” conservation as can be shown. As to the isospin it is proposed to replace one of its components by a bounded state, i. e. a mixture of χ- and φ-states which would lead in the case of the neutron for example to the components of the /?β-decay. Due to the relations ± k2 ɸ̅γλφ = ¼ηλρ,ρ +O(η2) and ηλu = ϑ[λμ], and in agreement with the reality conditions, it is possible to connect the parameters ϑλ with the electromagnetic field Aλ by setting ϑλ= 8 iAλ. Taking into consideration terms of higher order this would lead to a type of nonlinear electrodynamics.


2021 ◽  
Vol 2021 (9) ◽  
Author(s):  
Konstantin Alkalaev ◽  
Alexander Yan

Abstract We study a 3d/2d dimensional degression which is a Kaluza-Klein type mechanism in AdS3 space foliated into AdS2 hypersurfaces. It is shown that an AdS3 massless particle of spin s = 1, 2, …, ∞ degresses into a couple of AdS2 particles of equal energies E = s. Note that the Kaluza-Klein spectra in higher dimensions are always infinite. To formulate the AdS3/AdS2 degression we consider branching rules for AdS3 isometry algebra o(2,2) representations decomposed with respect to AdS2 isometry algebra o(1,2). We find that a given o(2,2) higher-spin representation lying on the unitary bound (i.e. massless) decomposes into two equal o(1,2) modules. In the field-theoretical terms, this phenomenon is demonstrated for spin-2 and spin-3 free massless fields. The truncation to a finite spectrum can be seen by using particular mode expansions, (partial) diagonalizations, and identities specific to two dimensions.


Chemosensors ◽  
2019 ◽  
Vol 7 (4) ◽  
pp. 54
Author(s):  
Elena Orlenko ◽  
Fedor Orlenko

The Wigner–Eckart theorem is used for considering the collective effects related to ordering spins in systems of identical particles in ferro- and antiferromagnetic electronic systems, as well as magnetic effects that occur in high spin systems. The Hamiltonian, written in the spin representation in the form obtained by Heisenberg, Dirac, and van Vleck used to describe spin ordering in systems of particles with spin ½, is not appropriate for a description of particle systems with a spin different from ½. “High” spin particles in the spin representation need other forms of the Hamiltonian of the exchange interaction in the spin representation. The Hamiltonian for high-spin particles has been developed from the first principles, and the effects of magnetic ordering in systems of identical particles with arbitrary spin are considered in this review. An effect of giant negative magnetoresistance in the Indium antimonide has been interpreted from the exchange contribution of a high spin heavy holes point of view.


2017 ◽  
Vol 31 (11) ◽  
pp. 1750123
Author(s):  
Xiao-Ming Zhao ◽  
Jing Yu ◽  
Jing He ◽  
Qiu-Bo Cheng ◽  
Ying Liang ◽  
...  

In this paper, we numerically study the non-Abelian statistics of the zero-energy Majorana fermions at the end of Majorana chain and show its application to quantum computing by mapping it to a spin model with special symmetry. In particular, by using transverse-field Ising model with Z2 symmetry, we verify the nontrivial non-Abelian statistics of Majorana fermions. Numerical evidence and comparison in both Majorana representation and spin representation are presented. The degenerate ground states of a symmetry protected spin chain therefore provide a promising platform for topological quantum computation.


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