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Register a new userOn the oscillator realization of conformal U(2,2) quantum particles and their particle-hole coherent states
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We revise the unireps. of $U(2,2)$ describing conformal particles with continuous mass spectrum from a many-body perspective, which shows massive conformal particles as compounds of two correlated massless particles. The statistics of the compound (boson/fermion) depends on the helicity $h$ of the massless components (integer/half-integer). Coherent states (CS) of particle-hole pairs (excitons) are also explicitly constructed as the exponential action of exciton (non-canonical) creation operators on the ground state of unpaired particles. These CS are labeled by points $Z$ ($2times 2$ complex matrices) on the Cartan-Bergman domain $mathbb D_4=U(2,2)/U(2)^2$, and constitute a generalized (matrix) version of Perelomov $U(1,1)$ coherent states labeled by points $z$ on the unit disk $mathbb D_1=U(1,1)/U(1)^2$. Firstly we follow a geometric approach to the construction of CS, orthonormal basis, $U(2,2)$ generators and their matrix elements and symbols in the reproducing kernel Hilbert space $mathcal H_lambda(mathbb D_4)$ of analytic square-integrable holomorphic functions on $mathbb D_4$, which carries a unitary irreducible representation of $U(2,2)$ with index $lambdainmathbb N$ (the conformal or scale dimension). Then we introduce a many-body representation of the previous construction through an oscillator realization of the $U(2,2)$ Lie algebra generators in terms of eight boson operators with constraints. This particle picture allows us for a physical interpretation of our abstract mathematical construction in the many-body jargon. In particular, the index $lambda$ is related to the number $2(lambda-2)$ of unpaired quanta and to the helicity $h=(lambda-2)/2$ of each massless particle forming the massive compound.
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Bilayer quantum Hall (BLQH) systems, which underlie a $U(4)$ symmetry, display unique quantum coherence effects. We study coherent states (CS) on the complex Grassmannian $mathbb G_2^4=U(4)/U(2)^2$, orthonormal basis, $U(4)$ generators and their matrix elements in the reproducing kernel Hilbert space $mathcal H_lambda(mathbb G_2^4)$ of analytic square-integrable holomorphic functions on $mathbb G_2^4$, which carries a unitary irreducible representation of $U(4)$ with index $lambdainmathbb N$. A many-body representation of the previous construction is introduced through an oscillator realization of the $U(4)$ Lie algebra generators in terms of eight boson operators. This particle picture allows us for a physical interpretation of our abstract mathematical construction in the BLQH jargon. In particular, the index $lambda$ is related to the number of flux quanta bound to a bi-fermion in the composite fermion picture of Jain for fractions of the filling factor $ u=2$. The simpler, and better known, case of spin-$s$ CS on the Riemann-Bloch sphere $mathbb{S}^2=U(2)/U(1)^2$ is also treated in parallel, of which Grassmannian $mathbb G_2^4$-CS can be regarded as a generalized (matrix) version.
We give a quantum mechanical description of accelerated relativistic particles in the framework of Coherent States (CS) of the (3+1)-dimensional conformal group SU(2,2), with the role of accelerations played by special conformal transformations and with the role of (proper) time translations played by dilations. The accelerated ground state $tildephi_0$ of first quantization is a CS of the conformal group. We compute the distribution function giving the occupation number of each energy level in $tildephi_0$ and, with it, the partition function Z, mean energy E and entropy S, which resemble that of an Einstein Solid. An effective temperature T can be assigned to this accelerated ensemble through the thermodynamic expression dE/dS, which leads to a (non linear) relation between acceleration and temperature different from Unruhs (linear) formula. Then we construct the corresponding conformal-SU(2,2)-invariant second quantized theory and its spontaneous breakdown when selecting Poincare-invariant degenerated theta-vacua (namely, coherent states of conformal zero modes). Special conformal transformations (accelerations) destabilize the Poincare vacuum and make it to radiate.
Nonrelativistic conformal groups, indexed by l=N/2, are analyzed. Under the assumption that the mass parametrizing the central extension is nonvanishing the coadjoint orbits are classified and described in terms of convenient variables. It is shown that the corresponding dynamical system describes, within Ostrogradski framework, the nonrelativistic particle obeying (N+1)-th order equation of motion. As a special case, the Schroedinger group and the standard Newton equations are obtained for N=1 (l=1/2).
We construct various systems of coherent states (SCS) on the $O(D)$-equivariant fuzzy spheres $S^d_Lambda$ ($d=1,2$, $D=d!+!1$) constructed in [G. Fiore, F. Pisacane, J. Geom. Phys. 132 (2018), 423-451] and study their localizations in configuration space as well as angular momentum space. These localizations are best expressed through the $O(D)$-invariant square space and angular momentum uncertainties $(Deltaboldsymbol{x})^2,(Deltaboldsymbol{L})^2$ in the ambient Euclidean space $mathbb{R}^D$. We also determine general bounds (e.g. uncertainty relations from commutation relations) for $(Deltaboldsymbol{x})^2,(Deltaboldsymbol{L})^2$, and partly investigate which SCS may saturate these bounds. In particular, we determine $O(D)$-equivariant systems of optimally localized coherent states, which are the closest quantum states to the classical states (i.e. points) of $S^d$. We compare the results with their analogs on commutative $S^d$. We also show that on $S^2_Lambda$ our optimally localized states are better localized than those on the Madore-Hoppe fuzzy sphere with the same cutoff $Lambda$.
The three-dimensional Klein-Gordon oscillator is shown to exhibit an algebraic structure known from supersymmetric quantum mechanics. The supersymmetry is found to be unbroken with a vanishing Witten index, and it is utilized to derive the spectral properties of the Klein-Gordon oscillator, which is closely related to that of the non-relativistic harmonic oscillator in three dimensions. Supersymmetry also enables us to derive a closed-form expression for the energy-dependent Greens function.
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