arXiv subjects

Hendrik B. Geyer

Publications and source records attributed to Hendrik B. Geyer.

9 recordsLinked to original sources

arXiv2012

PT-symmetric quantum systems with positive P

A new version of PT-symmetric quantum theory is proposed and illustrated by an N-site-lattice Legendre oscillator. The essence of the innovation lies in the replacement of parity P (serving as an indefinite metric in an auxiliary Krein space) by its non-involutory alternative P(positive)=Q>0 playing the role of a positive-definite nontrivial metric in an auxiliary, redundant, unphysical Hilbert space. It is shown that the QT-symmetry of this form remains appealing and technically useful.

quant-ph↗

arXiv2009

Sturm-Schroedinger equations: formula for metric

Sturm-Schroedinger equations $Hψ=E Wψ$ with $H\neq H^\dagger$ and $W\neq W^\dagger \neq I$ are considered, with a weak point of the theory lying in the purely numerical matrix-inversion form of the double-series definition of the necessary metric operator $Θ$ in the physical Hilbert space of states [M. Znojil, J. Phys. A: Math. Theor. 41 (2008) 215304]. This shortcoming is removed here via an amended, single-series definition of $Θ$.

quant-ph↗

arXiv2006

Construction of a unique metric in quasi-Hermitian quantum mechanics: non-existence of the charge operator in a 2 x 2 matrix model

For a specific exactly solvable 2 by 2 matrix model with a PT-symmetric Hamiltonian possessing a real spectrum, we construct all the eligible physical metrics and show that none of them admits a factorization CP in terms of an involutive charge operator C. Alternative ways of restricting the physical metric to a unique form are briefly discussed.

quant-ph↗

arXiv2004

Pattern formation in a metastable, gradient-driven sandpile

With a toppling rule which generates metastable sites, we explore the properties of a gradient-driven sandpile that is minimally perturbed at one boundary. In two dimensions we find that the transport of grains takes place along deep valleys, generating a set of patterns as the system approaches the stationary state. We use two versions of the toppling rule to analyze the time behavior and the geometric properties of clusters of valleys, also discussing the relation between this model and the general properties of models displaying self-organized criticality.

cond-mat.stat-mech↗

arXiv2003

Dynamical and invariant supersymmetry in the fermion pairing problem

We argue that fermion-boson mapping techniques represent a natural tool for studying many-body supersymmetry in fermionic systems with pairing. In particular, using the generalized Dyson mapping of a many-level fermion superalgebra with the SU(2) type of pairing we investigate two kinds of supersymmetry connecting excitations in the systems with even and odd particle numbers: dynamical supersymmetry, which ensures a unified classification of states for both even and odd populations, and invariant supersymmetry with actual degeneracies of states within the same supermultiplet. Dynamical supersymmetries based on the dynamical algebra of the type U(K/2Ω) (where K and 2Ωdenote the number of fermion-pair and single-fermion states, respectively) naturally arise in the bosonized description of the system. Conditions for invariant supersymmetry are determined in a restricted case of bilinear supercharge operators.

nucl-th↗

arXiv2003

A Matrix Model for ν_{k_1k_2}=\frac{k_1+k_2}{k_1 k_2} Fractional Quantum Hall States

We propose a matrix model to describe a class of fractional quantum Hall (FQH) states for a system of (N_1+N_2) electrons with filling factor more general than in the Laughlin case. Our model, which is developed for FQH states with filling factor of the form ν_{k_1k_2}=\frac{k_1+k_2}{k_1k_2} (k_1 and k_2 odd integers), has a U(N_1)\times U(N_2) gauge invariance, assumes that FQH fluids are composed of coupled branches of the Laughlin type, and uses ideas borrowed from hierarchy scenarios. Interactions are carried, amongst others, by fields in the bi-fundamentals of the gauge group. They simultaneously play the role of a regulator, exactly as does the Polychronakos field. We build the vacuum configurations for FQH states with filling factors given by the series ν_{p_1p_2}=\frac{p_2}{p_1p_2-1}, p_1 and p_2 integers. Electrons are interpreted as a condensate of fractional D0-branes and the usual degeneracy of the fundamental state is shown to be lifted by the non-commutative geometry behaviour of the plane. The formalism is illustrated for the state at ν={2/5}.

hep-th↗

arXiv2003

Second Virial Coefficient for Noncommutative Space

The second virial coefficient $B_{2}^{nc}(T)$ for non-interacting particles moving in a two-dimensional noncommutative space and in the presence of a uniform magnetic field $\vec B$ is presented. The noncommutativity parameter $\te$ can be chosen such that the $B_{2}^{nc}(T)$ can be interpreted as the second virial coefficient for anyons of statistics $\al$ in the presence of $\vec B$ and living on the commuting plane. In particular in the high temperature limit $\be\lga 0$, we establish a relation between the parameter $\te$ and the statistics $\al$. Moreover, $B_{2}^{nc}(T)$ can also be interpreted in terms of composite fermions.

hep-th↗

arXiv2001

A microscopic framework for dynamical supersymmetry in nuclei

We discuss and explore new aspects of the generalized Dyson mapping of nuclear collective superalgebras composed of an arbitrary fermion-pair algebra and a set of single-fermion creation/annihilation operators. It is shown that a direct consequence of the particular mapping procedure is the conservation of the total number of ideal particles in the resulting boson-fermion system. This provides a microscopic framework for the phenomenological supersymmetric models based on the U(6/2Omega) dynamical superalgebras. Attention is paid to the mapping of single-fermion creation and annihilation operators whose detailed form cannot be determined on the phenomenological level. We derive the general expansion of the single-fermion images that result from the similarity transformation employed to ensure non-redundant bosonisation in the ideal space. The method is then illustrated in an application to the SO(4) collective algebra, a natural extension of the SU(2) seniority model.

nucl-th↗

arXiv2001

Parameter symmetries of quantum many-body systems

We analyze the occurrence of dynamically equivalent Hamiltonians in the parameter space of general many-body interactions for quantum systems, particularly those that conserve the total number of particles. As an illustration of the general framework, the appearance of parameter symmetries in the interacting boson model-1 and their absence in the Ginocchio SO(8) fermionic model are discussed.

nucl-th↗