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Herve Mohrbach

Publications and source records attributed to Herve Mohrbach.

At least 19 recordsLinked to original sources
arXiv2014

Quantization of soluble classical constrained systems

The derivation of the brackets among coordinates and momenta for classical constrained systems is a necessary step toward their quantization. Here we present a new approach for the determination of the classical brackets which does neither require Dirac's formalism nor the symplectic method of Faddeev and Jackiw. This approach is based on the computation of the brackets between the constants of integration of the exact solutions of the equations of motion. From them all brackets of the dynamical variables of the system can be deduced in a straightforward way.

hep-th↗
arXiv2010

Dirac Particles in a Gravitational Field

The semiclassical approximation for the Hamiltonian of Dirac particles interacting with an arbitrary gravitational field is investigated. The time dependence of the metrics leads to new contributions to the in-band energy operator in comparison to previous works on the static case. In particular we find a new coupling term between the linear momentum and the spin, as well as couplings which contribute to the breaking of the particle - antiparticle symmetry.

hep-th↗
arXiv2010

Polymorphic Dynamics of Microtubules

Starting from the hypothesis that the tubulin dimer is a conformationally bistable molecule - fluctuating between a curved and a straight configuration at room temperature - we develop a model for polymorphic dynamics of the microtubule lattice. We show that tubulin bistability consistently explains unusual dynamic fluctuations, the apparent length-stiffness relation of grafted microtubules and the curved-helical appearance of microtubules in general. Analyzing experimental data we conclude that taxol stabilized microtubules exist in highly cooperative yet strongly fluctuating helical states. When clamped by the end the microtubule undergoes an unusual zero energy motion - in its effect reminiscent of a limited rotational hinge.

q-bio.BM↗
arXiv2009

Diagonal Representation for a Generic Matrix Valued Quantum Hamiltonian

A general method to derive the diagonal representation for a generic matrix valued quantum Hamiltonian is proposed. In this approach new mathematical objects like non-commuting operators evolving with the Planck constant promoted as a running variable are introduced. This method leads to a formal compact expression for the diagonal Hamiltonian which can be expanded in a power series of the Planck constant. In particular, we provide an explicit expression for the diagonal representation of a generic Hamiltonian to the second order in the Planck constant. This last result is applied, as a physical illustration, to Dirac electrons and neutrinos in external fields.

math-ph↗
arXiv2008

Appearance of Gauge Fields and Forces beyond the adiabatic approximation

We investigate the origin of quantum geometric phases, gauge fields and forces beyond the adiabatic regime. In particular, we extend the notions of geometric magnetic and electric forces discovered in studies of the Born-Oppenheimer approximation to arbitrary quantum systems described by matrix valued quantum Hamiltonians. The results are illustrated by several physical relevant examples.

hep-th↗
arXiv2008

Semiclassical quantization of electrons in magnetic fields: the generalized Peierls substitution

A generalized Peierls substitution which takes into account a Berry phase term must be considered for the semiclassical treatment of electrons in a magnetic field. This substitution turns out to be an essential element for the correct determination of the semiclassical equations of motion as well as for the semiclassical Bohr-Sommerfeld quantization condition for energy levels. A general expression for the cross-sectional area is derived and used as an illustration for the calculation of the energy levels of Bloch and Dirac electrons.

cond-mat.mes-hall↗
arXiv2008

Bloch electrons interacting with an external electromagnetic field and Bloch electrons in interaction

We apply a general method developed recently for the derivation of the diagonal representation of an arbitrary matrix valued quantum Hamiltonian to the particular case of Bloch electrons in an external electromagnetic field. We find the diagonal representation as a series expansion to the second order in $\hbar .$ This result is the basis for the determination of the effective in-band Hamiltonian of interacting Bloch electrons living in different energy bands. Indeed, the description of effects such as magnetic moment-moment interactions mediated by the magnetic part of the full electromagnetic interaction requires a computation to second order in $\hbar $. It is found that the electronic current is made of two contributions: the first one comes from the velocity and the second one is a magnetic moment current similar to the spin current for Dirac particles. This last contribution is responsible for the interaction between magnetic moments similarly to the spin-spin interaction in the Breit Hamiltonian for Dirac electrons in interaction.

cond-mat.str-el↗
arXiv2008

Quantum Hamiltonian diagonalization and Equations of Motion with Berry Phase Corrections

It has been recently found that the equations of motion of several semiclassical systems must take into account anomalous velocity terms arising from Berry phase contributions. Those terms are for instance responsible for the spin Hall effect in semiconductors or the gravitational birefringence of photons propagating in a static gravitational field. Intensive ongoing research on this subject seems to indicate that actually a broad class of quantum systems might have their dynamics affected by Berry phase terms. In this article we review the implication of a new diagonalization method for generic matrix valued Hamiltonians based on a formal expansion in power of $\hbar$. In this approach both the diagonal energy operator and dynamical operators which depend on Berry phase terms and thus form a noncommutative algebra, can be expanded in power series in \hbar $. Focusing on the semiclassical approximation, we will see that a large class of quantum systems, ranging from relativistic Dirac particles in strong external fields to Bloch electrons in solids have their dynamics radically modified by Berry terms.

hep-th↗
arXiv2008

Bohlin-Arnold-Vassiliev's duality and conserved quantities

Bohlin-Arnold-Vassiliev's duality transformation establishes a correspondence between motions in different central potentials. It offers a very direct way to construct the dynamical conserved quantities associated to the isotropic harmonic oscillator (Fradkin-Jauch-Hill tensor) and to the Kepler's problem (Laplace-Runge-Lenz vector).

math-ph↗
arXiv2007

Duality properties of Gorringe-Leach equations

In the category of motions preserving the angular momentum's direction, Gorringe and Leach exhibited two classes of differential equations having elliptical orbits. After enlarging slightly these classes, we show that they are related by a duality correspondence of the Arnold-Vassiliev type. The specific associated conserved quantities (Laplace-Runge-Lenz vector and Fradkin-Jauch-Hill tensor) are then dual reflections one of the other

math-ph↗
arXiv2007

Recursive Diagonalization of Quantum Hamiltonians to all order in $\hbar$

We present a diagonalization method for generic matrix valued Hamiltonians based on a formal expansion in power of $\hbar $. Considering $\hbar $ as a running parameter, a differential equation connecting two diagonalization processes for two very close values of $\hbar $ is derived. The integration of this differential equation allows the recursive determination of the series expansion in powers of $\hbar $ for the diagonalized Hamiltonian. This approach results in effective Hamiltonians with Berry phase corrections of higher order in $\hbar $, and deepens previous works on the semiclassical diagonalization of quantum Hamiltonians which led notably to the discovery of the intrinsic spin Hall effect. As physical applications we consider spinning massless particles in isotropic inhomogeneous media and show that both the energy and the velocity get quantum corrections of order $\hbar ^{2}$. We also derive formally to all order in $\hbar $ the energy spectrum and the equations of motion of Bloch electrons in an external electric field.

cond-mat.mes-hall↗
arXiv2007

Semiclassical Diagonalization of Quantum Hamiltonian and Equations of Motion with Berry Phase Corrections

It has been recently found that the equations of motion of several semiclassical systems must take into account terms arising from Berry phases contributions. Those terms are responsible for the spin Hall effect in semiconductor as well as the Magnus effect of light propagating in inhomogeneous media. Intensive ongoing research on this subject seems to indicate that a broad class of quantum systems may be affected by Berry phase terms. It is therefore important to find a general procedure allowing for the determination of semiclassical Hamiltonian with Berry Phase corrections. This article presents a general diagonalization method at order $\hbar $ for a large class of quantum Hamiltonians directly inducing Berry phase corrections. As a consequence, Berry phase terms on both coordinates and momentum operators naturally arise during the diagonalization procedure. This leads to new equations of motion for a wide class of semiclassical system. As physical applications we consider here a Dirac particle in an electromagnetic or static gravitational field, and the propagation of a Bloch electrons in an external electromagnetic field.

hep-th↗
arXiv2007

Motor driven microtubule shape fluctuations - force from within the lattice

We develop a general theory of microtubule (MT) deformations by molecular motors generating internal force doublets within the MT lattice. We describe two basic internal excitations, the S and V shape, and compare them with experimental observations from literature. We explain the special role of tubulin vacancies and the dramatic deformation amplifying effect observed for katanin acting at positions of defects. Experimentally observed shapes are used to determine the ratio of MT shear and stretch moduli ($\approx 6\times10^{-5}$) and to estimate the forces induced in the MT lattice by katanin (10's of pN). For many motors acting on a single MT we derive expressions for the end-to-end distance reduction and provide criteria for dominance of this new effect over thermal fluctuations. We conclude that molecular motors if acting cooperatively can ''animate'' MTs from within the lattice and induce slack even without cross-bridging to other structures, a scenario very much reminiscent of the motor driven axoneme.

cond-mat.soft↗
arXiv2007

Semiclassical Dynamics of Dirac particles interacting with a Static Gravitational Field

The semiclassical limit for Dirac particles interacting with a static gravitational field is investigated. A Foldy-Wouthuysen transformation which diagonalizes at the semiclassical order the Dirac equation for an arbitrary static spacetime metric is realized. In this representation the Hamiltonian provides for a coupling between spin and gravity through the torsion of the gravitational field. In the specific case of a symmetric gravitational field we retrieve the Hamiltonian previously found by other authors. But our formalism provides for another effect, namely, the spin hall effect, which was not predicted before in this context.

hep-th↗
arXiv2007

Spin Hall effect of Photons in a Static Gravitational Field

Starting from a Hamiltonian description of the photon within the set of Bargmann-Wigner equations we derive new semiclassical equations of motion for the photon propagating in static gravitational field. These equations which are obtained in the representation diagonalizing the Hamiltonian at the order $\hbar $, present the first order corrections to the geometrical optics. The photon Hamiltonian shows a new kind of helicity-magnetotorsion coupling. However, even for a torsionless space-time, photons do not follow the usual null geodesic as a consequence of an anomalous velocity term. This term is responsible for the gravitational birefringence phenomenon: photons with distinct helicity follow different geodesics in a static gravitational field.

hep-th↗
arXiv2006

Spin Hall effect and Berry phase of spinning particles

We consider the adiabatic evolution of the Dirac equation in order to compute its Berry curvature in momentum space. It is found that the position operator acquires an anomalous contribution due to the non Abelian Berry gauge connection making the quantum mechanic algebra noncommutative. A generalization to any known spinning particles is possible by using the Bargmann-Wigner equation of motions. The noncommutativity of the coordinates is responsible of the topological spin transport of spinning particle similarly to the spin Hall effect in spintronic physics or the Magnus effect in optics. As an application we predict new dynamics for nonrelativistic particles in an electric field and for photons in a gravitational field.

hep-th↗