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1.
M. Combescot O. Betbeder-Matibet F. Dubin 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(2):181-189
We have recently constructed a many-body theory for composite excitons, in
which the possible carrier exchanges between N excitons can be treated
exactly through a set of dimensionless “Pauli scatterings” between two
excitons. Many-body effects with free excitons turn out to be rather
simple because these excitons are the exact one-pair
eigenstates of the semiconductor Hamiltonian, in the absence of localized
traps. They consequently form a complete orthogonal basis for one-pair
states. As essentially all quantum particles known as bosons are
composite bosons, it is highly desirable to
extend this free exciton many-body theory to other kinds of
“cobosons” — a contraction for composite bosons — the physically
relevant ones being possibly not the exact one-pair eigenstates of
the system Hamiltonian. The purpose of this paper is
to derive the “Pauli scatterings” and the “interaction scatterings” of
these cobosons in terms of their wave functions and the interactions
which exist between the fermions from which they are
constructed. It is also explained how to calculate many-body effects in
such a very general composite boson system. 相似文献
2.
M. Combescot W. Pogosov 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(2):161-181
We present a many-body theory for Frenkel excitons which takes into account their composite nature exactly. Our approach is
based on four commutators similar to the ones we previously proposed for Wannier excitons. They allow us to calculate any
physical quantity dealing with N excitons in terms of “Pauli scatterings” for carrier exchange in the absence of carrier interaction
and “interaction scatterings” for carrier interactions in the absence of carrier exchange. We show that Frenkel excitons have
a novel “transfer assisted exchange scattering”, specific to these excitons. It comes from indirect Coulomb processes between
localized atomic states. These indirect processes, commonly called “electron-hole exchange” in the case of Wannier excitons
and most often neglected, are crucial for Frenkel excitons, as they are the only ones responsible for the excitation transfer.
We also show that in spite of the fact that Frenkel excitons are made of electrons and holes on the same atomic site, so that
we could naively see them as elementary particles, they definitely are composite objects, their composite nature appearing
through various properties, not always easy to guess. The present many-body theory for Frenkel excitons is thus going to appear
as highly valuable to securely tackle their many-body physics, as in the case of nonlinear optical effects in organic semiconductors. 相似文献
3.
M. Combescot O. Betbeder-Matibet 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(1):63-76
The purpose of this paper is to show how the diagrammatic expansion
in fermion exchanges of scalar products of N-composite-boson
(“coboson”) states can be obtained in a practical way. The hard
algebra on which this expansion is based, will be given in an independent publication.
Due to the composite nature of the particles, the scalar products
of N-coboson states do not reduce to a set of Kronecker symbols, as
for elementary bosons, but contain subtle exchange terms between two or
more cobosons. These terms originate from Pauli exclusion between the
fermionic components of the particles. While our many-body
theory for composite bosons leads to write these scalar products as
complicated sums of products of “Pauli scatterings” between
two cobosons, they in fact correspond to fermion exchanges
between any number P of quantum particles, with
2 ≤P≤N. These P-body exchanges are nicely represented by the
so-called “Shiva diagrams”, which are topologically different from
Feynman diagrams, due to the intrinsic many-body nature of the Pauli
exclusion from which they originate. These Shiva diagrams in fact
constitute the novel part of our composite-exciton many-body theory
which was up to now missing to get its full
diagrammatic representation. Using them, we can now “see” through
diagrams the physics of any quantity in which enters N interacting
excitons — or more generally N composite bosons —, with fermion
exchanges included in an
exact — and transparent — way. 相似文献
4.
M. Combescot 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(3):289-303
We reconsider the procedure
developed for atoms a few decades ago by Girardeau, in the light of
the composite-boson many-body theory we recently proposed. The
Girardeau's procedure makes use of a so called “unitary Fock-Tani
operator” which in an exact way transforms one composite bound
atom into one bosonic “ideal” atom. When used to transform the
Hamiltonian of interacting atoms, this operator generates an extremely
complex set of effective scatterings between ideal bosonic atoms and free
fermions which makes the transformed Hamiltonian impossible to write
explicitly, in this way forcing to some truncation. The scatterings
restricted to the ideal-atom subspace are shown to read rather simply in
terms of the two elementary scatterings of the composite-boson many-body
theory, namely, the energy-like direct interaction scatterings
— which describe fermion interactions without fermion exchange — and
the dimensionless Pauli scatterings — which describe fermion exchanges
without fermion interaction. We here show
that, due to a fundamental difference in the scalar products of
elementary and composite bosons, the Hamiltonian expectation
value for N ground state atoms
obtained by staying in the ideal-atom subspace and working
with boson operators only, differ from the exact ones even for N = 2 and
a mapping to the ideal-atom subspace performed, as advocated, from
the fully antisymmetrical atomic state, i.e., the state which obeys the
so-called “subsidiary condition”. This shows that, within this
Girardeau's procedure too, we cannot completely forget the underlying
fermionic components of the particles if we want to correctly describe
their interactions. 相似文献
5.
D. I. Dimitrov L. I. Klushin A. Skvortsov A. Milchev K. Binder 《The European physical journal. E, Soft matter》2009,29(1):9-25
A flexible polymer chain under good solvent conditions, end-grafted on a flat repulsive substrate surface and compressed by
a piston of circular cross-section with radius L may undergo the so-called “escape transition” when the height of the piston D above the substrate and the chain length N are in a suitable range. In this transition, the chain conformation changes from a quasi-two-dimensional self-avoiding walk
of “blobs” of diameter D to an inhomogeneous “flower” state, consisting of a “stem” (stretched string of blobs extending from the grafting site to
the piston border) and a “crown” outside of the confining piston. The theory of this transition is developed using a Landau
free-energy approach, based on a suitably defined (global) order parameter and taking also effects due to the finite chain
length N into account. The parameters of the theory are determined in terms of known properties of limiting cases (unconfined mushroom,
chain confined between infinite parallel walls). Due to the non-existence of a local order parameter density, the transition
has very unconventional properties (negative compressibility in equilibrium, non-equivalence between statistical ensembles
in the thermodynamic limit, etc.). The reasons for this very unusual behavior are discussed in detail. Using Molecular Dynamics
(MD) simulation for a simple bead-spring model, with N in the range 50
N
300 , a comprehensive study of both static and dynamic properties of the polymer chain was performed. Even though for the
considered rather short chains the escape transition is still strongly rounded, the order parameter distribution does reveal
the emerging transition clearly. Time autocorrelation functions of the order parameter and first passage times and their distribution
indicate clearly the strong slowing down associated with the chain escape. The theory developed here is in good agreement
with all these simulation results. 相似文献
6.
We discuss various aspects of resummed chiral perturbation theory, which was developed recently in order to consistently include
the possibility of large vacuum fluctuations of the s̄s pairs and the scenario with smaller value of the q̄q condensate for
Nf=3. The subtleties of this approach are illustrated using a concrete example of observables connected with πη scattering.
This process seems to be a suitable theoretical laboratory for this purpose due to its sensitivity to the values of the O(p4) LECs, namely to the values of the fluctuation parameters L4 and L6. We discuss several issues in detail, namely the choice of “good” observables and properties of their bare expansions, the
“safe” reparametrization in terms of physical observables, the implementation of exact perturbative unitarity and exact renormalization
scale independence, the role of higher order remainders and estimates of their influence. We make a detailed comparison with
standard chiral perturbation theory and use generalized χPT as well as resonance chiral theory to estimate the higher order
remainders. 相似文献
7.
Frieder Kleefeld 《Czechoslovak Journal of Physics》2005,55(9):1123-1134
On the basis of a new method for the derivation of the effective action the nonperturbative concept of “ dynamical generation”
is explained. A non-trivial, non-Hermitian and PT-symmetric solution for Wightman's scalar field theory in four dimensions
is dynamically generated, rehabilitating Symanzik's precarious φ4-theory with a negative quartic coupling constant as a candidate for an asymptotically free theory of strong interactions.
Finally it is shown making use of the dynamical generation that a Symanzik-like field theory with scalar confinement for the
theory of strong interactions can be even suggested by experiment.
Presented at the 3rd International Workshop “Pseudo-Hermitian Hamiltonians in Quantum Physics”, Istanbul, Turkey, June 20–22,
2005. 相似文献
8.
Reconstruction of the Fermi surface of high-temperature superconducting cuprates in the pseudogap state is analyzed within
a nearly exactly solvable model of the pseudogap state, induced by short-range order fluctuations of the antiferromagnetic
(AFM), spin-density wave (SDW), or a similar charge-density wave (CDW) order parameter, competing with the superconductivity.
We explicitly demonstrate the evolution from “Fermi arcs” (on the “large” Fermi surface) observed in the ARPES experiments
at relatively high temperatures (when both the amplitude and phase of the density waves fluctuate randomly) towards the formation
of typical “small” electron and hole “pockets,” which are apparently observed in the de Haas-van Alphen and Hall resistance
oscillation experiments at low temperatures (when only the phase of the density waves fluctuate and the correlation length
of the short-range order is large enough). A qualitative criterion for the quantum oscillations in high magnetic fields to
be observable in the pseudogap state is formulated in terms of the cyclotron frequency, the correlation length of fluctuations,
and the Fermi velocity.
The text was submitted by the authors in English. 相似文献
9.
Yu. M. Basalaev P. V. Demushin E. V. Nikolaeva A. V. Silinin 《Moscow University Physics Bulletin》2011,66(1):39-44
It is demonstrated that the crystalline structure of MgGeN2 can be reduced to the superposition of “approximated” high-symmetry Bravais sublattices by shifting atoms in a unit cell
within the range of 5% of the lattice constant. The superimposed Brillouin zones were plotted for crystal lattices and sublattices.
The computational results are presented for the electronic structure of MgGeN2 in terms of the theory of the density function. The influence of “hidden” symmetry in this crystal on zone spectra is described. 相似文献
10.
Modelling fluctuations of financial time series: from cascade process to stochastic volatility model 总被引:4,自引:0,他引:4
J.F. Muzy J. Delour E. Bacry 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(3):537-548
In this paper, we provide a simple, “generic” interpretation of multifractal scaling laws and multiplicative cascade process
paradigms in terms of volatility correlations. We show that in this context 1/f power spectra, as recently observed in reference [23], naturally emerge. We then propose a simple solvable “stochastic volatility”
model for return fluctuations. This model is able to reproduce most of recent empirical findings concerning financial time
series: no correlation between price variations, long-range volatility correlations and multifractal statistics. Moreover,
its extension to a multivariate context, in order to model portfolio behavior, is very natural. Comparisons to real data and
other models proposed elsewhere are provided.
Received 22 May 2000 相似文献
11.
In this paper we derive a model for the evolution of the particle radius density for a system of many particles that evolve
according to the Mullins–Sekerka problem. The derived model is a correction of the classical LSW theory that takes the effect
of the fluctuations of the particle density into account. The main difference between the model derived in this paper and
the classical LSW theory is the presence of a second order term which yields a boundary layer effect for large particles.
In particular this model provides a possible solution for the so-called “selection problem” in the LSW theory. 相似文献
12.
This paper investigates stimulated emission and absorption near resonance for a driven system of interacting two-level atoms.
Microscopic kinetic equations for the density matrix elements of N-atom states including atomic motion are built, taking into account atom-field and atom-atom interactions. Analytical solutions
are given for the resulting macroscopic equations in different limits, for a system composed of a strong coherent “pump” field
and a weak counter-propagating “probe” field. It was shown that the existence of a dipole-dipole (long-range) interaction
between atoms separated by distance less than the pump wave-length can cause the formation of periodic polarization and population
structures (gratings in time and space) in the pumped medium without a probe field. The magnitude of pump induced population
grating can have a strong dependence on the relation between the pump field detuning and the polarization decay rate. The
“interaction” between pump and probe induced polarization/population gratings through a dipole-dipole interaction mechanism
causes the absorption line shape asymmetry. Under certain conditions, this asymmetry is revealed in increasing probe gain
for the “red”-shifted (relative to pump) probe and suppressing the gain for the “blue”-shifted probe field when pump is “red”-shifted
relative to the ensemble averaged resonant frequency. The theoretical results are consistent with experimental data for the
probe gain or absorption as the function of frequency and the dependance of the gain on atomic density for sodium vapor when
the pump laser is tuned near the D
2 line. Here the dependance of gain on particle density was explained in the terms of the long-range interaction between the
atoms. 相似文献
13.
Armin Uhlmann 《Foundations of Physics》2011,41(3):288-298
Transition Probability (fidelity) for pairs of density operators can be defined as a “functor” in the hierarchy of “all” quantum
systems and also within any quantum system. The Introduction of “amplitudes” for density operators allows for a more intuitive
treatment of these quantities, also pointing to a natural parallel transport. The latter is governed by a remarkable gauge
theory with strong relations to the Riemann-Bures metric. 相似文献
14.
15.
Thomas Filk 《International Journal of Theoretical Physics》2006,45(6):1166-1180
The famous “spooky action at a distance” in the EPR-scenario is shown to be a local interaction, once entanglement is interpreted as a kind of “nearest neighbor” relation among quantum systems. Furthermore, the wave function itself is interpreted as encoding the “nearest neighbor” relations between a quantum system and spatial points. This interpretation becomes natural, if we view space and distance in terms of relations among spatial points. Therefore, “position” becomes a purely relational concept. This relational picture leads to a new perspective onto the quantum mechanical formalism, where many of the “weird” aspects, like the particle-wave duality, the non-locality of entanglement, or the “mystery” of the double-slit experiment, disappear. Furthermore, this picture circumvents the restrictions set by Bell’s inequalities, i.e., a possible (realistic) hidden variable theory based on these concepts can be local and at the same time reproduce the results of quantum mechanics.
PACS: 03.65.Ud, 04.60.Nc 相似文献
16.
G. P. Berman A. R. Bishop D. A. R. Dalvit G. V. Shlyapnikov N. Tarkhanov E. M. Timmermans 《International Journal of Theoretical Physics》2008,47(9):2393-2408
We rigorously analyze the stability of the “quasi-classical” dynamics of a Bose-Einstein condensate with repulsive and attractive
interactions, trapped in an effective 1D toroidal geometry. The “classical” dynamics, which corresponds to the Gross-Pitaevskii
mean field theory, is stable in the case of repulsive interaction, and unstable (under some conditions) in the case of attractive
interaction. The corresponding quantum dynamics for observables is described by using a closed system of linear partial differential
equations. In both cases of stable and unstable quasi-classical dynamics the quantum effects represent a singular perturbation
to the quasi-classical solutions, and are described by the terms in these equations which consist of a small quasi-classical
parameter which multiplies high-order “spatial” derivatives. We demonstrate that as a result of the quantum singularity for
observables a convergence of quantum solutions to the corresponding classical solutions exists only for limited times, and
estimate the characteristic time-scales of the convergence. 相似文献
17.
A. M. M. Pruisken 《International Journal of Theoretical Physics》2009,48(6):1736-1765
It is shown that the “massless chiral edge excitations” are an integral and universal aspect of the low energy dynamics of
the ϑ vacuum that has historically gone unnoticed. Within the SU(M+N)/S(U(M)×U(N)) non-linear sigma model we introduce an effective theory of “edge excitations” that fundamentally explains the quantum Hall
effect. In sharp contrast to the common beliefs in the field our results indicate that this macroscopic quantization phenomenon
is, in fact, a super universal strong coupling feature of the ϑ angle with the replica limit M=N=0 only playing a role of secondary importance. To demonstrate super universality we revisit the large N expansion of the CP
N−1 model. We obtain, for the first time, explicit scaling results for the quantum Hall effect including quantum criticality
of the quantum Hall plateau transition. Consequently a scaling diagram is obtained describing the cross-over between the weak
coupling “instanton phase” and the strong coupling “quantum Hall phase” of the large N theory. Our results are in accordance with the “instanton picture” of the ϑ angle but fundamentally invalidate all the ideas, expectations and conjectures that are based on the historical “large N picture.” 相似文献
18.
W. M. Reiff E. H. Witten J. Takacs J. H. Zhang C. C. Torardi 《Hyperfine Interactions》1990,56(1-4):1723-1728
The extremes of single ion slow paramagnetic relaxation and cooperative 3D-antiferromagnetic order are exemplified in a series
of structurally characterized complexes based on the anhydrous FeCl3-α-di-imine system. “Soft” Cl−Cl contacts, C−C (π-π) and hydrogen bonding interactions are found to lead to surprisingly strong
magnetic exchange among five and six coordinate high-spin iron III monomers. The latter form the building blocks of novel
“double chain” polymer magnets held together via the preceding “weak” interactions. 相似文献
19.
20.
Paul J. Werbos 《International Journal of Theoretical Physics》2008,47(11):2862-2874
The classic “Bell’s Theorem” of Clauser, Holt, Shimony and Horne tells us that we must give up at least one of: (1) objective
reality (aka “hidden variables”); (2) locality; or (3) time-forwards macroscopic statistics (aka “causality”). The orthodox
Copenhagen version of physics gives up the first. The many-worlds theory of Everett and Wheeler gives up the second. The backwards-time
theory of physics (BTP) gives up the third. Contrary to conventional wisdom, empirical evidence strongly favors Everett-Wheeler
over orthodox Copenhagen. BTP allows two major variations—a many-worlds version and a neoclassical version based on Partial
Differential Equations (PDE), in the spirit of Einstein. Section 2 of this paper discusses the origins of quantum measurement
according to BTP, focusing on the issue of how we represent condensed matter objects like polarizers in a model “Bell’s Theorem”
experiment. The backwards time telegraph (BTT) is not ruled out in BTP, but is highly speculative for now, as will be discussed.
The views herein are not anyone’s official views, but this does constitute work produced on government time. 相似文献