Publications L.G. Suttorp before 1991.<br>
(Publications after 1990 are found <a href="publlgs.html" > here </a>)<br>
<br>
</ul>
Thesis
<ul>
<li>On the covariant derivation of macroscopic electrodynamics from 
electron theory, LGS, Thesis, University of Amsterdam, 1968. </li>
</ul>
Books
<ul>
<li>Foundations of Electrodynamics, S.R. de Groot and LGS, North-Holland, 1972.</li>
<li>Elektrodinamika, russ. ed. of  Foundations of 
Electrodynamics, S.R. de Groot and LGS, Nauka, Moscow, 1982.<br>
Abstract: Electrodynamics may be said to consist of two parts at different
levels: microscopic and macroscopic theory. The first contains the laws
that govern the interaction of fields and point particles-often grouped
into stable sets such as atoms and molecules-and the second those that
describe the interaction of fields and continuous media. The two theories
are linked together, since the phenomena at the macroscopic level may be
looked upon as being the result of the interplay of many
particles. Therefore one should be able to obtain the electromagnetic laws
for continuous media from those for point particles. Such a derivation,
together with a discussion of the microscopic starting points, forms the
subject of this book. The programme is carried out in the framework of both
classical and quantum theory both covariantly and in the nonrelativistic
approximation. The book is intended both as a textbook for graduate
students and as a monograph for research physicists. A number of problems
serve as exercises and illustrations for the main text.<br>
Full text:
<a href="articles/found_table_of_contents.pdf" > table of contents </a>,
<a href="articles/found_chap1.pdf" > chapter1 </a>,
<a href="articles/found_chap2.pdf" > chapter2 </a>,
<a href="articles/found_chap3.pdf" > chapter3 </a>,
<a href="articles/found_chap4.pdf" > chapter4 </a>,
<a href="articles/found_chap5.pdf" > chapter5 </a>,
<a href="articles/found_chap6.pdf" > chapter6 </a>,
<a href="articles/found_chap7.pdf" > chapter7 </a>,
<a href="articles/found_chap8.pdf" > chapter8 </a>,
<a href="articles/found_chap9.pdf" > chapter9 </a>,
<a href="articles/found_chap10.pdf" > chapter10 </a>,
<a href="articles/found_indexes.pdf" > indexes </a><br>
</li>
</ul>
Articles
<ul>
<li>Long-time tails of time correlation functions for an ionic mixture in a magnetic
field and the validity of magnetohydrodynamics, LGS, in: Strongly Coupled Plasma
Physics, ed. S. Ichimaru, Elsevier (1990) pp. 325-328.<br>
Abstract: Mode-coupling theory is used to determine the long-time behaviour of
the Green-Kubo integrands for the heat conductivity and the diffusion
coefficients of an ionic mixture in a magnetic field. It is shown that the
presence of several species of particles with a different ratio of charges
and masses is a prerequisite for the validity of dissipative
magnetohydrodynamics.<br>
Full text: <a href="articles/japan.pdf" > pdf </a></li><br>  

<li>On the validity of magnetohydrodynamics for ionic mixtures, 
A.J. Schoolderman and LGS, Journal of Statistical Physics 58 
(1990) pp. 997-1027.<br>
Abstract: The collective mode spectrum of the magnetized ionic mixture consisting
of s components is studied by starting from the microscopic balance
equations and the fluctuation formulas for the microscopic densities. Apart
from a heat mode and s-1 diffusion modes with frequencies of second order
in the wavenumber, four modes with complex finite frequencies for vanishing
wavenumber are found. If the mixture consist of particles with equal ratios
of charge and mass, these four modes become similar to the gyroplasmon
modes of the magnetized one-component plasma of which the frequencies are
real in lowest order in the wavenumber. Green-Kubo relations are derived
for the transport coefficients which appear in the frequencies of the heat
mode and the diffusion modes. The long-time behavior of the integrands of
the Green-Kubo expressions is evaluated with the help of mode-coupling
theory. The static transport coefficients are found to be finite unless the
mixture consists of species with equal ratios of charge and mass. It is
concluded that the presence of species with different charge-mass ratios is
essential for the validity of magnetohydrodynamics for an ionic
mixture.<br>
Full text: <a href="articles/school6.pdf" > pdf </a></li><br>

<li>Phase instabilities in absorptive optical bistability, A.J. van
Wonderen and LGS, Optics Communications 73 (1989) pp. 165-168.<br>
Abstract: The authors report that for absorptive optical bistability in a
Fabry-Perot cavity fluctuations in the phases of the fields can generate
side-mode instabilities. These phase instabilities can occur in the
one-atom branch of the bistability curve. Results are based on the
linearized Maxwell-Bloch equations for a Fabry-Perot cavity with non-ideal
mirrors. They strongly depend on the value of the mirror transmission
coefficient and the ratio of the medium damping coefficients.<br>
Full text: <a href="articles/wonderen4.pdf" > pdf </a></li><br>

<li>Uniform-field theory of phase instabilities in absorptive optical
bistability, A.J. van Wonderen and LGS, Physica A 161 (1989)
pp. 447-456.<br>
Abstract: Starting from the Maxwell-Bloch theory in the uniform-field
approximation the authors investigate the stability of the phase of the
output field for absorptive optical bistability in a Fabry-Perot
cavity. Their main results are analytical. They show that a truncation of
the Maxwell-Bloch hierarchy introduced serious anomalies in the instability
spectrum. For the full Maxwell-Bloch hierarchy phase instabilities are
found to occur only if the ratio gamma /sub ||// gamma /sub perpendicular
to / of the medium damping coefficients is larger than 1. In that case
phase instabilities can be present along the upper branch of the
steady-state curve.<br>
Full text: <a href="articles/wonderen3.pdf" > pdf </a></li><br>

<li>Instabilities for absorptive optical bistabilities in a nonideal
Fabry-Perot cavity, A.J. van Wonderen and LGS, Physical Review A 40 (1989)
pp. 7104-7112.<br>
Abstract: Instabilities are predicted for absorptive optical bistability in a
nonideal Fabry-Perot cavity on the basis of Maxwell-Bloch theory. The
authors show that the stability problem of the Maxwell-Bloch equations can
be formulated in terms of a Riccati differential equation with boundary
conditions. They have integrated this equation numerically. The results
crucially depend on the value of the transmission coefficient of the
mirrors. For finite values of this quantity they find that the nearest side
mode is responsible for two disconnected instability domains in the plane
spanned by the output intensity and the medium response time. One of these
domains can generate instabilities in the upper and the lower branch of the
steady-state curve if the cooperation parameter is sufficiently
large. Higher side modes can give rise to positive-slope instabilities as
well. From these findings it can be understood why a recent experimental
search for instabilities in absorptive optical bistability has led to a
negative result. The authors finally demonstrate that the instability
spectra of a Fabry-Perot cavity and a so-called equivalent ring cavity
differ considerably.<br>
Full text: <a href="articles/wonderen2.pdf" > pdf </a></li><br>

<li>Stability analysis for absorptive optical bistability in a Fabry-Perot
cavity, A.J. van Wonderen, B.J. Douwes and LGS, Physica A 157 (1989)
pp. 907-932.<br>
Abstract: A stability analysis is performed for absorptive optical bistability in
a medium of arbitrary absorption coefficient, which is contained in a
Fabry-Perot cavity with nonideal mirrors. In order to describe this system
the authors use a hierarchical set of equations which is obtained from
Maxwell-Bloch theory by expanding the polarization and population inversion
in slowly varying harmonics. They reduce the stability problem to two pairs
of coupled differential equations for the amplitudes and the phases of the
space-dependent deviations of the forward and the backward electric field
envelopes. The coefficients of these equations depend on the stationary
inversion fields for which a representation in terms of Chebyshev
polynomials depending on the electric field envelopes is given. The
influence of a truncation of the Bloch hierarchy on the instabilities is
studied numerically in the uniform-field limit.<br>
Full text: <a href="articles/wonderen1.pdf" > pdf </a></li><br>

<li>Equilibrium properties of ionic mixtures - derivation of 
fluctuation formulas from the grand-canonical ensemble, LGS, 
Contributions in Plasma Physics 29 (1989) pp. 335-342.<br>
Abstract: The grand-canonical ensemble is used to derive fluctuation formulae for
the particle densities, the pressure and the energy density of a
multi-component ionic mixture. As an intermediate step sum rules are
established for the two-particle Ursell functions.<br>
Full text: <a href="articles/wustrow.pdf" > pdf </a></li><br>

<li>Statistical foundations of electrodynamic theory, LGS, 
in:  Physics in the Making, eds. A. Sarlemijn and M.J. Sparnaay, 
Elsevier Publ. (1989) pp. 167-194.<br>
Abstract: A review is given of recent advances in the understanding of the
statistical foundations of macroscopic electrodynamics. Both theoretical
and experimental developments are discussed in some detail. <br>
Full text: <a href="articles/making89.pdf" > pdf </a></li><br>


<li>Long-time tails of the heat-conductivity time correlation functions for
a magnetized plasma - a kinetic theory approach, A.J.  Schoolderman and
LGS, Physica A 156 (1989) pp. 795-822.<br>
Abstract: The long-time behaviour of the longitudinal and the transverse heat
conductivity time correlation functions for a magnetized one-component
plasma is studied by means of kinetic theory. To that end these correlation
functions, which are defined as the inverse Laplace transforms of the
dynamic heat conductivity coefficients, are expressed in terms of matrix
elements of the kernel that appears in the kinetic equation for the
phase-space density time correlation function. The explicit expression for
the collision kernel in the disconnected approximations is used to write
the dominant contributions to the heat conductivity time correlation
functions for large t as integrals over products of reduced time
correlation functions for the particle density, the momentum density and
the kinetic energy density. By substituting the asymptotic expressions for
the latter the decay of the long-time tails of the heat conductivity time
correlation functions is found to be proportional to t/sup -1/2/.<br>
Full text: <a href="articles/school5.pdf" > pdf </a></li><br>

<li>Kinetic theory of time correlation functions for a dense one-component plasma in
a magnetic field, A.J. Schoolderman and LGS, Journal of Statistical Physics 53
(1988) pp. 1237-1260.<br>
Abstract: The time-dependent correlations of a one-component plasma in a uniform
magnetic field are studied with the help of kinetic theory. The time
correlation functions of the particle density, the momentum density, and
the kinetic energy density are evaluated for large time intervals. In the
collision-dominated regime the results agree with those found from
linearized magnetohydrodynamics.<br>
Full text: <a href="articles/school4.pdf" > pdf </a></li><br>


<li>Equilibrium properties of a multi-component ionic mixture II.
Fluctuations formulas, A.J. van Wonderen and LGS, Physica A 145 (1987)
pp. 557-583.<br>
Abstract: For pt.I see ibid., vol.145A, no.3, p.533-56 (1987). The complete set
of fluctuation formulae for the partial densities, the pressure and the
energy density of a multi-component ionic mixture is derived from
equilibrium statistical mechanics. Sum rules for the pair correlation
functions are used to write the fluctuation formulae in terms of
thermodynamical quantities.<br>
Full text: <a href="articles/wonderen2p.pdf" > pdf </a></li><br>

<li>Equilibrium properties of a multi-component ionic mixture I. Sum rules
for correlation functions, LGS and A.J. van Wonderen, Physica A 145 (1987)
pp. 533-556.<br>
Abstract: Equilibrium statistical methods are used to derive sum rules for two-
and three-particle correlation functions of a multi-component ionic
mixture. Some of these rules are general consequences of the electrostatic
character of the interaction, whereas others depend on specific
thermodynamic properties of the system. The first group of rules follows
from the BBGKY hierarchy and a clustering hypothesis for Ursell
functions. The sum rules of the second group are obtained by describing the
system with the help of a restricted grand-canonical ensemble in which the
particle numbers of the various components in the mixture fluctuate under
the condition that the total charge in the system remains constant.<br>
Full text: <a href="articles/wonderen1p.pdf" > pdf </a></li><br>

<li>Collective modes and mode-coupling for a dense plasma in a 
magnetic field, LGS, in:  Strongly Coupled Plasma Physics, 
eds. F.J. Rogers and H.E. Dewitt, Plenum (1987) pp. 431-440.<br>
Abstract: A review is given of the derivation of the collective modes and
the long-time behaviour of the velocity autocorrelation function for a
magnetized plasma. As a model we adopt the classical one-component plasma,
consisting of charged particles whic are immersed in a neutralizing inert
background and which interact through a Coulomb potential. The external
field is assumed to be static and uniform in space.<br>
Full text: <a href="articles/santacruz.pdf" > pdf </a></li><br>

<li>Small-wavenumber divergency in the mode-coupling amplitudes for the
heat-current time correlation function of a dense one-component plasma in a
magnetic field, A.J. Schoolderman and LGS, Physica A 144 (1987)
pp. 513-529.<br>
Abstract: The long-time behaviour of the heat-current time correlation
function of a one-component plasma in a magnetic field is studied with the
use of mode-coupling theory. The coupling of two gyro-plasmon modes gives
rise to contributions with amplitudes that are divergent for small
wavenumber. These imply a slowly decaying long-time tail of the Green-Kubo
integrand. As such a behaviour would lead to a divergency in the static
heat conductivity, it is concluded that mode-coupling theory with diverging
coupling amplitudes is not a reliable starting point for the study of the
long-time behaviour of Green-Kubo integrands.<br>
Full text: <a href="articles/school3.pdf" > pdf </a></li><br>

<li>Interference effects in the long-time tail of the velocity
auto-correlation function for a dense one-component plasma in a magnetic
field, LGS and A.J. Schoolderman, Physica A 143 (1987) pp. 494-506.<br>
Abstract: The long-time behaviour of the velocity autocorrelation function that
describes the motion of a tagged particle through a one-component plasma in
a uniform magnetic field has been determined with the use of mode-coupling
theory. The long-time tail depends on the orientation of the velocity with
respect to the magnetic field. Owing to the anisotropy of the collective
mode spectrum the mode-coupling integrals are afflicted with interference
effects. As a consequence the long-time behaviour of the velocity
autocorrelation function for a plasma in a magnetic field differs
qualitatively from that found for an unmagnetized plasma.<br>
Full text: <a href="articles/school2.pdf" > pdf </a></li><br>

<li>Collective modes and generalized transport coefficients for a dense
one-component plasma in a magnetic field, LGS and A.J.  Schoolderman,
Physica A 141 (1987) pp. 1-23.<br>
Abstract: The collective modes for a one-component Coulomb plasma in a magnetic
field are derived from the microscopic balance equations. The mode
frequencies contain nine independent generalized transport coefficients for
which Green-Kubo expressions are determined. The discontinuity in the mode
spectrum for wave vectors orthogonal to the magnetic field is discussed in
detail. The connexion with the results obtained by means of kinetic theory
is established.<br>
Full text: <a href="articles/school1.pdf" > pdf </a></li><br>

<li>Kinetic theory of the collective modes for a dense one-component plasma
in a magnetic field, LGS and J.S. Cohen, Physica A 133 (1985)
pp. 370-396.<br>
Abstract: The collective modes for a classical magnetized Coulomb plasma are
determined with the use of kinetic theory. A comparison is made with the
results from magnetohydrodynamics. It is shown that only four of the nine
independent static transport coefficients are accessible through the
damping terms of the purely dissipative modes. One of these is the
convective cell mode which decays relatively slowly for strong magnetic
fields, it exists solely when the wave vector is purely perpendicular to
the field. The oscillating modes contain generalized transport
coefficients, evaluated at finite frequencies.<br>
Full text: <a href="articles/cohen8.pdf" > pdf </a></li><br>

<li>Fluctuations in a dense one-component plasma, LGS and J.S. Cohen,
Physica A 133 (1985) pp. 357-369.<br>
Abstract: The complete set of fluctuation formulae for the density, the pressure
and the energy density of a one-component plasma is derived. The momentum
balance equation contains a source term proportional to the electric field
generated by the density fluctuations. This term, which diverges for small
wave number, is shown to have a profound influence on the fluctuation
formulae.<br>
Full text: <a href="articles/cohen7.pdf" > pdf </a></li><br>

<li>The effect of dynamical screening on self-diffusion in a dense
magnetized plasma, J.S. Cohen and LGS, Physica A 126 (1984)
pp. 308-327.<br>
Abstract: The coefficient of self-diffusion along an external magnetic field in a
dense plasma is evaluated with the use of a kinetic equation that takes
dynamical screening effects into account. It is found that the
self-diffusion coefficient diminishes monotonously as the magnetic field
strength increases. Qualitatively the present calculation corroborates a
result obtained recently in a cruder approximation in which only static
screening effects are considered.<br>
Full text: <a href="articles/cohen6.pdf" > pdf </a></li><br>

<li>Self-diffusion in a dense magnetized plasma, J.S. Cohen and LGS,
Physica A 123 (1984) pp. 560-576.<br>
Abstract: Self-diffusion through dense classical one-component plasmas in a
uniform magnetic field is studied by means of renormalized kinetic
theory. Extensions of the Landau and the Rostoker equations to plasmas of
high density are derived. The coefficient of self-diffusion along the
magnetic field is evaluated from the 1-Sonine approximation of the Landau
kernel. The results show how the diffusion process is gradually impeded as
the magnetic field strength increases.<br>
Full text: <a href="articles/cohen5.pdf" > pdf </a></li><br>

<li>Self-diffusion for a weakly-coupled plasma in a magnetic field,
J.S. Cohen and LGS, Physica A 123 (1984) pp. 549-559.<br>
Abstract: The longitudinal self-diffusion coefficient for a magnetized plasma
with a small plasma parameter is calculated from kinetic theory in the
weak-coupling approximation. Asymptotic expressions for this coefficient
are derived in the limits of weak and of strong magnetic field. For
intermediate strength of the magnetic field numerical results are
presented.<br>
Full text: <a href="articles/cohen4.pdf" > pdf </a></li><br>

<li>On the equivalence of convergent kinetic equations for hot dilute
plasmas. Collisions terms with effective interactions, J.S. Cohen and LGS,
Physica A 115 (1982) pp. 155-168.<br>
Abstract: For pt.II see ibid., vol.111, p.443 (1982). A general class of
approximate expressions for the pair correlation function of a classical
one-component plasma with small plasma parameter epsilon is discussed. The
collision terms which follow from these approximate correlation functions
are characterized by effective potentials that differ from the bare Coulomb
potential by modulation factors depending on the interparticle distance. It
is shown that for small epsilon the transport coefficients are independent
of the precise form of the modulation factors.<br>
Full text: <a href="articles/cohen3.pdf" > pdf </a></li><br>

<li>On the equivalence of convergent kinetic equations for hot dilute
plasmas. Generating functions for collision brackets, J.S. Cohen and LGS,
Physica A 111 (1982) pp. 443-461.<br>
Abstract: For pt.I see ibid., vol.110, no.1-2, p.81-105 (1982). The generating
functions for the collision brackets associated with two alternative
convergent kinetic equations are derived for small values of the plasma
parameter. It is shown that the first few terms in the asymptotic
expansions of these generating functions are identical. Consequently, both
kinetic equations give rise to the same transport coefficients in
arbitrarily high order of the Chapman-Cowling truncation scheme.<br>
Full text: <a href="articles/cohen2.pdf" > pdf </a></li><br>

<li>On the equivalence of convergent kinetic equations for hot dilute
plasmas. Transport coefficients in first Chapman-Cowling approximation,
J.S. Cohen and LGS, Physica A 110 (1982) pp. 81-105.<br>
Abstract: Two competitive convergent kinetic equations for a one-component
Coulomb plasma with small plasma parameter epsilon are discussed. It is
shown how a Chapman-Enskog scheme can be set up to calculate the heat
conductivity and the viscosity. Both kinetic equations are found to yield
identical transport coefficients for small epsilon , at least in lowest
order of the Chapman-Cowling truncation procedure.<br>
Full text: <a href="articles/cohen1.pdf" > pdf </a></li><br>

<li>On anisotropy of the pressure tensor and the force density for a 
polarizable fluid in an electromagnetic field, LGS and S.R. de 
Groot, Physica A 108 (1981) pp. 361-370.<br>
Abstract: By means of a statistical derivation it is shown that the
momentum-balance equation of a polarized fluid contains a force term that
is the divergence of an anisotropic tensor (1/5)PP+(1/10)P/sup 2/U, where P
is the polarization. However, for a fluid in equilibrium this force term is
compensated by an anisotropic part in the pressure tensor. The same is true
for a fluid in an optical field if time-averaged quantities are considered.<br>
Full text: <a href="articles/degroota.pdf" > pdf </a></li><br>

<li>Radiation pressure on the boundary of a fluid and a metal. Waves 
of finite width, LGS and S.R. de Groot, Proceedings Koninklijke 
Nederlandse Akademie van Wetenschappen B 84 (1981) pp. 325-334.<br>
Abstract: For pt.I see ibid., vol.84, no.3, p.315-24 (1981). The effect of the
finite width of a beam on its radiation pressure is studied. To that end
the appropriate Fresnel relations are used in conjunction with the balance
equation for the momentum flow at the fluid-metal boundary. An explicit
expression is obtained for the radiation pressure that is exerted by a wide
beam of Gaussian shape.<br>
Full text: <a href="articles/KNAW2.pdf" > pdf </a></li><br>

<li>Radiation pressure on the boundary of a fluid and a metal. Waves 
of infinite width, LGS and S.R. de Groot, Proceedings Koninklijke 
Nederlandse Akademie van Wetenschappen B 84 (1981) pp. 315-324.<br>
Abstract: The radiation pressure is evaluated for a plane electromagnetic wave
that impinges obliquely through a polarized fluid on a metal surface. The
starting point is the time-averaged momentum-balance equation in which both
the pressure and the force density are specified. The results are in
accordance with the recent experimental findings of Jones and Leslie
(1978).<br>
Full text: <a href="articles/KNAW1.pdf" > pdf </a></li><br>

<li>Quantum-kinetic equations for time correlation functions in 
higher-order perturbation theory, M.C.J. Leermakers and LGS, 
Physica A 108 (1981) pp. 333-360.<br>
Abstract: The memory kernel of the kinetic equation for the time correlation
function of a quantum fluid is determined both in third order of the
interaction strength and in the low-density approximation. The results are
obtained with the help of a diagram representation for the kernel. The
connection with the kinetic theory for classical fluids is established.<br>
Full text: <a href="articles/leermakers.pdf" > pdf </a></li><br>

<li>Kinetic theory of self-diffusion in a moderately dense 
one-component plasma, LGS, Physica A 104 (1980) pp. 25-47.<br>
Abstract: A microscopic description of self-diffusion in a moderately dense
classical one-component plasma is given on the basis of renormalized
kinetic theory. The effects of close binary collisions and of collective
interactions in the plasma are taken into account through the use of a
composite memory kernel that includes both the Boltzmann and the Balescu
Guernsey-Lenard kernels as special cases. The composite kernel satisfies
the lowest-order sum rule by virtue of the approximate validity of the
hypernetted-chain equation for the static plasma correlation function. The
ensuing values of the self-diffusion coefficient are obtained numerically
for several plasma densities and are compared with the results of previous
theories and of molecular dynamics.<br>
Full text: <a href="articles/self.pdf" > pdf </a></li><br>

<li>The retarded energy shift and pair polarizabilities of 
interacting atoms in an external field. Application of resummed 
field-theoretical perturbation theory, M.A.J. Michels and LGS, 
Molecular Physics 40 (1980) pp. 1089-1105.<br>
Abstract: The interaction energy of two atoms in the presence of an external
electrostatic field is evaluated up to sixth order with the help of
covariant field-theoretical perturbation theory. The divergent Feynman
diagrams entering the calculation are resummed according to a systematic
procedure that the authors developed in a previous paper (1979). The pair
polarizability and first hyperpolarizability that give the response of the
interacting atoms to the external field are subsequently obtained from the
energy shift by virtue of a Hellman-Feynman theorem. The retardation
effects showing up in the pair polarizability are discussed in detail.<br>
Full text: <a href="articles/retarded.pdf" > pdf </a></li><br>

<li>Relativistic bound-state equations for fermions with 
instantaneous interactions, LGS, Annals of Physics 122 (1979) 
pp. 397-435.<br>
Abstract: Three types of relativistic bound-state equations for a fermion pair
with instantaneous interaction are studied, viz., the instantaneous
Bethe-Salpeter equation, the quasi-potential equation, and the two-particle
Dirac equation. General forms for the equations describing bound states
with arbitrary spin, parity, and charge parity are derived. For the special
case of spinless states bound by interactions with a Coulomb-type potential
the properties of the ground-state solutions of the three equations are
investigated both analytically and numerically. The coupling-constant
spectrum turns out to depend strongly on the spinor structure of the
fermion interaction. If the latter is chosen such that the nonrelativistic
limits of the equations coincide, an analogous spectrum is found for the
instantaneous Bethe-Salpeter and the quasi-potential equations, whereas the
two-particle Dirac equation yields qualitatively different results.<br>
Full text: <a href="articles/instantaneous.pdf" > pdf </a></li><br>

<li>Block diagrams and the cancellation of divergences in 
energy-level perturbation theory, M.A.J. Michels and LGS, Physica 
A 96 (1979) pp. 487-505.<br>
Abstract: The effective Hamiltonian for the degenerate energy-eigenvalue problem
in adiabatic perturbation theory is cast in a form that permits an
expansion in Feynman diagrams. By means of a block representation a
resummation of these diagrams is carried out such that in the adiabatic
limit no divergencies are encountered. The resummed form of the effective
Hamiltonian is used to establish a connexion with the S matrix.<br>
Full text: <a href="articles/block.pdf" > pdf </a></li><br>

<li>Energy shifts and the S matrix in degenerate perturbation 
theory, M.A.J. Michels and LGS, Journal of Physics A 12 
(1979) pp. 1321-1323.<br>
Abstract: Adiabatic perturbation theory is employed to establish a relationship
between the S-matrix and the averaged energy shift of a degenerate
level.<br>
Full text: <a href="articles/shifts.pdf" > pdf </a></li><br>

<li>Diagrammatic analysis of adiabatic and time-dependent perturbation theory for
degenerate energy levels, M.A.J. Michels and LGS, Chemical Physics Letters 58
(1978) pp. 385-388.<br>
Abstract: Time-ordered folded diagrams are used to represent the effective
hamiltonian in the adiabatic formalism. Resummation of the diagrams is
shown to give a term-by-term correspondence with time-independent
perturbation theory.<br>
Full text: <a href="articles/diagram.pdf" > pdf </a></li><br>

<li>On adiabatic perturbation theory for the energy eigenvalue 
problem, M.A.J. Michels and LGS, Physica A 93 (1978) pp. 559-573.<br>
Abstract: The adiabatic perturbation formalism is used to derive several
alternative expressions for the effective Hamiltonian of a discrete energy
level. In the nondegenerate case these expressions may be cast in the form
of linked-cluster expansions. The connection between the energy shifts and
the scattering matrix is investigated.<br>
Full text: <a href="articles/adiabatic.pdf" > pdf </a></li><br>

<li>Numerical solution of the spinor Bethe-Salpeter equation and 
the Goldstein problem, LGS, Annals of Physics 113 (1978) 
pp. 257-276.<br>
Abstract: The spinor Bethe-Salpeter equation describing bound states of a
fermion-antifermion pair with massless-boson exchange reduces to a single
(uncoupled) partial differential equation for special combinations of the
fermion-boson couplings. For spinless bound states with positive or
negative parity this equation is a generalization to nonvanishing
bound-state masses of equations studied by Kummer (1964) and Goldstein
(1953), respectively. In the tight-binding limit the Kummer equation has a
discrete spectrum, in contrast to the Goldstein equation, while for loose
binding only the generalized Goldstein equation has a nonrelativistic
limit. For intermediate binding energies the equations are solved
numerically. The generalized Kummer equation is shown to possess a discrete
spectrum of coupling constants for all bound-state masses.<br>
Full text: <a href="articles/numerical.pdf" > pdf </a></li><br>

<li>Retardation in the atomic pair polarizability, M.A.J. Michels 
and LGS, Chemical Physics Letters 46 (1977) pp. 391-394.<br>
Abstract: The atomic pair polarizability for hydrogen atoms is calculated within
the framework of covariant quantum electrodynamics. Retardation effects are
shown to change the dependence on the interatomic separation R from R/sup
-6/ to R/sup -7/ for R large compared with a characteristic wavelength of
the atomic spectrum. For harmonic oscillators the pair polarizability is
proved to be independent of the interparticle interaction.<br>
Full text: <a href="articles/pair.pdf" > pdf </a></li><br>

<li>Form-factor representation and multipole expansion of the 
retareded interatomic dispersion energy, M.A.J. Michels and LGS, 
Molecular Physics 33 (1977) pp. 245-254.<br>
Abstract: Dispersion-relation methods are used to derive a form-factor
representation for the retarded dispersion energy of two hydrogen atoms
that are described by relativistic electron theory. By expressing the
electromagnetic form factors in terms of atomic transition matrix elements,
the complete multipole expansion of the interatomic dispersion energy is
obtained. The long-range asymptotic limit of the successive multipole
interactions is given explicitly.<br>
Full text: <a href="articles/formfactor.pdf" > pdf </a></li><br>

<li>Normalization and perturbation theory for tightly bound 
states of the spinor Bethe-Salpeter equation, LGS, Nuovo Cimento A 
33 (1976) pp. 257-280.<br>
Abstract: The normalisation integrals for the tightly-bound-state solutions of
the spinor Bethe-Salpeter equation that have been derived recently are
evaluated. Ghost states are found to appear when the continuous parameters
characterising the type of fermion-boson interaction reach a critical
value. Perturbation-theoretical methods are used to determine, for a pair
of fermions with slightly different masses, the strength of the couplings
that give rise to bound states with small values of the rest frame energy.<br>
Full text: <a href="articles/nuovcim76.pdf" > pdf </a></li><br>

<li>Exact solutions of the spinor Bethe-Salpeter equation for 
tightly bound states, LGS, Nuovo Cimento A 29 (1975) pp. 225-255.<br>
Abstract: Exact solutions are obtained for the spinor Bethe-Salpeter equation
that describes tightly bound states of spin-/sup 1///sub 2/ fermions with
massless-boson exchange. The corresponding coupling constants form a
discrete spectrum that depends continuously on the parameters
characterizing the type of fermion-boson interaction.<br>
Full text: <a href="articles/nuovcim75.pdf" > pdf </a></li><br>

<li>Multipole expansion of the retarded interatomic potential energy: 
dispersion and induction energy for relativistic hydrogen atoms, M.A.J. 
Michels and LGS, Physica 67 (1973) pp. 137-165.<br>
Abstract: For pt. V, see abstr. A26612 of 1973. The inductive and dispersive
retarded interaction energies of two ground- state hydrogen atoms described
by Dirac theory are derived up to all multipole orders. The results are
obtained by evaluation of Feynman diagrams and with the help of
dispersion-relation methods. the nonrelativistic and semi-relativistic
approximations of the interaction energy are given in a form that shows
explicitly the contributions of electron spin.<br>
Full text: <a href="articles/multipole6.pdf" > pdf </a></li><br>

<li>Multipole expansion of the retarded interatomic potential 
energy: derivation from relativistic electron theory, M.A.J. Michels and 
LGS, Physics Letters A 42 (1973) pp. 473-474.<br>
Abstract: The inductive and dispersive retarded interaction energies of two
ground state hydrogen atoms described by Dirac theory are obtained up to
all multipole orders. The long range terms are given as symmetric
expressions in the electric and magnetic dipole moments.<br>
Full text: <a href="articles/multipolepl.pdf" > pdf </a></li><br>

<li>Multipole expansion of the retarded interatomic potential 
energy: derivation with the use of a dispersion relation, LGS, 
Physica 64 (1973) pp. 217-246.<br>
Abstract: For pt IV see abstr. A79889 of 1972. A dispersion relation technique is
used to obtain the retarded dispersion energy of two neutral atoms in
nondegenerate ground states. To that end multipole expansions are derived
for the electromagnetic form factors occurring in the vertex function that
characterizes the interaction of a neutral atom with a pair of photons on
the mass shell. The long-range asymptotic expression for the dispersion
energy is shown to contain electric and diamagnetic matrix elements in a
symmetric way.<br>
Full text: <a href="articles/multipole5.pdf" > pdf </a></li><br>

<li>Isospin sum rules for inclusive cross-sections, P. Rotelli 
and LGS, Physics Letters B 40 (1972) pp. 579-582.<br>
Abstract: A systematic analysis of isospin sum rules is presented for the
distribution functions of strong, electromagnetic weak inclusive
processes. The general expression for these sum rules is given and some new
examples are presented.<br>
Full text: <a href="articles/isospin.pdf" > pdf </a></li><br>

<li>Multipole expansion of the retarded interatomic potential 
energy: induction energy for degenerate ground-state atoms, M.A.J. Michels 
and LGS, Physica 61 (1972) pp. 517-526.<br>
Abstract: For pt. III see ibid., vol. 61, 506 (1972). The inductive contribution
to the retarded interatomic potential energy of two atoms in degenerate
ground states is calculated up to all multipole orders on the basis of
quantum electrodynamics. The result, which is found to have nonretarded
character, is written in such a way as to show the induction effects
brought about in each of the atoms by the electrostatic and magnetostatic
fields of the oter.<br>
Full text: <a href="articles/multipole4.pdf" > pdf </a></li><br>

<li>Multipole expansion of the retarded interatomic dispersion energy: the long and
the short range behaviour, M.A.J. Michels and LGS, Physica 61 (1972)
pp. 506-516.<br>
Abstract: For pt. II see ibid., vol. 61, 481 (1972). The long-range asymptotic
expression for the multipole expansion of the retarded interatomic
dispersion energy is shown to consist of contributions from electric
dipole-dipole, dipole-quadrupole and quadrupole-quadrupole interactions,
all varying as the inverse seventh power of the interatomic separation. The
general expressions for these interactions lead to short-range series
expansions which extend results obtained earlier with the help of the Breit
hamiltonian.<br>
Full text: <a href="articles/multipole3.pdf" > pdf </a></li><br>

<li>Multipole expansion of the retarded interatomic dispersion 
energy: evaluation in the spherical-tensor formalism, M.A.J. Michels and 
LGS, Physica 61 (1972) pp. 481-505.<br>
Abstract: For pt. I see abstr. A49935 of 1972. The multipole expansion of the
retarded interatomic dispersion energy is evaluated in the spherical-tensor
formalism. The multipole expansion of the electrostatic dispersion energy
follows as a special case.<br>
Full text: <a href="articles/multipole2.pdf" > pdf </a></li><br>

<li>Multipole expansion of the retarded interatomic dispersion energy: derivation
from quantum electrodynamics, M.A.J. Michels and LGS, Physica 59 (1972)
pp. 609-633.<br>
Abstract: The multipole expansion of the retarded dispersion energy of two atoms
in nondegenerate ground states is derived. The result shows that multipoles
of different order may give rise to dispersion energies varying in the same
way for large interatomic separations.<br>
Full text: <a href="articles/multipole1.pdf" > pdf </a></li><br>

<li>Covariant equations of motion for a charged particle with a 
magnetic dipole moment, LGS and S.R. de Groot, Nuovo Cimento A 
65 (1970) pp. 245-274.<br>
Abstract: The Hamiltonian for a Dirac particle with anomalous magnetic moment in
an electromagnetic field is transformed to even form up to terms linear in
the coupling constant and without derivatives of the field. The even parts
of the position and spin operators are derived by imposing conditions of
covariance. Covariant equations of motion and of spin are then deduced;
they turn out to have the same form as the classical equations for a
composite particle with magnetic dipole moment.<br>
Full text: <a href="articles/nuovcim70.pdf" > pdf </a></li><br>

<li>Covariant equations of motion for a charged particle with a 
magnetic dipole moment, LGS and S.R. de Groot, Physics 
Letters A 29 (1969) pp. 249-250.<br>
Abstract: By choosing a covariant position and spin operator equations of motion
are derived for a Dirac particle in a non-uniform and time dependent
field.<br>
Full text: <a href="articles/covariantpl.pdf" > pdf </a></li><br>

<li>The relativistic energy-momentum tensor in polarized media: 
discussion of the results in connexion with previous work, S.R. de Groot and 
LGS, Physica 39 (1968) pp. 84-93.<br>
Abstract: The literature on the relativistic energy-moment tensor in
polarized media falls apart in treatments based on microscopic first
principles and considerations starting from macroscopic postulates. Only
papers of the first category, such as Lorentz's and Einstein-Laub's, can be
considered as derivations, whereas treatments of the second category, such
as Minkowski's and Abraham's, based on ad hoc assumptions, do not give
unique results.<br>
Full text: <a href="articles/energy7.pdf" > pdf </a></li><br>

<li>The relativistic energy-momentum tensor in polarized media: 
the difference between the energy-momentum tensor in the presence and in the 
absence of external fields, S.R. de Groot and LGS, Physica 
39 (1968) pp. 77-83.<br>
Abstract: The difference of the relativistic energy-momentum tensors of a
substance with and without fields is derived for the case of thermodynamic
equilibrium and linear constitutive relations. It may be looked upon as the
field part of the total energy-momentum tensor. The remainder is then the
corresponding material part. The negative divergence of the field tensor is
the ponderomotive force corresponding to pressure and internal energy
defined at zero fields. It constitutes a relativistic generalization of the
Helmholtz force. A comparison with the tensors of Minkowski and Abraham
shows that these cannot be justified from a microscopic point of view.<br>
Full text: <a href="articles/energy6.pdf" > pdf </a></li><br>

<li>The relativistic energy-momentum tensor in polarized media: 
statistical thernodynamics of electrodynamic phenomena, S.R. de Groot and 
LGS, Physica 39 (1968) pp. 61-76.<br>
Abstract: The relativistic first law of thermodynamics for polarized media
is derived from the conservation law of energy-momentum. The
nonrelativistic second law for these systems is obtained from equilibrium
thermodynamics and generalized to the relativistic case. The entropy
balance equation is then derived from the first and second laws.<br>
Full text: <a href="articles/energy5.pdf" > pdf </a></li><br>

<li>The relativistic energy-momentum tensor in polarized media: the macroscopic
material energy-momentum tensor, S.R. de Groot and LGS, Physica 39 (1968)
pp. 41-60.<br>
The relativistic material energy-momentum tensor in polarized media, which
contains bulk terms, fluctuation terms and correlation terms, is studied
especially in the nonrelativistic limit. On this basis explicit forms of
the energy-momentum and angular momentum laws are given. Contributions
quadratic in the polarization are proved to be contained in the correlation
terms. For this reason a redefinition of the field and material part of
the total energy-momentum tensor may be introduced.<br>
Full text: <a href="articles/energy4.pdf" > pdf </a></li><br>

<li>The relativistic energy-momentum tensor in polarized media: statistical theory
of the energy-momentum laws, S.R. de Groot and LGS, Physica 39 (1968)
pp. 28-40.<br>
Abstract: From the atomic conservation laws of energy-momentum the
corresponding macroscopic laws are derived with the help of a covariant
averaging procedure. The total energy-momentum tensor is found as a
statistical expression in terms of atomic quantities. It can be split into
a field part containing the macroscopic fields and polarizations, and a
material part which forms the relativistic generalization of the ususal
energy and momentum expressions.<br>
Full text: <a href="articles/energy3.pdf" > pdf </a></li><br>

<li>The relativistic energy-momentum tensor in polarized media: 
the angular momentum laws and the symmetry of the energy-momentum tensor, 
S.R. de Groot and LGS, Physica 37 (1967) pp. 297-308.<br>
Abstract: The angular momentum balance of matter in an electromagnetic
field on the atomic level is derived from microscopic theory. As a
consequence an energy-momentum tensor can be constructed, which is
completely symmetrical. Both its material and field parts are given
explicitly in terms of the atomic parameters.<br>
Full text: <a href="articles/energy2.pdf" > pdf </a></li><br>

<li>The relativistic energy-momentum tensor in polarized media: the atomic
energy-mo-men-tum conservation laws, S.R. de Groot and LGS, Physica 37 (1967)
pp. 284-296.<br>
Abstract: The relativistic conservation laws of energy and momentum in a
substance, which consists of atoms carrying both electric and magnetic
dipoles, is derived from the microscopic force laws for point particles in
the presence of an electromagnetic field. The energy-momentum tensor which
occurs in these `atomic' conservation laws, consists of a material part and
a field part for which explicit expressions are obtained.<br>
Full text: <a href="articles/energy1.pdf" > pdf </a></li><br>

<li>On the uniqueness of the relativistic energy-momentum tensor 
in polarized media, S.R. de Groot and LGS, Physics Letters A 
25 (1967) pp. 103-104.<br>
Abstract:The energy-momentum tensor in a polarized medium, as derived from
microscopic theory, can be looked upon as the sum of a material part,
defined at zero field, and a field part. It can then be shown that both
Minkowski's and Abraham's tensors are unjustifiable.<br>
Full text: <a href="articles/unique.pdf" > pdf </a></li><br>

<li>The relativistic energy-momentum tensor in polarized media, 
S.R. de Groot and LGS, Physics Letters A 24 (1967) pp. 385-387.<br>
Abstract: The relativistic energy-momentum tensor of the electromagnetic
field in electric and magnetic dipole substances is derived and compared
with the proposals of Lorentz, Einstein-Laub, Minkowski and Abraham.<br>
Full text: <a href="articles/energypl.pdf" > pdf </a></li><br>

<li>The relativistic energy-momentum tensor in a dielectric, 
S.R. de Groot and LGS, Physics Letters 21 (1966) pp. 297-298.<br>
Abstract: The relativistic energy-momentum tensor of the electromagnetic
field is derived from electron theory and compared with the forms proposed
by Abraham and Minkowski.<br>
Full text: <a href="articles/energydpl.pdf" > pdf </a></li><br>

<li>Covariant derivation of the Maxwell equations: multipole expansion of the
polarization tensor to all orders, S.R. de Groot and LGS, Physica 31 (1965)
pp. 1713-1727.<br>
Abstract: The Maxwell equations are derived in covariant manner from the
microscopic equations for the electromagnetic field in the presence of
point charges. The polarization tensor is given as an expansion to all
orders in the atomic electromagnetic moments, defined in atomic rest
frames.<br>
Full text: <a href="articles/maxwell.pdf" > pdf </a></li><br>


(Publications after 1991 are found <a href="publlgs.html" > here </a>)<br>