1,014 research outputs found
Regularization schemes and the multiplicative anomaly
Elizalde, Vanzo, and Zerbini have shown that the effective action of two free
Euclidean scalar fields in flat space contains a `multiplicative anomaly' when
zeta-function regularization is used. This is related to the Wodzicki residue.
I show that there is no anomaly when using a wide range of other regularization
schemes and further that this anomaly can be removed by an unusual choice of
renormalisation scales. I define new types of anomalies and show that they have
similar properties. Thus multiplicative anomalies encode no novel physics. They
merely illustrate some dangerous aspects of zeta-function and Schwinger proper
time regularization schemes.Comment: 11 pages, LaTeX2e, major revision 15th December 1998 with focus now
on renormalisation scales. Appendix and a few minor comments included which
are not in Phys.Lett.B. published versio
Non-perturbative calculations of a global U(1) theory at finite density and temperature
We use an optimised hopping parameter expansion for the free energy (linear
delta expansion) to study the phase transitions at finite temperature and
finite charge density in a global U(1) scalar Higgs sector on the lattice at
large lattice couplings. We are able to plot out phase diagrams in lattice
parameter space and find that the standard second-order phase transition with
temperature at zero chemical potential becomes first order as the chemical
potential increases.Comment: 24 pages, 11 figure
Representation of nonequilibrium steady states in large mechanical systems
Recently a novel concise representation of the probability distribution of
heat conducting nonequilibrium steady states was derived. The representation is
valid to the second order in the ``degree of nonequilibrium'', and has a very
suggestive form where the effective Hamiltonian is determined by the excess
entropy production. Here we extend the representation to a wide class of
nonequilibrium steady states realized in classical mechanical systems where
baths (reservoirs) are also defined in terms of deterministic mechanics. The
present extension covers such nonequilibrium steady states with a heat
conduction, with particle flow (maintained either by external field or by
particle reservoirs), and under an oscillating external field. We also simplify
the derivation and discuss the corresponding representation to the full order.Comment: 27 pages, 3 figure
Thermal Green Functions at Zero Energy
The thermal expectation values of all possible bosonic generalised retarded
functions evaluated at zero energy are studied. The relationship of such
functions to calculational schemes, technical problems and physical
applications is outlined. It is then shown that all generalised retarded
functions constructed from any one set of bosonic fields are equal at zero
energy. This is done completely generally and is not limited to any
approximation scheme such as perturbation theory.Comment: 16 pages, LaTeX (no figures), available through anonymous ftp as
LaTeX from ftp://euclid.tp.ph.ic.ac.uk/papers/94-5_26.tex or as LaTeX or
postscript at http://euclid.tp.ph.ic.ac.uk/Papers/index.htm
Gender and race distribution of dental graduates (1985 - 2004) and first year dental students (2000 - 2005) in South Africa
This paper, written at the close of a decade
of democracy in South Africa, sets
out to analyse the demographic profile
of dental graduates from 1985-2004 at
the five Faculties/Schools of Dentistry in
South Africa. A comparison of the profiles
for the pre-democracy (1985-1994) and
post-apartheid (1995-2004) periods has
been made. The demographic profile of
first year dental students from 2000-2005
is also presented. From 1985-1994, most
dental graduates were male (79%), but
this changed substantially from 1995-2004,
with females comprising 46% of those
graduating. In the pre-democracy period,
more than three-quarters of all graduates
were White (78%), decreasing to 46% in
the post-apartheid period under review.
Black graduates increased from 6% to 24%
across the two study periods. Amongst the
first year dental student intake from 2000-
2005, females comprised 57%. There was
an almost equal distribution across the
White, Black and Asian groups.
Dental faculties/schools have made important
strides in transforming the demographic
profile of their students. The percentage
of Black graduates, however, needs to be
significantly increased if it is to reflect the
national population. Faculties/schools must
further ensure that able students from working
class background are identified and
considered for acceptance into the undergraduate
dental programme, and should
then be offered the necessary academic
and mentoring support to enable success
Wick's Theorem at Finite Temperature
We consider Wick's Theorem for finite temperature and finite volume systems.
Working at an operator level with a path ordered approach, we show that
contrary to claims in the literature, expectation values of normal ordered
products can be chosen to be zero and that results obtained are independent of
volume. Thus the path integral and operator approaches to finite temperature
and finite volume quantum field theories are indeed seen to be identical. The
conditions under which normal ordered products have simple symmetry properties
are also considered.Comment: 15 pages, LaTeX (no figures), available through anonymous ftp as
LaTeX from ftp://euclid.tp.ph.ic.ac.uk/papers/95-6_18.tex or as LaTeX or
postscript at http://euclid.tp.ph.ic.ac.uk/Papers/index.htm
The Emergence of Leadership in Social Networks
We study a networked version of the minority game in which agents can choose
to follow the choices made by a neighbouring agent in a social network. We show
that for a wide variety of networks a leadership structure always emerges, with
most agents following the choice made by a few agents. We find a suitable
parameterisation which highlights the universal aspects of the behaviour and
which also indicates where results depend on the type of social network.Comment: 22 pages (as in Physica A but with a few extra references to
supplementary material) plus 11 pages of supplementary material not in
Physica A versio
A Generalized Fluctuation-Dissipation Theorem for Nonlinear Response Functions
A nonlinear generalization of the Fluctuation-Dissipation Theorem (FDT) for
the n-point Green functions and the amputated 1PI vertex functions at finite
temperature is derived in the framework of the Closed Time Path formalism. We
verify that this generalized FDT coincides with known results for n=2 and 3.
New explicit relations among the 4-point nonlinear response and correlation
(fluctuation) functions are presented.Comment: 34 pages, Revte
Identity of the imaginary-time and real-time thermal propagators for scalar bound states in a one-generation Nambu-Jona-Lasinio model
By rigorous reanalysis of the results, we have proven that the propagators at
finite temperature for scalar bound states in one-generation fermion condensate
scheme of electroweak symmetry breaking are in fact identical in the
imaginary-time and the real-time formalism. This dismisses the doubt about
possible discrepancy between the two formalisms in this problem. Identity of
the derived thermal transformation matrices of the real-time matrix propagators
for scalar bound states without and with chemical potential and the ones for
corresponding elementary scalar particles shows similarity of thermodynamic
property between the two types of particles. Only one former inference is
modified, i.e. when the two flavors of fermions have unequal nonzero masses,
the amplitude of the composite Higgs particle will decay instead grow in time.Comment: 5 pages, revtex4, no figure
Extended Clausius Relation and Entropy for Nonequilibrium Steady States in Heat Conducting Quantum Systems
Recently, in their attempt to construct steady state thermodynamics (SST),
Komatsu, Nakagwa, Sasa, and Tasaki found an extension of the Clausius relation
to nonequilibrium steady states in classical stochastic processes. Here we
derive a quantum mechanical version of the extended Clausius relation. We
consider a small system of interest attached to large systems which play the
role of heat baths. By only using the genuine quantum dynamics, we realize a
heat conducting nonequilibrium steady state in the small system. We study the
response of the steady state when the parameters of the system are changed
abruptly, and show that the extended Clausius relation, in which "heat" is
replaced by the "excess heat", is valid when the temperature difference is
small. Moreover we show that the entropy that appears in the relation is
similar to von Neumann entropy but has an extra symmetrization with respect to
time-reversal. We believe that the present work opens a new possibility in the
study of nonequilibrium phenomena in quantum systems, and also confirms the
robustness of the approach by Komtatsu et al.Comment: 19 pages, 2 figure
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