1,977 research outputs found
What can biologists say about galaxy evolution ?
It is possible to borrow from a topic of biology called phylogenetic
systematics, concepts and tools for a logical and objective classification of
galaxies. It is based on observable properties of objects - characters - either
qualitative (like morphology) or quantitative (like luminosity, mass or
spectrum). Distance analysis can readily be performed using a method called
phenetics and based on characters. But the most promising approach is
cladistics. It makes use of characters that can exist in at least two states,
one being ancestral and the other one derived. Objects are gathered depending
on the derived states they share. We illustrate a first application of this
method to astrophysics, that we name astrocladistics, with dwarf galaxies from
the Local Group.Comment: Kiel Euroconference (2002) "The Evolution of Galaxies III. From
Simple Approaches to Self-Consistent Models", Kluwer Academic Publishers (in
press
Surface Tension at Finite Tempearture in the MIT Bag Model
At the surface tension in the MIT bag model for a
single hadron is known to be negligible as compared to the bag pressure . We show that at finite temperature it has a substantial value of 50 -
70 MeV which also differ from hadron to hadron. We also find that the dynamics
of the Quark-Gluon Plasma is such that the creation of hybrids
with massive quarks will predominate over the creation of
mesons.Comment: Substantial changes in the revised version and a new author included,
13 pages in Latex and one figur
Ghost Busting: PT-Symmetric Interpretation of the Lee Model
The Lee model was introduced in the 1950s as an elementary quantum field
theory in which mass, wave function, and charge renormalization could be
carried out exactly. In early studies of this model it was found that there is
a critical value of g^2, the square of the renormalized coupling constant,
above which g_0^2, the square of the unrenormalized coupling constant, is
negative. Thus, for g^2 larger than this critical value, the Hamiltonian of the
Lee model becomes non-Hermitian. It was also discovered that in this
non-Hermitian regime a new state appears whose norm is negative. This state is
called a ghost state. It has always been assumed that in this ghost regime the
Lee model is an unacceptable quantum theory because unitarity appears to be
violated. However, in this regime while the Hamiltonian is not Hermitian, it
does possess PT symmetry. It has recently been discovered that a non-Hermitian
Hamiltonian having PT symmetry may define a quantum theory that is unitary. The
proof of unitarity requires the construction of a new time-independent operator
called C. In terms of C one can define a new inner product with respect to
which the norms of the states in the Hilbert space are positive. Furthermore,
it has been shown that time evolution in such a theory is unitary. In this
paper the C operator for the Lee model in the ghost regime is constructed
exactly in the V/N-theta sector. It is then shown that the ghost state has a
positive norm and that the Lee model is an acceptable unitary quantum field
theory for all values of g^2.Comment: 20 pages, 9 figure
Strong coupling expansion of chiral models
A general precedure is outlined for an algorithmic implementation of the
strong coupling expansion of lattice chiral models on arbitrary lattices. A
symbolic character expansion in terms of connected values of group integrals on
skeleton diagrams may be obtained by a fully computerized approach.Comment: 2 pages, PostScript file, contribution to conference LATTICE '9
Dynamical confinement in bosonized QCD2
In the bosonized version of two dimensional theories non trivial boundary
conditions (topology) play a crucial role. They are inevitable if one wants to
describe non singlet states. In abelian bosonization, color is the charge of a
topological current in terms of a non-linear meson field. We show that
confinement appears as the dynamical collapse of the topology associated with
its non trivial boundary conditions.Comment: 11 pages, figures not included, ftuv/92-
The Dynamics of a Meandering River
We present a statistical model of a meandering river on an alluvial plane
which is motivated by the physical non-linear dynamics of the river channel
migration and by describing heterogeneity of the terrain by noise. We study the
dynamics analytically and numerically. The motion of the river channel is
unstable and we show that by inclusion of the formation of ox-bow lakes, the
system may be stabilised. We then calculate the steady state and show that it
is in agreement with simulations and measurements of field data.Comment: Revtex, 12 pages, 2 postscript figure
Effective Lagrangian for strongly coupled domain wall fermions
We derive the effective Lagrangian for mesons in lattice gauge theory with
domain-wall fermions in the strong-coupling and large-N_c limits. We use the
formalism of supergroups to deal with the Pauli-Villars fields, needed to
regulate the contributions of the heavy fermions. We calculate the spectrum of
pseudo-Goldstone bosons and show that domain wall fermions are doubled and
massive in this regime. Since we take the extent and lattice spacing of the
fifth dimension to infinity and zero respectively, our conclusions apply also
to overlap fermions.Comment: 26 pp. RevTeX and 3 figures; corrected error in symmetry breaking
scheme and added comments to discussio
Instantons and Monopoles in General Abelian Gauges
A relation between the total instanton number and the quantum-numbers of
magnetic monopoles that arise in general Abelian gauges in SU(2) Yang-Mills
theory is established. The instanton number is expressed as the sum of the
`twists' of all monopoles, where the twist is related to a generalized Hopf
invariant. The origin of a stronger relation between instantons and monopoles
in the Polyakov gauge is discussed.Comment: 28 pages, 8 figures; comments added to put work into proper contex
High Energy Bounds on Soft N=4 SYM Amplitudes from AdS/CFT
Using the AdS/CFT correspondence, we study the high-energy behavior of
colorless dipole elastic scattering amplitudes in N=4 SYM gauge theory through
the Wilson loop correlator formalism and Euclidean to Minkowskian analytic
continuation. The purely elastic behavior obtained at large impact-parameter L,
through duality from disconnected AdS_5 minimal surfaces beyond the
Gross-Ooguri transition point, is combined with unitarity and analyticity
constraints in the central region. In this way we obtain an absolute bound on
the high-energy behavior of the forward scattering amplitude due to the
graviton interaction between minimal surfaces in the bulk. The dominant
"Pomeron" intercept is bounded by alpha less than or equal to 11/7 using the
AdS/CFT constraint of a weak gravitational field in the bulk. Assuming the
elastic eikonal approximation in a larger impact-parameter range gives alpha
between 4/3 and 11/7. The actual intercept becomes 4/3 if one assumes the
elastic eikonal approximation within its maximally allowed range L larger than
exp{Y/3}, where Y is the total rapidity. Subleading AdS/CFT contributions at
large impact-parameter due to the other d=10 supergravity fields are obtained.
A divergence in the real part of the tachyonic KK scalar is cured by
analyticity but signals the need for a theoretical completion of the AdS/CFT
scheme.Comment: 25 pages, 3 eps figure
Monte Carlo Simulation Calculation of Critical Coupling Constant for Continuum \phi^4_2
We perform a Monte Carlo simulation calculation of the critical coupling
constant for the continuum {\lambda \over 4} \phi^4_2 theory. The critical
coupling constant we obtain is [{\lambda \over \mu^2}]_crit=10.24(3).Comment: 11 pages, 4 figures, LaTe
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