10,472 research outputs found
Numerical calculation of the combinatorial entropy of partially ordered ice
Using a one-parameter case as an example, we demonstrate that multicanonical
simulations allow for accurate estimates of the residual combinatorial entropy
of partially ordered ice. For the considered case corrections to an
(approximate) analytical formula are found to be small, never exceeding 0.5%.
The method allows one as well to calculate combinatorial entropies for many
other systems.Comment: Extended version: 7 pages, 10 figures (v1 is letter-type version
Thermodynamics of two lattice ice models in three dimensions
In a recent paper we introduced two Potts-like models in three dimensions,
which share the following properties: (A) One of the ice rules is always
fulfilled (in particular also at infinite temperature). (B) Both ice rules hold
for groundstate configurations. This allowed for an efficient calculation of
the residual entropy of ice I (ordinary ice) by means of multicanonical
simulations. Here we present the thermodynamics of these models. Despite their
similarities with Potts models, no sign of a disorder-order phase transition is
found.Comment: 5 pages, 7 figure
Form-factors of the sausage model obtained with bootstrap fusion from sine-Gordon theory
We continue the investigation of massive integrable models by means of the
bootstrap fusion procedure, started in our previous work on O(3) nonlinear
sigma model. Using the analogy with SU(2) Thirring model and the O(3) nonlinear
sigma model we prove a similar relation between sine-Gordon theory and a
one-parameter deformation of the O(3) sigma model, the sausage model. This
allows us to write down a free field representation for the
Zamolodchikov-Faddeev algebra of the sausage model and to construct an integral
representation for the generating functions of form-factors in this theory. We
also clear up the origin of the singularities in the bootstrap construction and
the reason for the problem with the kinematical poles.Comment: 16 pages, revtex; references added, some typos corrected. Accepted
for publication in Physical Review
The Green Movement: Implications for Animals
The Green movement, a newly emerging political movement that is both global in scope and firmly anchored to each local region at the grassroots level, is destined to be of great import to those concerned with the status of nonhuman animals in our society. Closely allied with deep ecology and bioregionalism, Green thinking embodies an alteration in our perception of the human organism: no longer seen as separate from and superior to all the other components of the ecosystem, our species is placed in context as one among many interdependent forms of life, with the attainment of a sustainable balance among all life forms being the desired goal in designing our human activities. Translation of this viewpoint into political action is the challenge of Green organizations on several continents today
A Search for Very Low-mass Stars and Brown Dwarfs in the Young sigma Orionis Cluster
We present a CCD-based photometric survey covering 870 sq. arcmin in a young
stellar cluster around the young multiple star sigma Orionis. Our survey
limiting R, I, and Z magnitudes are 23.2, 21.8, and 21.0, respectively. From
our colour-magnitude diagrams, we have selected 49 faint objects, which
smoothly extrapolate the photometric sequence defined by more massive known
members. Adopting the currently accepted age interval of 2-10 Myr for the Orion
1b association and considering recent evolutionary models, our objects may span
a mass range from 0.1 down to 0.02 Msun, well within the substellar regime.
Follow-up low-resolution optical spectroscopy (635-920 nm) for eight of our
candidates (I=16-19.5) shows that they have spectral types M6-M8.5 which are
consistent with the expectations for true members. Compared with their Pleiades
counterparts of similar types, Halpha emission is generally stronger, while NaI
and KI absorption lines appear weaker, as expected for lower surface gravities
and younger ages. Additionally, TiO bands and in particular VO bands appear
clearly enhanced in our candidate with the latest spectral type, SOri 45 (M8.5,
I=19.5), compared to objects of similar types in older clusters and the field.
We have estimated the mass of this candidate at only 0.020-0.040 Msun, hence it
is one of the least massive brown dwarfs yet discovered. We also discuss in
this paper the potential role of deuterium as a tracer of both substellar
nature and age in very young clusters.Comment: Accepted for publication in ApJ Main Journal. 32 pages of text and
tables + 9 pages of figures. Figures 3a and 3b (gif format) provided
separatel
On the Existence of Local Observables in Theories With a Factorizing S-Matrix
A recently proposed criterion for the existence of local quantum fields with
a prescribed factorizing scattering matrix is verified in a non-trivial model,
thereby establishing a new constructive approach to quantum field theory in a
particular example. The existence proof is accomplished by analyzing nuclearity
properties of certain specific subsets of Fermionic Fock spaces.Comment: 13 pages, no figures, comment in sect. 3 adde
Lagrangian for the Majorana-Ahluwalia Construct
The equations describing self/anti-self charge conjugate states, recently
proposed by Ahluwalia, are re-written to covariant form. The corresponding
Lagrangian for the neutral particle theory is proposed. From a
group-theoretical viewpoint the construct is an example of the
Nigam-Foldy-Bargmann-Wightman-Wigner-type quantum field theory based on the
doubled representations of the extended Lorentz group. Relations with the
Sachs-Schwebel and Ziino-Barut concepts of relativistic quantum theory are
discussed.Comment: 10pp., REVTeX 3.0 fil
Scanning the Landscape of Flux Compactifications: Vacuum Structure and Soft Supersymmetry Breaking
We scan the landscape of flux compactifications for the Calabi-Yau manifold
with two K\" ahler moduli by varying the value of
the flux superpotential over a large range of values. We do not include
uplift terms. We find a rich phase structure of AdS and dS vacua. Starting with
we reproduce the exponentially large volume scenario, but as
is reduced new classes of minima appear. One of them corresponds to the
supersymmetric KKLT vacuum while the other is a new, deeper non-supersymmetric
minimum. We study how the bare cosmological constant and the soft supersymmetry
breaking parameters for matter on D7 branes depend on , for these classes
of minima. We discuss potential applications of our results.Comment: draft format remove
Inelastic Processes in the Collision of Relativistic Highly Charged Ions with Atoms
A general expression for the cross sections of inelastic collisions of fast
(including relativistic) multicharged ions with atoms which is based on the
genelazition of the eikonal approximation is derived. This expression is
applicable for wide range of collision energy and has the standard
nonrelativistic limit and in the ultrarelativistic limit coincides with the
Baltz's exact solution ~\cite{art13} of the Dirac equation. As an application
of the obtained result the following processes are calculated: the excitation
and ionization cross sections of hydrogenlike atom; the single and double
excitation and ionization of heliumlike atom; the multiply ionization of neon
and argon atoms; the probability and cross section of K-vacancy production in
the relativistic collision. The simple analytic formulae
for the cross sections of inelastic collisions and the recurrence relations
between the ionization cross sections of different multiplicities are also
obtained. Comparison of our results with the experimental data and the results
of other calculations are given.Comment: 25 pages, latex, 7 figures avialable upon request,submitted to PR
- …