352 research outputs found
R-symmetry and Supersymmetry Breaking at Finite Temperature
We analyze the spontaneous symmetry breaking at finite temperature
for the simple O'Raifeartaigh-type model introduced in [1] in connection with
spontaneous supersymmetry breaking. We calculate the finite temperature
effective potential (free energy) to one loop order and study the thermal
evolution of the model. We find that the R-symmetry breaking occurs through a
second order phase transition. Its associated meta-stable supersymmetry
breaking vacuum is thermodynamically favored at high temperatures and the model
remains trapped in this state by a potential barrier, as the temperature lowers
all the way until T=0.Comment: 19 pages, 4 figures - Minor revisions, references added. To appear in
JHE
Assessing impacts of Common Agricultural Policy changes on regional use patterns with a decision support system. An application in Southern Portugal
This paper discusses research aiming at assessing Common Agricultural Policy impacts on agriculture and
forestry. For this purpose an approach is developed that includes a linear programming model to estimate
the Positive Mathematical Programming production cost function coefficients of current agricultural–
forestry activities. It further includes a heuristic — simulated annealing — to generate solutions for each
policy scenario. This model base approach is integrated within a decision support system (DSS) for testing
purposes. The DSS further encompasses a relational database that stores agricultural–forestry technical and
economic data and a geographic information system that stores topological data of regional farm-type land
units. The DSS Graphical User Interface provides tabular and geographical reporting capabilities. Results are
discussed for an application to the Alentejo region in Southern Portugal. Results demonstrate the usefulness
and relevance of the proposed approach to assess the impact of changes in prices and in agricultural policy
on land use patterns and on forestr
A Bound Quantum Particle in a Riemann-Cartan space with Topological Defects and Planar Potential
Starting from a continuum theory of defects, that is the analogous to
three-dimensional Einstein-Cartan-Sciama-Kibble gravity, we consider a charged
particle with spin 1/2 propagating in a uniform magnetic field coincident with
a wedge dispiration of finite extent. We assume the particle is bound in the
vicinity of the dispiration by long range attractive (harmonic) and short range
(inverse square) repulsive potentials. Moreover, we consider the effects of
spin-torsion and spin-magnetic field interactions. Exact expressions for the
energy eigenfunctions and eigenvalues are determined. The limit, in which the
defect region becomes singular, is considered and comparison with the
electromagnetic Aharonov-Bohm effect is made.Comment: 10 page
Interface optical phonons in spheroidal dots: Raman selection rules
The contribution of interface phonons to the first order Raman scattering in
nanocrystals with non spherical geometry is analyzed. Interface optical phonons
in the spheroidal geometry are discussed and the corresponding Frohlich-like
electron-phonon interaction is reported in the framework of the dielectric
continuum approach. It is shown that the interface phonon modes are strongly
dependent on the nanocrystal geometry, particularly on the ellipsoid's
semi-axis ratio. The new Raman selection rules have revealed that solely
interface phonon modes with even angular momentum are allowed to contribute to
the first order phonon-assisted scattering of light. On this basis we are able
to give an explanation for the observed low frequency shoulders present in the
Raman cross-section of several II-VI semiconductor nanostructures.Comment: 8 pages, 2 figure
Two Loop R-Symmetry Breaking
We analyze two loop quantum corrections for pseudomoduli in O'Raifeartaigh
like models. We argue that R-symmetry can be spontaneously broken at two loop
in non supersymmetric vacua. We provide a basic example with this property. We
discuss on phenomenological applications.Comment: 13 pages, 5 figures, JHEP3.cls, reference adde
Branching and annihilating Levy flights
We consider a system of particles undergoing the branching and annihilating
reactions A -> (m+1)A and A + A -> 0, with m even. The particles move via
long-range Levy flights, where the probability of moving a distance r decays as
r^{-d-sigma}. We analyze this system of branching and annihilating Levy flights
(BALF) using field theoretic renormalization group techniques close to the
upper critical dimension d_c=sigma, with sigma<2. These results are then
compared with Monte-Carlo simulations in d=1. For sigma close to unity in d=1,
the critical point for the transition from an absorbing to an active phase
occurs at zero branching. However, for sigma bigger than about 3/2 in d=1, the
critical branching rate moves smoothly away from zero with increasing sigma,
and the transition lies in a different universality class, inaccessible to
controlled perturbative expansions. We measure the exponents in both
universality classes and examine their behavior as a function of sigma.Comment: 9 pages, 4 figure
Generalized messenger sector for gauge mediation of supersymmetry breaking and the soft spectrum
We consider a generic renormalizable and gauge invariant messenger sector and
derive the sparticle mass spectrum using the formalism introduced for General
Gauge Mediation. Our results recover many expressions found in the literature
in various limits. Constraining the messenger sector with a global symmetry
under which the spurion field is charged, we analyze Extraordinary Gauge
Mediation beyond the small SUSY breaking limit. Finally, we include D-term
contributions and compute their corrections to the soft masses. This leads to a
perturbative framework allowing to explore models capable of fully covering the
parameter space of General Gauge Mediation to the Supersymmetric Standard
Model.Comment: Minor changes to clarify notation. Requirement of global symmetry is
relaxed in the derivation of scalar masses in the small SUSY breaking limi
Weak Segregation Theory and Non-Conventional Morphologies in the Ternary ABC Triblock Copolymers
The Leibler weak segregation theory in molten diblock copolymers is
generalized with due regard for the 2nd shell harmonics contributions defined
in the paper and the phase diagrams are built for the linear and miktoarm
ternary ABC triblock copolymers. The symmetric linear copolymers with the
middle block non-selective with respect to the side ones are shown to undergo
the continuous ODT not only into the lamellar phase but also into various
non-conventional cubic phases (depending on the middle block composition it
could be the simple cubic, face-centered cubic or non-centrosymmetric phase
revealing the symmetry of space group No.214 first predicted to appear in
molten block copolymers). For asymmetric linear ABC copolymers a region of
compositions is found where the weakly segregated gyroid (double gyroid) phase
exists between the planar hexagonal and lamellar or one of the non-conventional
cubic phases up to the very critical point. In contrast, the miktoarm ABC block
copolymers with one of its arm non-selective with respect to the two others are
shown to reveal a pronounced tendency towards strong segregation, which is
preceded by increase of stability of the conventional BCC phase and a peculiar
weakly segregated BCC phase (BCC3), where the dominant harmonics belong to the
3rd co-ordination sphere of the reciprocal lattice. The validity region of the
developed theory is discussed and outlined in the composition triangles both
for linear and miktoarm copolymers.Comment: 61 pages, 12 figure
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