381 research outputs found
On the Construction of Sorted Reactive Systems
We develop a theory of sorted bigraphical reactive systems. Every application of bigraphs in the literature has required an extension, a sorting, of pure bigraphs. In turn, every such application has required a redevelopment of the theory of pure bigraphical reactive systems for the sorting at hand. Here we present a general construction of sortings. The constructed sortings always sustain the behavioural theory of pure bigraphs (in a precise sense), thus obviating the need to redevelop that theory for each new application. As an example, we recover Milner’s local bigraphs as a sorting on pure bigraphs. Technically, we give our construction for ordinary reactive systems, then lift it to bigraphical reactive systems. As such, we give also a construction of sortings for ordinary reactive systems. This construction is an improvement over previous attempts in that it produces smaller and much more natural sortings, as witnessed by our recovery of local bigraphs as a sorting
Coherent dynamics of interwell excitons in GaAs/AlxGa1-xAs superlattices
Coherent exciton dynamics in a GaAs/AlxGa1−xAs narrow-miniband superlattice is studied by spectrally resolved transient four-wave mixing. Coherent optical properties of the investigated structure are found to be strongly affected by the existence of two different heavy-hole excitonic states. One of them, the 1s heavy-hole exciton, is almost identical to the same state in noninteracting quantum wells, while the other, the heavy-hole interwell exciton, is composed of an electron and a heavy hole in adjacent wells. The interwell exciton leads to a resonant enhancement in the four-wave mixing spectra and exhibits quantum beats with the 1s heavy-hole exciton. The dephasing of the interwell exciton is one order of magnitude faster than that of the heavy-hole exciton and is mostly due to intensity-independent scattering mechanisms
Higgs Sector in Extensions of the MSSM
Extensions of the Minimal Supersymmetric Standard Model (MSSM) with
additional singlet scalar fields solve the important mu-parameter fine tuning
problem of the MSSM. We compute and compare the neutral Higgs boson mass
spectra, including one-loop corrections, of the following MSSM extensions:
Next-to-Minimal Supersymmetric Standard Model (NMSSM), the nearly-Minimal
Supersymmetric Standard Model (nMSSM), and the U(1)'-extended Minimal
Supersymmetric Standard Model (UMSSM) by performing scans over model
parameters. We find that the Secluded U(1)'-extended Minimal Supersymmetric
Standard Model (sMSSM) is identical to the nMSSM if three of the additional
scalars decouple. The dominant part of the one-loop corrections are
model-independent since the singlet field does not couple to MSSM particles
other than the Higgs doublets. Thus, model-dependent parameters enter the
masses only at tree-level. We apply constraints from LEP bounds on the Standard
Model and MSSM Higgs boson masses and the MSSM chargino mass, the invisible Z
decay width, and the Z-Z' mixing angle. Some extended models permit a Higgs
boson with mass substantially below the SM LEP limit or above theoretical
limits in the MSSM. Ways to differentiate the models via masses, couplings,
decays and production of the Higgs bosons are discussed.Comment: 65 pages, 15 figures. Figure replaced and typos corrected. Version to
appear in Phys. Rev.
Binding of biexcitons in GaAs/AlxGa1-xAs superlattices
Binding of the heavy-hole excitons and biexcitons in GaAs/Al0.3Ga0.7As superlattices is studied using linear and nonlinear optical techniques. High biexciton binding energies characteristic of quasi two-dimensional biexcitons are observed in superlattices with considerable miniband dispersion
The New Fat Higgs: Slimmer and More Attractive
In this paper we increase the MSSM tree level higgs mass bound to a value
that is naturally larger than the LEP-II search constraint by adding to the
superpotential a term, as in the NMSSM, and UV
completing with new strong dynamics {\it before} becomes
non-perturbative. Unlike other models of this type the higgs fields remain
elementary, alleviating the supersymmetric fine-tuning problem while
maintaining unification in a natural way.Comment: 14 pages and 2 figures. Added references and updated argument about
constraints from reheating temperatur
Radial nanowire light-emitting diodes in the (Al<sub>x</sub>Ga<sub>1-x</sub>)<sub>y</sub>In<sub>1-y</sub>P material system
Exciton spin relaxation in single semiconductor quantum dots
We study the relaxation of the exciton spin (longitudinal relaxation time
) in single asymmetrical quantum dots due to an interplay of the
short--range exchange interaction and acoustic phonon deformation. The
calculated relaxation rates are found to depend strongly on the dot size,
magnetic field and temperature. For typical quantum dots and temperatures below
100 K, the zero--magnetic field relaxation times are long compared to the
exciton lifetime, yet they are strongly reduced in high magnetic fields. We
discuss explicitly quantum dots based on (In,Ga)As and (Cd,Zn)Se semiconductor
compounds.Comment: accepted for Phys. Rev.
Higgsino Dark Matter in a SUGRA Model with Nonuniversal Gaugino Masses
We study a specific SUGRA model with nonuniversal gaugino masses as an
alternative to the minimal SUGRA model in the context of supersymmetric dark
matter. The lightest supersymmetric particle in this model comes out to be a
Higgsino dominated instead of a bino dominated lightest neutralino. The thermal
relic density of this Higgsino dark matter is somewhat lower than the
cosmologically favoured range, which means it may be only a subdominant
component of the cold dark matter. Nonetheless, it predicts favourable rates of
indirect detection, which can be seen in square-km size neutrino telescopes.Comment: Version to appear in Phys. Rev. D. A few references added in the
bibliography and a comment added in Section 2. LaTex, 16 pages, 4 figure
- …