34 research outputs found
Symmetric coupling of four spin-1/2 systems
We address the non-binary coupling of identical angular momenta based upon
the representation theory for the symmetric group. A correspondence is pointed
out between the complete set of commuting operators and the
reference-frame-free subsystems. We provide a detailed analysis of the coupling
of three and four spin-1/2 systems and discuss a symmetric coupling of four
spin-1/2 systems.Comment: 20 pages, no figure
Inflation with racetrack superpotential and matter field
Several models of inflation with the racetrack superpotential for the volume
modulus coupled to a matter field are investigated. In particular, it is shown
that two classes of racetrack inflation models, saddle point and inflection
point ones, can be constructed in a fully supersymmetric framework with the
matter field F-term as a source of supersymmetry breaking and uplifting. Two
models of F-term supersymmetry breaking are considered: the Polonyi model and
the quantum corrected O'Raifeartaigh model. In the former case, both classes of
racetrack inflation models differ significantly from the corresponding models
with non-supersymmetric uplifting. The main difference is a quite strong
dominance of the inflaton by the matter field. In addition, fine-tuning of the
parameters is relaxed as compared to the original racetrack models. In the case
of the racetrack inflation models coupled to the O'Raifeartaigh model, the
matter field is approximately decoupled from the inflationary dynamics. In all
of the above models the gravitino mass is larger than the Hubble scale during
inflation. The possibility of having the gravitino much lighter than the Hubble
scale is also investigated. It is very hard to construct models with light
gravitino in which the volume modulus dominates inflation. On the other hand,
models in which the inflationary dynamics is dominated by the matter field are
relatively simple and seem to be more natural.Comment: 40 pages, 13 figures, references added, typos corrected, version to
be publishe
Dark Matter Signals from Cascade Annihilations
A leading interpretation of the electron/positron excesses seen by PAMELA and
ATIC is dark matter annihilation in the galactic halo. Depending on the
annihilation channel, the electron/positron signal could be accompanied by a
galactic gamma ray or neutrino flux, and the non-detection of such fluxes
constrains the couplings and halo properties of dark matter. In this paper, we
study the interplay of electron data with gamma ray and neutrino constraints in
the context of cascade annihilation models, where dark matter annihilates into
light degrees of freedom which in turn decay into leptons in one or more steps.
Electron and muon cascades give a reasonable fit to the PAMELA and ATIC data.
Compared to direct annihilation, cascade annihilations can soften gamma ray
constraints from final state radiation by an order of magnitude. However, if
dark matter annihilates primarily into muons, the neutrino constraints are
robust regardless of the number of cascade decay steps. We also examine the
electron data and gamma ray/neutrino constraints on the recently proposed
"axion portal" scenario.Comment: 36 pages, 11 figures, 7 tables; references adde
Transport Properties of Holographic Defects
We study the charge transport properties of fields confined to a
(2+1)-dimensional defect coupled to (3+1)-dimensional super-Yang-Mills at
large-\nc and strong coupling, using AdS/CFT techniques applied to linear
response theory. The dual system is described by \nf probe D5- or D7-branes
in the gravitational background of \nc black D3-branes. Surprisingly, the
transport properties of both defect CFT's are essentially identical -- even
though the D7-brane construction breaks all supersymmetries. We find that the
system possesses a conduction threshold given by the wave-number of the
perturbation and that the charge transport arises from a quasiparticle spectrum
which is consistent with an intuitive picture where the defect acquires a
finite width. We also examine finite- modifications arising from
higher derivative interactions in the probe brane action.Comment: 54 pages, 22 figures, references added, minor changes to figures and
comments, final version published in JHE
Characterizing free volumes and layer structures in polymeric membranes using slow positron annihilation spectroscopy
10.1088/1742-6596/262/1/012027Journal of Physics: Conference Series2621