4,710 research outputs found
Minimal Spin-3/2 Dark Matter in a simple -channel model
We consider a spin~-~3/2 fermionic dark matter candidate (DM) interacting
with Standard Model fermions through a vector mediator in the -channel. We
find that for pure vector couplings almost the entire parameter space of the DM
and mediator mass consistent with the observed relic density is ruled out by
the direct detection observations through DM-nucleon elastic scattering
cross-sections. In contrast, for pure axial-vector coupling, the most stringent
constraints are obtained from mono-jet searches at the Large Hadron Collider.Comment: 8 pages, 5 figures, Version accepted for publication in EPJ
Spin-3/2 dark matter in a simple -channel model
We consider a spin-3/2 fermionic dark matter (DM) particle interacting with
the Standard Model quarks through the exchange of a charged and coloured scalar
or vector mediator in a simple -channel model. It is found that for the
vector mediator case, almost the entire parameter space allowed by the observed
relic density is already ruled out by the direct detection LUX data. No such
bounds exist on the interaction mediated by scalar particles. Monojet + missing
energy searches at the Large Hadron Collider provide the most stringent bounds
on the parameters of the model for this case. The collider bounds put a lower
limit on the allowed DM masses.Comment: Published EPJC versio
Finite energy spin fluctuation as a pairing glue in systems with coexisting electron and hole bands
We study, within the fluctuation exchange approximation, the
spin-fluctuation-mediated superconductivity in Hubbard-type models possessing
electron and hole bands, and compare them with a model on a square lattice with
a large Fermi surface. In the square lattice model, superconductivity is more
enhanced for better nesting for a fixed band filling. By contrast, in the
models with electron and hole bands, superconductivity is optimized when the
Fermi surface nesting is degraded to some extent, where finite energy spin
fluctuation around the nesting vector develops. The difference lies in the
robustness of the nesting vector, namely, in models with electron and hole
bands, the wave vector at which the spin susceptibility is maximized is fixed
even when the nesting is degraded, whereas when the Fermi surface is large, the
nesting vector varies with the deformation of the Fermi surface. We also
discuss the possibility of realizing in actual materials the bilayer Hubbard
model, which is a simple model with electron and hole bands, and is expected to
have a very high T_c
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