29,483 research outputs found
Stop Co-Annihilation in the Minimal Supersymmetric Standard Model Revisited
We re-examine the stop co-annihilation scenario of the Minimal Supersymmetric Standard Model, wherein a bino-like lightest supersymmetric particle has a thermal relic density set by co-annihilations with a scalar partner of the top quark in the early universe. We concentrate on the case where only the top partner sector is relevant for the cosmology, and other particles are heavy. We discuss the cosmology with focus on low energy parameters and an emphasis on the implications of the measured Higgs boson mass and its properties. We find that the irreducible direct detection signal correlated with this cosmology is generically well below projected experimental sensitivity, and in most cases lies below the neutrino background. A larger, detectable, direct detection rate is possible, but is unrelated to the co-annihilation cosmology. LHC searches for compressed spectra are crucial for probing this scenario
Non-equilibrium conductance of a three-terminal quantum dot in the Kondo regime: Perturbative Renormalization Group
Motivated by recent experiments, we consider a single-electron transistor in
the Kondo regime which is coupled to three leads in the presence of large bias
voltages. Such a steady-state non-equilibrium system is to a large extent
governed by a decoherence rate induced by the current through the dot. As the
two-terminal conductance turns out to be rather insensitive to the decoherence
rate, we study the conductance in a three-terminal device using perturbative
renormalization group and calculate the characteristic splitting of the Kondo
resonance. The interplay between potential biases and anisotropy in coupling to
the three leads determines the decoherence rate and the conditions for strong
coupling.Comment: 4 pages, 4 figure
Hidden Order in
We review current attempts to characterize the underlying nature of the
hidden order in . A wide variety of experiments point to the
existence of two order parameters: a large primary order parameter of unknown
character which co-exists with secondary antiferromagnetic order. Current
theories can be divided into two groups determined by whether or not the
primary order parameter breaks time-reversal symmetry. We propose a series of
experiments designed to test the time-reversal nature of the underlying primary
order in and to characterize its local single-ion physics
Thermodynamics of Vortices in the Plane
The thermodynamics of vortices in the critically coupled abelian Higgs model,
defined on the plane, are investigated by placing vortices in a region of
the plane with periodic boundary conditions: a torus. It is noted that the
moduli space for vortices, which is the same as that of
indistinguishable points on a torus, fibrates into a bundle over the
Jacobi manifold of the torus. The volume of the moduli space is a product of
the area of the base of this bundle and the volume of the fibre. These two
values are determined by considering two 2-surfaces in the bundle corresponding
to a rigid motion of a vortex configuration, and a motion around a fixed centre
of mass. The partition function for the vortices is proportional to the volume
of the moduli space, and the equation of state for the vortices is in the thermodynamic limit, where is the pressure, the area of
the region of the plane occupied by the vortices, and the temperature.
There is no phase transition.Comment: 17 pages, DAMTP 93-3
Prediction of the capacitance lineshape in two-channel quantum dots
We propose a set-up to realize two-channel Kondo physics using quantum dots.
We discuss how the charge fluctuations on a small dot can be accessed by using
a system of two single electron transistors arranged in parallel. We derive a
microscopic Hamiltonian description of the set-up that allows us to make
connection with the two-channel Anderson model (of extended use in the context
of heavy-Fermion systems) and in turn make detailed predictions for the
differential capacitance of the dot. We find that its lineshape, which we
determined precisely, shows a robust behavior that should be experimentally
verifiable.Comment: 4 pages, 3 figure
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