2,444 research outputs found
Boundary Terms in Supergravity and Supersymmetry
We begin with the simplest possible introduction to supergravity. Then we
discuss its spin 3/2 stress tensor; these results are new. Next, we discuss
boundary conditions on fields and boundary actions for N=1 supergravity.
Finally, we discuss new boundary contributions to the mass and central charge
of monopoles in N=4 super Yang-Mills theory. All models are in 3+1 dimensions.Comment: 15 pages. Talk given by P. van Nieuwenhuizen at the
Einstein-celebration gravitational conference at Puri (India) in December
200
Majorana bound states without vortices in topological superconductors with electrostatic defects
Vortices in two-dimensional superconductors with broken time-reversal and
spin-rotation symmetry can bind states at zero excitation energy. These
socalled Majorana bound states transform a thermal insulator into a thermal
metal and may be used to encode topologically protected qubits. We identify an
alternative mechanism for the formation of Majorana bound states, akin to the
way in which Shockley states are formed on metal surfaces: An atomic-scale
electrostatic line defect can have a pair of Majorana bound states at the end
points. The Shockley mechanism explains the appearance of a thermal metal in
vortex-free lattice models of chiral p-wave superconductors and (unlike the
vortex mechanism) is also operative in the topologically trivial phase.Comment: 8 pages, 7 figures; the appendices are included as supplemental
material in the published versio
Biexciton recombination rates in self-assembled quantum dots
The radiative recombination rates of interacting electron-hole pairs in a
quantum dot are strongly affected by quantum correlations among electrons and
holes in the dot. Recent measurements of the biexciton recombination rate in
single self-assembled quantum dots have found values spanning from two times
the single exciton recombination rate to values well below the exciton decay
rate. In this paper, a Feynman path-integral formulation is developed to
calculate recombination rates including thermal and many-body effects. Using
real-space Monte Carlo integration, the path-integral expressions for realistic
three-dimensional models of InGaAs/GaAs, CdSe/ZnSe, and InP/InGaP dots are
evaluated, including anisotropic effective masses. Depending on size, radiative
rates of typical dots lie in the regime between strong and intermediate
confinement. The results compare favorably to recent experiments and
calculations on related dot systems. Configuration interaction calculations
using uncorrelated basis sets are found to be severely limited in calculating
decay rates.Comment: 11 pages, 4 figure
Transit peptide elements mediate selective protein targeting to two different types of chloroplasts in the single-cell C4 species Bienertia sinuspersici.
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Can people guess what happened to others from their reactions?
Are we able to infer what happened to a person from a brief sample of his/her behaviour? It has been proposed that mentalising skills can be used to retrodict as well as predict behaviour, that is, to determine what mental states of a target have already occurred. The current study aimed to develop a paradigm to explore these processes, which takes into account the intricacies of real-life situations in which reasoning about mental states, as embodied in behaviour, may be utilised. A novel task was devised which involved observing subtle and naturalistic reactions of others in order to determine the event that had previously taken place. Thirty-five participants viewed videos of real individuals reacting to the researcher behaving in one of four possible ways, and were asked to judge which of the four âscenariosâ they thought the individual was responding to. Their eye movements were recorded to establish the visual strategies used. Participants were able to deduce successfully from a small sample of behaviour which scenario had previously occurred. Surprisingly, looking at the eye region was associated with poorer identification of the scenarios, and eye movement strategy varied depending on the event experienced by the person in the video. This suggests people flexibly deploy their attention using a retrodictive mindreading process to infer events
Zero-voltage conductance peak from weak antilocalization in a Majorana nanowire
We show that weak antilocalization by disorder competes with resonant Andreev
reflection from a Majorana zero-mode to produce a zero-voltage conductance peak
of order e^2/h in a superconducting nanowire. The phase conjugation needed for
quantum interference to survive a disorder average is provided by particle-hole
symmetry - in the absence of time-reversal symmetry and without requiring a
topologically nontrivial phase. We identify methods to distinguish the Majorana
resonance from the weak antilocalization effect.Comment: 13 pages, 8 figures. Addendum, February 2014: Appendix B shows
results for weak antilocalization in the circular ensemble. (This appendix is
not in the published version.
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