9,176 research outputs found
Noncommutativity in Space and Primordial Magnetic Field
In this paper we show that noncommutativity in spatial coordinates can
generate magnetic field in the early Universe on a horizon scale. The strength
of such a magnetic field depends on the number density of massive charged
particles present at a given moment. This allows us to trace back the
temperature dependence of the noncommutativity scale from the bounds on
primordial magnetic field coming from nucleosynthesis.Comment: Revtex, 4 pages, v3: very minor changes, the version to appear in PR
Contact Injection into Polymer Light-Emitting Diodes
The variation of current I with voltage V for poly(phenylene vinylene) and
other polymer light-emitting diodes has been attributed to carriers tunneling
into broad conduction and valence bands. In actuality the electrons and holes
tunnel into polaron levels and transport is by hopping among these levels. We
show that for small injection the I-V characteristic is determined mainly by
the image force, for large injection by space charge effects, but in both cases
the strong variation of mobility with field due to disorder plays an important
role.Comment: 9 pages, two Postscript figures are aviable upon reques
Longevity of supersymmetric flat directions
We examine the fate of supersymmetric flat directions. We argue that the
non-perturbative decay of the flat direction via preheating is an unlikely
event. In order to address this issue, first we identify the physical degrees
of freedom and their masses in presence of a large flat direction VEV (Vacuum
Expectation Value). We explicitly show that the (complex) flat direction and
its fermionic partner are the only light {\it physical} fields in the spectrum.
If the flat direction VEV is much larger than the weak scale, and it has a
rotational motion, there will be no resonant particle production at all. The
case of multiple flat directions is more involved. We illustrate that in many
cases of physical interest, the situation becomes effectively the same as that
of a single flat direction, or collection of independent single directions. In
such cases preheating is not relevant. In an absence of a fast non-perturbative
decay, the flat direction survives long enough to affect thermalization in
supersymmetric models as described in hep-ph/0505050 and hep-ph/0512227. It can
also ``terminate'' an early stage of non-perturbative inflaton decay as
discussed in hep-ph/0603244.Comment: 9 revtex pages, v3: expanded discussion on two flat directions, minor
modifications, conclusions unchange
Controlling quantum transport through a single molecule
We investigate multi-terminal quantum transport through single monocyclic
aromatic annulene molecules, and their derivatives, using the nonequilibrium
Green function approach in the self-consistent Hartree-Fock approximation. A
new device concept, the Quantum Interference Effect Transistor (QuIET) is
proposed, exploiting perfect destructive interference stemming from molecular
symmetry, and controlling current flow by introducing decoherence and/or
elastic scattering that break the symmetry. This approach overcomes the
fundamental problems of power dissipation and environmental sensitivity that
beset many nanoscale device proposals.Comment: 4 pages, 5 figure
Seismic detection of acoustic sharp features in the CoRoT target HD49933
The technique of determining the acoustic location of layers of sharp changes
in the sound speed inside a star from the oscillatory signal in its frequencies
is applied on a solar-type star, the CoRoT target, HD49933. We are able to
determine the acoustic depth of the second helium ionisation zone of HD49933 to
be 794 +55/-68 seconds. The acoustic depth of the base of the convective zone
is found to be 1855 +173/-412 seconds where the large error bars reflect the
ambiguity in the result, which is difficult to determine with present precision
on the frequencies because of the intrinsically weak nature of the signal. The
positions of both these layers are consistent with those in a representative
stellar model of HD49933.Comment: Accepted for publication in Astronomy & Astrophysic
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