31,381 research outputs found
Comment on "Canonical formalism for Lagrangians with nonlocality of finite extent"
We show by some counterexamples that Lagrangian sysytems with nonlocality of
finite extent are not necessarily unstable.Comment: 8 pages, 1 figure Submitted to Phys. Rev.
Mass inflation in a D dimensional Reissner-Nordstrom black hole: a hierarchy of particle accelerators ?
We study the geometry inside the event horizon of perturbed D dimensional
Reissner-Nordstrom-(A)dS type black holes showing that, similarly to the four
dimensional case, mass inflation also occurs for D>4. First, using the
homogeneous approximation, we show that an increase of the number of spatial
dimensions contributes to a steeper variation of the metric coefficients with
the areal radius and that the phenomenon is insensitive to the cosmological
constant in leading order. Then, using the code reported in arXiv:0904.2669
[gr-qc] adapted to D dimensions, we perform fully non-linear numerical
simulations. We perturb the black hole with a compact pulse adapting the pulse
amplitude such that the relative variation of the black hole mass is the same
in all dimensions, and determine how the black hole interior evolves under the
perturbation. We qualitatively confirm that the phenomenon is similar to four
dimensions as well as the behaviour observed in the homogeneous approximation.
We speculate about the formation of black holes inside black holes triggered by
mass inflation, and about possible consequences of this scenario.Comment: 8 pages, 6 figure
A study of transport suppression in an undoped AlGaAs/GaAs quantum dot single-electron transistor
We report a study of transport blockade features in a quantum dot
single-electron transistor, based on an undoped AlGaAs/GaAs heterostructure. We
observe suppression of transport through the ground state of the dot, as well
as negative differential conductance at finite source-drain bias. The
temperature and magnetic field dependence of these features indicate the
couplings between the leads and the quantum dot states are suppressed. We
attribute this to two possible mechanisms: spin effects which determine whether
a particular charge transition is allowed based on the change in total spin,
and the interference effects that arise from coherent tunneling of electrons in
the dot
Emergent Critical Phase and Ricci Flow in a 2D Frustrated Heisenberg Model
We introduce a two-dimensional frustrated Heisenberg antiferromagnet on
interpenetrating honeycomb and triangular lattices. Classically the two
sublattices decouple, and "order from disorder" drives them into a coplanar
state. Applying Friedan's geometric approach to nonlinear sigma models, we show
that the scaling of the spin-stiffnesses corresponds to the Ricci flow of a 4D
metric tensor. At low temperatures, the relative phase between the spins on the
two sublattices is described by a six-state clock model with an emergent
critical phase.Comment: 4+ pages, 2 figure
The Generalized Ricci Flow for 3D Manifolds with One Killing Vector
We consider 3D flow equations inspired by the renormalization group (RG)
equations of string theory with a three dimensional target space. By modifying
the flow equations to include a U(1) gauge field, and adding carefully chosen
De Turck terms, we are able to extend recent 2D results of Bakas to the case of
a 3D Riemannian metric with one Killing vector. In particular, we show that the
RG flow with De Turck terms can be reduced to two equations: the continual Toda
flow solved by Bakas, plus its linearizaton. We find exact solutions which flow
to homogeneous but not always isotropic geometries
Radio-frequency reflectometry on an undoped AlGaAs/GaAs single electron transistor
Radio frequency reflectometry is demonstrated in a sub-micron undoped
AlGaAs/GaAs device. Undoped single electron transistors (SETs) are attractive
candidates to study single electron phenomena due to their charge stability and
robust electronic properties after thermal cycling. However these devices
require a large top-gate which is unsuitable for the fast and sensitive radio
frequency reflectometry technique. Here we demonstrate rf reflectometry is
possible in an undoped SET.Comment: Four pages, three figures, one supplementary fil
Herwig++ 2.0 Release Note
A new release of the Monte Carlo program Herwig++ (version 2.0) is now
available. This is the first version of the program which can be used for
hadron-hadron physics and includes the full simulation of both initial- and
final-state QCD radiation.Comment: Source code and additional information available at
http://hepforge.cedar.ac.uk/herwig
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