2,341 research outputs found
Microwave and millimeter wave spectroscopy in the slightly hole-doped ladders of SrCuO
We have measured the temperature- and frequency dependence of the microwave
and millimeter wave conductivity along both the ladder
(c-axis) and the leg (a-axis) directions in SrCuO. Below a
temperature (170 K), we observed a stronger frequency dependence in
than that in , forming a small
resonance peak developed between 30 GHz and 100 GHz. We also observed nonlinear
dc conduction along the c-axis at rather low electric fields below . These
results suggest some collective excitation contributes to the c-axis charge
dynamics of the slightly hole-doped ladders of SrCuO below
.Comment: 7 pages, 4 figure, to be published in Europhysics Letter
Suppression of the charge-density-wave state in Sr_14Cu_24O_41 by calcium doping
The charge response in the spin chain/ladder compound Sr_14-xCa_xCu_24O_41 is
characterized by DC resistivity, low-frequency dielectric spectroscopy and
optical spectroscopy. We identify a phase transition below which a
charge-density wave (CDW) develops in the ladder arrays. Calcium doping
suppresses this phase with the transition temperature decreasing from 210 K for
x=0 to 10 K for x=9, and the CDW gap from 130 meV down to 3 meV, respectively.
This suppression is due to the worsened nesting originating from the increase
of the inter-ladder tight-binding hopping integrals, as well as from disorder
introduced at the Sr sites. These results altogether speak in favor of
two-dimensional superconductivity under pressure.Comment: 4 pages, 4 figures, accepted for publication in PR
Non Supersymmetric Metastable Vacua in N=2 SYM Softly Broken to N=1
We find non-supersymmetric metastable vacua in four dimensional N=2 gauge
theories softly broken to N=1 by a superpotential term. First we study the
simplest case, namely the SU(2) gauge theory without flavors. We study the
spectrum and lifetime of the metastable vacuum and possible embeddings of the
model in UV complete theories. Then we consider larger gauge group theories
with flavors. We show that when we softly break them to N=1, the potential
induced on specific submanifolds of their moduli space is identical to the
potential in lower rank gauge theories. Then we show that the potential
increases when we move away from this submanifold, allowing us to construct
metastable vacua on them in the theories that can be reduced to the SU(2) case.Comment: 29 pages, 10 figure
Viable Supersymmetry and Leptogenesis with Anomaly Mediation
The seesaw mechanism that explains the small neutrino masses comes naturally
with supersymmetric (SUSY) grand unification and leptogenesis. However, the
framework suffers from the SUSY flavor and CP problems, and has a severe
cosmological gravitino problem. We propose anomaly mediation as a simple
solution to all these problems, which is viable once supplemented by the
D-terms for U(1)_Y and U(1)_{B-L}. Even though the right-handed neutrino mass
explicitly breaks U(1)_{B-L} and hence reintroduces the flavor problem, we show
that it lacks the logarithmic enhancement and poses no threat to the framework.
The thermal leptogenesis is then made easily consistent with the gravitino
constraint.Comment: 5 pages, one figure, uses Revtex4; Discussion on the upper bound on
the LSP mass added. The version published in PR
Transient dynamics for sequence processing neural networks
An exact solution of the transient dynamics for a sequential associative
memory model is discussed through both the path-integral method and the
statistical neurodynamics. Although the path-integral method has the ability to
give an exact solution of the transient dynamics, only stationary properties
have been discussed for the sequential associative memory. We have succeeded in
deriving an exact macroscopic description of the transient dynamics by
analyzing the correlation of crosstalk noise. Surprisingly, the order parameter
equations of this exact solution are completely equivalent to those of the
statistical neurodynamics, which is an approximation theory that assumes
crosstalk noise to obey the Gaussian distribution. In order to examine our
theoretical findings, we numerically obtain cumulants of the crosstalk noise.
We verify that the third- and fourth-order cumulants are equal to zero, and
that the crosstalk noise is normally distributed even in the non-retrieval
case. We show that the results obtained by our theory agree with those obtained
by computer simulations. We have also found that the macroscopic unstable state
completely coincides with the separatrix.Comment: 21 pages, 4 figure
Supersymmetric Axion-Neutrino Merger
The recently proposed supersymmetric model of the neutrino mass matrix
is modified to merge with a previously proposed axionic solution of the strong
CP problem. The resulting model has only one input scale, i.e. that of
symmetry breaking, which determines both the seesaw neutrino mass scale and the
axion decay constant. It also solves the problem and conserves R parity
automatically.Comment: 7 pages, no figur
Symmetric sequence processing in a recurrent neural network model with a synchronous dynamics
The synchronous dynamics and the stationary states of a recurrent attractor
neural network model with competing synapses between symmetric sequence
processing and Hebbian pattern reconstruction is studied in this work allowing
for the presence of a self-interaction for each unit. Phase diagrams of
stationary states are obtained exhibiting phases of retrieval, symmetric and
period-two cyclic states as well as correlated and frozen-in states, in the
absence of noise. The frozen-in states are destabilised by synaptic noise and
well separated regions of correlated and cyclic states are obtained. Excitatory
or inhibitory self-interactions yield enlarged phases of fixed-point or cyclic
behaviour.Comment: Accepted for publication in Journal of Physics A: Mathematical and
Theoretica
Transmission properties of double-gap asymmetric split ring resonators in terahertz region
We investigated the electromagnetic properties of the metamaterials that consist of double-gap split ring resonators (SRRs) in the terahertz region. We found that varying the position of one gap with respect to the other causes the resonant frequency of the SRRs to shift over a broad range. This frequency shift is attributed to the change in the combined capacitance that consists of two capacitances of gaps connected in series and an additional capacitance connected in parallel to the others. Our findings are also verified by obtaining good agreement between experiments and simulations
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