2,328 research outputs found
Supergravity Higgs Inflation and Shift Symmetry in Electroweak Theory
We present a model of inflation in a supergravity framework in the Einstein
frame where the Higgs field of the next to minimal supersymmetric standard
model (NMSSM) plays the role of the inflaton. Previous attempts which assumed
non-minimal coupling to gravity failed due to a tachyonic instability of the
singlet field during inflation. A canonical K\"{a}hler potential with
\textit{minimal coupling} to gravity can resolve the tachyonic instability but
runs into the -problem. We suggest a model which is free of the
-problem due to an additional coupling in the K\"{a}hler potential which
is allowed by the Standard Model gauge group. This induces directions in the
potential which we call K-flat. For a certain value of the new coupling in the
(N)MSSM, the K\"{a}hler potential is special, because it can be associated with
a certain shift symmetry for the Higgs doublets, a generalization of the shift
symmetry for singlets in earlier models. We find that K-flat direction has
This shift symmetry is broken by interactions coming from
the superpotential and gauge fields. This direction fails to produce successful
inflation in the MSSM but produces a viable model in the NMSSM. The model is
specifically interesting in the Peccei-Quinn (PQ) limit of the NMSSM. In this
limit the model can be confirmed or ruled-out not just by cosmic microwave
background observations but also by axion searches.Comment: matches the published version at JCA
Critical Exponents of the Three Dimensional Random Field Ising Model
The phase transition of the three--dimensional random field Ising model with
a discrete () field distribution is investigated by extensive Monte
Carlo simulations. Values of the critical exponents for the correlation length,
specific heat, susceptibility, disconnected susceptibility and magnetization
are determined simultaneously via finite size scaling. While the exponents for
the magnetization and disconnected susceptibility are consistent with a first
order transition, the specific heat appears to saturate indicating no latent
heat. Sample to sample fluctuations of the susceptibilty are consistent with
the droplet picture for the transition.Comment: Revtex, 10 pages + 4 figures included as Latex files and 1 in
Postscrip
Efficient routing of single photons by one atom and a microtoroidal cavity
Single photons from a coherent input are efficiently redirected to a separate
output by way of a fiber-coupled microtoroidal cavity interacting with
individual Cesium atoms. By operating in an overcoupled regime for the
input-output to a tapered fiber, our system functions as a quantum router with
high efficiency for photon sorting. Single photons are reflected and excess
photons transmitted, as confirmed by observations of photon antibunching
(bunching) for the reflected (transmitted) light. Our photon router is robust
against large variations of atomic position and input power, with the observed
photon antibunching persisting for intracavity photon number 0.03 \lesssim n
\lesssim 0.7
Learning by message-passing in networks of discrete synapses
We show that a message-passing process allows to store in binary "material"
synapses a number of random patterns which almost saturates the information
theoretic bounds. We apply the learning algorithm to networks characterized by
a wide range of different connection topologies and of size comparable with
that of biological systems (e.g. ). The algorithm can be
turned into an on-line --fault tolerant-- learning protocol of potential
interest in modeling aspects of synaptic plasticity and in building
neuromorphic devices.Comment: 4 pages, 3 figures; references updated and minor corrections;
accepted in PR
Role of the initial conditions on the enhancement of the escape time in static and fluctuating potentials
We present a study of the noise driven escape of an overdamped Brownian
particle moving in a cubic potential profile with a metastable state. We
analyze the role of the initial conditions of the particle on the enhancement
of the average escape time as a function of the noise intensity for fixed and
fluctuating potentials. We observe the noise enhanced stability effect for all
the initial unstable states investigated. For a fixed potential we find a
peculiar initial condition which separates the set of the initial
unstable states in two regions: those which give rise to divergences from those
which show nonmonotonic behavior of the average escape time. For fluctuating
potential at this particular initial condition and for low noise intensity we
find large fluctuations of the average escape time.Comment: 8 pages, 6 figures. Appeared in Physica A (2003
Noise-induced inhibitory suppression of malfunction neural oscillators
Motivated by the aim to find new medical strategies to suppress undesirable
neural synchronization we study the control of oscillations in a system of
inhibitory coupled noisy oscillators. Using dynamical properties of inhibition,
we find regimes when the malfunction oscillations can be suppressed but the
information signal of a certain frequency can be transmitted through the
system. The mechanism of this phenomenon is a resonant interplay of noise and
the transmission signal provided by certain value of inhibitory coupling.
Analyzing a system of three or four oscillators representing neural clusters,
we show that this suppression can be effectively controlled by coupling and
noise amplitudes.Comment: 10 pages, 14 figure
Boltzmann brains and the scale-factor cutoff measure of the multiverse
To make predictions for an eternally inflating "multiverse", one must adopt a
procedure for regulating its divergent spacetime volume. Recently, a new test
of such spacetime measures has emerged: normal observers - who evolve in pocket
universes cooling from hot big bang conditions - must not be vastly outnumbered
by "Boltzmann brains" - freak observers that pop in and out of existence as a
result of rare quantum fluctuations. If the Boltzmann brains prevail, then a
randomly chosen observer would be overwhelmingly likely to be surrounded by an
empty world, where all but vacuum energy has redshifted away, rather than the
rich structure that we observe. Using the scale-factor cutoff measure, we
calculate the ratio of Boltzmann brains to normal observers. We find the ratio
to be finite, and give an expression for it in terms of Boltzmann brain
nucleation rates and vacuum decay rates. We discuss the conditions that these
rates must obey for the ratio to be acceptable, and we discuss estimates of the
rates under a variety of assumptions.Comment: 32 pp, 2 figs. Modified to conform to the version accepted by Phys.
Rev. D. The last paragraph of Sec. V-A, about Boltzmann brains in Minkowski
space, has been significantly enlarged. Two sentences were added to the
introduction concerning the classical approximation and the hope of finding a
motivating principle for the measure. Several references were adde
Antibiotic prescribing in primary care and antimicrobial resistance in patients admitted to hospital with urinary tract infection: a controlled observational pilot study
There is growing evidence that primary care prescribed antibiotics lead to antibiotic resistance in bacteria causing minor infections or being carried by asymptomatic adults, but little research to date has investigated links between primary care prescribed antibiotics and resistance among more serious infections requiring hospital care. Knowledge of these effects is likely to have a major influence on public expectations for, and primary care use of, antibiotics. This study aimed to assess the feasibility of recruiting symptomatic adult patients admitted to hospital with urinary infections and to link primary and secondary data information to investigate the relationship between primary care prescribed antibiotics and antimicrobial resistance in these patients. A microbiology database search of in patients who had submitted a urine sample identified 740 patients who were potentially eligible to take part in the study. Of these, 262 patients did not meet the eligibility criteria, mainly due to use of a urinary catheter (40%). Two-hundred and forty three patients could not be recruited as the nurse was unable to visit the patients prior to discharge, as they were too unwell. Eighty patients provided complete information. Results indicate that there is evidence that prior antibiotic use is associated with resistant infections in hospital patients. A fully powered study, conducted using routinely collected data is proposed to fully clarify the precision of the association
Transform-limited pulses are not optimal for resonant multiphoton transitions
Maximizing nonlinear light-matter interactions is a primary motive for
compressing laser pulses to achieve ultrashort transform limited pulses. Here
we show how, by appropriately shaping the pulses, resonant multiphoton
transitions can be enhanced significantly beyond the level achieved by
maximizing the pulse's peak intensity. We demonstrate the counterintuitive
nature of this effect with an experiment in a resonant two-photon absorption,
in which, by selectively removing certain spectral bands, the peak intensity of
the pulse is reduced by a factor of 40, yet the absorption rate is doubled.
Furthermore, by suitably designing the spectral phase of the pulse, we increase
the absorption rate by a factor of 7.Comment: 4 pages, 3 figure
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