120 research outputs found
A Linear Systems Approach to Laser Generation of Ultrasound in Composites
Laser ultrasonic generation and detection systems have been shown to be effective in the inspection and evaluation of both metals and composite materials [1–3]. Advantages of these noncontact systems include rapid scanning capability, the inspection of parts with complex geometries, and the ability for use in hostile environments. Unfortunately, laser ultrasonic systems are somewhat less sensitive than conventional contact piezoelectric systems. In order to increase the sensitivity, careful consideration must be paid to the choice of both generation and detection laser systems. Although the sensitivity of current laser ultrasonic systems has been shown to be sufficient for several applications, small improvements may allow for a more wide-spread use.</p
Higgs Mass from D-Terms: a Litmus Test
We explore supersymmetric theories in which the Higgs mass is boosted by the
non-decoupling D-terms of an extended gauge symmetry, defined here to
be a general linear combination of hypercharge, baryon number, and lepton
number. Crucially, the gauge coupling, , is bounded from below to
accommodate the Higgs mass, while the quarks and leptons are required by gauge
invariance to carry non-zero charge under . This induces an irreducible
rate, BR, for relevant to
existing and future resonance searches, and gives rise to higher dimension
operators that are stringently constrained by precision electroweak
measurements. Combined, these bounds define a maximally allowed region in the
space of observables, (BR, ), outside of which is excluded by
naturalness and experimental limits. If natural supersymmetry utilizes
non-decoupling D-terms, then the associated boson can only be observed
within this window, providing a model independent `litmus test' for this broad
class of scenarios at the LHC. Comparing limits, we find that current LHC
results only exclude regions in parameter space which were already disfavored
by precision electroweak data.Comment: 7 pages, 9 figure
A Collective Breaking of R-Parity
Supersymmetric theories with an R-parity generally yield a striking missing
energy signature, with cascade decays concluding in a neutralino that escapes
the detector. In theories where R-parity is broken the missing energy is
replaced with additional jets or leptons, often making traditional search
strategies ineffective. Such R-parity violation is very constrained, however,
by resulting B and L violating signals, requiring couplings so small that LSPs
will decay outside the detector in all but a few scenarios. In theories with
additional matter fields, R-parity can be broken collectively, such that
R-parity is not broken by any single coupling, but only by an ensemble of
couplings. Cascade decays can proceed normally, with each step only sensitive
to one or two couplings at a time, but B and L violation requires the full set,
yielding a highly suppressed constraint. s-channel production of new scalar
states, typically small for standard RPV, can be large when RPV is broken
collectively. While missing energy is absent, making these models difficult to
discover by traditional SUSY searches, they produce complicated many object
resonances (MORes), with many different possible numbers of jets and leptons.
We outline a simple model and discuss its discoverability at the LHC.Comment: 28 pages, 10 figure
Single-Scale Natural SUSY
We consider the prospects for natural SUSY models consistent with current
data. Recent constraints make the standard paradigm unnatural so we consider
what could be a minimal extension consistent with what we now know. The most
promising such scenarios extend the MSSM with new tree-level Higgs interactions
that can lift its mass to at least 125 GeV and also allow for flavor-dependent
soft terms so that the third generation squarks are lighter than current bounds
on the first and second generation squarks. We argue that a common feature of
almost all such models is the need for a new scale near 10 TeV, such as a scale
of Higgsing or confinement of a new gauge group. We consider the question
whether such a model can naturally derive from a single mass scale associated
with supersymmetry breaking. Most such models simply postulate new scales,
leaving their proximity to the scale of MSSM soft terms a mystery. This
coincidence problem may be thought of as a mild tuning, analogous to the usual
mu problem. We find that a single mass scale origin is challenging, but suggest
that a more natural origin for such a new dynamical scale is the gravitino
mass, m_{3/2}, in theories where the MSSM soft terms are a loop factor below
m_{3/2}. As an example, we build a variant of the NMSSM where the singlet S is
composite, and the strong dynamics leading to compositeness is triggered by
masses of order m_{3/2} for some fields. Our focus is the Higgs sector, but our
model is compatible with a light stop (with the other generation squarks heavy,
or with R-parity violation or another mechanism to hide them from current
searches). All the interesting low-energy mass scales, including linear terms
for S playing a key role in EWSB, arise dynamically from the single scale
m_{3/2}. However, numerical coefficients from RG effects and wavefunction
factors in an extra dimension complicate the otherwise simple story.Comment: 32 pages, 3 figures; version accepted by JHE
Excess Higgs Production in Neutralino Decays
The ATLAS and CMS experiments have recently claimed discovery of a Higgs
boson-like particle at ~5 sigma confidence and are beginning to test the
Standard Model predictions for its production and decay. In a variety of
supersymmetric models, a neutralino NLSP can decay dominantly to the Higgs and
the LSP. In natural SUSY models, a light third generation squark decaying
through this chain can lead to large excess Higgs production while evading
existing BSM searches. Such models can be observed at the 8 TeV LHC in channels
exploiting the rare diphoton decays of the Higgs produced in the cascade decay.
Identifying a diphoton resonance in association with missing energy, a lepton,
or b-tagged jets is a promising search strategy for discovery of these models,
and would immediately signal new physics involving production of a Higgs boson.
We also discuss the possibility that excess Higgs production in these SUSY
decays can be responsible for enhancements of up to 50% over the SM prediction
for the observed rate in the existing inclusive diphoton searches, a scenario
which would likely by the end of the 8 TeV run be accompanied by excesses in
the diphoton + lepton/MET and SUSY multi-lepton/b searches and a potential
discovery in a diphoton + 2b search.Comment: 42 pages, 19 figure
Optimal Compensation for Temporal Uncertainty in Movement Planning
Motor control requires the generation of a precise temporal sequence of control signals sent to the skeletal musculature. We describe an experiment that, for good performance, requires human subjects to plan movements taking into account uncertainty in their movement duration and the increase in that uncertainty with increasing movement duration. We do this by rewarding movements performed within a specified time window, and penalizing slower movements in some conditions and faster movements in others. Our results indicate that subjects compensated for their natural duration-dependent temporal uncertainty as well as an overall increase in temporal uncertainty that was imposed experimentally. Their compensation for temporal uncertainty, both the natural duration-dependent and imposed overall components, was nearly optimal in the sense of maximizing expected gain in the task. The motor system is able to model its temporal uncertainty and compensate for that uncertainty so as to optimize the consequences of movement
Fungal endophytes from arid areas of Andalusia: high potential sources for antifungal and antitumoral agents
Native plant communities from arid areas present distinctive characteristics to survive in extreme
conditions. The large number of poorly studied endemic plants represents a unique potential
source for the discovery of novel fungal symbionts as well as host-specific endophytes not yet
described. The addition of adsorptive polymeric resins in fungal fermentations has been seen to
promote the production of new secondary metabolites and is a tool used consistently to generate
new compounds with potential biological activities. A total of 349 fungal strains isolated from 63
selected plant species from arid ecosystems located in the southeast of the Iberian Peninsula, were
characterized morphologically as well as based on their ITS/28S ribosomal gene sequences. The fungal
community isolated was distributed among 19 orders including Basidiomycetes and Ascomycetes,
being Pleosporales the most abundant order. In total, 107 different genera were identified being
Neocamarosporium the genus most frequently isolated from these plants, followed by Preussia and
Alternaria. Strains were grown in four different media in presence and absence of selected resins to
promote chemical diversity generation of new secondary metabolites. Fermentation extracts were
evaluated, looking for new antifungal activities against plant and human fungal pathogens, as well
as, cytotoxic activities against the human liver cancer cell line HepG2. From the 349 isolates tested,
126 (36%) exhibited significant bioactivities including 58 strains with exclusive antifungal properties
and 33 strains with exclusive activity against the HepG2 hepatocellular carcinoma cell line. After LCMS
analysis, 68 known bioactive secondary metabolites could be identified as produced by 96 strains,
and 12 likely unknown compounds were found in a subset of 14 fungal endophytes. The chemical
profiles of the differential expression of induced activities were compared. As proof of concept, ten
active secondary metabolites only produced in the presence of resins were purified and identified. The
structures of three of these compounds were new and herein are elucidated.This work was supported by Fundación MEDINA and the Andalusian Government grant
RNM-7987 ‘Sustainable use of plants and their fungal parasites from arid regions of Andalucía for new molecules
useful for antifungals and neuroprotectors’
A nonlinear updating algorithm captures suboptimal inference in the presence of signal-dependent noise
Bayesian models have advanced the idea that humans combine prior beliefs and sensory observations to optimize behavior. How the brain implements Bayes-optimal inference, however, remains poorly understood. Simple behavioral tasks suggest that the brain can flexibly represent probability distributions. An alternative view is that the brain relies on simple algorithms that can implement Bayes-optimal behavior only when the computational demands are low. To distinguish between these alternatives, we devised a task in which Bayes-optimal performance could not be matched by simple algorithms. We asked subjects to estimate and reproduce a time interval by combining prior information with one or two sequential measurements. In the domain of time, measurement noise increases with duration. This property takes the integration of multiple measurements beyond the reach of simple algorithms. We found that subjects were able to update their estimates using the second measurement but their performance was suboptimal, suggesting that they were unable to update full probability distributions. Instead, subjects’ behavior was consistent with an algorithm that predicts upcoming sensory signals, and applies a nonlinear function to errors in prediction to update estimates. These results indicate that the inference strategies employed by humans may deviate from Bayes-optimal integration when the computational demands are high
Natural SUSY Predicts: Higgs Couplings
We study Higgs production and decays in the context of natural SUSY, allowing
for an extended Higgs sector to account for a 125 GeV lightest Higgs boson.
Under broad assumptions, Higgs observables at the LHC depend on at most four
free parameters with restricted numerical ranges. Two parameters suffice to
describe MSSM particle loops. The MSSM loop contribution to the diphoton rate
is constrained from above by direct stop and chargino searches and by
electroweak precision tests. Naturalness, in particular in demanding that rare
B decays remain consistent with experiment without fine-tuned cancellations,
provides a lower (upper) bound to the stop contribution to the Higgs-gluon
coupling (Higgs mass). Two parameters suffice to describe Higgs mixing, even in
the presence of loop induced non-holomorphic Yukawa couplings. Generic classes
of MSSM extensions, that address the fine-tuning problem, predict sizable
modifications to the effective bottom Yukawa, yb. Non-decoupling gauge
extensions enhance yb, while a heavy SM singlet reduces yb. A factor of 4-6
enhancement in the diphoton rate at the LHC, compared to the SM prediction, can
be accommodated. The ratio of the enhancements in the diphoton vs. the WW and
ZZ channels cannot exceed 1.4. The h to bbbar rate in associated production
cannot exceed the SM rate by more than 50%.Comment: 31 pages, 11 figure
Displaced Supersymmetry
The apparent absence of light superpartners at the LHC strongly constrains
the viability of the MSSM as a solution to the hierarchy problem. These
constraints can be significantly alleviated by R-parity violation (RPV).
Bilinear R-parity violation, with the single operator L H_u, does not require
any special flavor structure and can be naturally embedded in a GUT while
avoiding constraints from proton decay (unlike baryon-number-violating RPV).
The LSP in this scenario can be naturally long-lived, giving rise to displaced
vertices. Many collider searches, particularly those selecting b-jets or
leptons, are insensitive to events with such detector-scale displaced decays
owing to cuts on track quality and impact parameter. We demonstrate that for
decay lengths in the window ~1-1000 mm, constraints on superpartner masses can
be as low as ~450 GeV for squarks and ~40 GeV for LSPs. In some parts of
parameter space light LSPs can dominate the Higgs decay width, hiding the Higgs
from existing searches. This framework motivates collider searches for
detector-scale displaced vertices. LHCb may be ideally suited to trigger on
such events, while ATLAS and CMS may need to trigger on missing energy in the
event.Comment: 35 pages, 4 figure
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