933 research outputs found
Shining LUX on Isospin-Violating Dark Matter Beyond Leading Order
Isospin-violating dark matter (IVDM) has been proposed as a viable scenario
to reconcile conflicting positive and null results from direct detection dark
matter experiments. We show that the lowest-order dark matter-nucleus
scattering rate can receive large and nucleus-dependent corrections at
next-to-leading order (NLO) in the chiral expansion. The size of these
corrections depends on the specific couplings of dark matter to quark flavors
and gluons. In general the full NLO dark-matter-nucleus cross-section is not
adequately described by just the zero-energy proton and neutron couplings.
These statements are concretely illustrated in a scenario where the dark matter
couples to quarks through scalar operators. We find the canonical IVDM scenario
can reconcile the null XENON and LUX results and the recent CDMS-Si findings
provided its couplings to second and third generation quarks either lie on a
special line or are suppressed. Equally good fits with new values of the
neutron-to-proton coupling ratio are found in the presence of nonzero heavy
quark couplings. CDMS-Si remains in tension with LUX and XENON10/100 but is not
excluded.Comment: 11 pages, 5 figure
Probing Supersymmetry With Third-Generation Cascade Decays
The chiral structure of supersymmetric particle couplings involving third
generation Standard Model fermions depends on left-right squark and slepton
mixings as well as gaugino-higgsino mixings. The shapes and intercorrelations
of invariant mass distributions of a first or second generation lepton with
bottoms and taus arising from adjacent branches of SUSY cascade decays are
shown to be a sensitive probe of this chiral structure. All possible cascade
decays that can give rise to such correlations within the MSSM are considered.
For bottom-lepton correlations the distinctive structure of the invariant mass
distributions distinguishes between decays originating from stop or sbottom
squarks through either an intermediate chargino or neutralino. For decay
through a chargino the spins of the stop and chargino are established by the
form of the distribution. When the bottom charge is signed through soft muon
tagging, the structure of the same-sign and opposite-sign invariant mass
distributions depends on a set function of left-right and gaugino-higgsino
mixings, as well as establishes the spins of all the superpartners in the
sequential two-body cascade decay. Tau-lepton and tau-tau invariant mass
distributions arising from MSSM cascade decays are likewise systematically
considered with particular attention to their dependence on tau polarization.
All possible tau-lepton and tau-tau distributions are plotted using a
semi-analytic model for hadronic one-prong taus. Algorithms for fitting tau-tau
and tau-lepton distributions to data are suggested.Comment: 35 pages, 17 .eps figure
Neutrinoless double beta decay in chiral effective field theory: lepton number violation at dimension seven
We analyze neutrinoless double beta decay () within the
framework of the Standard Model Effective Field Theory. Apart from the
dimension-five Weinberg operator, the first contributions appear at dimension
seven. We classify the operators and evolve them to the electroweak scale,
where we match them to effective dimension-six, -seven, and -nine operators. In
the next step, after renormalization group evolution to the QCD scale, we
construct the chiral Lagrangian arising from these operators. We develop a
power-counting scheme and derive the two-nucleon currents up
to leading order in the power counting for each lepton-number-violating
operator. We argue that the leading-order contribution to the decay rate
depends on a relatively small number of nuclear matrix elements. We test our
power counting by comparing nuclear matrix elements obtained by various methods
and by different groups. We find that the power counting works well for nuclear
matrix elements calculated from a specific method, while, as in the case of
light Majorana neutrino exchange, the overall magnitude of the matrix elements
can differ by factors of two to three between methods. We calculate the
constraints that can be set on dimension-seven lepton-number-violating
operators from experiments and study the interplay between
dimension-five and -seven operators, discussing how dimension-seven
contributions affect the interpretation of in terms of the
effective Majorana mass .Comment: Matches version published in JHE
Compression creep of filamentary composites
Axial and transverse strain fields induced in composite laminates subjected to compressive creep loading were compared for several types of laminate layups. Unidirectional graphite/epoxy as well as multi-directional graphite/epoxy and graphite/PEEK layups were studied. Specimens with and without holes were tested. The specimens were subjected to compressive creep loading for a 10-hour period. In-plane displacements were measured using moire interferometry. A computer based data reduction scheme was developed which reduces the whole-field displacement fields obtained using moire to whole-field strain contour maps. Only slight viscoelastic response was observed in matrix-dominated laminates, except for one test in which catastrophic specimen failure occurred after a 16-hour period. In this case the specimen response was a complex combination of both viscoelastic and fracture mechanisms. No viscoelastic effects were observed for fiber-dominated laminates over the 10-hour creep time used. The experimental results for specimens with holes were compared with results obtained using a finite-element analysis. The comparison between experiment and theory was generally good. Overall strain distributions were very well predicted. The finite element analysis typically predicted slightly higher strain values at the edge of the hole, and slightly lower strain values at positions removed from the hole, than were observed experimentally. It is hypothesized that these discrepancies are due to nonlinear material behavior at the hole edge, which were not accounted for during the finite-element analysis
Future considerations in the diagnosis and treatment of compressive neuropathies of the upper extremity
Compressive neuropathies of the upper extremity are among the most common conditions seen by hand surgeons. The diagnoses of carpal tunnel syndrome and cubital tunnel syndrome have traditionally been made by a combination of history, physical examination, and electrodiagnostic testing. However, findings can be nonspecific and electrodiagnostic testing is invasive for the patient. The diagnosis of compressive neuropathies continues to evolve as technology advances, and newer diagnostic modalities predominantly focus on preoperative diagnostic imaging with ultrasound and magnetic resonance imaging/neurography. With the advent of cheaper, faster, and less invasive imaging, the future may bring a paradigm shift away from electrophysiology as the gold standard for the preoperative diagnosis of compressive neuropathies. Intraoperative imaging of nerve health is an emerging concept that warrants further investigation, whereas postoperative imaging of nerve recovery with ultrasound and magnetic resonance imaging currently has a limited role because of nonspecific findings and potential for misinterpretation. Advances in surgical treatment of compressive neuropathies appear to center around the use of imaging for less invasive neurolysis techniques and other adjunctive treatments with nerve decompression. The management of failed peripheral nerve decompressions and recurrent compressive neuropathies remains challenging
Question Generation from Concept Maps
In this paper we present a question generation approach suitable for tutorial dialogues. The approach is based on previous psychological theories that hypothesize questions are generated from a knowledge representation modeled as a concept map. Our model automatically extracts concept maps from a textbook and uses them to generate questions. The purpose of the study is to generate and evaluate pedagogically-appropriate questions at varying levels of specificity across one or more sentences. The evaluation metrics include scales from the Question Generation Shared Task and Evaluation Challenge and a new scale specific to the pedagogical nature of questions in tutoring
Seiberg Duality and e+ e- Experiments
Seiberg duality in supersymmetric gauge theories is the claim that two
different theories describe the same physics in the infrared limit. However,
one cannot easily work out physical quantities in strongly coupled theories and
hence it has been difficult to compare the physics of the electric and magnetic
theories. In order to gain more insight into the equivalence of two theories,
we study the ``e+ e-'' cross sections into ``hadrons'' for both theories in the
superconformal window. We describe a technique which allows us to compute the
cross sections exactly in the infrared limit. They are indeed equal in the
low-energy limit and the equality is guaranteed because of the anomaly matching
condition. The ultraviolet behavior of the total ``e+ e-'' cross section is
different for the two theories. We comment on proposed non-supersymmetric
dualities. We also analyze the agreement of the ``\gamma\gamma'' and ``WW''
scattering amplitudes in both theories, and in particular try to understand if
their equivalence can be explained by the anomaly matching condition.Comment: 24 pages, 2 figures, uses psfi
A neutrinoless double beta decay master formula from effective field theory
We present a master formula describing the neutrinoless-double-beta decay
() rate induced by lepton-number-violating (LNV) operators up
to dimension nine in the Standard Model Effective Field Theory. We provide an
end-to-end framework connecting the possibly very high LNV scale to the nuclear
scale, through a chain of effective field theories. Starting at the electroweak
scale, we integrate out the heavy Standard Model degrees of freedom and we
match to an effective theory. After
evolving the resulting effective Lagrangian to the QCD scale, we use chiral
perturbation theory to derive the lepton-number-violating chiral Lagrangian.
The chiral Lagrangian is used to derive the two-nucleon
transition operators to leading order in the chiral power counting. Based on
renormalization arguments we show that in various cases short-range two-nucleon
operators need to be enhanced to leading order. We show that all required
nuclear matrix elements can be taken from existing calculations. Our final
result is a master formula that describes the rate in terms of
phase-space factors, nuclear matrix elements, hadronic low-energy constants,
QCD evolution factors, and high-energy LNV Wilson coefficients, including all
the interference terms. Our master formula can be easily matched to any model
where LNV originates at energy scales above the electroweak scale. As an
explicit example, we match our formula to the minimal left-right-symmetric
model in which contributions of operators of different dimension compete, and
we discuss the resulting phenomenology.Comment: Published versio
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