2,368 research outputs found
Holographic Electroweak Symmetry Breaking from D-branes
We observe several interesting phenomena in a technicolor-like model of
electroweak symmetry breaking based on the D4-D8-D8bar system of Sakai and
Sugimoto. The benefit of holographic models based on D-brane configurations is
that both sides of the holographic duality are well understood. We find that
the lightest technicolor resonances contribute negatively to the
Peskin-Takeuchi S-parameter, but heavy resonances do not decouple and lead
generically to large, positive values of S, consistent with standard estimates
in QCD-like theories. We study how the S parameter and the masses and decay
constants of the vector and axial-vector techni-resonances vary over a
one-parameter family of D8-brane configurations. We discuss possibilities for
the consistent truncation of the theory to the first few resonances and suggest
some generic predictions of stringy holographic technicolor models.Comment: REVTeX, 25 pages, 8 eps figures, version published in PR
Large-scale multielectrode recording and stimulation of neural activity
Large circuits of neurons are employed by the brain to encode and process information. How this encoding and processing is carried out is one of the central questions in neuroscience. Since individual neurons communicate with each other through electrical signals (action potentials), the recording of neural activity with arrays of extracellular electrodes is uniquely suited for the investigation of this question. Such recordings provide the combination of the best spatial (individual neurons) and temporal (individual action-potentials) resolutions compared to other large-scale imaging methods. Electrical stimulation of neural activity in turn has two very important applications: it enhances our understanding of neural circuits by allowing active interactions with them, and it is a basis for a large variety of neural prosthetic devices. Until recently, the state-of-the-art in neural activity recording systems consisted of several dozen electrodes with inter-electrode spacing ranging from tens to hundreds of microns. Using silicon microstrip detector expertise acquired in the field of high-energy physics, we created a unique neural activity readout and stimulation framework that consists of high-density electrode arrays, multi-channel custom-designed integrated circuits, a data acquisition system, and data-processing software. Using this framework we developed a number of neural readout and stimulation systems: (1) a 512-electrode system for recording the simultaneous activity of as many as hundreds of neurons, (2) a 61-electrode system for electrical stimulation and readout of neural activity in retinas and brain-tissue slices, and (3) a system with telemetry capabilities for recording neural activity in the intact brain of awake, naturally behaving animals. We will report on these systems, their various applications to the field of neurobiology, and novel scientific results obtained with some of them. We will also outline future directions
Search for Heavy Leptons at Hadron Colliders
Four models are considered which contain heavy leptons beyond the three
families of the standard model. Two are fourth-generation extensions of the
standard model in which the right-handed heavy leptons are either isosinglets
or in an isodoublet; the other two are motivated by the aspon model of CP
violation. In all these models, the heavy neutrino can either be heavier than,
or comparable in mass to, the charged lepton leading to the possibility that
the charged lepton is very long-lived. Production cross section and signatures
for the heavy leptons are computed for the SSC and LHC.Comment: 17 pages(8 figures are not included),TRI-PP-92-9
Search for Intermediate Mass Magnetic Monopoles and Nuclearites with the SLIM experiment
SLIM is a large area experiment (440 m2) installed at the Chacaltaya cosmic
ray laboratory since 2001, and about 100 m2 at Koksil, Himalaya, since 2003. It
is devoted to the search for intermediate mass magnetic monopoles (107-1013
GeV/c2) and nuclearites in the cosmic radiation using stacks of CR39 and
Makrofol nuclear track detectors. In four years of operation it will reach a
sensitivity to a flux of about 10-15 cm-2 s-1 sr-1. We present the results of
the calibration of CR39 and Makrofol and the analysis of a first sample of the
exposed detector.Comment: Presented at the 22nd ICNTS, Barcelona 200
Is diversity good?
Prominent ethical and policy issues such as affirmative action and female
enrollment in science and engineering revolve around the idea that diversity is
good. However, even though diversity is an ambiguous concept, a precise
definition is seldom provided. We show that diversity may be construed as a
factual description, a craving for symmetry, an intrinsic good, an instrumental
good, a symptom, or a side effect. These acceptions differ vastly in their
nature and properties. The first one cannot lead to any action and the second
one is mistaken. Diversity as intrinsic good is a mere opinion, which cannot be
concretely applied; moreover, the most commonly invoked forms of diversity
(sexual and racial) are not intrinsically good. On the other hand, diversity as
instrumental good can be evaluated empirically and can give rise to policies,
but these may be very weak. Finally, symptoms and side effects are not actually
about diversity. We consider the example of female enrollment in science and
engineering, interpreting the various arguments found in the literature in
light of this polysemy.
Keywords: ethics, policy, higher education, female students, minority
students, affirmative actionComment: 7 page
An Improved upper limit on the decay K^+ -> pi^+ mu^+ e^-
Based on results of a search for the lepton-family-number-violating decay
with data collected by experiment E865 at the
Alternating Gradient Synchrotron of Brookhaven National Laboratory, we place an
upper limit on the branching ratio at (90% C.L.).
Combining the results with earlier E865 data and those of a previous
experiment, E777, an upper limit on the branching ratio of (90% C.L.) is obtained.Comment: v2: 13 pages, submitted to the Phys. Rev. D v3: 13 pages, resubmitted
to Phys. Rev. D (corrections include: a more detailed overview of the
combined analysis of the available experimntal data
Higgs and Dark Matter Hints of an Oasis in the Desert
Recent LHC results suggest a standard model (SM)-like Higgs boson in the
vicinity of 125 GeV with no clear indications yet of physics beyond the SM. At
the same time, the SM is incomplete, since additional dynamics are required to
accommodate cosmological dark matter (DM). In this paper we show that
interactions between weak scale DM and the Higgs which are strong enough to
yield a thermal relic abundance consistent with observation can easily
destabilize the electroweak vacuum or drive the theory into a non-perturbative
regime at a low scale. As a consequence, new physics--beyond the DM
itself--must enter at a cutoff well below the Planck scale and in some cases as
low as O(10 - 1000 TeV), a range relevant to indirect probes of flavor and CP
violation. In addition, this cutoff is correlated with the DM mass and
scattering cross-section in a parameter space which will be probed
experimentally in the near term. Specifically, we consider the SM plus
additional spin 0 or 1/2 states with singlet, triplet, or doublet electroweak
quantum numbers and quartic or Yukawa couplings to the Higgs boson. We derive
explicit expressions for the full two-loop RGEs and one-loop threshold
corrections for these theories.Comment: 29 pages, 13 figure
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