6,376 research outputs found
Goldilocks Supersymmetry: Simultaneous Solution to the Dark Matter and Flavor Problems of Supersymmetry
Neutralino dark matter is well motivated, but also suffers from two
shortcomings: it requires gravity-mediated supersymmetry breaking, which
generically violates flavor constraints, and its thermal relic density \Omega
is typically too large. We propose a simple solution to both problems:
neutralinos freezeout with \Omega ~10-100, but then decay to ~1 GeV gravitinos,
which are simultaneously light enough to satisfy flavor constraints and heavy
enough to be all of dark matter. This scenario is naturally realized in
high-scale gauge-mediation models, ameliorates small scale structure problems,
and implies that ``cosmologically excluded'' models may, in fact, be
cosmologically preferred.Comment: 4 pages; v2: references added; v3: published versio
Minimal Supergravity with m_0^2 < 0
We extend the parameter space of minimal supergravity to negative values of
m_0^2, the universal scalar mass parameter defined at the grand unified scale.
After evolving to the weak scale, all scalars can be non-tachyonic with masses
consistent with collider constraints. This region of parameter space is
typically considered excluded by searches for charged dark matter, since the
lightest standard model superpartner is a charged slepton. However, if the
gravitino is the lightest supersymmetric particle, the charged slepton decays,
and this region is allowed. This region provides qualitatively new
possibilities for minimal supergravity, including spectra with light sleptons
and very heavy squarks, and models in which the lightest slepton is the
selectron. We show that the m_0^2 < 0 region is consistent with low energy
precision data and discuss its implications for particle colliders. These
models may provide signals of supersymmetry in even the first year of operation
at the Large Hadron Collider.Comment: 16 page
SuperWIMP Cosmology and Collider Physics
Dark matter may be composed of superWIMPs, superweakly-interacting massive
particles produced in the late decays of other particles. We focus here on the
well-motivated supersymmetric example of gravitino LSPs. Gravitino superWIMPs
share several virtues with the well-known case of neutralino dark matter: they
are present in the same supersymmetric frameworks (supergravity with R-parity
conservation) and naturally have the desired relic density. In contrast to
neutralinos, however, gravitino superWIMPs are impossible to detect by
conventional dark matter searches, may explain an existing discrepancy in Big
Bang nucleosynthesis, predict observable distortions in the cosmic microwave
background, and imply spectacular signals at future particle colliders.Comment: 12 pages, to appear in the proceedings of SUSY2004, the 12th
International Conference on Supersymmetry and Unification of Fundamental
Interactions, Tsukuba, Japan, 17-23 June 200
Collider Signatures of SuperWIMP Warm Dark Matter
SuperWeakly-Interacting Massive Particles (superWIMPs) produced in the late
decays of other particles are well-motivated dark matter candidates and may be
favored over standard Weakly-Interacting Massive Particles (WIMPs) by small
scale structure observations. Among the most promising frameworks that
incorporate superWIMPs are R-parity conserving supersymmetry models in which
the lightest supersymmetric particle (LSP) is the gravitino or the axino. In
these well-defined particle models, astrophysical observations have direct
implications for possible measurements at future colliders.Comment: Contributed to the 2005 International Linear Collider Physics and
Detector Workshop and 2nd ILC Accelerator Workshop, Snowmass, Colorado, 14-27
Aug 2005. 3 pages, LaTeX, 1 figur
MAGICCARPET: Verified Detection and Recovery for Hardware-based Exploits
Abstract—MAGICCARPET is a new approach to defending systems against exploitable processor bugs. MAGICCARPET uses hardware to detect violations of invariants involving security-critical processor state and uses firmware to correctly push software’s state past the violations. The invariants are specified at run time. MAGICCARPET focuses on dynamically validating updates to security-critical processor state. In this work, (1) we generate correctness proofs for both MAGICCARPET hardware and firmware; (2) we prove that processor state and events never violate our security invariants at runtime; and (3) we show that MAGICCARPET copes with hardware-based exploits discovered post-fabrication using a combination of verified reconfigurations of invariants in the fabric and verified recoveries via reprogrammable software. We implement MAGICCARPET inside a popular open source processor on an FPGA platform. We evaluate MAGICCARPET using a diverse set of hardware-based attacks based on escaped and exploitable commercial processor bugs. MAGICCARPET is able to detect and recover from all tested attacks with no software run-time overhead in the attack-free case
Early-type stars observed in the ESO UVES Paranal Observatory Project - V. Time-variable interstellar absorption
The structure and properties of the diffuse interstellar medium (ISM) on
small scales, sub-au to 1 pc, are poorly understood. We compare interstellar
absorption-lines, observed towards a selection of O- and B-type stars at two or
more epochs, to search for variations over time caused by the transverse motion
of each star combined with changes in the structure in the foreground ISM. Two
sets of data were used: 83 VLT- UVES spectra with approximately 6 yr between
epochs and 21 McDonald observatory 2.7m telescope echelle spectra with 6 - 20
yr between epochs, over a range of scales from 0 - 360 au. The interstellar
absorption-lines observed at the two epochs were subtracted and searched for
any residuals due to changes in the foreground ISM. Of the 104 sightlines
investigated with typically five or more components in Na I D, possible
temporal variation was identified in five UVES spectra (six components), in Ca
II, Ca I and/or Na I absorption-lines. The variations detected range from 7\%
to a factor of 3.6 in column density. No variation was found in any other
interstellar species. Most sightlines show no variation, with 3{\sigma} upper
limits to changes of the order 0.1 - 0.3 dex in Ca II and Na I. These
variations observed imply that fine-scale structure is present in the ISM, but
at the resolution available in this study, is not very common at visible
wavelengths. A determination of the electron densities and lower limits to the
total number density of a sample of the sightlines implies that there is no
striking difference between these parameters in sightlines with, and sightlines
without, varying components.Comment: 19 pages, 11 figures, accepted for publication in MNRA
The Development of the WISE (Writing to Inspire Successful Education) Writing Mentoring Program: A University-School Collaboration
Abstract
This paper describes the development of a service learning writing mentoring program designed to close the achievement gap in writing proficiency for economically disadvantaged seventh grade students. Compared to writing mentoring studies found in the published literature, this program has three distinguishing components. First, it focused on economically disadvantaged middle school students. Second, it provided writing mentoring through a university-school partnership in which college students provided the intervention in collaboration with a seventh-grade teacher. Third, the program used technology to facilitate the mentoring process. Over the course of an academic year, mentors created videos with feedback on 19 writing assignments. The writing mentoring program was associated with a four-fold increase in the percentage of students who were graded as ‘proficient’ on a state standardized writing exam. These results suggest that semi-virtual, intensive writing mentoring and individualized feedback from college students can close the achievement gap and improve the quality of middle level education provided to economically disadvantaged students
3D fault architecture controls the dynamism of earthquake swarms
The vibrant evolutionary patterns made by earthquake swarms are incompatible with standard, effectively two-dimensional (2D) models for general fault architecture. We leverage advances in earthquake monitoring with a deep-learning algorithm to image a fault zone hosting a 4-year-long swarm in southern California. We infer that fluids are naturally injected into the fault zone from below and diffuse through strike-parallel channels while triggering earthquakes. A permeability barrier initially limits up-dip swarm migration but ultimately is circumvented. This enables fluid migration within a shallower section of the fault with fundamentally different mechanical properties. Our observations provide high-resolution constraints on the processes by which swarms initiate, grow, and arrest. These findings illustrate how swarm evolution is strongly controlled by 3D variations in fault architecture
3D fault architecture controls the dynamism of earthquake swarms
The vibrant evolutionary patterns made by earthquake swarms are incompatible with standard, effectively two-dimensional (2D) models for general fault architecture. We leverage advances in earthquake monitoring with a deep-learning algorithm to image a fault zone hosting a 4-year-long swarm in southern California. We infer that fluids are naturally injected into the fault zone from below and diffuse through strike-parallel channels while triggering earthquakes. A permeability barrier initially limits up-dip swarm migration but ultimately is circumvented. This enables fluid migration within a shallower section of the fault with fundamentally different mechanical properties. Our observations provide high-resolution constraints on the processes by which swarms initiate, grow, and arrest. These findings illustrate how swarm evolution is strongly controlled by 3D variations in fault architecture
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