359,192 research outputs found
Gravitino dark matter from gluino late decay in split supersymmetry
In split-supersymmetry (split-SUSY), gluino is a metastable particle and thus
can freeze out in the early universe. The late decay of such a long-life gluino
into the lightest supersymmetric particle (LSP) may provide much of the cosmic
dark matter content. In this work, assuming the LSP is gravitino produced from
the late decay of the metastable gluino, we examine the WMAP dark matter
constraints on the gluino mass. We find that to provide the full abundance of
dark matter, the gluino must be heavier than about 14 TeV and thus not
accessible at the CERN Large Hadron Collider (LHC).Comment: discussions added (version in PRD
Phase transition from hadronic matter to quark matter
We study the phase transition from nuclear matter to quark matter within the
SU(3) quark mean field model and NJL model. The SU(3) quark mean field model is
used to give the equation of state for nuclear matter, while the equation of
state for color superconducting quark matter is calculated within the NJL
model. It is found that at low temperature, the phase transition from nuclear
to color superconducting quark matter will take place when the density is of
order 2.5 - 5. At zero density, the quark phase will appear
when the temperature is larger than about 148 MeV. The phase transition from
nuclear matter to quark matter is always first order, whereas the transition
between color superconducting quark matter and normal quark matter is second
order.Comment: 18 pages, 11 figure
Liquid-gas phase transition in nuclear matter including strangeness
We apply the chiral SU(3) quark mean field model to study the properties of
strange hadronic matter at finite temperature. The liquid-gas phase transition
is studied as a function of the strangeness fraction. The pressure of the
system cannot remain constant during the phase transition, since there are two
independent conserved charges (baryon and strangeness number). In a range of
temperatures around 15 MeV (precise values depending on the model used) the
equation of state exhibits multiple bifurcates. The difference in the
strangeness fraction between the liquid and gas phases is small when they
coexist. The critical temperature of strange matter turns out to be a
non-trivial function of the strangeness fraction.Comment: 15 pages, 7 figure
The GAP-TPC
Several experiments have been conducted worldwide, with the goal of observing
low-energy nuclear recoils induced by WIMPs scattering off target nuclei in
ultra-sensitive, low-background detectors. In the last few decades noble liquid
detectors designed to search for dark matter in the form of WIMPs have been
extremely successful in improving their sensitivities and setting the best
limits. One of the crucial problems to be faced for the development of large
size (multi ton-scale) liquid argon experiments is the lack of reliable and low
background cryogenic PMTs: their intrinsic radioactivity, cost, and borderline
performance at 87 K rule them out as a possible candidate for photosensors. We
propose a brand new concept of liquid argon-based detector for direct dark
matter search: the Geiger-mode Avalanche Photodiode Time Projection Chamber
(GAP-TPC) optimized in terms of residual radioactivity of the photosensors,
energy and spatial resolution, light and charge collection efficiencyComment: 7 pages, 5 figures, Accepted for publication on JINS
Competing Quantum Orderings in Cuprate Superconductors: A Minimal Model
We present a minimal model for cuprate superconductors. At the unrestricted
mean-field level, the model produces homogeneous superconductivity at large
doping, striped superconductivity in the underdoped regime and various
antiferromagnetic phases at low doping and for high temperatures. On the
underdoped side, the superconductor is intrinsically inhomogeneous and global
phase coherence is achieved through Josephson-like coupling of the
superconducting stripes. The model is applied to calculate experimentally
measurable ARPES spectra.Comment: 5 pages, 4 eps included figure
Topological code Autotune
Many quantum systems are being investigated in the hope of building a
large-scale quantum computer. All of these systems suffer from decoherence,
resulting in errors during the execution of quantum gates. Quantum error
correction enables reliable quantum computation given unreliable hardware.
Unoptimized topological quantum error correction (TQEC), while still effective,
performs very suboptimally, especially at low error rates. Hand optimizing the
classical processing associated with a TQEC scheme for a specific system to
achieve better error tolerance can be extremely laborious. We describe a tool
Autotune capable of performing this optimization automatically, and give two
highly distinct examples of its use and extreme outperformance of unoptimized
TQEC. Autotune is designed to facilitate the precise study of real hardware
running TQEC with every quantum gate having a realistic, physics-based error
model.Comment: 13 pages, 17 figures, version accepted for publicatio
Fabrication of Embedded Microvalve on PMMA Microfluidic Devices through Surface Functionalization
The integration of a PDMS membrane within orthogonally placed PMMA
microfluidic channels enables the pneumatic actuation of valves within bonded
PMMA-PDMS-PMMA multilayer devices. Here, surface functionalization of PMMA
substrates via acid catalyzed hydrolysis and air plasma corona treatment were
investigated as possible techniques to permanently bond PMMA microfluidic
channels to PDMS surfaces. FTIR and water contact angle analysis of
functionalized PMMA substrates showed that air plasma corona treatment was most
effective in inducing PMMA hydrophilicity. Subsequent fluidic tests showed that
air plasma modified and bonded PMMA multilayer devices could withstand fluid
pressure at an operational flow rate of 9 mircoliters/min. The pneumatic
actuation of the embedded PDMS membrane was observed through optical microscopy
and an electrical resistance based technique. PDMS membrane actuation occurred
at pneumatic pressures of as low as 10kPa and complete valving occurred at
14kPa for 100 micrometers x 100 micrometers channel cross-sections.Comment: Submitted on behalf of EDA Publishing Association
(http://irevues.inist.fr/handle/2042/16838
Defending against Sybil Devices in Crowdsourced Mapping Services
Real-time crowdsourced maps such as Waze provide timely updates on traffic,
congestion, accidents and points of interest. In this paper, we demonstrate how
lack of strong location authentication allows creation of software-based {\em
Sybil devices} that expose crowdsourced map systems to a variety of security
and privacy attacks. Our experiments show that a single Sybil device with
limited resources can cause havoc on Waze, reporting false congestion and
accidents and automatically rerouting user traffic. More importantly, we
describe techniques to generate Sybil devices at scale, creating armies of
virtual vehicles capable of remotely tracking precise movements for large user
populations while avoiding detection. We propose a new approach to defend
against Sybil devices based on {\em co-location edges}, authenticated records
that attest to the one-time physical co-location of a pair of devices. Over
time, co-location edges combine to form large {\em proximity graphs} that
attest to physical interactions between devices, allowing scalable detection of
virtual vehicles. We demonstrate the efficacy of this approach using
large-scale simulations, and discuss how they can be used to dramatically
reduce the impact of attacks against crowdsourced mapping services.Comment: Measure and integratio
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