12,529 research outputs found
Higgs bosons of a supersymmetric model at the ILC
We study the scalar Higgs sector of the next-to-minimal supersymmetric
standard model with an extra U(1), which has two Higgs doublets and a Higgs
singlet, in the light leptophobic scenario where the extra neutral gauge
boson does not couple to charged leptons. In this model, we find that the
sum of the squared coupling coefficients of the three neutral scalar Higgs
bosons to , normalized by the corresponding SM coupling coefficient is
noticeably smaller than unity, due to the effect of the extra U(1), for a
reasonable parameter space of the model, whereas it is unity in the
next-to-minimal supersymmetric standard model. Thus, these two models may be
distinguished if the coupling coefficients of neutral scalar Higgs bosons to
are measured at the future International Linear Collider by producing them
via the Higgs-strahlung, fusion, and fusion processes.Comment: 12 pages, 2 figures, 1 table, PR
Axial anomaly and magnetism of nuclear and quark matter
We consider the response of the QCD ground state at finite baryon density to
a strong magnetic field B. We point out the dominant role played by the
coupling of neutral Goldstone bosons, such as pi^0, to the magnetic field via
the axial triangle anomaly. We show that, in vacuum, above a value of B ~
m_pi^2/e, a metastable object appears - the pi^0 domain wall. Because of the
axial anomaly, the wall carries a baryon number surface density proportional to
B. As a result, for B ~ 10^{19} G a stack of parallel pi^0 domain walls is
energetically more favorable than nuclear matter at the same density.
Similarly, at higher densities, somewhat weaker magnetic fields of order B ~
10^{17}-10^{18} G transform the color-superconducting ground state of QCD into
new phases containing stacks of axial isoscalar (eta or eta') domain walls. We
also show that a quark-matter state known as ``Goldstone current state,'' in
which a gradient of a Goldstone field is spontaneously generated, is
ferromagnetic due to the axial anomaly. We estimate the size of the fields
created by such a state in a typical neutron star to be of order
10^{14}-10^{15} G.Comment: 18 pages, v2: added a discussion of the energy cost of neutralizing
the domain wall charg
Clustering of vacancy defects in high-purity semi-insulating SiC
Positron lifetime spectroscopy was used to study native vacancy defects in
semi-insulating silicon carbide. The material is shown to contain (i) vacancy
clusters consisting of 4--5 missing atoms and (ii) Si vacancy related
negatively charged defects. The total open volume bound to the clusters
anticorrelates with the electrical resistivity both in as-grown and annealed
material. Our results suggest that Si vacancy related complexes compensate
electrically the as-grown material, but migrate to increase the size of the
clusters during annealing, leading to loss of resistivity.Comment: 8 pages, 5 figure
Real-time pion propagation in finite-temperature QCD
We argue that in QCD near the chiral limit, at all temperatures below the
chiral phase transition, the dispersion relation of soft pions can be expressed
entirely in terms of three temperature-dependent quantities: the pion screening
mass, a pion decay constant, and the axial isospin susceptibility. The
definitions of these quantities are given in terms of equal-time (static)
correlation functions. Thus, all three quantities can be determined directly by
lattice methods. The precise meaning of the Gell-Mann--Oakes--Renner relation
at finite temperature is given.Comment: 25 pages, 2 figures; v2: discussion on the region of applicability
expanded, to be published in PR
Characterizing HMX/AP Cocrystal Propellant Through Planar Laser Induced Fluorescence
Energetic cocrystals, or energetic materials that consist of two or more components that form a unique crystalline structure with unique properties, are currently being investigated as a possible method for decreasing the sensitivity of high energy density explosives for use in powerful solid composite propellants. Fuels more powerful than those in current use have not been practical because of their increased safety hazard due to higher sensitivity to being ignited. This has been one of the barriers that has prevented solid composite propellants from seeing significant improvements in performance. This study is an attempt to characterize a cocrystal of HMX and ammonium perchlorate (AP) of 2:3 molar mass ratio. The cocrystal was compared to the equivalent physical mix and baseline propellants of HMX and AP. Planar laser induced fluorescence (PLIF) was performed to measure hydroxyl (OH) concentrations in the propellants’ flames. It appeared that the flame structure of the cocrystal was very similar to that of HMX, as well as the distribution of OH concentrations around the flame. The results were inconclusive, and it is believed that the cocrystal’s constituents were not sufficiently bonded at the molecular level; thus, the cocrystal was instead more a mixture of smaller individual crystals of HMX and AP. Future research could include cocrystals created by varying methods, and perform cyano (CN) PLIF to characterize these cocrystals, which may display a better defined region of interest in the flame that can be more closely studied and answer more questions
Development of a telescope for medium-energy gamma-ray astronomy
The Advanced Energetic Pair Telescope (AdEPT) is being developed at GSFC as a future NASA MIDEX mission to explore the medium-energy (5–200 MeV) gamma-ray range. The enabling technology for AdEPT is the Three- Dimensional Track Imager (3-DTI), a gaseous time projection chamber. The high spatial resolution 3-D electron tracking of 3-DTI enables AdEPT to achieve high angular resolution gamma-ray imaging via pair production and triplet production (pair production on electrons) in the medium-energy range. The low density and high spatial resolution of 3-DTI allows the electron positron track directions to be measured before they are dominated by Coulomb scattering. Further, the significant reduction of Coulomb scattering allows AdEPT to be the first medium-energy gamma-ray telescope to have high gamma-ray polarization sensitivity. We review the science goals that can be addressed with a medium-energy pair telescope, how these goals drive the telescope design, and the realization of this design with AdEPT. The AdEPT telescope for a future MIDEX mission is envisioned as a 8 m3 active volume filled with argon at 2 atm. The design and performance of the 3-DTI detectors for the AdEPT telescope are described as well as the outstanding instrument challenges that need to be met for the AdEPT mission
Trick or Heat? Manipulating Critical Temperature-Based Control Systems Using Rectification Attacks
Temperature sensing and control systems are widely used in the closed-loop
control of critical processes such as maintaining the thermal stability of
patients, or in alarm systems for detecting temperature-related hazards.
However, the security of these systems has yet to be completely explored,
leaving potential attack surfaces that can be exploited to take control over
critical systems.
In this paper we investigate the reliability of temperature-based control
systems from a security and safety perspective. We show how unexpected
consequences and safety risks can be induced by physical-level attacks on
analog temperature sensing components. For instance, we demonstrate that an
adversary could remotely manipulate the temperature sensor measurements of an
infant incubator to cause potential safety issues, without tampering with the
victim system or triggering automatic temperature alarms. This attack exploits
the unintended rectification effect that can be induced in operational and
instrumentation amplifiers to control the sensor output, tricking the internal
control loop of the victim system to heat up or cool down. Furthermore, we show
how the exploit of this hardware-level vulnerability could affect different
classes of analog sensors that share similar signal conditioning processes.
Our experimental results indicate that conventional defenses commonly
deployed in these systems are not sufficient to mitigate the threat, so we
propose a prototype design of a low-cost anomaly detector for critical
applications to ensure the integrity of temperature sensor signals.Comment: Accepted at the ACM Conference on Computer and Communications
Security (CCS), 201
Cooper pairing near charged black holes
We show that a quartic contact interaction between charged fermions can lead
to Cooper pairing and a superconducting instability in the background of a
charged asymptotically Anti-de Sitter black hole. For a massless fermion we
obtain the zero mode analytically and compute the dependence of the critical
temperature T_c on the charge of the fermion. The instability we find occurs at
charges above a critical value, where the fermion dispersion relation near the
Fermi surface is linear. The critical temperature goes to zero as the marginal
Fermi liquid is approached, together with the density of states at the Fermi
surface. Besides the charge, the critical temperature is controlled by a four
point function of a fermionic operator in the dual strongly coupled field
theory.Comment: 1+33 pages, 4 figure
On the sign of the dilaton in the soft wall models
We elaborate on the existence of a spurious massless scalar mode in the
vector channel of soft-wall models with incorrectly chosen sign of the
exponential profile defining the wall. We re-iterate the point made in our
earlier paper and demonstrate that the presence of the mode is robust,
depending only on the infra-red asymptotics of the wall. We also re-emphasize
that desired confinement properties can be realized with the correct sign
choice.Comment: 10 page
- …