178,337 research outputs found
Supersymmetric U(1) Gauge Realization of the Dark Scalar Doublet Model of Radiative Neutrino Mass
Adding a second scalar doublet (eta^+,eta^0) and three neutral singlet
fermions N_{1,2,3} to the Standard Model of particle interactions with a new
Z_2 symmetry, it has been shown that Re(eta^0) or Im(eta^0) is a good
dark-matter candidate and seesaw neutrino masses are generated radiatively. A
supersymmetric U(1) gauge extension of this new idea is proposed, which
enforces the usual R parity of the Minimal Supersymmetric Standard Model, and
allows this new Z_2 symmetry to emerge as a discrete remnant.Comment: 8 pages, 3 figure
Utility of a Special Second Scalar Doublet
This Brief Review deals with the recent resurgence of interest in adding a
second scalar doublet (eta^+,eta^0) to the Standard Model of particle
interactions. In most studies, it is taken for granted that eta^0 should have a
nonzero vacuum expectation value, even if it may be very small. What if there
is an exactly conserved symmetry which ensures =0? The phenomenological
ramifications of this idea include dark matter, radiative neutrino mass,
leptogenesis, and grand unification.Comment: 9 pages, 1 figur
Nearly Mass-Degenerate Majorana Neutrinos: Double Beta Decay and Neutrino Oscillations
Assuming equal tree-level Majorana masses for the standard-model neutrinos,
either from the canonical seesaw mechanism or from a heavy scalar triplet, I
discuss how their radiative splitting may be relevant to neutrinoless double
beta decay and neutrino oscillations.Comment: 12 pages, including 4 figures, talk at NANP9
Dynamic Model and Phase Transitions for Liquid Helium
This article presents a phenomenological dynamic phase transition theory --
modeling and analysis -- for superfluids. As we know, although the
time-dependent Ginzburg-Landau model has been successfully used in
superconductivity, and the classical Ginzburg-Landau free energy is still
poorly applicable to liquid helium in a quantitative sense. The study in this
article is based on 1) a new dynamic classification scheme of phase
transitions, 2) new time-dependent Ginzburg-Landau models for general
equilibrium transitions, and 3) the general dynamic transition theory. The
results in this article predict the existence of a unstable region H, where
both solid and liquid He II states appear randomly depending on fluctuations
and the existence of a switch point M on the lambda-curve, where the
transitions changes types
Singlet fermion dark matter and electroweak baryogenesis with radiative neutrino mass
The model of radiative neutrino mass with dark matter proposed by one of us
is extended to include a real singlet scalar field. There are then two
important new consequences. One is the realistic possibility of having the
lightest neutral singlet fermion (instead of the lightest neutral component of
the dark scalar doublet) as the dark matter of the Universe. The other is a
modification of the effective Higgs potential of the Standard Model, consistent
with electroweak baryogenesis.Comment: 9 pages, no figure
Solid-state interdiffusion reactions in Ni/Ti and Ni/Zr multilayered thin films
We have performed a comparative transmission electron microscopy study of solid-state interdiffusion reactions in multilayered Ni/Zr and Ni/Ti thin films. The Ni-Zr reaction product was amorphous while the Ni-Ti reaction product was a simple intermetallic compound. Because thermodynamic and chemical properties of these two alloy systems are similar, we suggest kinetic origins for this difference in reaction product
Frequency response in short thermocouple wires
Theoretical expressions are derived for the steady state frequency response of a thermocouple wire. In particular, the effects of axial heat conduction are demonstrated for a nonuniform wire with unequal material properties and wire diameters across the junction. The amplitude ratio at low frequency omega approaches 0 agrees with the results of Scadron and Warshawsky (1952) for a steady state temperature distribution. Moreover, the frequency response for a nonuniform wire in the limit of infinite length l approaches infinity is shown to reduce to a simple expression that is analogous to the classic first order solution for a thermocouple wire with uniform properties. Theoretical expressions are also derived for the steady state frequency response of a supported thermocouple wire. In particular, the effects of axial heat conduction are demonstrated for both a supported one material wire and a two material wire with unequal material properties across the junction. For the case of a one material supported wire, an exact solution is derived which compares favorably with an approximate expression that only matches temperatures at the support junction. Moreover, for the case of a two material supported wire, an analytical expression is derived that closely correlates numerical results. Experimental measurements are made for the steady state frequency response of a supported thermocouple wire. In particular, the effects of axial heat conduction are demonstrated for both a supported one material wire (type K) and a two material wire (type T) with unequal material properties across the junction. The data for the amplitude ratio and phase angle are correlated to within 10 pct. with the theoretical predictions of Forney and Fralick (1991). This is accomplished by choosing a natural frequency omega sub n for the wire data to correlate the first order response at large gas temperature frequencies. It is found that a large bead size, however, will increase the amplitude ratio at low frequencies but decrease the natural frequency of the wire. The phase angle data are also distorted for imperfect junctions
Thermal effects on lattice strain in hcp Fe under pressure
We compute the c/a lattice strain versus temperature for nonmagnetic hcp iron
at high pressures using both first-principles linear response quasiharmonic
calculations based on the full potential linear-muffin-tin-orbital (LMTO)
method and the particle-in-cell (PIC) model for the vibrational partition
function using a tight-binding total-energy method. The tight-binding model
shows excellent agreement with the all-electron LMTO method. When hcp structure
is stable, the calculated geometric mean frequency and Helmholtz free energy of
hcp Fe from PIC and linear response lattice dynamics agree very well, as does
the axial ratio as a function of temperature and pressure. On-site
anharmonicity proves to be small up to the melting temperature, and PIC gives a
good estimate of its sign and magnitude. At low pressures, hcp Fe becomes
dynamically unstable at large c/a ratios, and the PIC model might fail where
the structure approaches lattice instability. The PIC approximation describes
well the vibrational behavior away from the instability, and thus is a
reasonable approach to compute high temperature properties of materials. Our
results show significant differences from earlier PIC studies, which gave much
larger axial ratio increases with increasing temperature, or reported large
differences between PIC and lattice dynamics results.Comment: 9 figure
Nonlinear Dynamics in the Resonance Lineshape of NbN Superconducting Resonators
In this work we report on unusual nonlinear dynamics measured in the
resonance response of NbN superconducting microwave resonators. The nonlinear
dynamics, occurring at relatively low input powers (2-4 orders of magnitude
lower than Nb), and which include among others, jumps in the resonance
lineshape, hysteresis loops changing direction and resonance frequency shift,
are measured herein using varying input power, applied magnetic field, white
noise and rapid frequency sweeps. Based on these measurement results, we
consider a hypothesis according to which local heating of weak links forming at
the boundaries of the NbN grains are responsible for the observed behavior, and
we show that most of the experimental results are qualitatively consistent with
such hypothesis.Comment: Updated version (of cond-mat/0504582), 16 figure
High--Resolution 3D Simulations of Relativistic Jets
We have performed high-resolution 3D simulations of relativistic jets with
beam flow Lorentz factors up to 7, a spatial resolution of 8 cells per beam
radius, and for up to 75 normalized time units to study the morphology and
dynamics of 3D relativistic jets. Our simulations show that the coherent fast
backflows found in axisymmetric models are not present in 3D models. We further
find that when the jet is exposed to non-axisymmetric perturbations, (i) it
does not display the strong perturbations found for 3D classical hydrodynamic
and MHD jets (at least during the period of time covered by our simulations),
and (ii) it does propagate according to the 1D estimate. Small 3D effects in
the relativistic beam give rise to a lumpy distribution of apparent speeds like
that observed in M87. The beam is surrounded by a boundary layer of high
specific internal energy. The properties of this layer are briefly discussed.Comment: 15 pages, 4 figures. Accepted to be publish in the ApJ Letters.
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