6,852 research outputs found
Multi-parameter approach to R-parity violating SUSY couplings
We introduce and implement a new, extended approach to placing bounds on
trilinear R-parity violating couplings. We focus on a limited set of leptonic
and semi-leptonic processes involving neutrinos, combining multidimensional
plotting and cross-checking constraints from different experiments. This allows
us to explore new regions of parameter space and to relax a number of bounds
given in the literature. We look for qualitatively different results compared
to those obtained previously using the assumption that a single coupling
dominates the R-parity violating contributions to a process (SCD). By combining
results from several experiments, we identify regions in parameter space where
two or more parameters approach their maximally allowed values. In the same
vein, we show a circumstance where consistency between independent bounds on
the same combinations of trilinear coupling parameters implies mass constraints
among slepton or squark masses. Though our new bounds are in most cases weaker
than the SCD bounds, the largest deviations we find on individual parameters
are factors of two, thus indicating that a conservative, order of magnitude
bound on an individual coupling is reliably estimated by making the SCD
assumption.Comment: 30 pages, 8 figures, 2 tables. Typos fixed, two references added and
references updated. Eq. (41) removed, Eq. (40) and text modified. Published
versio
Centralizers of maximal regular subgroups in simple Lie groups and relative congruence classes of representations
In the paper we present a new, uniform and comprehensive description of
centralizers of the maximal regular subgroups in compact simple Lie groups of
all types and ranks. The centralizer is either a direct product of finite
cyclic groups, a continuous group of rank 1, or a product, not necessarily
direct, of a continuous group of rank 1 with a finite cyclic group. Explicit
formulas for the action of such centralizers on irreducible representations of
the simple Lie algebras are given.Comment: 27 page
Accessibility of the resources of near Earth space using multi-impulse transfers
Most future concepts for exploration and exploitation of space require a large initial mass in low Earth orbit. Delivering this mass requires overcoming Earth's natural gravity well, which imposes a distinct obstacle to space-faring. An alternative for future space progress is to search for resources in-situ among the near Earth asteroid population. This paper examines the scenario of future utilization of asteroid resources. The near Earth asteroid resources that could be transferred to a bound Earth orbit are determined by integrating the probability of finding asteroids inside the Keplerian orbital element space of the set of transfers with an specific energy smaller than a given threshold. Transfers are defined by a series of impulsive maneuvers and computed using the patched-conic approximation. The results show that even moderately low energy transfers enable access to a large mass of resources
Electric-field noise from carbon-adatom diffusion on a Au(110) surface: first-principles calculations and experiments
The decoherence of trapped-ion quantum gates due to heating of their motional
modes is a fundamental science and engineering problem. This heating is
attributed to electric-field noise arising from the trap-electrode surfaces. In
this work, we investigate the source of this noise by focusing on the diffusion
of carbon-containing adsorbates on the surface of Au(110). We show by density
functional theory, based on detailed scanning probe microscopy, how the carbon
adatom diffusion on the gold surface changes the energy landscape, and how the
adatom dipole moment varies with the diffusive motion. A simple model for the
diffusion noise, which varies quadratically with the variation of the dipole
moment, qualitatively reproduces the measured noise spectrum, and the estimate
of the noise spectral density is in accord with measured values.Comment: 8 pages, 6 figure
The solar maximum satellite capture cell: Impact features and orbital debris and micrometeoritic projectile materials
The physical properties of impact features observed in the Solar Max main electronics box (MEB) thermal blanket generally suggest an origin by hypervelocity impact. The chemistry of micrometeorite material suggests that a wide variety of projectile materials have survived impact with retention of varying degrees of pristinity. Impact features that contain only spacecraft paint particles are on average smaller than impact features caused by micrometeorite impacts. In case both types of materials co-occur, it is belevied that the impact feature, generally a penetration hole, was caused by a micrometeorite projectile. The typically smaller paint particles were able to penetrate though the hole in the first layer and deposit in the spray pattern on the second layer. It is suggested that paint particles have arrived with a wide range of velocities relative to the Solar Max satellite. Orbiting paint particles are an important fraction of materials in the near-Earth environment. In general, the data from the Solar Max studies are a good calibration for the design of capture cells to be flown in space and on board Space Station. The data also suggest that development of multiple layer capture cells in which the projectile may retain a large degree of pristinity is a feasible goal
The Generation of Fullerenes
We describe an efficient new algorithm for the generation of fullerenes. Our
implementation of this algorithm is more than 3.5 times faster than the
previously fastest generator for fullerenes -- fullgen -- and the first program
since fullgen to be useful for more than 100 vertices. We also note a
programming error in fullgen that caused problems for 136 or more vertices. We
tabulate the numbers of fullerenes and IPR fullerenes up to 400 vertices. We
also check up to 316 vertices a conjecture of Barnette that cubic planar graphs
with maximum face size 6 are hamiltonian and verify that the smallest
counterexample to the spiral conjecture has 380 vertices.Comment: 21 pages; added a not
Discovery of Five Binary Radio Pulsars
We report on five binary pulsars discovered in the Parkes multibeam Galactic
plane survey. All of the pulsars are old, with characteristic ages 1-11 Gyr,
and have relatively small inferred magnetic fields, 5-90e8 G. The orbital
periods range from 1.3 to 15 days. As a group these objects differ from the
usual low-mass binary pulsars (LMBPs): their spin periods of 9-88 ms are
relatively long; their companion masses, 0.2-1.1 Msun, are, in at least some
cases, suggestive of CO or more massive white dwarfs; and some of the orbital
eccentricities, 1e-5 < e < 0.002, are unexpectedly large. We argue that these
observed characteristics reflect binary evolution that is significantly
different from that of LMBPs. We also note that intermediate-mass binary
pulsars apparently have a smaller scale-height than LMBPs.Comment: 5 pages, 4 embedded EPS figs, accepted for publication by ApJ Letter
Making Sense of the Legendre Transform
The Legendre transform is an important tool in theoretical physics, playing a
critical role in classical mechanics, statistical mechanics, and
thermodynamics. Yet, in typical undergraduate or graduate courses, the power of
motivation and elegance of the method are often missing, unlike the treatments
frequently enjoyed by Fourier transforms. We review and modify the presentation
of Legendre transforms in a way that explicates the formal mathematics,
resulting in manifestly symmetric equations, thereby clarifying the structure
of the transform algebraically and geometrically. Then we bring in the physics
to motivate the transform as a way of choosing independent variables that are
more easily controlled. We demonstrate how the Legendre transform arises
naturally from statistical mechanics and show how the use of dimensionless
thermodynamic potentials leads to more natural and symmetric relations.Comment: 11 pages, 3 figure
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