146,032 research outputs found
Annotated List of Stoneflies (Plecoptera) from Stebbins Gulch in Northeastern Ohio
(excerpt)
Stebbins Gulch is situated within property owned by The Holden Arboretum in northwestern Geauga County, Ohio, approximately 8.0 km east of the village of Kirtland (Fig. 1). Physiographically, the Arboretum is included within the Southern New York Section of the Appalachian Plateau Province (Feldman et al., 1977). This Section was overridden by several advances of Pleistocene glaciation, the latest of which receded some 13,000 years ago. It is characterized by poorly drained surfaces containing many bogs, ponds, and lakes, except near the Portage Escarpment where small rivers have excavated relatively deep valleys
Quantum fields, dark matter and non-standard Wigner classes
The Elko field of Ahluwalia and Grumiller is a quantum field for massive
spin-1/2 particles. It has been suggested as a candidate for dark matter. We
discuss our attempts to interpret the Elko field as a quantum field in the
sense of Weinberg. Our work suggests that one should investigate quantum fields
based on representations of the full Poincar\'e group which belong to one of
the non-standard Wigner classes.Comment: 6 pages. Submitted to proceedings of Dark2009, Christchurch, New
Zealand, January 200
How to squeeze the toothpaste back into the tube
We consider "bridges" for the simple exclusion process on Z, either symmetric
or asymmetric, in which particles jump to the right at rate p and to the left
at rate 1-p. The initial state O has all negative sites occupied and all
non-negative sites empty. We study the probability that the process is again in
state O at time t, and the behaviour of the process on [0,t] conditioned on
being in state O at time t. In the case p=1/2, we find that such a bridge
typically goes a distance of order t (in the sense of graph distance) from the
initial state. For the asymmetric systems, we note an interesting duality which
shows that bridges with parameters p and 1-p have the same distribution; the
maximal distance of the process from the original state behaves like c(p)log(t)
for some constant c(p) depending on p. (For p>1/2, the front particle therefore
travels much less far than the bridge of the corresponding random walk, even
though in the unconditioned process the path of the front particle dominates a
random walk.) We mention various further questions.Comment: 15 page
Conditions for Equality between Lyapunov and Morse Decompositions
Let be a continuous principal bundle whose group is
reductive. A flow of automorphisms of endowed with an ergodic
probability measure on the compact base space induces two decompositions of
the flag bundles associated to . A continuous one given by the finest Morse
decomposition and a measurable one furnished by the Multiplicative Ergodic
Theorem. The second is contained in the first. In this paper we find necessary
and sufficient conditions so that they coincide. The equality between the two
decompositions implies continuity of the Lyapunov spectra under pertubations
leaving unchanged the flow on the base space
Dirac Triplet Extension of the MSSM
In this paper we explore extensions of the Minimal Supersymmetric Standard
Model involving two triplet chiral superfields that share a
superpotential Dirac mass yet only one of which couples to the Higgs fields.
This choice is motivated by recent work using two singlet superfields with the
same superpotential requirements. We find that, as in the singlet case, the
Higgs mass in the triplet extension can easily be raised to
without introducing large fine-tuning. For triplets that carry hypercharge, the
regions of least fine tuning are characterized by small contributions to the
parameter, and light stop squarks, ; the latter is a result of the dependence of
the triplet contribution to the Higgs mass. Despite such light stop masses,
these models are viable provided the stop-electroweakino spectrum is
sufficiently compressed.Comment: 26 pages, 4 figure
Exact and Fast Numerical Algorithms for the Stochastic Wave Equation
On the basis of integral representations we propose fast numerical methods to solve the Cauchy problem for the stochastic wave equation without boundaries and with the Dirichlet boundary conditions. The algorithms are exact in a probabilistic sense
Stationary distributions of multi-type totally asymmetric exclusion processes
We consider totally asymmetric simple exclusion processes with n types of
particle and holes (-TASEPs) on and on the cycle . Angel recently gave an elegant construction of the stationary measures
for the 2-TASEP, based on a pair of independent product measures. We show that
Angel's construction can be interpreted in terms of the operation of a
discrete-time queueing server; the two product measures correspond to
the arrival and service processes of the queue. We extend this construction to
represent the stationary measures of an n-TASEP in terms of a system of queues
in tandem. The proof of stationarity involves a system of n 1-TASEPs, whose
evolutions are coupled but whose distributions at any fixed time are
independent. Using the queueing representation, we give quantitative results
for stationary probabilities of states of the n-TASEP on , and
simple proofs of various independence and regeneration properties for systems
on .Comment: Published at http://dx.doi.org/10.1214/009117906000000944 in the
Annals of Probability (http://www.imstat.org/aop/) by the Institute of
Mathematical Statistics (http://www.imstat.org
The Bose gas beyond mean field
We study a homogeneous Bose gas with purely repulsive forces. Using the Kac
scaling of the binary potential we derive analytically the form of the
thermodynamic functions of the gas for small but finite values of the scaling
parameter in the low density regime. In this way we determine dominant
corrections to the mean-field theory. It turns out that repulsive forces
increase the pressure at fixed density and decrease the density at given
chemical potential (the temperature is kept constant). They also flatten the
Bose momentum distribution. However, the present analysis cannot be extended to
the region where the mean-field theory predicts the appearence of condensate.Comment: 19 pages, 3 figure
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