13,130 research outputs found
General solution of an exact correlation function factorization in conformal field theory
We discuss a correlation function factorization, which relates a three-point
function to the square root of three two-point functions. This factorization is
known to hold for certain scaling operators at the two-dimensional percolation
point and in a few other cases. The correlation functions are evaluated in the
upper half-plane (or any conformally equivalent region) with operators at two
arbitrary points on the real axis, and a third arbitrary point on either the
real axis or in the interior. This type of result is of interest because it is
both exact and universal, relates higher-order correlation functions to
lower-order ones, and has a simple interpretation in terms of cluster or loop
probabilities in several statistical models. This motivated us to use the
techniques of conformal field theory to determine the general conditions for
its validity.
Here, we discover a correlation function which factorizes in this way for any
central charge c, generalizing previous results. In particular, the
factorization holds for either FK (Fortuin-Kasteleyn) or spin clusters in the
Q-state Potts models; it also applies to either the dense or dilute phases of
the O(n) loop models. Further, only one other non-trivial set of highest-weight
operators (in an irreducible Verma module) factorizes in this way. In this case
the operators have negative dimension (for c < 1) and do not seem to have a
physical realization.Comment: 7 pages, 1 figure, v2 minor revision
Custodial Isospin Violation in the Lee-Wick Standard Model
We analyze the tension between naturalness and isospin violation in the
Lee-Wick Standard Model (LW SM), by computing tree-level and fermionic one-loop
contributions to the post-LEP electroweak parameters and the Zbb coupling. The
model is most natural when the LW partners of the gauge bosons and fermions are
light, but small partner masses can lead to large isospin violation. The
post-LEP parameters yield a simple picture in the LW SM: the gauge sector
contributes to Y and W only, with leading contributions arising at tree-level,
while the fermion sector contributes to S-hat and T-hat only, with leading
corrections arising at one loop. Hence, W and Y constrain the masses of the LW
gauge bosons to satisfy M1, M2 > 2.4 TeV at 95% CL. Likewise, experimental
limits on T-hat reveal that the masses of the LW fermions must satisfy Mq, Mt >
1.6 TeV at 95% CL if the Higgs mass is light and tend to exclude the LW SM for
any LW fermion masses if the Higgs mass is heavy. Contributions from the
top-quark sector to the Zbb coupling can be even more stringent, placing a
lower bound of 4 TeV on the LW fermion masses at 95% CL.Comment: 16 pages, 8 embedded eps figure
First-principles thermoelasticity of bcc iron under pressure
We investigate the elastic and isotropic aggregate properties of
ferromagnetic bcc iron as a function of temperature and pressure by computing
the Helmholtz free energies for the volume-conserving strained structures using
the first-principles linear response linear-muffin-tin-orbital method and the
generalized-gradient approximation. We include the electronic excitation
contributions to the free energy from the band structures, and phonon
contributions from quasi-harmonic lattice dynamics. We make detailed
comparisons between our calculated elastic moduli and their temperature and
pressure dependences with available experimental and theoretical data.Comment: 5 figures, 2 table
Measurement of temperature profiles in hot gases and flames
Computer program was written for calculation of molecular radiative transfer from hot gases. Shape of temperature profile was approximated in terms of simple geometric forms so profile could be characterized in terms of few parameters. Parameters were adjusted in calculations using appropriate radiative-transfer expression until best fit was obtained with observed spectra
The Flavor Structure of the Three-Site Higgsless Model
We study the flavor structure of the three-site Higgsless model and evaluate
the constraints on the model arising from flavor physics. We find that current
data constrain the model to exhibit only minimal flavor violation at tree
level. Moreover, at the one-loop level, by studying the leading chiral
logarithmic corrections to chirality-preserving Delta F = 1 and Delta F = 2
processes from new physics in the model, we show that the combination of
minimal flavor violation and ideal delocalization ensures that these
flavor-changing effects are sufficiently small that the model remains
phenomenologically viable.Comment: 23 pages, 22 pdf figures include
Encapsulation of phosphorus dopants in silicon for the fabrication of a quantum computer
The incorporation of phosphorus in silicon is studied by analyzing phosphorus
delta-doped layers using a combination of scanning tunneling microscopy,
secondary ion mass spectrometry and Hall effect measurements. The samples are
prepared by phosphine saturation dosing of a Si(100) surface at room
temperature, a critical annealing step to incorporate phosphorus atoms, and
subsequent epitaxial silicon overgrowth. We observe minimal dopant segregation
(5 nm), complete electrical activation at a silicon growth temperature of 250
degrees C and a high two-dimensional electron mobility of 100 cm2/Vs at a
temperature of 4.2 K. These results, along with preliminary studies aimed at
further minimizing dopant diffusion, bode well for the fabrication of
atomically precise dopant arrays in silicon such as those found in recent
solid-state quantum computer architectures.Comment: 3 pages, 4 figure
Low-Energy Effective Theory, Unitarity, and Non-Decoupling Behavior in a Model with Heavy Higgs-Triplet Fields
We discuss the properties of a model incorporating both a scalar electroweak
Higgs doublet and an electroweak Higgs triplet. We construct the low-energy
effective theory for the light Higgs-doublet in the limit of small (but
nonzero) deviations in the rho parameter from one, a limit in which the triplet
states become heavy. For small deviations in the rho parameter from one,
perturbative unitarity of WW scattering breaks down at a scale inversely
proportional to the renormalized vacuum expectation value of the triplet field
(or, equivalently, inversely proportional to the square-root of the deviation
of the rho parameter from one). This result imposes an upper limit on the
mass-scale of the heavy triplet bosons in a perturbative theory; we show that
this upper bound is consistent with dimensional analysis in the low-energy
effective theory. Recent articles have shown that the triplet bosons do not
decouple, in the sense that deviations in the rho parameter from one do not
necessarily vanish at one-loop in the limit of large triplet mass. We clarify
that, despite the non-decoupling behavior of the Higgs-triplet, this model does
not violate the decoupling theorem since it incorporates a large dimensionful
coupling. Nonetheless, we show that if the triplet-Higgs boson masses are of
order the GUT scale, perturbative consistency of the theory requires the
(properly renormalized) Higgs-triplet vacuum expectation value to be so small
as to be irrelevant for electroweak phenomenology.Comment: Revtex, 11 pages, 7 eps figures included; references updated and
three footnotes adde
The St. James walkway study
Prior to the opening of the St James Walkway in 1981, David Simmons of the Department of
Parks, Recreation and Tourism at Lincoln College, proposed a five year research programme
to the New Zealand Walkways Commission. This proposal took advantage of the 1981
opening to initiate a longitudinal study which could identify any subsequent changes in use
or use impacts on the Walkway. The general aims of this research were to:
(i) Describe the user population of the Walkway and any changes to it over the study
period;
(ii) Describe the role played by the Walkway in the recreation life histories of users; and
(iii) Identify any physical impacts from use that occurred following the opening of the
new track.
This paper presents a compilation, summary and assessment of data gathered from the
research programme
Recreation demand estimation in New Zealand : An example of the Kaimanawa and Kaweka Forest Parks
This paper is in two parts. The first examines methods of recreation resource evaluation while the second uses an existing data base to discuss the potential applications of one such method in New Zealand.
The specific objectives of the report are:
1. To discuss common economic methods of resource valuation, highlighting both their limitations, and potential contributions to the land use debate.
2. To demonstrate the use of one of these methods in valuing a New Zealand recreational resource
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