110,357 research outputs found
Renormalization Scheme Ambiguities in the Models with More than One Coupling
The process of renormalization to eliminate divergences arising in quantum
field theory is not uniquely defined; one can always perform a finite
renormalization, rendering finite perturbative results ambiguous. The
consequences of making such finite renormalizations have been examined in the
case of there being one or two couplings. In this paper we consider how finite
renormalizations can affect more general models in which there are more than
two couplings. In particular, we consider the Standard Model in which there are
essentially five couplings. We show that in this model (when neglecting all
mass parameters) if we use mass independent renormalization, then the
renormalization group beta-functions are not unique beyond one loop order, that
it is not in general possible to eliminate all terms beyond certain order for
all these beta-functions, but that for a physical process all contributions
beyond one loop order can be subsumed into the beta-functions
Multiple Couplings and Renormalization Scheme Ambiguities
The ambiguities inherent in renormalization are considered when using
mass-independent renormalization in massless theories that involve two coupling
coupling constants. We review how there is no renormalization scheme in which
the beta-functions can be chosen to vanish beyond a certain order in
perturbation theory, but that the beta-functions always contain ambiguities
beyond first order. We examine how the coupling constants depend on the
coefficients of the beta-function beyond one loop order. A way of
characterizing renormalization schemes that doesn't use coefficients of the
beta-function is considered for models with either one or two couplings. The
renormalization scheme ambiguities of physical quantities computed to finite
order in perturbation theory are also examined. We demonstrate how summation of
the logarithms that have explicit dependence on the renormalization scale
parameter mu in a physical quantity R leads to a cancellation with the implicit
dependence of R on mu through the running couplings. It is also shown that
there exists a renormalization scheme in which all radiative effects beyond
lowest order are incorporated into the behaviour of the running couplings
Light Front Quantization with the Light Cone Gauge
The Dirac procedure for dealing with constraints is applied to the
quantization of gauge theories on the light front. The light cone gauge is used
in conjunction with the first class constraints that arise and the resulting
Dirac brackets are found. These gauge conditions are not used to eliminate
degrees of freedom from the action prior to applying the Dirac constraint
procedure. This approach is illustrated by considering Yang-Mills theory and
the superparticle in a 2 + 1 dimensional target space
Evidence for very strong electron-phonon coupling in YBa_{2}Cu_{3}O_{6}
From the observed oxygen-isotope shift of the mid-infrared two-magnon
absorption peak of YBaCuO, we evaluate the oxygen-isotope
effect on the in-plane antiferromagnetic exchange energy . The exchange
energy in YBaCuO is found to decrease by about 0.9% upon
replacing O by O, which is slightly larger than that (0.6%) in
LaCuO. From the oxygen-isotope effects, we determine the lower
limit of the polaron binding energy, which is about 1.7 eV for
YBaCuO and 1.5 eV for LaCuO, in quantitative
agreement with angle-resolved photoemission data, optical conductivity data,
and the parameter-free theoretical estimate. The large polaron binding energies
in the insulating parent compounds suggest that electron-phonon coupling should
also be strong in doped superconducting cuprates and may play an essential role
in high-temperature superconductivity.Comment: 4 pages, 1 figur
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Effects of natural soiling and weathering on cool roof energy savings for dormitory buildings in Chinese cities with hot summers
Roofs with high-reflectance (solar reflectance) coating, commonly known as cool roofs, can stay cool in the sun, thereby reducing building energy consumption and mitigating the urban heat island. However, chemical-physical degradation and biological growth can decrease their solar reflectance and the ability to save energy. In this study, the solar spectral reflectance of 12 different roofing products with an initial albedo of 0.56–0.90 was measured before exposure and once every three months over 32 months. Specimens were exposed on the roofs of dormitory buildings in Xiamen and Chengdu, each major urban areas with hot summers. The albedos of high and medium-lightness coatings stabilized in the ranges 0.45–0.62 and 0.36–0.59 in both cities, respectively. This study yielded albedo loss exceeded those reported in the latest Chinese standard by 0.08–0.15. Finally, DesignBuilder (EnergyPlus) simulations estimate that a new cool roof with albedo 0.78 on a six-story dormitory building will yield annual site energy savings (heating and cooling) for the top floor, which are 8.01 kWh/m2 (24.2%) and 9.12 kWh/m2 (26.3%) per unit floor area in Xiamen and Chengdu, respectively; while an aged cool roof with albedo 0.45 and 0.56 will yield the annual savings by 5.12 kWh/m2 (15.4%) and 2.47 kWh/m2 (10.5%) in these two cities
Kernel Regression For Determining Photometric Redshifts From Sloan Broadband Photometry
We present a new approach, kernel regression, to determine photometric
redshifts for 399,929 galaxies in the Fifth Data Release of the Sloan Digital
Sky Survey (SDSS). In our case, kernel regression is a weighted average of
spectral redshifts of the neighbors for a query point, where higher weights are
associated with points that are closer to the query point. One important design
decision when using kernel regression is the choice of the bandwidth. We apply
10-fold cross-validation to choose the optimal bandwidth, which is obtained as
the cross-validation error approaches the minimum. The experiments show that
the optimal bandwidth is different for diverse input patterns, the least rms
error of photometric redshift estimation arrives at 0.019 using color+eClass as
the inputs, the less rms error amounts to 0.020 using ugriz+eClass as the
inputs. Here eClass is a galaxy spectra type. Then the little rms scatter is
0.021 with color+r as the inputs.Comment: 6 pages,2 figures, accepted for publication in MNRA
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