117,124 research outputs found
Effective Field calculations of the Energy Spectrum of the -Symmetric () Potential
In this work, we show that the traditional effective field approach can be
applied to the -symmetric wrong sign () quartic
potential. The importance of this work lies in the possibility of its extension
to the more important -symmetric quantum field theory while the
other approaches which use complex contours are not willing to be applicable.
We calculated the effective potential of the massless theory as well
as the full spectrum of the theory. Although the calculations are carried out
up to first order in the coupling, the predicted spectrum is very close to the
exact one taken from other works. The most important result of this work is
that the effective potential obtained, which is equivalent to the Gaussian
effective potential, is bounded from below while the classical potential is
bounded from above. This explains the stability of the vacuum of the theory.
The obtained quasi-particle Hamiltonian is non-Hermitian but
-symmetric and we showed that the calculation of the metric
operator can go perturbatively. In fact, the calculation of the metric operator
can be done even for higher dimensions (quantum field theory) which, up till
now, can not be calculated in the other approaches either perturbatively or in
a closed form due to the possible appearance of field radicals. Moreover, we
argued that the effective theory is perturbative for the whole range of the
coupling constant and the perturbation series is expected to converge rapidly
(the effective coupling ).Comment: 14 pages, 5 figure
Non-Empirically Tuned Range-Separated DFT Accurately Predicts Both Fundamental and Excitation Gaps in DNA and RNA Nucleobases
Using a non-empirically tuned range-separated DFT approach, we study both the
quasiparticle properties (HOMO-LUMO fundamental gaps) and excitation energies
of DNA and RNA nucleobases (adenine, thymine, cytosine, guanine, and uracil).
Our calculations demonstrate that a physically-motivated, first-principles
tuned DFT approach accurately reproduces results from both experimental
benchmarks and more computationally intensive techniques such as many-body GW
theory. Furthermore, in the same set of nucleobases, we show that the
non-empirical range-separated procedure also leads to significantly improved
results for excitation energies compared to conventional DFT methods. The
present results emphasize the importance of a non-empirically tuned
range-separation approach for accurately predicting both fundamental and
excitation gaps in DNA and RNA nucleobases.Comment: Accepted by the Journal of Chemical Theory and Computatio
Calculating two- and three-body decays with FeynArts and FormCalc
The Feynman diagram generator FeynArts and the computer algebra program
FormCalc allow for an automatic computation of 2->2 and 2->3 scattering
processes in High Energy Physics. We have extended this package by four new
kinematical routines and adapted one existing routine in order to accomodate
also two- and three-body decays of massive particles. This makes it possible to
compute automatically two- and three-body particle decay widths and decay
energy distributions as well as resonant particle production within the
Standard Model and the Minimal Supersymmetric Standard Model at the tree- and
loop-level. The use of the program is illustrated with three standard examples:
h->b\bar{b}, \mu->e\bar{\nu}_e\nu_\mu, and Z->\nu_e\bar{\nu}_e.Comment: 8 pages, 1 figur
The spatial structure of networks
We study networks that connect points in geographic space, such as
transportation networks and the Internet. We find that there are strong
signatures in these networks of topography and use patterns, giving the
networks shapes that are quite distinct from one another and from
non-geographic networks. We offer an explanation of these differences in terms
of the costs and benefits of transportation and communication, and give a
simple model based on the Monte Carlo optimization of these costs and benefits
that reproduces well the qualitative features of the networks studied.Comment: 5 pages, 3 figure
Optimal design of spatial distribution networks
We consider the problem of constructing public facilities, such as hospitals,
airports, or malls, in a country with a non-uniform population density, such
that the average distance from a person's home to the nearest facility is
minimized. Approximate analytic arguments suggest that the optimal distribution
of facilities should have a density that increases with population density, but
does so slower than linearly, as the two-thirds power. This result is confirmed
numerically for the particular case of the United States with recent population
data using two independent methods, one a straightforward regression analysis,
the other based on density dependent map projections. We also consider
strategies for linking the facilities to form a spatial network, such as a
network of flights between airports, so that the combined cost of maintenance
of and travel on the network is minimized. We show specific examples of such
optimal networks for the case of the United States.Comment: 6 pages, 5 figure
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