580 research outputs found
Refined gluino and squark pole masses beyond leading order
The physical pole and running masses of squarks and gluinos have recently
been related at two-loop order in a mass-independent renormalization scheme. I
propose a general method for improvement of such formulas, and argue that
better accuracy results. The improved version gives an imaginary part of the
pole mass that agrees exactly with the direct calculation of the physical width
at next-to-leading order. I also find the leading three-loop contributions to
the gluino pole mass in the case that squarks are heavier, using effective
field theory and renormalization group methods. The efficacy of these
improvements for the gluino and squarks is illustrated with numerical examples.
Some necessary three-loop results for gauge coupling and fermion mass beta
functions and pole masses in theories with more than one type of fermion
representation, which are not directly accessible from the published
literature, are presented in an Appendix.Comment: 14 pages. v2: typos in equations (A.11), (A.17), and (A.18) fixe
Two-loop scalar self-energies and pole masses in a general renormalizable theory with massless gauge bosons
I present the two-loop self-energy functions for scalar bosons in a general
renormalizable theory, within the approximation that vector bosons are treated
as massless or equivalently that gauge symmetries are unbroken. This enables
the computation of the two-loop physical pole masses of scalar particles in
that approximation. The calculations are done simultaneously in the
mass-independent \bar{MS}, \bar{DR}, and \bar{DR}' renormalization schemes, and
with arbitrary covariant gauge fixing. As an example, I present the two-loop
SUSYQCD corrections to squark masses, which can increase the known one-loop
results by of order one percent. More generally, it is now straightforward to
implement all two-loop sfermion pole mass computations in supersymmetry using
the results given here, neglecting only the electroweak vector boson masses
compared to the superpartner masses in the two-loop parts.Comment: 16 pages, 4 figures. v2: typo in eq. (5.30) fixe
Numerical evaluation of the general massive 2-loop 4-denominator self-mass master integral from differential equations
The differential equation in the external invariant p^2 satisfied by the
master integral of the general massive 2-loop 4-denominator self-mass diagram
is exploited and the expansion of the master integral at p^2=0 is obtained
analytically. The system composed by this differential equation with those of
the master integrals related to the general massive 2-loop sunrise diagram is
numerically solved by the Runge-Kutta method in the complex p^2 plane. A
numerical method to obtain results for values of p^2 at and close to thresholds
and pseudo-thresholds is discussed in details.Comment: Latex, 20 pages, 7 figure
Strong and Yukawa two-loop contributions to Higgs scalar boson self-energies and pole masses in supersymmetry
I present results for the two-loop self-energy functions for neutral and
charged Higgs scalar bosons in minimal supersymmetry. The contributions given
here include all terms involving the QCD coupling, and those following from
Feynman diagrams involving Yukawa couplings and scalar interactions that do not
vanish as the electroweak gauge couplings are turned off. The impact of these
contributions on the computation of pole masses of the neutral and charged
Higgs scalar bosons is studied in a few examples.Comment: 23 pages, 9 figures, revtex4. New paragraph in introduction, more
explanation of Figure
Master integrals for the two-loop light fermion contributions to and
We give the analytic expressions of the eight master integrals entering our
previous computation of two-loop light fermion contributions to and
. The results are expressed in terms of generalized
harmonic polylogarithms with maximum weight four included.Comment: 9 pages, 6 figure
Neuroconductor: an R platform for medical imaging analysis
Neuroconductor (https://neuroconductor.org) is an open-source platform for rapid testing and dissemination of reproducible computational imaging software. The goals of the project are to: (i) provide a centralized repository of R software dedicated to image analysis, (ii) disseminate software updates quickly, (iii) train a large, diverse community of scientists using detailed tutorials and short courses, (iv) increase software quality via automatic and manual quality controls, and (v) promote reproducibility of image data analysis. Based on the programming language R (https://www.r-project.org/), Neuroconductor starts with 51 inter-operable packages that cover multiple areas of imaging including visualization, data processing and storage, and statistical inference. Neuroconductor accepts new R package submissions, which are subject to a formal review and continuous automated testing. We provide a description of the purpose of Neuroconductor and the user and developer experience
A FLEXIBLE GENERAL CLASS OF MARGINAL AND CONDITIONAL RANDOM INTERCEPT MODELS FOR BINARY OUTCOMES USING MIXTURES OF NORMALS
Random intercept models for binary data are useful tools for addressing between subject heterogeneity. Unlike linear models, the non-linearity of link functions used for binary data force a distinction between marginal and conditional interpretations. This distinction is blurred in probit models with a normally distributed random intercept because the resulting model implies a probit marginal link as well. That is, this model is closed in the sense that the distribution associated with the marginal and conditional link functions and the random effect distribution are all of the same family. In this manuscript we explore another family of random intercept models with this property. In particular, we consider instances when the distributions associated with the conditional and marginal link functions and the random effect distribution are mixtures of normals. We show that this flexible family of models is related to several others presented in the literature. Moreover, we also show that this family of models offers considerable computational benefits. A diverse series of examples illustrates the wide applicability of the approach
Two-Loop Bhabha Scattering in QED
In the context of pure QED, we obtain analytic expressions for the
contributions to the Bhabha scattering differential cross section at order
alpha^4 which originate from the interference of two-loop photonic vertices
with tree-level diagrams and from the interference of one-loop photonic
diagrams amongst themselves. The ultraviolet renormalization is carried out.
The IR-divergent soft-photon emission corrections are evaluated and added to
the virtual cross section. The cross section obtained in this manner is valid
for on-shell electrons and positrons of finite mass, and for arbitrary values
of the center of mass energy and momentum transfer. We provide the expansion of
our results in powers of the electron mass, and we compare them with the
corresponding expansion of the complete order alpha^4 photonic cross section,
recently obtained in hep-ph/0501120. As a by-product, we obtain the
contribution to the Bhabha scattering differential cross section of the
interference of the two-loop photonic boxes with the tree-level diagrams, up to
terms suppressed by positive powers of the electron mass. We evaluate
numerically the various contributions to the cross section, paying particular
attention to the comparison between exact and expanded results.Comment: 35 pages, 18 figure
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