71 research outputs found
Exponentially Modified QCD Coupling
We present a specific class of models for an infrared-finite analytic QCD
coupling, such that at large space-like energy scales the coupling differs from
the perturbative one by less than any inverse power of the energy scale. This
condition is motivated by the ITEP Operator Product Expansion philosophy.
Allowed by the ambiguity in the analytization of the perturbative coupling, the
proposed class of couplings has three parameters. In the intermediate energy
region, the proposed coupling has low loop-level and renormalization scheme
dependence. The present modification of perturbative QCD must be considered as
a phenomenological attempt, with the aim of enlarging the applicability range
of the theory of the strong interactions at low energies.Comment: two references adde
Neutrino Mixing Predictions of a Minimal SO(10) Model with Suppressed Proton Decay
During the past year, a minimal renormalizable supersymmetric SO(10) model
has been proposed with the following properties: it predicts a naturally stable
dark matter and neutrino mixing angles theta_atm and theta_13 while at the same
time accommodating CKM CP violation among quarks with no SUSY CP problem.
Suppression of proton decay for all allowed values of tan beta strongly
restricts the flavor structure of the model making it predictive for other
processes as well. We discuss the following predictions of the model in this
paper, e.g. down-type quark masses, and neutrino oscillation parameters, U_e3,
delta_MNSP, which will be tested by long baseline experiments such as T2K and
subsequent experiments using the neutrino beam from JPARC. We also calculate
lepton flavor violation and the lepton asymmetry of the Universe in this model.Comment: 22 pages, 11 figure
SUSY dark matter and lepton flavor violation
We study lepton flavor-violating (LFV) processes within a supersymmetric
type-I seesaw framework with flavor-blind universal boundary conditions,
properly accounting for the effect of the neutrino sector on the dark matter
relic abundance. We consider several possibilities for the neutrino Yukawa
coupling matrix and show that in regions of SUSY parameter space that yield the
correct neutralino relic density, LFV rates can differ from naive estimates by
up to two orders of magnitude. Contrary to common belief, we find that current
LFV limits do not exclude neutrino Yukawa couplings larger than top Yukawa
couplings. We introduce the ISAJET-M program that was used for the
computations.Comment: 37 pages, 9 figures, 6 tables. Version to appear in PR
Decays of Scalar and Pseudoscalar Higgs Bosons into Fermions: Two-loop QCD Corrections to the Higgs-Quark-Antiquark Amplitude
As a first step in the aim of arriving at a differential description of
neutral Higgs boson decays into heavy quarks, , to second
order in the QCD coupling , we have computed the
amplitude at the two-loop level in QCD for a general neutral Higgs boson which
has both scalar and pseudoscalar couplings to quarks. This amplitude is given
in terms of a scalar and a pseudoscalar vertex form factor, for which we
present closed analytic expressions in terms of one-dimensional harmonic
polylogarithms of maximum weight 4. The results hold for arbitrary
four-momentum squared, , of the Higgs boson and of the heavy quark mass,
. Moreover we derive the approximate expressions of these form factors near
threshold and in the asymptotic regime .Comment: 56 pages, 2 figure
New Uncertainties in QCD-QED Rescaling Factors using Quadrature Method
In this paper we briefly outline the quadrature method for estimating
uncertainties in a function of several variables and apply it to estimate the
numerical uncertainties in QCD-QED rescaling factors. We employ here the
one-loop order in QED and three-loop order in QCD evolution equations of
fermion mass renormalization. Our present calculations are found to be new and
also reliable compared to the earlier values employed by various authors.Comment: 14 page
Supersymmetric Higgs Yukawa Couplings to Bottom Quarks at next-to-next-to-leading Order
The effective bottom Yukawa couplings are analyzed for the minimal
supersymmetric extension of the Standard Model at two-loop accuracy within
SUSY-QCD. They include the resummation of the dominant corrections for large
values of tg(beta). In particular the two-loop SUSY-QCD corrections to the
leading SUSY-QCD and top-induced SUSY-electroweak contributions are addressed.
The residual theoretical uncertainties range at the per-cent level.Comment: 25 pages, 9 figures, added comments and references, typos corrected,
results unchanged, published versio
Low-energy gluon contributions to the vacuum polarization of heavy quarks
We calculate a correction to the electromagnetic current induced by a heavy
quark loop. The contribution of this correction to the vacuum polarization
function appears at the O(alpha_s^3) order of perturbation theory and has a
qualitatively new feature -- its absorptive part starts at zero energy in
contrast to other contributions where the absorptive parts start at the
two-particle threshold. Our result imposes a constraint on the order n of the
moments used in the heavy-quark sum rules, n<4.Comment: 8 pages in LaTeX, 1 PostScript figure included in the tex
Wilson Expansion of QCD Propagators at Three Loops: Operators of Dimension Two and Three
In this paper we construct the Wilson short distance operator product
expansion for the gluon, quark and ghost propagators in QCD, including
operators of dimension two and three, namely, A^2, m^2, m A^2, \ovl{\psi} \psi
and m^3. We compute analytically the coefficient functions of these operators
at three loops for all three propagators in the general covariant gauge. Our
results, taken in the Landau gauge, should help to improve the accuracy of
extracting the vacuum expectation values of these operators from lattice
simulation of the QCD propagators.Comment: 20 pages, no figure
A New Algorithm For The Generation Of Unitarity-Compatible Integration By Parts Relations
Many multi-loop calculations make use of integration by parts relations to
reduce the large number of complicated Feynman integrals that arise in such
calculations to a simpler basis of master integrals. Recently, Gluza, Kajda,
and Kosower argued that the reduction to master integrals is complicated by the
presence of integrals with doubled propagator denominators in the integration
by parts relations and they introduced a novel reduction procedure which
eliminates all such integrals from the start. Their approach has the advantage
that it automatically produces integral bases which mesh well with generalized
unitarity. The heart of their procedure is an algorithm which utilizes the
weighty machinery of computational commutative algebra to produce complete sets
of unitarity-compatible integration by parts relations. In this paper, we
propose a conceptually simpler algorithm for the generation of complete sets of
unitarity-compatible integration by parts relations based on recent results in
the mathematical literature. A striking feature of our algorithm is that it can
be described entirely in terms of straightforward linear algebra.Comment: 20 pages; My apologies to Krzysztof Kajda for misspelling his name in
v1; in v3: the labeling of the variables in (4.5) and eqs. (4.20) and (4.21)
was adjusted to match the notation used in the rest of Section 4. I thank
York Schroeder for pointing out the notational inconsistenc
A New Model for Fermion Masses in Supersymmetric Grand Unified Theories
We present a simple model for fermion mass matrices and quark mixing in the
context of supersymmetric grand unified theories and show its agreement with
experiment. Our model realizes the GUT mass relations , , in a new way and is easily consistent with values of
suggested by MSSM fits to LEP data.Comment: Latex, 8 p., ITP-SB-93-37 (revised version contains minor changes in
some wording and citations; no changes in analytic or numerical results.
- …