56 research outputs found
Constraining General Two Higgs Doublet Models by the Evolution of Yukawa Couplings
We study how general two Higgs doublet models can be constrained by
considering their properties under renormalization group evolution of the
Yukawa couplings. We take into account both the appearance of a Landau pole as
well as off-diagonal Yukawa couplings leading to flavour changing neutral
currents in violation with experimental constraints at the electroweak scale.
We find that the latter condition can be used to limit the amount of Z2
symmetry breaking allowed in a given model.Comment: 28 pages, 10 figures, added discussion of evolution from high to low
scales, to be published in JHE
Renormalization scale uncertainty in tne DIS 2+1 jet cross-section
The deep inelastic scattering 2+1 jet cross- section is a useful observable
for precision tests of QCD, e.g. measuring the strong coupling constant
alpha(s). A consistent analysis requires a good understanding of the
theoretical uncertainties and one of the most fundamental ones in QCD is due to
the renormalization scheme and scale ambiguity. Different methods, which have
been proposed to resolve the scale ambiguity, are applied to the 2+1 jet
cross-section and the uncertainty is estimated. It is shown that the
uncertainty can be made smaller by choosing the jet definition in a suitable
way.Comment: 24 pages, uuencoded compressed tar file, DESY 94-082, TSL-ISV-94-009
Diffractive Higgs boson production at the Tevatron and LHC
Improved possibilities to find the Higgs boson in diffractive events, having
less hadronic activity, depend on whether the cross section is large enough.
Based on the soft color interaction models that successfully describe
diffractive hard scattering at HERA and the Tevatron, we find that only a few
diffractive Higgs events may be produced at the Tevatron, but we predict a
substantial rate at the LHC.Comment: 4 pages, 4 figures, uses Revtex
Tribimaximal Neutrino Mixing and a Relation Between Neutrino- and Charged Lepton-Mass Spectra
Brannen has recently pointed out that the observed charged lepton masses
satisfy the relation m_e +m_\mu +m_\tau = {2/3}
(\sqrt{m_e}+\sqrt{m_\mu}+\sqrt{m_\tau})^2, while the observed neutrino masses
satisfy the relation m_{\nu 1} +m_{\nu 2} +m_{\nu 3} = {2/3} (-\sqrt{m_{\nu
1}}+\sqrt{m_{\nu 2}}+\sqrt{m_{\nu 3}})^2. It is discussed what neutrino Yukawa
interaction form is favorable if we take the fact pointed out by Brannen
seriously.Comment: 13 pages, presentation modifie
Soft Color Interactions and Diffractive Hard Scattering at the Fermilab Tevatron
An improved understanding of nonperturbative QCD can be obtained by the
recently developed soft color interaction models. Their essence is the
variation of color string-field topologies, giving a unified description of
final states in high energy interactions, e.g., diffractive and nondiffractive
events in ep and ppbar. Here we present a detailed study of such models (the
soft color interaction model and the generalized area law model) applied to
ppbar, considering also the general problem of the underlying event including
beam particle remnants. With models tuned to HERA ep data, we find a good
description also of Tevatron data on production of W, beauty and jets in
diffractive events defined either by leading antiprotons or by one or two
rapidity gaps in the forward or backward regions. We also give predictions for
diffractive J/psi production where the soft exchange mechanism produces both a
gap and a color singlet ccbar state in the same event. This soft color
interaction approach is also compared with Pomeron-based models for
diffraction, and some possibilities to experimentally discriminate between
these different approaches are discussed.Comment: 35 pages, 15 figures, uses REVTeX. Minor changes, version to appear
in Phys. Rev.
New perturbation theory representation of the conformal symmetry breaking effects in gauge quantum field theory models
We propose a hypothesis on the detailed structure for the representation of
the conformal symmetry breaking term in the basic Crewther relation generalized
in the perturbation theory framework in QCD renormalized in the scheme. We establish the validity of this representation in the
approximation. Using the variant of the generalized Crewther
relation formulated here allows finding relations between specific
contributions to the QCD perturbation series coefficients for the flavor
nonsinglet part of the Adler function for the electron-positron
annihilation in hadrons and to the perturbation series coefficients for the
Bjorken sum rule for the polarized deep-inelastic lepton-nucleon
scattering. We find new relations between the coefficients of
and . Satisfaction of one of them serves as an
additional theoretical verification of the recent computer analytic
calculations of the terms of order in the expressions for these
two quantities.Comment: 12 pages, Title modified, abstract modified, improved and extended
variant of the talks, presented at Int. Seminar "Quarks-2010" (6-12 June,
2010, Kolomna) and Int. Workshop Hadron Structure and QCD: From Low to High
Energies (5-9 July 2010, Gatchina
On the Behavior of the Effective QCD Coupling alpha_tau(s) at Low Scales
The hadronic decays of the tau lepton can be used to determine the effective
charge alpha_tau(m^2_tau') for a hypothetical tau-lepton with mass in the range
0 < m_tau' < m_tau. This definition provides a fundamental definition of the
QCD coupling at low mass scales. We study the behavior of alpha_tau at low mass
scales directly from first principles and without any renormalization-scheme
dependence by looking at the experimental data from the OPAL Collaboration. The
results are consistent with the freezing of the physical coupling at mass
scales s = m^2_tau' of order 1 GeV^2 with a magnitude alpha_tau ~ 0.9 +/- 0.1.Comment: 15 pages, 4 figures, submitted to Physical Review D, added
references, some text added, no results nor figures change
The Two-Loop Scale Dependence of the Static QCD Potential including Quark Masses
The interaction potential V(Q^2) between static test charges can be used to
define an effective charge and a physically-based
renormalization scheme for quantum chromodynamics and other gauge theories. In
this paper we use recent results for the finite-mass fermionic corrections to
the heavy-quark potential at two-loops to derive the next-to-leading order term
for the Gell Mann-Low function of the V-scheme. The resulting effective number
of flavors in the scheme is determined as a
gauge-independent and analytic function of the ratio of the momentum transfer
to the quark pole mass. The results give automatic decoupling of heavy quarks
and are independent of the renormalization procedure. Commensurate scale
relations then provide the next-to-leading order connection between all
perturbatively calculable observables to the analytic and gauge-invariant
scheme without any scale ambiguity and a well defined number of
active flavors. The inclusion of the finite quark mass effects in the running
of the coupling is compared with the standard treatment of finite quark mass
effects in the scheme.Comment: 27 pages, 13 figure
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