307 research outputs found
Cosmological Sign of Neutrino CP Violation
It is shown how, in a class of models, the sign of the baryon number of the
universe can be related to CP violation in neutrino oscillation experiments.Comment: 3 pages LaTe
Measurement of the Higgs Boson Mass with a Linear e+e- Collider
The potential of a linear e+e- collider operated at a centre-of-mass energy
of 350 GeV is studied for the measurement of the Higgs boson mass. An
integrated luminosity of 500 fb-1 is assumed. For Higgs boson masses of 120,
150 and 180 GeV the uncertainty on the Higgs boson mass measurement is
estimated to be 40, 65 and 70 MeV, respectively. The effects of beam related
systematics, namely a bias in the beam energy measurement, the beam energy
spread and the luminosity spectrum due to beamstrahlung, on the precision of
the Higgs boson mass measurement are investigated. In order to keep the
systematic uncertainty on the Higgs boson mass well below the level of the
statistical error, the beam energy measurement must be controlled with a
relative precision better than 10-4.Comment: 19 pages, 10 Figure
D-Terms, Unification, and the Higgs Mass
We study gauge extensions of the MSSM that contain non-decoupling D-terms,
which contribute to the Higgs boson mass. These models naturally maintain gauge
coupling unification and raise the Higgs mass without fine-tuning. Unification
constrains the structure of the gauge extensions, limiting the Higgs mass in
these models to roughly less than 150 GeV. The D-terms contribute to the Higgs
mass only if the extended gauge symmetry is broken at energies of a few TeV,
leading to new heavy gauge bosons in this mass range.Comment: 30+1 pages, 7 figure
model for the electroweak interactions
Assuming the existence of right-handed neutrinos, we consider an electroweak
model based on the gauge symmetry . We study the neutral
currents coupled to all neutral vector bosons present in the theory. There are
no flavor changing neutral currents at tree level, coupled with the lightest
neutral vector boson.Comment: Revtex 11 pages, preprint IFT-P.003/9
Distinguishable RGE running effects between Dirac neutrinos and Majorana neutrinos with vanishing Majorana CP-violating phases
In a novel parametrization of neutrino mixing and in the approximation of
-lepton dominance, we show that the one-loop renormalization-group
equations (RGEs) of Dirac neutrinos are different from those of Majorana
neutrinos even if two Majorana CP-violating phases vanish. As the latter can
keep vanishing from the electroweak scale to the typical seesaw scale, it makes
sense to distinguish between the RGE running effects of neutrino mixing
parameters in Dirac and Majorana cases. The differences are found to be quite
large in the minimal supersymmetric standard model with sizable ,
provided the masses of three neutrinos are nearly degenerate or have an
inverted hierarchy.Comment: 12 pages, 5 figure
Upper Bound on the Mass of the Type III Seesaw Triplet in an SU(5) Model
We investigate correlation between gauge coupling unification, fermion mass
spectrum, proton decay, perturbativity and ultraviolet cutoff within an SU(5)
grand unified theory with minimal scalar content and an extra adjoint
representation of fermions. We find strong correlation between the upper bound
on the mass of both the bosonic and fermionic SU(2) triplets and the cutoff.
The upper bound on the mass of fermionic triplet responsible for Type III
seesaw mechanism is 10^{2.1} GeV for the Planck scale cutoff. In that case both
the idea of grand unification and nature of seesaw mechanism could be tested at
future collider experiments through the production of those particles.
Moreover, the prediction for the proton decay lifetime is at most an order of
magnitude away from the present experimental limits. If the cutoff is lowered
these predictions change significantly. In the most general scenario, if one
does (not) neglect a freedom in the quark and lepton mixing angles, the upper
bound on the fermionic triplet mass is at 10^{5.4} GeV (10^{10} GeV). Since the
predictions of the model critically depend on the presence of the
higher-dimensional operators and corresponding cutoff we address the issue of
their possible origin and also propose alternative scenarios that implement the
hybrid seesaw framework of the original proposal.Comment: 13 pages, 2 figures, minor changes introduced to match the JHEP
versio
The importance of flavor in leptogenesis
We study leptogenesis from the out-of-equilibrium decays of the lightest
heavy neutrino in the medium (low) temperature regime, T\lsim 10^{12}
GeV ( GeV), where the rates of processes mediated by the (and
) Yukawa coupling are non negligible, implying that the effects of lepton
flavors must be taken into account. We find important quantitative and
qualitative differences with respect to the case where flavor effects are
ignored: (i) The cosmic baryon asymmetry can be enhanced by up to one order of
magnitude; (ii) The sign of the asymmetry can be opposite to what one would
predict from the sign of the total lepton asymmetry ; (iii)
Successful leptogenesis is possible even with .Comment: 27 pages, 2 figures. Added 3 reference
One-Loop QCD Mass Effects in the Production of Polarized Bottom and Top Quarks
The analytic expressions for the production cross sections of polarized
bottom and top quarks in annihilation are explicitly derived at the
one-loop order of strong interactions. Chirality-violating mass effects will
reduce the longitudinal spin polarization for the light quark pairs by an
amount of , when one properly considers the massless limit for the final
quarks. Numerical estimates of longitudinal spin polarization effects in the
processes and are presented.Comment: 17 p. (5 figs available upon request), LaTeX, MZ-TH/93-30, RAL/93-81,
FTUV/93-4
Stability and leptogenesis in the left-right symmetric seesaw mechanism
We analyze the left-right symmetric type I+II seesaw mechanism, where an
eight-fold degeneracy among the mass matrices of heavy right-handed neutrinos
M_R is known to exist. Using the stability property of the solutions and their
ability to lead to successful baryogenesis via leptogenesis as additional
criteria, we discriminate among these eight solutions and partially lift their
eight-fold degeneracy. In particular, we find that viable leptogenesis is
generically possible for four out of the eight solutions.Comment: 25 pages, 11 figures, latex; minor changes, published versio
Obtaining the Gauge Invariant Kinetic Term for a SU(n) x SU(m) Lagrangian
We propose a generalized way to formally obtain the gauge invariance of the
kinetic part of a field Lagrangian over which a gauge transformation ruled by
an coupling symmetry is applied. As an
illustrative example, we employ such a formal construction for reproducing the
standard model Lagrangian. This generalized formulation is supposed to
contribute for initiating the study of gauge transformation applied to
generalized symmetries as well as for
complementing an introductory study of the standard model of elementary
particles.Comment: 6 page
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