5,391 research outputs found
Flavor mixing in a Lee-type model
An exactly solvable Quantum Field Theory (QFT) model of Lee-type is
constructed to study how neutrino flavor eigenstates are created through
interactions and how the localization properties of neutrinos follows from the
parent particle that decays. The two-particle states formed by the neutrino and
the accompanying charged lepton can be calculated exactly as well as their
creation probabilities. We can show that the coherent creation of neutrino
flavor eigenstates follows from the common negligible contribution of neutrino
masses to their creation probabilities. On the other hand, it is shown that it
is not possible to associate a well defined "flavor" to mixed states of charged
leptons.Comment: v2: 25pp in preprint form, typos corrected and references added, one
paragraph around Eq.(90) added in conclusion
Physical parameters and basis transformations in the Two-Higgs-Doublet model
A direct connection between physical parameters of general Two-Higgs-Doublet
Model (2HDM) potentials after electroweak symmetry breaking (EWSB) and the
parameters that define the potentials before EWSB is established. These
physical parameters, such as the mass matrix of the neutral Higgs bosons, have
well defined transformation properties under basis transformations transposed
to the fields after EWSB. The relations are also explicitly written in a basis
covariant form. Violation of these relations may indicate models beyond 2HDMs.
In certain cases the whole potential can be defined in terms of the physical
parameters. The distinction between basis transformations and
reparametrizations is pointed out. Some physical implications are discussed.Comment: 11 pages. 1 figure. v2: references and comments adde
Simple derivation of general Fierz-type identities
General Fierz-type identities are examined and their well known connection
with completeness relations in matrix vector spaces is shown. In particular, I
derive the chiral Fierz identities in a simple and systematic way by using a
chiral basis for the complex matrices. Other completeness relations
for the fundamental representations of SU(N) algebras can be extracted using
the same reasoning.Comment: 9pages. Few sentences modified in introduction and in conclusion.
Typos corrected. An example added in introduction. Title modifie
Structure of potentials with Higgs doublets
Extensions of the Standard Model with Higgs doublets are simple
extensions presenting a rich mathematical structure. An underlying Minkowski
structure emerges from the study of both variable space and parameter space.
The former can be completely parametrized in terms of two future lightlike
Minkowski vectors with spatial parts forming an angle whose cosine is
. For the parameter space, the Minkowski parametrization enables
one to impose sufficient conditions for bounded below potentials, characterize
certain classes of local minima and distinguish charge breaking vacua from
neutral vacua. A particular class of neutral minima presents a degenerate mass
spectrum for the physical charged Higgs bosons.Comment: 11 pages. Revtex4. Typos corrected. Few comments adde
Formation and Disruption of Cosmological Low Mass Objects
We investigate the evolution of cosmological low mass (low virial
temperature) objects and the formation of the first luminous objects. First,
the `cooling diagram' for low mass objects is shown. We assess the cooling rate
taking into account the contribution of H_2, which is not in chemical
equilibrium generally, with a simple argument of time scales. The reaction
rates and the cooling rate of H_2 are taken from the recent results by Galli &
Palla (1998). Using this cooling diagram, we also estimate the formation
condition of luminous objects taking into account the supernova (SN) disruption
of virialized clouds. We find that the mass of the first luminous object is
several times 10^7 solar mass, because smaller objects may be disrupted by the
SNe before they become luminous. Metal pollution of low mass (Ly-alpha) clouds
also discussed. The resultant metallicity of the clouds is about 1/1000 of the
solar metallicity.Comment: 11 pages, 2 figures, To appear in ApJ
Altitude variations of cosmic-ray soft and hard components observed by airborne detectors
The altitude variations of cosmic-ray total and hard components were measured up to 12,000 m on board a jet liner over Japan island on December, 1981. Observed results together with soft component are presented comparing with the model calculations through the atmosphere by applying the hadronic cascade
Soft CP violation in K-meson systems
We consider a model with soft CP violation which accommodate the CP violation
in the neutral kaons even if we assume that the Cabibbo-Kobayashi-Maskawa
mixing matrix is real and the sources of CP violation are three complex vacuum
expectation values and a trilinear coupling in the scalar potential. We show
that for some reasonable values of the masses and other parameters the model
allows to explain all the observed CP violation processes in the
- system.Comment: 19 pages, RevTeX 4. Minor modification
Photodissociative Regulation of Star Formation in Metal-Free Pregalactic Clouds
We study the H2 photodissociation regions around OB stars in primordial gas
clouds whose virial temperatures are between a few hundred and a few thousand
Kelvin. In such small objects, a single O star can photodissociate a mass equal
to that of the cloud itself. As a result, the clouds deplete their molecular
coolant and cannot cool in a free-fall time, and subsequent star formation is
totally quenched. This indicates that stars do not form efficiently in small
objects and that these objects contribute little to the reionization of the
universe.Comment: 9 pages. ApJ, 518, in pres
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