1,845 research outputs found
Comparison of the extended linear sigma model and chiral perturbation theory
The pion-nucleon scattering amplitudes are calculated in tree approximation
with the use of the extended linear sigma model (ELSM) as well as heavy baryon
chiral perturbation theory (HBPT), and the non-relativistic forms of the
ELSM results are compared with those of HBPT. We find that the amplitudes
obtained in ELSM do not agree with those derived from the more fundamental
effective approach, HBPT.Comment: 7 page
Orbifold Family Unification in SO(2N) Gauge Theory
We study the possibility of family unification on the basis of SO(2N) gauge
theory on the five-dimensional space-time, . Several SO(10),
or SU(5) multiplets come from a single
bulk multiplet of SO(2N) after the orbifold breaking. Other multiplets
including brane fields are necessary to compose three families of quarks and
leptons.Comment: 28 page
Neutrino masses and flavor symmetries
The problem of neutrino masses and mixing angles is analysed in a class of
supersymmetric grand unified models, with SO(10) gauge symmetry and global U(2)
flavour symmetry. Adopting the seesaw mechanism for the generation of the
neutrino masses, one obtains a mass matrix for the left-handed neutrinos which
is directly related to the parameters of the charged sector, while the unknown
parameters of the right-handed Majorana mass matrix are inglobed in a single
factor.Comment: 17 pages, 1 eps figure, uses graphicx.sty, LaTeX 2e, to be published
on "Il Nuovo Cimento
Relation between the neutrino and quark mixing angles and grand unification
We argue that there exists simple relation between the quark and lepton
mixings which supports the idea of grand unification and probes the underlying
robust bi-maximal fermion mixing structure of still unknown flavor physics. In
this framework the quark mixing matrix is a parameter matrix describing the
deviation of neutrino mixing from exactly bi-maximal, predicting
theta_{sol}+theta_C=pi/4, where theta_C is the Cabibbo angle,
theta_{atm}+theta_{23}^{CKM}=pi/4 and theta_{13}^{MNS} ~ theta_{13}^{CKM} ~
O(lambda^3), in a perfect agreement with experimental data. Both non-Abelian
and Abelian flavor symmetries are needed for such a prediction to be realistic.
An example flavor model capable to explain this flavor mixing pattern, and to
induce the measured quark and lepton masses, is outlined.Comment: references added, title changed in journa
Quark-lepton mass unification at TeV scales
A scenario combining a model of early (TeV) unification of quarks and leptons
with the physics of large extra dimensions provides a natural mechanism linking
quark and lepton masses at TeV scale. This has been dubbed as early
quark-lepton mass unification by one of us (PQH) in one of the two models of
early quark-lepton unification, which are consistent with data, namely SU(4)_PS
\otimes SU(2)_L \otimes SU(2)_R \otimes SU(2)_H. In particular, it focused on
the issue of naturally light Dirac neutrino. The present paper will focus on
similar issues in the other model, namely SU(4)_PS \otimes SU(3)_L \otimes
SU(3)_H.Comment: Accepted for publication in PRD: The new version is in agreement with
the accepted manuscrip
Discussions on Stability of Diquarks
Since the birth of the quark model, the diquark which is composed of two
quarks has been considered as a substantial structure of color anti-triplet.
This is not only a mathematical simplification for dealing with baryons, but
also provides a physical picture where the diquark would behave as a whole
object. It is natural to ask whether such a structure is sufficiently stable
against external disturbance. The mass spectra of the ground states of the
scalar and axial-vector diquarks which are composed of two-light (L-L),
one-light-one-heavy (H-L) and two-heavy quarks (H-H) respectively have been
calculated in terms of the QCD sum rules. We suggest a criterion as the
quantitative standard for the stability of the diquark. It is the gap between
the masses of the diquark and where is the threshold of the
excited states and continuity, namely the larger the gap is, the more stable
the diquark would be. In this work, we calculate the masses of the type H-H to
complete the series of the spectra of the ground state diquarks. However, as
the criterion being taken, we find that all the gaps for the various diquaks
are within a small range, especially the gap for the diquark with two heavy
quarks which is believed to be a stable structure, is slightly smaller than
that for other two types of diquarks, therefore we conclude that because of the
large theoretical uncertainty, we cannot use the numerical results obtained
with the QCD sum rules to assess the stability of diquarks, but need to invoke
other theoretical framework.Comment: 14 pages, 4 figure
Measurement in Quantum Physics
The conceptual problems in quantum mechanics -- related to the collapse of
the wave function, the particle-wave duality, the meaning of measurement --
arise from the need to ascribe particle character to the wave function. As will
be shown, all these problems dissolve when working instead with quantum fields,
which have both wave and particle character. Otherwise the predictions of
quantum physics, including Bell's inequalities, coincide with those of the
standard treatments. The transfer of the results of the quantum measurement to
the classical realm is also discussed.Comment: 34 pages, in Latex, revised and expanded version with an extra
appendix on decoherenc
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