10,172 research outputs found
N K and Delta K states in the chiral SU(3) quark model
The isospin I=0 and I=1 kaon-nucleon , , , wave phase shifts are
studied in the chiral SU(3) quark model by solving the resonating group method
(RGM) equation. The calculated phase shifts for different partial waves are in
agreement with the experimental data. Furthermore, the structures of the
states with L=0, I=1 and I=2 are investigated. We find that the
interaction between and in the case of L=0, I=1 is attractive,
which is not like the situation of the system, where the -wave
interactions between and for both I=0 and I=1 are repulsive. Our
numerical results also show that when the model parameters are taken to be the
same as in our previous and scattering calculations, the
state with L=0 and I=1 is a weakly bound state with about 2 MeV binding energy,
while the one with I=2 is unbound in the present one-channel calculation.Comment: 14 pages, 6 figures. PRC70,064004(2004
Massive and Massless Neutrinos on Unbalanced Seesaws
The observation of neutrino oscillations requires new physics beyond the
standard model (SM). A SM-like gauge theory with p lepton families can be
extended by introducing q heavy right-handed Majorana neutrinos but preserving
its SU(2)_L x U(1)_Y gauge symmetry. The overall neutrino mass matrix M turns
out to be a symmetric (p+q) x (p+q) matrix. Given p>q, the rank of M is in
general equal to 2q, corresponding to 2q non-zero mass eigenvalues. The
existence of (p-q) massless left-handed Majorana neutrinos is an exact
consequence of the model, independent of the usual approximation made in
deriving the Type-I seesaw relation between the effective p x p light Majorana
neutrino mass matrix M_\nu and the q x q heavy Majorana neutrino mass matrix
M_R. In other words, the numbers of massive left- and right-handed neutrinos
are fairly matched. A good example to illustrate this seesaw fair play rule is
the minimal seesaw model with p=3 and q=2, in which one massless neutrino sits
on the unbalanced seesaw.Comment: RevTex 8 pages, 1 PS figure. Two crucial references adde
Lepton masses and mixing without Yukawa hierarchies
We investigate the neutrino masses and mixing patten in a version of the
model with one extra exotic charged
lepton per family as introduced by Ozer. It is shown that an extended scalar
sector, together with a discrete symmetry, is able to reproduce a
consistent lepton mass spectrum without a hierarchy in the Yukawa coupling
constants, the former as a carefull balance between one universal see-saw and
two radiative mechanisms.Comment: 7 pages, 2 figures, accepted for publication in Phys. Rev. D
Updated Values of Running Quark and Lepton Masses
Reliable values of quark and lepton masses are important for model building
at a fundamental energy scale, such as the Fermi scale M_Z \approx 91.2 GeV and
the would-be GUT scale \Lambda_GUT \sim 2 \times 10^16 GeV. Using the latest
data given by the Particle Data Group, we update the running quark and
charged-lepton masses at a number of interesting energy scales below and above
M_Z. In particular, we take into account the possible new physics scale (\mu
\sim 1 TeV) to be explored by the LHC and the typical seesaw scales (\mu \sim
10^9 GeV and \mu \sim 10^12 GeV) which might be relevant to the generation of
neutrino masses. For illustration, the running masses of three light Majorana
neutrinos are also calculated. Our up-to-date table of running fermion masses
are expected to be very useful for the study of flavor dynamics at various
energy scales.Comment: 23 pages, 6 tables, 2 figures; version published in PR
CMB Signals of Neutrino Mass Generation
We propose signals in the cosmic microwave background to probe the type and
spectrum of neutrino masses. In theories that have spontaneous breaking of
approximate lepton flavor symmetries at or below the weak scale, light
pseudo-Goldstone bosons recouple to the cosmic neutrinos after nucleosynthesis
and affect the acoustic oscillations of the electron-photon fluid during the eV
era. Deviations from the Standard Model are predicted for both the total energy
density in radiation during this epoch, \Delta N_nu, and for the multipole of
the n'th CMB peak at large n, \Delta l_n. The latter signal is difficult to
reproduce other than by scattering of the known neutrinos, and is therefore an
ideal test of our class of theories. In many models, the large shift, \Delta
l_n \approx 8 n_S, depends on the number of neutrino species that scatter via
the pseudo-Goldstone boson interaction. This interaction is proportional to the
neutrino masses, so that the signal reflects the neutrino spectrum. The
prediction for \Delta N_nu is highly model dependent, but can be accurately
computed within any given model. It is very sensitive to the number of
pseudo-Goldstone bosons, and therefore to the underlying symmetries of the
leptons, and is typically in the region of 0.03 < \Delta N_nu < 1. This signal
is significantly larger for Majorana neutrinos than for Dirac neutrinos, and,
like the scattering signal, varies as the spectrum of neutrinos is changed from
hierarchical to inverse hierarchical to degenerate.Comment: 40 pages, 4 figure
The Null Decomposition of Conformal Algebras
We analyze the decomposition of the enveloping algebra of the conformal
algebra in arbitrary dimension with respect to the mass-squared operator. It
emerges that the subalgebra that commutes with the mass-squared is generated by
its Poincare subalgebra together with a vector operator. The special cases of
the conformal algebras of two and three dimensions are described in detail,
including the construction of their Casimir operators.Comment: 31 page
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
SU(4) Skyrmions and Activation Energy Anomaly in Bilayer Quantum Hall Systems
The bilayer QH system has four energy levels in the lowest Landau level,
corresponding to the layer and spin degrees of freedom. We investigate the
system in the regime where all four levels are nearly degenerate and equally
active. The underlying group structure is SU(4). At the QH state is a
charge-transferable state between the two layers and the SU(4) isospin
coherence develops spontaneously. Quasiparticles are isospin textures to be
identified with SU(4) skyrmions. The skyrmion energy consists of the Coulomb
energy, the Zeeman energy and the pseudo-Zeeman energy. The Coulomb energy
consists of the self-energy, the capacitance energy and the exchange energy. At
the balanced point only pseudospins are excited unless the tunneling gap is too
large. Then, the SU(4) skyrmion evolves continuously from the
pseudospin-skyrmion limit into the spin-skyrmion limit as the system is
transformed from the balanced point to the monolayer point by controlling the
bias voltage. Our theoretical result explains quite well the experimental data
due to Murphy et al. and Sawada et al. on the activation energy anomaly induced
by applying parallel magnetic field.Comment: 22 pagets, 6 figures, the final version to be published in PR
Renormalization group evolution of neutrino masses and mixing in seesaw models: A review
We consider different extensions of the standard model which can give rise to
the small active neutrino masses through seesaw mechanisms, and their mixing.
These tiny neutrino masses are generated at some high energy scale by the heavy
seesaw fields which then get sequentially decoupled to give an effective
dimension-5 operator. The renormalization group evolution of the masses and the
mixing parameters of the three active neutrinos in the high energy as well as
the low energy effective theory is reviewed in this article.Comment: 54 pages. Invited review submitted to IJMP
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