14,666 research outputs found
SO(10) and Large nu_mu - nu_tau Mixing
A general approach to understanding the large mixing seen in atmospheric
neutrinos is explained, as well as a highly predictive SO(10) model which
implements this approach. It is also seen how bimaximal mixing naturally arises
in this scheme. (Talk presented at NNN99, SUNY Stony Brook, Sept. 22-26, 1999)Comment: 10 pages, LaTe
Explicit SO(10) Supersymmetric Grand Unified Model
A complete set of Higgs and matter superfields is introduced with
well-defined SO(10) properties and U(1) \times Z_2 \times Z_2 family charges
from which the Higgs and Yukawa superpotentials are constructed. The Higgs
fields solve the doublet-triplet splitting problem, while the structures of the
four Dirac fermion mass matrices obtained involve just six effective Yukawa
operators. The right-handed Majorana matrix, M_R, arises from one Higgs field
coupling to several pairs of superheavy conjugate neutrino singlets. In terms
of 10 input parameters to the mass matrices, the model accurately yields the 20
masses and mixings of the lightest quarks and leptons, as well as the masses of
the 3 heavy right-handed neutrinos. The bimaximal atmospheric and solar
neutrino vacuum solutions are favored in this simplest version with a moderate
hierarchy in M_R. The large mixing angle MSW solution is obtainable, on the
other hand, with a considerably larger hierarchy in M_R which is also necessary
to obtain baryogenesis through the leptogenesis mechanism.Comment: 11 pages including 4 figures, contribution to NEUTRINO 2000 and talk
presented at SUSY2
Raman gain against a background of non-thermal ion fluctuations in a plasma
A complex stimulated Raman scattering event against a background of non-thermal ion acoustic waves in an inhomogeneous plasma is described. We obtain analytic forms for the Raman gain due to a five-wave interaction consisting of conventional three-wave Raman scattering followed by the decay of the Raman Langmuir wave into a second Langmuir wave (or a second scattered light wave) and an ion acoustic wave. Very modest levels of ion waves produce a. significant effect on Raman convective gain. A combination of plasma inhomogeneity and suprathermal ion fluctuations may offer a means for the control of Raman gain
Transverse mass and invariant mass observables for measuring the mass of a semi-invisibly decaying heavy particle
Formulae are derived for the positions of end-points in the invariant mass
and transverse mass distributions obtained from the products of heavy states
decaying to pairs of semi-invisibly decaying lighter states. Formulae are
derived both for the special case where the two decay chains are identical and
the more general case where they are different. The formulae are tested with a
simple case study of heavy SUSY higgs particles decaying to gauginos at the
LHC.Comment: 13 pages, 8 eps figure
Anthropic tuning of the weak scale and of m_u/m_d in two-Higgs-doublet models
It is shown that in a model in which up-type and down-type fermions acquire
mass from different Higgs doublets, the anthropic tuning of the Higgs mass
parameters can explain the fact that the observed masses of the and
quarks are nearly the same with slightly heavier. If Yukawa couplings are
assumed not to "scan" (vary among domains), this would also help explain why
the t quark is much heavier than the b quark. It is also pointed out that the
existence of dark matter invalidates some earlier anthropic arguments against
the viability of domains where the Standard Model Higgs has positive ,
but makes other even stronger arguments possible.Comment: 31 pages, 7 figure
Natural Gauge Hierarchy in SO(10)
It is shown that a natural gauge hierarchy and doublet-triplet splitting can
be achieved in SO(10) using the Dimopoulos-Wilczek mechanism. Artificial
cancellations (fine-tuning) and arbitrary forms of the superpotential are
avoided, the superpotential being the most general compatible with a symmetry.
It is shown by example that the Dimopoulos-Wilczek mechanism can be protected
against the effects of higher-dimension operators possibly induced by
Planck-scale physics. Natural implementation of the mechanism leads to an
automatic Peccei-Quinn symmetry. The same local symmetries that would protect
the gauge hierarchy against Planck-scale effects tend to protect the axion
also. It is shown how realistic quark and lepton masses might arise in this
framework. It is also argued that ``weak suppression'' of proton decay can be
implemented more economically than can ``strong suppression'', offering some
grounds to hope (in the context of SO(10)) that proton decay could be seen at
Superkamiokande.Comment: 26 pages in plain LaTeX, 5 figures available on request, BA-94-0
The stransverse mass, MT2, in special cases
This document describes some special cases in which the stransverse mass,
MT2, may be calculated by non-iterative algorithms. The most notable special
case is that in which the visible particles and the hypothesised invisible
particles are massless -- a situation relevant to its current usage in the
Large Hadron Collider as a discovery variable, and a situation for which no
analytic answer was previously known. We also derive an expression for MT2 in
another set of new (though arguably less interesting) special cases in which
the missing transverse momentum must point parallel or anti parallel to the
visible momentum sum. In addition, we find new derivations for already known
MT2 solutions in a manner that maintains manifest contralinear boost invariance
throughout, providing new insights into old results. Along the way, we stumble
across some unexpected results and make conjectures relating to geometric forms
of M_eff and H_T and their relationship to MT2.Comment: 11 pages, no figures. v2 corrects minor typos. v3 corrects an
incorrect statement in footnote 8 and inserts a missing term in eq (3.9). v4
and v5 correct minor typos spotted by reader
Ruling out a higher spin field solution to the cosmological constant problem
We consider the modification of Newton's gravity law in Dolgov's higher spin
models designed to compensate the cosmological constant. We find that the
effective Planck mass is unacceptably large in these models. We also point out
that the properties of gravitational waves are entirely different in these
models as compared to general relativity.Comment: 7 pages, LaTe
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