542 research outputs found
Truly Minimal Left-Right Model of Quark and Lepton Masses
We propose a left-right model of quarks and leptons based on the gauge group
, where the scalar
sector consists of only two doublets: (1,2,1,1) and (1,1,2,1). As a result, any
fermion mass, whether it be Majorana or Dirac, must come from dimension-five
operators. This allows us to have a common view of quark and lepton masses,
including the smallness of Majorana neutrino masses as the consequence of a
double seesaw mechanism.Comment: Version to appear in PRL, title changed by journal to "Left-right
model of quark and lepton masses without a scalar bidoublet
Structure and stability of human telomeric sequence
Telomeric DNA of a variety of vertebrates including humans contains the tandem repeat d(TTAGGG)n. We have investigated the structural properties of the human telomeric repeat oligonucleotide models d(T2AG3)4, d(G3T2A)3G3, and d(G3T2AG3) using CD, gel electrophoresis, and chemical probing techniques. The sequences d(G3T2A)3G3 and d(T2AG3)4 assume an antiparallel G quartet structure by intramolecular folding, while the sequence d(G3T2AG3) also adopts an antiparallel G quartet structure but by dimerization of hairpins. In all the above cases, adenines are in the loop. The TTA loops are oriented at the same end of the G tetrad stem in the case of hairpin dimer. Further, the oligonucleotide d(G3T2AG3) forms a higher order structure by the association of two hairpin dimers via stacking of G tetrad planes. Here we show that N-7 of adenine in the hairpin dimer is Hoogsteen hydrogen-bonded. The partial reactivity of loop adenines with DEPC in d(T2AG3)4 suggests that the intramolecular G quartet structure is highly polymorphic and structures with different loop orientations and topologies are formed in solution. Intra- and interloop hydrogen bonding schemes for the TTA loops are proposed to account for the observed diethyl pyrocarbonate reactivities of adenines. Sodium-induced G quartet structures differ from their potassium-induced counterparts not only in stability but also in loop conformation and interactions. Thus, the overall structure and stability of telomeric sequences are modulated by the cation present, loop sequence, and the number of G tracts, which might be important for the telomere function
Recent direct measurement of the Top quark mass and quasi-infrared fixed point
We note that the recent direct measurement of the top quark mass at by D0 collaboration severely constrains the
theoretically attractive infra-red fixed point scenario of the top quark Yukawa
coupling in supersymmetric GUTs. For one-step unified models the above
mentioned measurement bounds the arbitrary but experimentally determinable
parameter to the range . Further
crunch on the top quark mass may determine even more accurately
within the fixed point scenario. On the other hand an experimental value of
will rule out the fixed point scenario bounding
to 0.022 from above.Comment: 7 pages, Latex with epsf style, 1 figure, captions.st
Asymmetric neutrino Yukawa matrices and neutrino mixing
We study leptonic CKM mixing matrices when the neutrino Yukawa matrices are
antisymmetric which gives rise to mass patterns suitable to explain solar,
atmospheric and LSND neutrino oscillation experiments. Taking diagonal leptonic
matrices which can give rise to hierarchical lepton masses, we compute the
leptonic CKM matrix.Comment: version to appear in Phys. Rev.
Constrained analytical interrelations in neutrino mixing
Hermitian squared mass matrices of charged leptons and light neutrinos in the
flavor basis are studied under general additive lowest order perturbations away
from the tribimaximal (TBM) limit in which a weak basis with mass diagonal
charged leptons is chosen. Simple analytical expressions are found for the
three measurable TBM-deviants in terms of perturbation parameters appearing in
the neutrino and charged lepton eigenstates in the flavor basis. Taking
unnatural cancellations to be absent and charged lepton perturbation parameters
to be small, interrelations are derived among masses, mixing angles and the
amount of CP-violation.Comment: To be published in the Springer Proceedings in the Physics Series
under the heading of the XXI DAE-BRNS Symposium (Guwahati, India
Proton Decay and Related Processes in Unified Models with Gauged Baryon Number:
In unification models based on SU(15) or SU(16), baryon number is part of the
gauge symmetry, broken spontaneously. In such models, we discuss various
scenarios of important baryon number violating processes like proton decay and
neutron-antineutron oscillation. Our analysis depends on the effective operator
method, and covers many variations of symmetry breaking, including different
intermediate groups and different Higgs boson content. We discuss processes
mediated by gauge bosons and Higgs bosons parallely. We show how accidental
global or discrete symmetries present in the full gauge invariant Lagrangian
restrict baryon number violating processes in these models. In all cases, we
find that baryon number violating interactions are sufficiently suppressed to
allow grand unification at energies much lower than the usual GeV.Comment: (32 pages LATEX) [DOE-ER\,40757-022, CPP-93-22] {Small changes made
and two references added. This version will appear in Phys. Rev. D
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