Symmetry Scheme for Amino Acid Codons

Group theoretical concepts are invoked in a specific model to explain how only twenty amino acids occur in nature out of a possible sixty four. The methods we use enable us to justify the occurrence of the recently discovered twenty first amino acid selenocysteine, and also enables us to predict the possible existence of two more, as yet undiscovered amino acids.Comment: 18 pages which include 4 figures & 3 table

Z', new fermions and flavor changing processes, constraints on E6_6 models from μ\mu --> eee

We study a new class of flavor changing interactions, which can arise in models based on extended gauge groups (rank $>$4) when new charged fermions are present together with a new neutral gauge boson. We discuss the cases in which the flavor changing couplings in the new neutral current coupled to the $Z^\prime$ are theoretically expected to be large, implying that the observed suppression of neutral flavor changing transitions must be provided by heavy $Z^\prime$ masses together with small $Z$-$Z^\prime$ mixing angles. Concentrating on E$_6$ models, we show how the tight experimental limit on $\mu \rightarrow eee$ implies serious constraints on the $Z^\prime$ mass and mixing angle. We conclude that if the value of the flavor changing parameters is assumed to lie in a theoretically natural range, in most cases the presence of a $Z^\prime$ much lighter than 1 TeV is unlikely.Comment: plain tex, 22 pages + 2 pages figures in PostScript (appended after `\bye'), UM-TH 92-1

Implications of LEP Results for SO(10) Grandunification with Two Intermediate Stages

We consider the breaking of the grand unification group $SO(10)$ to the standard model gauge group through several chains containing two intermediate stages. Using the values of the gauge coupling constants at scale $M_Z$ derived from recent LEP data, we determine the range of their intermediate and unification scales. In particular, we identify those chains that permit new gauge structure at relatively low energy $(\sim 1\, {\rm TeV})$.Comment: (LATEX, 9 pages + 3 pages of figures not included) OITS-48

Possible Candidates for SUSY SO(10) Model with an Intermediate Scale

We study the possibility of an intermediate scale existing in supersymmetric SO(10) grand unified theories: The intermediate scale is demanded to be around 10^{12} GeV so that neutrinos can obtain masses suitable for explaining the experimental data on the deficit of solar neutrino with Mikheev-Smirnov-Wolfenstein solution and the existence of hot dark matter. We show that any Pati-Salam type intermediate symmetries are excluded by requiring reasonable conditions and only $SU(2)_L\times SU(2)_R \times SU(3)_C\times U(1)_{B-L}$ is likely to be realized as an intermediate symmetry.Comment: LaTeX, 8 pages + 1 uuencoded eps figure (Error corrected

Flavor Alignment in SUSY GUTs

A Supersymmetric Grand unified model is constructed based on SO(10)xSO(10) symmetry in which new types of Yukawa matrices couple standard and exotic fermions. Evolution of these couplings from the Grand Unified scale to the electroweak scale causes some of them to be driven to their fixed points. This solves the supersymmetric alignment problem and ensures that there are no observable flavor changing neutral currents mediated by supersymmetric particles. Fermion hierarchy and neutrino mixing constraints are automatically satisfied in this formalism.Comment: 20 pages, 1 figur

Baryon and Lepton Number Assignment in E6E_6 Models

In $E_6$ models there are new particles whose baryon number is not uniquely assigned. We point out that the baryon and lepton number assignment to these particles can change the baryogenesis scenario significantly. We consider left-right symmetric extension of the standard model in which $(B-L)$ quantum number is gauged. The identification of $(B-L)$ with a generator of $E_6$ is used to define the baryon and lepton numbers for the exotic particles in a way that the electroweak baryon and lepton number anomaly corresponding to the $SU(2)_L$ group vanishes, {\it i.e.}, there is no non-perturbative baryon or lepton number violation during the electroweak phase transition. We study some consequences of the new assignment.Comment: 14 pages, LaTeX file, 1 submitted Figure file(.eps

Sterile neutrino dark matter in B−LB-L extension of the standard model and galactic 511 keV line

Sterile right-handed neutrinos can be naturally embedded in a low scale gauged $U(1)_{B-L}$ extension of the standard model. We show that, within a low reheating scenario, such a neutrino is an interesting candidate for dark matter. We emphasize that if the neutrino mass is of order of MeV, then it accounts for the measured dark matter relic density and also accommodates the observed flux of 511 keV photons from the galactic bulge.Comment: 10 pages, 1 figure, references added, final version appeared in JCA

Maximal supergravity in D=10: forms, Borcherds algebras and superspace cohomology

We give a very simple derivation of the forms of $N=2,D=10$ supergravity from supersymmetry and SL(2,\bbR) (for IIB). Using superspace cohomology we show that, if the Bianchi identities for the physical fields are satisfied, the (consistent) Bianchi identities for all of the higher-rank forms must be identically satisfied, and that there are no possible gauge-trivial Bianchi identities ($dF=0$) except for exact eleven-forms. We also show that the degrees of the forms can be extended beyond the spacetime limit, and that the representations they fall into agree with those predicted from Borcherds algebras. In IIA there are even-rank RR forms, including a non-zero twelve-form, while in IIB there are non-trivial Bianchi identities for thirteen-forms even though these forms are identically zero in supergravity. It is speculated that these higher-rank forms could be non-zero when higher-order string corrections are included.Comment: 15 pages. Published version. Some clarification of the tex

Flavour Issues in Leptogenesis

We study the impact of flavour in thermal leptogenesis, including the quantum oscillations of the asymmetries in lepton flavour space. In the Boltzmann equations we find different numerical factors and additional terms which can affect the results significantly. The upper bound on the CP asymmetry in a specific flavour is weaker than the bound on the sum. This suggests that -- when flavour dynamics is included -- there is no model-independent limit on the light neutrino mass scale,and that the lower bound on the reheat temperature is relaxed by a factor ~ (3 - 10).Comment: 19 pages, corrected equations for flavour oscillation

A twistor-like D=10 superparticle action with manifest N=8 world-line supersymmetry

We propose a new formulation of the $D=10$ Brink-Schwarz superparticle which is manifestly invariant under both the target-space super-Poincar\'e group and the world-line local $N=8$ superconformal group. This twistor-like construction naturally involves the sphere $S^8$ as a coset space of the $D=10$ Lorentz group. The action contains only a finite set of auxiliary fields, but they appear in unusual trilinear combinations. The origin of the on-shell $D=10$ fermionic $\kappa$ symmetry of the standard Brink-Schwarz formulation is explained. The coupling to a $D=10$ super-Maxwell background requires a new mechanism, in which the electric charge appears only on shell as an integration constant.Comment: 22pages, standard LATEX fil